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Who Wants Zero Cooling Drag?

I was reading some tech stuff at NASA.gov and misread something that spawned a thought. Why not use the leading edge as a water-air heat exchanger? A liquid cooled engine and a setup like that would actually reduce drag due to the temp difference between the skin and the air. A step further brings water-air and water-oil heat exhangers for an oil cooler and intercooler. Then there's the free, albeit limited, anti-ice.

The only practical way I can see would include a water-water exchanger to keep the wing section unpressurised for simplicity of construction. No composites allowed either, heat conduction is too low.

Obviously this would create more weight and complexity so it'd only benefit clean fast aircraft. No offense, but that leaves most of you out. Still, I am interested in everyone's thoughts and constructive criticism.
 
I think it is an interesting idea. The thing that would make it most difficult would be replicating the surface area per unit volume for heat transfer. If you look at a radiator with all of the fins there is a lot of surface area that liquid gets exposed to when traveling through the radiator. The tubes are fairly small with a lot fins for heat transfer. The problem would be trying to replicate that it a wing. This would be a surface area per volume problem. The surface area would likely be there (in theory), but the volume of the wing would be very large. So the efficiency of the cooling system would likely be poor not to mention the weight.

I guess the one thing that might help is that if it was limited reservoir similar to the fuel tank, there may be some additional heat transfer by conduction too other parts of the wing, which is not the case in an automobile radiator.

Dave Syvertson
 
Like so many things in aviation, this was explored way back in the 40's during development of the fast liquid-cooled fighters (Spitfire, Mustang, etc).

The real problem with wing-based cooling is in the thermodynamics of air-to-liquid cooling, i.e. efficiency is directly related to pressure and velocity. Small cooling systems require large surface area, low velocity and high pressure differential --- exactly the opposite of the conditions on the leading edge of a wing.

With a leading-edge configuration -- or any wing-based cooing system for that matter -- the engine would actually get hotter the faster you go....as pressure drops (lift) and velocity increases, the system becomes less efficient at dissipating heat.

The P51 Mustang has the most efficient air-liquid system yet devised for aircraft. Under ideal conditions it can actually generate nominal thrust (negative drag).
 
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The P51 system has been evaluated at great length and the latest conclusion was that no net thrust was present in fact. I think it was quoted that it did offset the equivalent of 150hp in cooling drag compared to short, underwing rad systems like the BF109 and Spitfire.

Surface conduction cooling was used on the HE100 and Maachi speed record aircraft but it requires huge amounts of area, finicky construction techniques and vast amounts of coolant (weight).

Leading edge radiators like used in the Mosquito, Hornet and especially Westland Whirlwind with aft wing exits might have been even more efficient that the P51. Implementation of this layout in an RV is very problematical due to fuel tank placement.

Other systems like steam condensation type cooling was even used in RAF service on a couple of types. This shows considerable theoretical advantages but in practical use it was not successful.

Ventrally located rads with a well designed duct employing a controllable exit flap have shown to be the most successful at cooling with low drag on several Subaru powered designs. This looks to be the most practical solution so far.
 
I looked very seriously at doing this with a water-cooled diesel in a 9A, to the point of spending some money on a good thermodynamics engineer to help me crunch the numbers. Bottom line - it's just BARELY possible to dump enough heat through the leading edge via the fuel itself as a secondary coolant loop. A primary coolant would need to be run through a liquid-liquid exchanger to dump the heat into the fuel via a separate electric pump circulating fuel through the wings to spread the heat load. Draw from the wing root, return to the furthest bay, using BOTH wings. The equilibrium heat load obtained by the fuel in high-power operation (150 hp modeled) would require diesel fuel or Jet A - gasoline would be too close to vapor lock, and it gets worse with altitude. The additional weight does not quite kill all the returns from the lack of cooling drag, but the additional complexity and risk of mission-critical component failure made the decision for me.

Electric pumps are needed for the liquid-liquid heat exchanger flow and pressure required, and they draw a lot of power, requiring a larger alternator which runs harder and hotter. If you lose your electrical system, you need a LOT of battery backup for those electrical pumps to keep the engine cool long enough to find the ground - more weight. One pump (circulating one wing) is not enough to keep the engine cool, you need both operational. More weight, more complexity, more cost, more single-point failure exposure. Our best guesstimate for added weight on this system was between 180 and 220 pounds, including the beefed up electrical system for the pumps, the heat exchanger, the plumbing, etc. Is it possible? Yes. Is it reasonable? Not with this equipment flying this mission. At some point you hit diminishing returns, and this idea is right on that line. The idea was bashed about (literally) in this thread - http://www.vansairforce.com/community/showthread.php?t=11470 - but I was too stubborn to let it go until I had hard numbers in front of me that I couldn't argue with.

Turbodiesel is the way to go for fuel efficiency - but the fuel-as-coolant idea has been shelved permanently in my mind. If there is a decent turbodiesel setup available when I'm ready to order my engine, I'll get one and use radiators. Otherwise, it's an XPIO360 and I'll build the airplane to go either way.
 
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"...the concept worked well. Military applications were not successfull due in large part to the VULNERABILITY of large-area radiators to enemy fire. The concepts worked fine but were not feasible in combat applications."

Since most of the reasearch on such things was conducted during WWII, I think this quote from the other thread seems appropriate. Thanks for the link BTW.

Regarding fuel as a medium, I never considered it for one reason. In my mind, it runs 'till it's dry. Anything else is unacceptable. I did briefly think of having a wet wing inside the exchanger and the added cooling it would provide, but that's not a continuous benefit. I also thought avoiding any chance of fuel contamination was enough of a reason to sepparate them.

Additional weight of 25 lbs is acceptable in my mind (it's not all additive, several parts get removed/reduced). A prime example is dirt bikes. For them, weight is as critical as it is for us. Reliability, power, and robustness are also major concerns, yet without the FAA telling them how to spend/waste $, they made the change a few decades ago.

I've done enough math to make it work. What I haven't looked into is the manufacturing (sure to be a PITA), fatigue life, and corrosion problems/solutions.

I'm not saying this'll work for you, but I want something different. I had hoped it would be possible with an all aluminum aircraft, but the math didn't work and it'll have to be mostly G/CFRP. I hate plastic planes, but if that's what it takes...

My goal? 2 seats + 100 lbs baggage, 5 hr endurance, 300+ mph cruise (that's cruise not WOT dash), at less than 15 gph, and 12G ultimate so it can actually use that kind of speed. Yes, tell me it's a pipe dream. They told the Wright brothers the same things. At the same time, with fuel prices going where they are you can bet all those new VLJs are going to have a hard time competeing with the next generation of prop planes this will be comprable to. Remember unducted fans? They're not dead, just biding their time.

