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Ground run shroud

RV8RIVETER

Well Known Member
Patron
I have been planning on starting the break-in on the ground for many years. Now that I have actually experience doing it, I thought I would post this for anyone else thinking the same.

It was fairly simple to build. The hardest part is making the scalloped tabs that bend over and rivet to the top skin. Used the old ECi overhaul crews recommendation of 1 cubic foot of inlet area for each cylinder. The cable in the center I think now is overkill, but didn't want to take any chances. When bolted on it is rock solid.

Did my first break-in ground run this morning, 50 minutes 80% power. The shroud worked well, with the highest CHT htting 330 deg. I need to increase the size of the oil cooler inlet some as the oil max'd out at 250 deg. I used an extra Van's eyeball vent rear end and thought it may be too small, but wasn't sure how much pressure I was going to get.

I know there are those out there who like all the technical data, like me, (no offense Dan :) ) , but we are trying to get this plane to Oshkosh, so I am sorry there is no time to try and modify my engine plenum press box to take readings. If I have time after Mel has given the plane his OK, may try and get pressure data, because I would like to know. On the other hand there is the old, "it just works" way of thinking.








 
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Just curious?

It's quite a set up.
Out of curiosity, what are you hoping to gain from running your engine on the ground?
Your 8 looks like it's ready to fly, why not do the breakin in the air.
I am sure you have a good reason.
 
I like it, nice set-up. Extra time spent on options like this are well worth it. Piece of mind as well as safety.
 
It's quite a set up.
Out of curiosity, what are you hoping to gain from running your engine on the ground?
Your 8 looks like it's ready to fly, why not do the breakin in the air.
I am sure you have a good reason.

Speaking for myself only, we all have our opinions and choices. I do not feel comfortable test flying a new plane AND a new engine, too much going on, cuts the safety margin. Also, my airpark has no good options if the engine quits on take-off, so it is good to know the engine is running well and has been run hard for the most critical part of the break-in. When it flys, we only have to concentrate on how it is flying.
 
I like it!

The constraints associated with doing a proper engine break in seem to me to be incompatible with flight testing activities, this has been a niggling concern in the back of my mind. I may do the same as you.
 
All Good reasons!

You mention all good reasons for doing the ground tests.
How many hours are you planning on doing this?
Your concerns have been shared by many others before you, I have just never actually seen anybody do what you are doing.
I suppose if you keep your cylinder temps under control and keep the oil from cooking, your engine will break in just fine.
Hope you make it to Oshkosh, and good luck on your first flight.
 
ground run

The optimum for ground break in is a test club. Any of the engine shops that have test cell would probably discuss the test props.
 
The only reason to have a test club is nobody wants a full size, very expensive, prop in their test cell. I guess another would be known hp, if you have a test club pitched so that you know it takes 180hp or 200hp to make full RPM then you have a poor mans dyno check. Other than that there is no difference.

According the test guru at ECi, they used this method for many years on all of their overhauls until they built their test cell. You can even see a picture in their engine break in pamphlet.
 
How many hours are you planning on doing this?


Your concerns have been shared by many others before you, I have just never actually seen anybody do what you are doing.

The engine is running very well so while I orginally planned to try and get 4 hours, I think I will be happy with one more hour.


Yes, I remember a thread long ago where people said "you can't run it on the ground" and "pay the engine builder to do extra runs" ect.. Some nay sayers out there, some think it is way to complicated. It is not that much time to make, took me 2 days. And it shows, made from scraps and didn't want it pretty, just rigid. Based on my first numbers CHT cooling is better on the ground. The engine doesn't know the difference. The only down side is you had bettter be on good relations with your neighbors. :)
 
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Request for more info...

What engine RPM and MP were you using? Did you sweep the area around the aircraft pretty carefully? I prefer to be moving before I have my prop turning over 1800 RPM because it is quite easy to suck up a rock and ding it.

Your comment re noise got me wondering if this method with a fixed pitch prop would be louder because of higher engine/propeller speed.

Do you have approximate dimensions of your shroud or did you just eyeball it?

Looks like a good idea to me. I won't have many options for forced landings around W52 either (guess I could "drop in unexpectedly" on Jon at Parkside). I can hear the occasional plane take-off from W52 from my house, which is about 1 1/4 miles away. I know our airport owner has had noise complaints from neighbors. I think they are from low level overflights from aircraft making improper departures, but I expect that running at high power for an extended time period would meet with similar objections from the same people.

Larry T
 
What engine RPM and MP were you using? Did you sweep the area around the aircraft pretty carefully? I prefer to be moving before I have my prop turning over 1800 RPM because it is quite easy to suck up a rock and ding it.

Do you have approximate dimensions of your shroud or did you just eyeball it?

.....but I expect that running at high power for an extended time period would meet with similar objections from the same people.

Larry T

Most of the time spent above 23 inches and 2400 rpm. From there gradually increased to 25/2500, 26/2600 and then about 5 min at full power.

Size. See first post, 1 sq ft per cylinder, so 4 cyl is 4 sq ft. Mine is more like 4.2 sq ft due to how I eyeballed it.

Yes we swept the ramp very thoroughly. In a 3pt attitude there is quite a bit of ground clearance, but who wants to take chances. Nothing on the prop but bug guts. :)

The comment about the neighbors was kind of toungue in cheek. Quite a few turned out, to what was making the noise, but no real complaints. We live on airpark after all. Made sure late morning and would only run one time a day. If you are worried I would ask around about what time is best. It probably didn't help to be so close to the hanger with the door open. Makes a nice megaphone for the opposite side of the runway.
 