Unfortunately no one makes an acceptable power plant yet. I'll pass on the auto conversions thx. TCM was happy to build an experiment with our tax $ with no intention of production...but that's a different story. Unlike the Curtis-Wright SCRE dream, better than .3 BSFC is possible, and in production (.27 BSFC), with a 2-stroke piston engine. http://people.bath.ac.uk/ccsshb/12cyl/ I'd be happy with a properly sized version @ .35!

Yes, I'm aware of Zoche/DeltaHawk/OPOC/etc, but they seems about as productive as Inodyne at this point. I'm watching, but I won't hold my breath...
 
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Engineers have done that been there

No such thing as zero cooling drag. Also water cooling has many negatives. The famed P51 system actually had marginal cooling, especially on the ground abd climb. Also be careful about scaling things from planes that can fly at near 450 mph. For small planes air cooling, although has its own negatives, is overall the most efficient and lightest, and probably always will be.

Look at the state of the art or pinnacle of piston fighters and piston airliners, all most all are air cooled (not withstanding the P-51). Than jets came, but in the peak, most piston planes where air cooled. Even the military used piston thru the 1970's, all air cooled. Take a hint. The state-O-art of piston engine plans have been there and done that, and none involve water cooling.

Keep in mind also Lycs, especially the angle valve heads with piston squirters are actually air/oil cooled, which is what the Porsche 911's are. 911's have like 20 liters of oil in the engine and large coolers!

Obviously if you have a Rotax, Mazda, Subaru or what ever you have to figure out what to do with the water/air heat exchanger (radiator). The problem with a tractor driven plane designed for an air cooled engine is everything you do is a work around or jury rig. Regardless it will be heavier for SURE; you can't beat the installed weight per pound of a Lycoming. When it comes to cars, where weight and high speed drag is not critical, water cooling is king, clearly.

Second you are likely to be guaranteed to have more drag. Why, well we are going 200 mph and we have lots and lots of air. The problem with radiators is they are draggy and there is no place to put them. The pushers like the COZY have room to develop ducts and ramps leading to and from radiators.

I am not trying to be a downer, just the engineers from the 1940's to the early 1980's have crunched all the numbers regarding small engines. There is no need to reinvent the wheel. The NACA file server has all the research papers and you can spend weeks and months going over the data.
 
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Much as it pains me to actually agree with George :p, I have to on this point.

I was about as far off into never-never land as you can get on the liquid-cooled turbodiesel tangent, about where you are now, until I started some actual no-BS engineering studies of what it would take. The shiny started wearing off real quick. It can be done, just not easily or cheaply. It will be heavy, it will include a large increase in the mission-critical parts count, and payoff is minimal.

I don't want to discourage you though - mount up and charge at the windmill. Keep us informed on your experiments - you might accidentally teach us all a thing or two.
 
rv6ejguy said:
...Other systems like steam condensation type cooling was even used in RAF service on a couple of types. This shows considerable theoretical advantages but in practical use it was not successful...
This gave me an idea. Phase change heat transfer is very efficient but boiling water in the cooling jacket causes some problems with varying cooling rates at different locations within the engine.
Try this out: liquid-liquid heat exchanger where the engine coolant boils a convenient second heat transfer liquid (e.g. one of the freons) creating a low pressure vapor that could be condensed in direct contact with the leading edge then pumped back to the boiler.
The low pressure secondary circuit would be easier to corral than a steam circuit.

Maybe something like this can be debugged.

-mike
 
Even if it would work...

Do you really want those HOT water lines running inside you cockpit? Just think what would happen if one of those lines sprung a leak. Can you say "Larry the Lobster"?
 
There was much interest in phase change (steam) cooling in the '30s and Rolls Royce spent a lot of effort along these lines. I'd have to dig out my research on this. Very cool idea and maybe with lots of time spent, could be successful. I'd welcome experimentation on the idea.

My testing has actually shown that modern radiators are not draggy compared to flow past a traditional air cooled head for instance. This is a big myth. What has not been properly quantified with modern materials and designs is the total package heat dissipation vs. drag of the core and duct. Careful historical study of frontal area vs. hp and speed of many WW2 aircraft shows that in most cases, liquid cooled aircraft are faster for the same installed hp. Of particular interest were the Merlin engined Beaufighters vs. the air cooled Hercules ones and the Sabre powered Tempest I vs. the Centaurus powered ones. These are better apples to apples comparisons that say Bearcat vs. P51 at Reno.

On the surface conduction front, I'd recheck the calcs on the leading edge only idea. My calcs showed something like 120 square feet of aluminum would be required on a 200hp engine on a 100F day with 200F coolant. Naturally there are many unknowns to solve for so who knows until a test section could be actually tested. This is a crazy idea for a GA aircraft and nearly impossible to implement on an RV IMO.

Electric water pumps are widely available with current draws in the 4.5 to 8 amp range and flow rates up to 35GPM. These are not heavy and are way more than adequate to cool a 200hp engine. That would be the easy part.
 
Shhh....

Quiet, please..Let these guys buy all the water cooled engines they want. It'll keep the prices of the Lycosaureses down so we can buy 'em :D

No re-engineering Van's for me..
 
Good one

pierre smith said:
Quiet, please..Let these guys buy all the water cooled engines they want. It'll keep the prices of the Lycosaureses down so we can buy 'em :D

No re-engineering Van's for me..

Zinnnngggggger!!!!!! I agree. I firmly believe that if an engine was in a car, intended for car or planned for a car it should not be allowed in an airplane.

I like flying too much to be dorking with an auto engine in an airplane. For those that do, enjoy!!!
 
Yeah but...

Don't give up! Look at what you can do with the water and exhaust from a water cooled engine! Dump the alternator for a solid state Seebeck junction generator!

Electric power from exhaust heat

Do we make a jump away from lycoclones just for this? :D
 
RV7Guy said:
Zinnnngggggger!!!!!! I agree. I firmly believe that if an engine was in a car, intended for car or planned for a car it should not be allowed in an airplane.

I like flying too much to be dorking with an auto engine in an airplane. For those that do, enjoy!!!
Does that include snowmobile engines? Ithink Rotax holds its own for its class.
 
rv6ejguy said:
On the surface conduction front, I'd recheck the calcs on the leading edge only idea. My calcs showed something like 120 square feet of aluminum would be required on a 200hp engine on a 100F day with 200F coolant.
:eek: Yes, I came up with large numbers as well (300hp @ 120F, ever been to PHX in July?). Using laminar flow at low speed only reduces efficeincy farther aft, hence my "leading edge" assumption. Still, with the assumption it won't be doing touch and gos in that heat it's workable, although seriously reduced IC efficiency would result with the combined system I envision. With 300 hp, area would include tail surfaces and routing to them. I think the big difference in our numbers comes from my assumption of the increased thermal efficiency of a 2-stroke diesel.

As for auto conversions, you guys brought that up. If you wish to wear blinders that's you choice...it's a free country after all. If you'll reffer to my original post you'll notice I encourage constructive critism. I'll also encourage those not willing or unable to provide same not to waste the time of those that truly wish the think and learn. Same goes for the "lobsters" out there that never realised the heaters in their cars have never burned them. Maybe you'll even remember your comment the next time you light a cigarette and reach for the fuel selector...

The more people say "it can't be done" the more energy I expend making it happen, in a safe and efficient manner.

Now that I'm done with my rant, can the few remaining continue with a productive conversation in peace?
 
rzbill said:
Don't give up! Look at what you can do with the water and exhaust from a water cooled engine! Dump the alternator for a solid state Seebeck junction generator!

Electric power from exhaust heat

Do we make a jump away from lycoclones just for this? :D

This is what I love about this forum - the fact that there is always at least one or two readers who are willing to take a slightly off-center idea and elevate it to the altitude of, oh, say, Saturn's orbit.
 
Not a really possible method

Sadly the obvoius trolls about WC engines, and the Merlin and Griffon and Allison were aircraft engines BTW. On topic, this idea has been rather completely discussed and eliminated as impractical. Most recently this was a subject for Peter Garison's Technicalities column in Flying magazine. It ran about a year ago if memory serves me. The early efforts using this system were on Snyder Cup floatplanes and covered almost the entire fuselage. The floats also allowed the balance to be maintained. Not practical for our use.
Bill Jepson
 
I know the air cooled guys love to say that water cooling is draggier but never produce any facts to support. Here are some tidbits I dug up:

Bristol Beaufighter. 1280hp Merlin 330 mph, 1590 hp Bristol Hercules 323 mph.

Tempest I. 2240hp Napier Sabre 466 mph. Tempest II 2520hp Bristol Centaurus 440 mph.

Reggiane RE 2001. 1175hp Alfa Romeo 337 mph. RE 2002. 1175hp Piaggio 329 mph.

DC-4/ Northstar. 353mph with 1760hp Merlins, 280 mph with 1450hp Pratt R2000s.

Note these are identical or close to identical airframes save changes for the different engine installations. In the case of the Merlin engined Beau and Northstar, these used the Rolls Royce "power egg" system of engine/ radiator in one, firewall forward- hardly the most efficient from a drag standpoint but making engine changes much quicker.

The Tempest in particular shows how much more efficient liquid cooling can be with 280 hp less and 26 mph faster at about the same altitude. The Tempest I had nicely done leading edge mounted rads.

This is why I pursue the dream on RVs and water pumpers.
 
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rv6ejguy said:
I know the air cooled guys love to say that water cooling is draggier but never produce any facts to support. Here are some tidbits I dug up:

Bristol Beaufighter. 1280hp Merlin 330 mph, 1590 hp Bristol Hercules 323 mph.

Tempest I. 2240hp Napier Sabre 466 mph. Tempest II 2520hp Bristol Centaurus 440 mph.

Reggiane RE 2001. 1175hp Alfa Romeo 337 mph. RE 2002. 1175hp Piaggio 329 mph.

DC-4/ Northstar. 353mph with 1760hp Merlins, 280 mph with 1450hp Pratt R2000s.

Note these are identical or close to identical airframes save changes for the different engine installations. In the case of the Merlin engined Beau and Northstar, these used the Rolls Royce "power egg" system of engine/ radiator in one, firewall forward- hardly the most efficient from a drag standpoint but making engine changes much quicker.

The Tempest in particular shows how much more efficient liquid cooling can be with 280 hp less and 26 mph faster at about the same altitude. The Tempest I had nicely done leading edge mounted rads.

This is why I pursue the dream on RVs and water pumpers.

Ross,
Obviously I agree with you because I'm using a water cooled engine. But a very interesting comparison in the RV "real world" would be Tracy Crook winning the Sun 'n Fun 100 with his wankel powered RV-4. His cowling isn't as clean as it could be but he won his class twice. With an optomized radiator and oil coolers ( which he freely admits he doesn't have ) he could go a lot faster. He averaged 217.5 mph a year later with 160-170 HP.

Bill Jepson

PS BTW auto engine naysayers Tracy's RV-4 has flown for 1600+ hours behind only a Mazda rotary engine.
 
Rotary10-RV said:
Ross,
Obviously I agree with you because I'm using a water cooled engine. But a very interesting comparison in the RV "real world" would be Tracy Crook winning the Sun 'n Fun 100 with his wankel powered RV-4. His cowling isn't as clean as it could be but he won his class twice. With an optomized radiator and oil coolers ( which he freely admits he doesn't have ) he could go a lot faster. He averaged 217.5 mph a year later with 160-170 HP.

Bill Jepson

PS BTW auto engine naysayers Tracy's RV-4 has flown for 1600+ hours behind only a Mazda rotary engine.

I spoke with Tracy Cook briefly at SNF when he came by the EGG display. Very nice, agreeable person, and so is his wife. He was inspecting the GEN3 PSRU.

The EGG factory has figured out a way to use radiators with about 30% more cooling surface without changing the RV inlet except for a plenum on the inside. There also is plenum feature for the oil cooler by moving it down and aft about 6". This all being done with a James cowl.

My concern about it is prop obstruction of incoming air. One would think a prop blast would increase air flow, but that is not always true. I get much better cooling at 1700 rpm than 2500, even at a relatively high air speed. The prop must be acting like a barn door at the higher rpms. Maybe that's why the 51 radiator was where it is and I noticed also, the FW190 had a turbine like fan aft of the prop, probably to facilitate air flow.

It is interesting in that after some 70-80 years of trial and error, we are yet to come up with a perfect system. Cooling and drag are an eternal challenge. :)
 
Eureka

Rotary10-RV said:
Tracy Crook winning the Sun 'n Fun 100 with his wankel powered RV-4. His cowling isn't as clean as it could be but he won his class twice. With an optomized radiator and oil coolers ( which he freely admits he doesn't have ) he could go a lot faster. He averaged 217.5 mph a year later with 160-170 HP. Bill Jepson

PS BTW auto engine naysayers Tracy's RV-4 has flown for 1600+ hours behind only a Mazda rotary engine.
Bill with respect he was flying in the "160 hp RV" class, while he claims he makes +180 hp. I also think the field in the class is pretty sparce. Also Tracy tinkers with this plane constantly and constantly says its not finished. That is a good metephore for an alterantave engine.

The Sun 100 race fast movers are in 180 hp RV class. Stock 180 hp RV with some tweaked airframe work (gear legs, cowl, wheel pants) are doing well over 230-237 mph on the same 100 mile course. If Tracy would race those birds with 180 hp, which is what he claims his rotary makes, he would be last. This is just to put it in perspective and takes nothing away from Tracy and all the work he has done. Also I think he is running what engine? Renesis? That's a lot more engine than the 13B's people use.

My point is the first place finish in class is a tribute to the builder and pilot for a job well done. However to competitive in the class he should be in, 180 hp class, and he needs to find almost 20 mph to place in that show.

I also would point to (shyly, this is racing after all) fuel burn; how much gas did he burn? I guarantee you if this a longer 2-3 hour cross country race, fuel burn would be an issue. That is of course the nagging negative of the mazda, fuel burn and noise.

PS: Note the Sun N Fun speeds are notoriously over stated (for all racers). Richard Vangrunsven wrote about this a few years ago in the RVator. Its great for bragging rights but its not a true 100 mile course. Your REAL world speed is lower.


David-aviator said:
I spoke with Tracy Cook briefly at SNF when he came by the EGG display. Very nice, agreeable person, and so is his wife.

It is interesting in that after some 70-80 years of trial and error, we are yet to come up with a perfect system. Cooling and drag are an eternal challenge. :)
I have talked to Mr/Mrs Tracy and they are nice folks. I would comment some 70-80 years of trial and error, a perfect system has been accomplished for small planes, its called an air cooled lycoming. :eek: :rolleyes:
 
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Not perfect George...if they were perfect, they would never break, and we would all want them. They do break, and we don't all want them.

Water cooling is, and always has been a challenge though.

__________________

Subaru%20Power%20avitar.jpg
 
Good on you

cjensen said:
Not perfect George...if they were perfect, they would never break, and we would all want them. They do break, and we don't all want them. Water cooling is, and always has been a challenge though.
Yep you took the joke well, good, you are right nothing is perfect. :D
 
Lose the logo

cjensen said:
Not perfect George...if they were perfect, they would never break, and we would all want them. They do break, and we don't all want them.

Water cooling is, and always has been a challenge though.

__________________

Subaru%20Power%20avitar.jpg


Lose the logo. I think I'm going to barf :eek:
 
David-aviator said:
I spoke with Tracy Cook briefly at SNF when he came by the EGG display. Very nice, agreeable person, and so is his wife. He was inspecting the GEN3 PSRU.

The EGG factory has figured out a way to use radiators with about 30% more cooling surface without changing the RV inlet except for a plenum on the inside. There also is plenum feature for the oil cooler by moving it down and aft about 6". This all being done with a James cowl.

My concern about it is prop obstruction of incoming air. One would think a prop blast would increase air flow, but that is not always true. I get much better cooling at 1700 rpm than 2500, even at a relatively high air speed. The prop must be acting like a barn door at the higher rpms. Maybe that's why the 51 radiator was where it is and I noticed also, the FW190 had a turbine like fan aft of the prop, probably to facilitate air flow.

It is interesting in that after some 70-80 years of trial and error, we are yet to come up with a perfect system. Cooling and drag are an eternal challenge. :)

The last line is the true one David. They are also true of both air and water cooled engines. What we need to do in an alternate engines forum is to quit baiting and switching and bi*ching about those of us who want to use auto conversions. There are MANY SUCCESSFULL EGG and rotary conversions now flying. My comments about Tracy's success are to encourage people to the fact that many other systems work well. Not that they are without effort, I continually stress that a CONVERSION is just that and if you aren't up to engineering many of the parts yourself just buy one from Eggenfellner or put in a Lyc.
That said David I can describe EXACTLY why you have the problem with your Egg converssion that you do. The configuration of the radiators is done the way they are because it is expedient, not the best system. The setup is well made but not optimised for radiator location. The obstructions caused by the cylinders on the EXIT of the radiators is why you have a problem at speed. Other manufacturers have done a better job on the radiators than Egg. I'm sure Jan will tell you that big improvements could be made if he wanted to use a cowl that was designed for an alternate location. He wants to be able to sell the SYSTEM as a bolt-up replacement, and has done a good job of designing the system to fit in a basicly standard cowl. The package is nicely done, but in no way optimised cooling wise.The Subaru is a wonderfully solid engine, VERY STOUT and better built than any Lyc, but to work it's best Jan has had to turn up the RPMS. This poses no trouble for the Subaru engine, it is very solid. The problems are with using a standard cowl, designed for a air-cooled engine. As has been noted by many they are not the same. The testing done on water cooled engines pretty much stopped with the P-51 in higher power applications. The radiator system they designed wasnt even optimised until the last versions using a K&W style bell shaped duct.
If I remember correctly yours was the plane used for the belt reduction drive tests? While I never liked the belt drive, the cowl used with it extended the openings forward and for the first time allowed a semi-decent inlet duct. The exit still sucked but improvements tend to be small. I'm sure cooling problems will plague the higher powered H-6 versions until a better cowling is eventually demanded. The old NACA and K&W tests proved in 1944-45 that the exit is as, if not more important than the inlet! On Subaru conversions I actually think NSI did a better job with the radiators than Egg, but failed to provide the "rest of the package." Some of the British experiments using leading edge inlets and wing aft exits showed promise but just disappeared with the jet age.
Anyway I'm too long already, but if you'er interested David send me a private message and I'll forward you some of the SAE and NACA war era files I have on disk. No system works without handling the details. BTW Ed Anderson's discussion of his work in the latest issue of CONTACT magazine is very informative for anyone doing an under-the-standard-cowl conversion.
Bill Jepson
 
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Zero cooling drag

Just coming back to the original posting re Zero Cooling Drag - I ran into Zoche Junior at the company display at AERO Friedrichshafen last week, and after querying him about the delay in getting his product to market ( I looked at the Zoche Aero Diesel back in 1990 ) he explained the reasons why it has taken so long. That is a whole other story, but he did explain that they are expecting to get positive thrust, or at worst, zero cooling drag, from their engines by ducting the cooling air effectively. Given the design of the engine, I can see that it may be possible, but I am not holding my breath that we will see any flying for a while yet....

Martin in Oz
 
Rotary10-RV said:
.....If I remember correctly yours was the plane used for the belt reduction drive tests? While I never liked the belt drive, the cowl used with it extended the openings forward and for the first time allowed a semi-decent inlet duct....
Anyway I'm too long already, but if you'er interested David send me a private message and I'll forward you some of the SAE and NACA war era files I have on disk. No system works without handling the details. BTW Ed Anderson's discussion of his work in the latest issue of CONTACT magazine is very informative for anyone doing an under-the-standard-cowl conversion.
Bill Jepson

It was Tom Moore's airplane that bit the dust when the belt drive failed, not mine.

My machine bit the dust back in '03 when a super charger belt jumped its pulley and tangled with the timing belt after penetrating the plasic belt cover. That was with the 2.5 engine. The H6 has a timing chain under a metal cover which is one reason I now have it.

Thanks for the offer on the SAE and NACA war era files. When you have time, send the most informative to [email protected] or if it would be easier to burn a disk, I will pay shipping, handling and disk cost.


 
Aircooled State of the Art?????

I disagree. Look at the new Diamond twin. Twin diesel automobile engines with gearboxes and radiators. Flying magazine called this plane the first light twin introduced in decades. It has simple-start FADEC injection system and a simplified prop feather system if you lose one of the engines. No mixture to worry about. It runs on jet A fuel. They did the research and I guess the decision was based on how long are the greenies going to let small planes burn unleaded fuel. We are living in a Al Gore Global Warming phobic world and it does not take a Einstein to read the writing on the wall. Leaded 100L makes up 1% of the market (from a EAA article on the subject).

Why would a new company go with such new technology? Well to my knowledge Diamonds are made in Austria so the European market is also important and leaded aviation fuel is harder to come by in Europe. But if you get a Hurricane Katrina this summer across one of the few refineries that make 100L, we all will wish we were burning something else.
 
Its pretty exciting the work you all do

Rotary10-RV said:
The last line is the true one David. They are also true of both air and water cooled engines. What we need to do in an alternate engines forum is to quit baiting and switching and bi*ching about those of us who want to use auto conversions. There are MANY SUCCESSFULL EGG and rotary conversions now flying. My comments about Tracy's success are to encourage people to the fact that many other systems work well.
Bill Jepson
I absolutely agree, but we need facts, realities and known real documented results.

I have noticed a great improvement in the Alt-Eng communities knowledge, realistic expectations and goals. My concern has always been smoke a hype was being substituted for fact. Fact is Tracy of RWS, flys what he sells, and flys the heck of it. He also has been very honest about his numbers. Clearly he does it for the love of it and not to get rich. He has made steady, constant progress and improvements. I saw his earily plane when he first got the Mazda flying long ago; it was crude. If we had more Tracy's I think the evolution would continue. However there is unlikely to be a quantum leap in performance or efficiency.

You do the Alt-Eng thing for different reasons today than saving money. A HOT Button debate which turns emotional is safety. I think with great care the Alt-Eng can be as safe, however they have a whole plate of DIFFERENT things that can go wrong. Even Tracy had a recall on his Re-drive because he found some problems during a routine tear-down inspection of his unit.

There is a great reason to go with a Rotary and Tracy's RWS, he flys and test his stuff. No disrespect to Eggy, he is a good natural engineer and sells a nice package, buts its so off the shelf it kind of takes away from the fun of having something unique and that has your stamp on. Also he sells stuff that does not have lots of time on it today or in the past. Fortunately its worked out OK, but there are some issues. If you don't mind the issues and want to solve them, this is the way to go. You want to fly and not be a pioneer or inventor, the Lyc is the way to go. The Subaru does not have as much individual development as the Mazda builders, except notably Ross, who is doing great stuff. I can't wait to hear about his Subaru RV-10 flying. Its going to be a success no matter what and an achievement to be proud of regardless of top speed or mpg.

One of the biggest issue is getting better cooling with less Drag. It gets better and the knowledge base gets greater all the time with several Guys on the list like you and Ross. Everyone is for you Guys to have a huge success and teach others how to do it. As generous as you all are with your knowledge, it will only get better, but there is a ceiling somewhere, but how high you guys can get is still open and being explored. That is exciting. :D The only reason to not over-hype and my bi*ching is to challenge you guys to go beyond the status-quo.
 
If the Lyco boys have anything actually useful to put forth about the subject on liquid cooled engine drag reduction, I'm all ears. :confused:
 
gmcjetpilot said:
<snip>No disrespect to Eggy, he is a good natural engineer and sells a nice package, buts its so off the shelf it kind of takes away from the fun of having something unique and that has your stamp on.<snip>
This is exactly ONE of the reasons I like it. It IS off the shelf of his production facility. There is no engineering for me to do...unless I want to. I don't feel that a homegrown Subaru is necessary to have fun with it. I simply don't want to roll my own (if I had Ross's skills, I certainly would though), and the package has really evolved over the years, and is a TOTALLY viable option for those of us that want a FWF package ready to go.


gmcjetpilot said:
Also he sells stuff that does not have lots of time on it today or in the past.
For the recency of his package coming to the market, I think the times are pretty good. Getting close to 1,000 hours on one of the E4's and 500 on an E6. Of course, more is always better, but this conversion hasn't been around for 70 years either.

And, Jan DOES fly his own stuff.

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Thanks for the info.

cjensen said:
This is exactly ONE of the reasons I like it. For the recency of his package coming to the market, I think the times are pretty good. Getting close to 1,000 hours on one of the E4's and 500 on an E6.
Thanks for the correction. That is good stuff. Yea my personal idea of doing the alternative thing is doing it yourself, however clearly the FWF Eggys have a market and a definite appeal. I am a little skeptical about the E6 being too heavy for the two seat RV's. I just hate weight on my own gut and my plane. Clearly he has been in business for many years while one, two or three of his competition in the alt-eng market have come and gone. I am a big free market guy; the market will speak. Clearly he is developing and growing to stay vital. That is only good for us. Also he is selling the used engines that are more echonomical. The new engine packages are too much money for most. If Subaru comes out with the Diesel for the North American market next year I am going to buy one, not for a plane but the whole car to drive. I loved my 1982 four door Subaru GL. I drove the heck out of it and traded it in, and I still regret it 14 years later.
 
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Subarus in all forms have far more flight hours on them than Wankels and their core reliability has been exceptional. Subes are the standard power plant for the RAF 2000 and Groen Brothers Sparrow Hawk gyros.

The Egg Subes alone have unquestionably accumulated way more flight hours than Tracy Crook has as well. Tracy has been the powerful drive in the rotary world and my hat is off to him for producing redrives and ECUs for the Wankel crowd. What Jan has done is to produce a FF package that comes in a crate, ready to bolt up to the airframe. In the numbers he produces, this is a staggering task. Not a perfect conversion to be sure but the best currently available to buyers. Certainly missteps have been made by Jan but such is part of being in this area of endeavor, especially considering limited budgets and the ability to do as much testing as he would like.

I think more reality about performance and weight on auto engine conversions has trickled down in the last year or two so buyers with a bit of common sense understand the tradeoffs of choosing one of these conversions.

As far as my -10 goes, the aim is to mainly advance knowledge on liquid cooled installations. I hope to equal or better IO-540 overall performance but that remains to be proven by the flight test data. I could easily fail at this goal. Much will be learned along the way however.
 
No problem George! One more thing...and it's just a clarification of the used engines no longer being available. IIRC, there was a special batch that became available late last year, and they are sold as far as I know.

At Sun N Fun, they came really close to selling out for this year, and may have by the end of the show.

Sorry for the thread creep...tends to happen...

:eek:

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And, Jan DOES fly his own stuff.

And crash his own stuff....

Chad,

when you get your plane fininshed I will be interested to hear how it goes. I just haven't been able to swallow most of the claims...including the install simplicity, based on numerous websites of end users (Brian Meyette seems to be pretty skilled for example, but his engine was deifinitely not installed in an afternoon).

Hopefully we will get the straight dirt from you once your plane is done, and flying.

Even where these have gone well, by the time you cut up the cockpit, and floor, etc...for all the different penetrations and so forth, and when you factor in the dramatic wiring complexity, this simple "FWF Solution" takes longer to install than does a simple baffled Vans approach. Or at least it has on every single installation and panel I am aware of.
 
Jconard said:
And, Jan DOES fly his own stuff.

And crash his own stuff....

Well, gosh, I guess no one should be flying around in a Piper Meridian or Malibu, or Challenger business jets, or any number of any other airplane. Yes, all of those have had crashes in their initial test phases. Jan's accident was an initial test on an airplane from a customer WITH HIS PERMISSION TO USE IT AS A TEST AIRPLANE. The cause of that accident has been elimintated from the package. That was a bad idea, and testing proved it.



Jconard said:
Chad,

when you get your plane fininshed I will be interested to hear how it goes. I just haven't been able to swallow most of the claims...including the install simplicity, based on numerous websites of end users (Brian Meyette seems to be pretty skilled for example, but his engine was deifinitely not installed in an afternoon).

Hopefully we will get the straight dirt from you once your plane is done, and flying.

Even where these have gone well, by the time you cut up the cockpit, and floor, etc...for all the different penetrations and so forth, and when you factor in the dramatic wiring complexity, this simple "FWF Solution" takes longer to install than does a simple baffled Vans approach. Or at least it has on every single installation and panel I am aware of.
Well, I will be a straight shooter on my install. I'm not gonna BS any numbers, and I will tell you all EXACTLY what I find, what I like, what I don't like.

Installation has come a LONG way, and I DO know several H6 installs that have been on and running in a day or two. I've heard the "installed in an afternoon" story too, but I don't know who it was or if it's even true. I don't really care. You work at your own pace. If it takes me a month or six to install, so be it. It won't be because of complexity. It will be my work pace. I've installed an O-360 in my Cherokee, and with three of us working on it, it took us three months (we rebuilt the engine baffling from scratch as part of this). We were meticulous, and were in no rush.

Brian can speak for himself here, but I know he is frustrated with his install. The STi engine is a different animal altogether as far as installation goes. He is just hoping it's all worth it at this point...which will be up to HIM to determine, not us.

Have you done both installations? How do you know it takes longer? I'm not trying to be argumentative here, but come on! If I take longer to install my H6 than you do your Lyco, that proves it? Install both, then tell me.

I can post a picture of the FW penetrations for the H6 when I get it on my website. There are seven holes, and two are for the optional heater (which I will have :cool: ). This may be two more than a carby'd Lyco and maybe one more than an FI engine. The floor has one hole for a drain.

What exactly are we cutting up in the cockpit and floor? :confused: That's a new one for me.

Dramatic wiring? Well, there is a lot of wiring, I'll give you that. It is already bundled and plugs in to an ECU. There are several other wires that need to be routed to switches, but the instructions are clear. I don't see this as being a problem.

Again, I will tell my story as I see it happening in front of me.

One thing I like about David and Ross, is that they are straight shooters as well. If it doesn't work, they'll tell you. I'll do the same.

:)

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Gmcjetpilot...a note

You mentioned " Also I think he is running what engine? Renesis? That's a lot more engine than the 13B's people use." a while back.

The Renesis IS a 13B- mostly the same parts, rotors, etc- the difference is that the Renesis uses side ports instead of the older setup that combined peripheral exhaust/side port intake. The Renesis breathes a little better at high speed, mostly because the side ports are larger, and has a few other tweaks that handle high speeds (>6000 rpm) a little safer. For aircraft use, it is debatable whether the Renesis is better than the older blocks- they tend to run a little hotter (side ports have more surface area exposed to exhaust heat) and the output is similiar with modern/improved intake systems.

With a rotary, the power/torque has a linear relationship to engine speed. Engine speed is largely dependent on the intake system. The Renesis has no problems running below 8000 rpms continually; most older 13B's fall off around 6K. A well designed rotary engine, with p-port intake and exhaust, can ouput 400hp, particularly with turbocharging. An OEM Renesis falls between 200-230hp, depending on type.

The real powerhouse rotary (race) engines use peripheral ports for both intake and exhaust- they scream at full power but they don't idle very well- due to contamination of intake charge with exhaust gas.

You implied that Tracy "fudged" his engine output at SnF. Tracy's SnF plane used a crude 3-motorcycle carb intake that did a little better than the Mazda OEM 140 hp 13B rating. The 160hp Tracy claimed was estimated based on fuel flow. He now gets a bit better efficiency and power with his FI system.
 
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Jconard said:
And, Jan DOES fly his own stuff.

And crash his own stuff....

Hmmm. I can think of at least 2 light jet crashes in the last year during the test flying phase. Not sure what your point is here...

Test flying new parts and airframes undoubtedly involves higher risk than the same old stuff. In order to establish reliability, uncover problems and implement fixes, test flying is a required evil. What would you have Jan do, machine up parts and sell them to customers with no test flight time?
:confused:

This would be like Van's offering RV12 kits without any stall/ spin testing being done.
 
Kudos to Tracy Cook for at least trying something different, but the fact is (as someone already mentioned) rotaries are thirsty. Curtiss-Wright came up with a SCRE (Stratified Charge Rotary Engine) and did work with NASA years ago. They claimed they could get very good SFC numbers, low .3s. A few decades and owners later and the last test I saw had a best case SFC around .42, no better than a Lyc. Still, it was a diesel/Jet A engine so per gallon consumption would be better than a Lyc. I've played with rotaries for years (no, not in planes) and can honestly say this is their downfall, otherwise the engine is hard to beat.

Harold, any more info on Zoche? They claim great SFC, but with no apparent activity it's hard to have faith. I also find it hard to believe their numbers with their current setup. DeltaHawk is also using crossflow ports with much more realistic SFC numbers if you take the time to read past the advertising. I still think the poppet valve exhaust engine will eventually be the winner, ie TCM or OPOC. Too bad TCM just took the money and ran...

As for my original thought about cooling, I just gave up on it after realising a fatal flaw. With low to medium speed, the leading edges would have anti-ice, but runback would be excessive/unacceptable. Even light icing conditions would be unacceptable. Still, if anyone wants to discuss my idea for day vfr only just shoot me an email and I'll tell you what I've come up with.
 
D-Cat:
Rotary "best case SFC around .42, no better than a Lyc"

I believe the best BSFC Mazda got is around 0.46, but that near-equality is a plus in my book; Lycs do very well fuel use-wise, as long as they run at economical cruise, but not at full rated power levels.

The rotary can run economically with very lean mixtures (>20:1), supposedly due to a natural tendency to stratify the charge near the spark plugs and they do not have a problem with detonation, at least while naturally aspirated. Rotary use in autos need richer mixtures to achieve acceptable idle and low-speed torque requirements.
 
Its all good and all a trade off

WilliamDCat and rtry9a:

Good points but we can talk all day about it and cut it any way you want to make a case or mitigate or promote one view or another. If you are really into the physics of what is going on in a rotary you end up with a really long skinny combustion shape that is just not efficient. Other aspects of the rotary hummmmmmmmm are absolutely neat.

However noise and fuel econ, weight, cooling drag and performance are all real or potential negatives of the mazda. Great strides in weight, cooling drag and performance have been made. Remember the Powersport rotary engine kits. Remember the two RV-8's with their rotaries (sadly one was destroyed). Remember Van's side by side flight test between them and Vans Lyc prototypes? The Wankel's gas burn was crazy and the ground noise was much louder. Performance and and weight, not too shabby. Powersport is currently inactive gone. The price of engine, reduction and expensive elect MT prop was pretty steep.

If I was building a "Rotary RV" it would be TURBO'ED and it would be for one main flight mission, flying long distance at very high O2 mask altitudes, where the turbo and fuel econ are most ideal. That is where the mazda shines, way way up high. Down low and full throttle will make you wallet cry and your airport neighbor's ear's bleed.

 
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gmcjetpilot said:
WilliamDCat and rtry9a:

Good points but we can talk all day about it and cut it any way you want to make a case or mitigate or promote one view or another. If you are really into the physics of what is going on in a rotary you end up with a really long skinny combustion shape that is just not efficient. Other aspects of the rotary hummmmmmmmm are absolutely neat.

However noise and fuel econ, weight, cooling drag and performance are all real or potential negatives of the mazda. Great strides in weight, cooling drag and performance have been made. Remember the Powersport rotary engine kits. Remember the two RV-8's with their rotaries (sadly one was destroyed). Remember Van's side by side flight test between them and Vans Lyc prototypes? The Wankel's gas burn was crazy and the ground noise was much louder. Performance and and weight, not too shabby. Powersport is currently inactive gone. The price of engine, reduction and expensive elect MT prop was pretty steep.

If I was building a "Rotary RV" it would be TURBO'ED and it would be for one main flight mission, flying long distance at very high O2 mask altitudes, where the turbo and fuel econ are most ideal. That is where the mazda shines, way way up high. Down low and full throttle will make you wallet cry and your airport neighbor's ear's bleed.


George,
I'll do this once and then not waste the time trying to convince the general population. The "physics" of the long skinny combustion chamber are NOT proven to be a problem in fuel consumption. The Mazda car that won LeMans outright in 1991 did so against all RPE competion in a FUEL LIMITED YEAR. They produced competitive (actually winning) power at .46 BSFC. There's a SAE paper written about it.
The 2 powersport powered planes suffered from what has killed or limited Powersport sales, their lack of money and development. The Powersports engine management system was and is lacking in development. I say this sadly as most of the mechanicals are fairly good. You can't judge all cars from one poorly jetted example. For a while the VW tuners tried running the Webber 48 ida 2 barrel carb on a long manifold they ran fine but got about 10-11 mpg in street use. Totally unacceptable. I hope Tracy will run the RV-8 up to Vans when he gets it flying. Tracy leans the engine before TAKEOFF! He claims it's because he 's a cheapskate. (his own words not mine) It would seem that the better the conversions get the louder the protest from the Lycoming supporters. The goal here is to make ALL the planes better. This will require pioneering work on somebodys part. Should we all just stop and build Wright flyers circa 1904? I just don't understand the general level of protest. Conversions should be banned etc.. (not you George, I know) if your already flying your RV behind a Lyc I'm not trying to stop you, go have fun. There are many among us who simply, "took the road less traveled by, and that makes all the difference."
Bill Jepson
Rotary10-RV
 
George:

Your comment that " noise and fuel econ, weight, cooling drag and performance are all real or potential negatives of the mazda" are probably true with ANY engine, including the Lycs/Conts. I think part of the problem lies in comparative difficulties.

The installed weight of the rotary compares favorably with the O-320's and O-360's, generally around 325 lbs, but the power output can vary anywhere between 150-300+ hp depending on the induction setup and the planned engine operating speeds. Which Lyc engine do you pick for comparison- by peak output, probably the heavier O-560's? Frankly, I dont see weight as a big issue.

Noise- the rotary is noisy and ideally needs a muffler. They do sound different, with a higher pitch (more like a race car) so people notice the rotary sound more often than the Lycs. Unmufflled lycs are also noisy. A muffled rotary is quieter than most Lycs at the airport.

Fuel burn- I agree with you, sort of- the Rotary is probably a bit less efficient at cruise, but the difference's are not that great when both engines are correctly leaned for best cruise- probably less than prop/drag differences between test planes. Van's Powersport comparison were not the best examples to compare, as they were not capable of leaning mixtures as most FI rotaries are these days. The fuel burn rates are about the same or less at high power levels, because the rotary is water cooled and quite resistant to detonation/heat problems with leaner mixtures. The biggest fuel related downside to the rotary is the requirement to lubricate rotors with oil somehow- most mix 2-cycle oil with fuel. As far as cost/mile, the rotary is a clear winner- it uses 92 octane mogas (or avgas when required).

I also agree with your cooling drag comment- the air cooled engine will be more efficient because it runs twice as hot as a water cooled engine- BUT, is that a plus when durability and maintenance issues are involved. I do not mind a little more cooling drag if it results in longer engine life.

In my opinion, the rotary has an advantage with cost, durability and smooth running, the Lyc is by far the easier installation and will be easier to sell. Like anything mechanical, everything is a compromise, a tradeoff. To each his own.
 
Wankel's air pump

rtry9a said:
As far as cost/mile, the rotary is a clear winner- it uses 92 octane mogas (or avgas when required).

I hope that's with a turbo. Normally aspirated rotaries like the cheap stuff much better (check the physics if you disagree).

For anyone interested in running a rotary, be aware that while their great resistance to detonation (same reasons as above) can allow them to "run" with extreme timing and leaning, it will cause excessive apex seal wear and consequently low TBOs. Normally detonation is not possible with a N/A rotary running on anything better than diesel, but it is possible with turbo/supercharged rotaries and typically results in catastrophic failure almost instantly.

On the plus side, a major concern for geared motors is engine drag. I never looked into the physics, but geared Lyconosaurs seem to live much shorter lives when power is reduced significantly during desents on a regular basis, even while avoiding shock cooling. With the low drag of a rotary (you can easily turn them over by hand with just the alternator pulley), I'd think there'd be significantly fewer PSRU problems.
 
rtry9a said:
Noise- the rotary is noisy and ideally needs a muffler. They do sound different, with a higher pitch (more like a race car) so people notice the rotary sound more often than the Lycs. Unmufflled lycs are also noisy. A muffled rotary is quieter than most Lycs at the airport.


I also agree with your cooling drag comment- the air cooled engine will be more efficient because it runs twice as hot as a water cooled engine- BUT, is that a plus when durability and maintenance issues are involved. I do not mind a little more cooling drag if it results in longer engine life.

Wankels are earsplitting in unmuffled form, some being measured at over 125 decibels at 30 feet. The same acoustical signature and very high EGTs makes a reliable muffler relatively heavy.

My research shows unquestionably that when properly executed, liquid cooled engine installations exhibit lower drag than air cooled engines. This is not as simple as just Delta T as I have said before. What remains to be seen is if an efficient radiator system can be reasonably fitted to an RV airframe.

Wankel engines have had many problems with torsional vibration on their redrive systems just as piston engines have.

Weight wise, I have not seen a rotary installation which is actually lighter than an equivalent Lycoming installation. In fact, there are few if any auto conversions which fit into this category.

The Wankel is a neat engine with advantages and disadvantages like any other engine. It is no magic bullet.
 
R6ejguy,
A lot of the rotary crowd use the automotive Spintech or Dynoflow mufflers with good results, others have tried their own designs with varied results, mostly bad. Tracy Crook reports from observers on the ground that his plane is quieter than most Lycs he's been around. Not scientific results, but interesting.

A few notes on the weight issue, Ive seen several comparisons and generally the weights are very close. Rotary installations are a bit lighter than the Subi engines are. My stock OEM Renesis motor w/metal pallet and bands shipped (from Australia) at 190 lbs, complete with heavy OEM manifolds and a bunch of stuff not used in the aircraft. Need to add the PSRU (37lbs), cooling system, fluids (26lbs) to that.

One problem is the Lyc weights are all over the place with the many engine variants. To be fair, the rotary installations can vary a lot also, particularly with the engine mount designs and radiators used.

Tracy used a relatively heavy sandwiched mounting plate/redesigned Vans/Lyc mount in an older model 13B, multiple thick radiators mounted in front of the engine, and 3 carburetors and a heavy modified Mazda intake manifold in his plane- he reported 345 lbs FWf w/fluids. That weight compares favorably with 320/360 engine installations. To reduce weight further, a Shertz beam mount can be used, lighter tuned tubular intake/exhaust manifolds used, the Renesis motor is a few lbs lighter than earlier motors, as is the fuel injection vs carb. The rotaries can produce more HP than other piston engines per lb.

Paul Lemar posted a power:weight scattergraph of various engines in aircraft- the rotaries were all significantly lighter than the lycs and heavier than the turbine engines.

"Wankel engines have had many problems with torsional vibration on their redrive systems just as piston engines have." I know of past problems associated with linking rotary engines to dynometers, not in actual installations. Torsional vibs are handled through rubber bushings in the PSRU, I believe.

The Wankel is a neat engine with advantages and disadvantages like any other engine. It is no magic bullet. I completely agree. :rolleyes: I like the Subi's and Lycs as well- who knows which is "THE BEST"= it depends.
 
rv6ejguy said:
Wankels are earsplitting in unmuffled form, some being measured at over 125 decibels at 30 feet. The same acoustical signature and very high EGTs makes a reliable muffler relatively heavy.

My research shows unquestionably that when properly executed, liquid cooled engine installations exhibit lower drag than air cooled engines. This is not as simple as just Delta T as I have said before. What remains to be seen is if an efficient radiator system can be reasonably fitted to an RV airframe.

Wankel engines have had many problems with torsional vibration on their redrive systems just as piston engines have.

Weight wise, I have not seen a rotary installation which is actually lighter than an equivalent Lycoming installation. In fact, there are few if any auto conversions which fit into this category.

The Wankel is a neat engine with advantages and disadvantages like any other engine. It is no magic bullet.

Well, we have total thread creep in this thread! We started out with William talking about leading edge cooling, which is totally appropriate in an alternate engine forum. Why this always degenerates into something else baffles me. I'll mea culpa in that I have some defensive comments about my own engine of choice. The fact is that selection of a powerplant for an aircraft requires a series of logical steps, depending on which type of engine you choose. Air or water cooling? One requires radiators and plumbing, the other a series of baffles. Whatever engine you choose you will have to do a good job putting it in. If the choice you make doesn't have a good support system you better be able to engineer some of the parts yourself. The IDEA of leading edge cooling or whole wing cooling is very attractive. Anything that might improve your performance with minimal losses is worth investigating. The people who have investigated this idea found it lacking in most circumstances. High power or small area ( a particular problem on a 2 seat short wing RV ) require a lot of mods to make it work. There are some layouts that have been mentioned the DO work and show promise. If you are willing to do this much design work I'd suggest that moving the tanks out 1 rib bay and running a LE inlet/burried radiator such as Ross mentioned earlier shows the most benifit in a somewhat exotic layout. The P-51 scoop is easier and also effective. You make your choice based on available information and then build it and test. No matter how good it looks on paper, it may or may not work. If you succeed, and I for one hope you do document what you have done and why. You can then help the rest of us "improve the breed" which is the truest spirit of experimental aircraft.
Bill Jepson
 
While many engine weights look good on paper, the true test is ready to run in the aircraft. Various databases exist which list empty weights for several popular homebuilt designs with both Lycoming and auto engines. I've never seen an equivalent auto engine airframe weigh less than the Lycoming ones.

While the Subaru and Wankel could probably match a Lycoming installation in weight per hp if done correctly, few if any have to date.

I find much of what Paul Lamar writes as questionable and much very theoretical. The man has been a self appointed Wankel "expert" for years but has never actually completed a Wankel powered aircraft. Tracy Crook on the other hand has done tremendous work with Rotaries and really been the big driving force behind putting them in the air. He has respect from almost everyone involved in flying Wankels and is a very smart guy in many areas. The doers are much more important than the dreamers when it comes to this field IMO.
 
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