Yes we did. The neighbors ramp has 1/2" J bolts ( I think) sunk in the ramp to use as tie downs. Very interesting, when we untied it we found the bolt bent over about 10 deg and no one ever saw the tail come off the ground. Stick was full aft all the time.
 
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shroud images

Hi Wade, do you still have the images of your ground run shroud? They seem to be lost on the imageshack.us site. Thanks, Mickey
 
I will be breaking my engine in on the ground as well. Googling and you tubing ground engine run shroud or something similar will show some good examples. Also airboat Lycoming pics also use something similar.

It looks very easy to do. Just the problem with the noise. The other benefit is you are testing your entire engine installation on the ground, instead of with your pink body several thousand feet in the air.
 
Where is the oil cooler?

I wonder if it was something like this?
http://rv7preflight.blogspot.com/ -scroll down to the 2nd December 2011 post.

Perhaps it's just the perspective, but I don't see an oil cooler mounted on that shroud. For those that have their oil cooler mounted on the engine mount or the firewall all you really would need is to duct some scat tube to your oil cooler installation.

Charlie
 
shroud

Found this one - I guess it's what is being suggested. Seems simple and solid.

Shroud.jpg
 
I couldn't open the photos but will search for and check the reference.

IIRC, test clubs provided the important benefit of reducing the effect of harmonics in the crank if ran "unloaded"
 
I noticed the post above that mentioned tying down the tailwheel. I seem to recall from a few years ago where some guys were doing that to their planes and doing full power run-ups for some reason or another (comparing amount of power or something like that), and ended up damaging their fuselage by bending that bulkhead back there...

An awful lot of airplanes out there that have done their engine break-ins "the old-fashioned way"...by flying.
 
I looked over your blog post as well.

I assume for break in on the ground you'll run at high (full?) power; do you think the clecos will hold? That would make me nervous. Perhaps in order to store flat you could secure some of it with nylocks and screws or bolts?
 
Clecos

I looked over your blog post as well.

I assume for break in on the ground you'll run at high (full?) power; do you think the clecos will hold? That would make me nervous. Perhaps in order to store flat you could secure some of it with nylocks and screws or bolts?
I think they will hold, but might switch to pop rivets anyway - I have lots of spares. I know a guy that flew with his front skin clecoed on, which gave me confidence that they will hold.

While taking a shower last night I realized I should have just used hinge to fit the pieces together - that would hold securely, look nice, and be easy to fold. Oh well - next time!
 
Ground run

Did a few runs today with the shroud - couple of things I learned:

  • the engine moves *a lot* - the shroud was of course trying to keep up with the engine shaking, and struggling. When the engine was not shaking during higher RPMs, all was fine.
  • The airflow caused the top to bulge up several inches - this is very stiff 2mm (~0.075") aluminum sheet - very thick - I'll add some angle tomorrow
  • the cooling was much better - I was getting close to 360 with no shroud, during some 2-3 min ground tests, and today the max temp I saw was 265. Perhaps too much cooling. OAT was about 3°c. (38°F according to the GRT EFIS)
  • I could not bring myself to bring it up to 2700 RPM - max I hit was just under 2000 - I was quite terrified that if something broke lose I would launch into the air like a scud missile. This baby wanted to take off! I will add a second strap to the tailwheel.
  • I will add some additional strength to the shroud - the math says it's fine, but the idea of that thing breaking loose and slamming into the windscreen didn't seem pleasant. :eek:
 
Just a thought, but how about a single piece of aluminum that is bent into a half pipe that is bolted to each side of the engine similar to what you have now? No seams and you could cut it so that it creates a cone.
 
single piece shroud

Just a thought, but how about a single piece of aluminum that is bent into a half pipe that is bolted to each side of the engine similar to what you have now? No seams and you could cut it so that it creates a cone.
I think this is a great idea.

You could probably do it with with flexible enough sheet, and some good geometry to cut out the shape flat and then just install it. With the amount of cooling I seem to be getting, sealing it up tightly at the back does not seem to be very critical.
 
I don't think a whole lot is critical. Except maybe being strong enough so that it doesn't fly apart and damage the very expensive stuff right behind it.

Think hurricane force winds.
 
I ve got a question...

I could not bring myself to bring it up to 2700 RPM - max I hit was just under 2000 -

I really like what you are doing here. so please keep us posted. But don't you need to really run her hard to properly break in those jugs? I am no expert but 2000 will no be enough I am assuming?

That actually brings me to a question. If one were to do this with a F/P he would only see 2300isch depending on prop even at full power. Is that the same as far as breaking in the engine as 2700 in flight? I mean the engine is producing max manifold but cant swing the bigger pitch. In other words can you use this with the C/S by reducing RPM on ground but still use full Manifold.
 
Fuel flow

... But don't you need to really run her hard to properly break in those jugs? I am no expert but 2000 will no be enough I am assuming?

That actually brings me to a question. If one were to do this with a F/P he would only see 2300isch depending on prop even at full power. Is that the same as far as breaking in the engine as 2700 in flight? I mean the engine is producing max manifold but cant swing the bigger pitch. In other words can you use this with the C/S by reducing RPM on ground but still use full Manifold.
Based on all the reading I've done, you are absolutely right - to break in the rings/cylinder walls you need a lot of power. I think the key thing to look at is the fuel flow - to get close to 2000RPM I was just under 6 GPH - no where near enough power.

My plan is to add another strap to the tailwheel and car to give me 2000 Kg of holding force there - no idea what's needed but I assume far less - and try again tomorrow. I've just beefed up my shroud, removed the clecos, and replaced them with 8-32 screws. Hopefully it will go well and I won't end up with a shroud in my teeth!

img_9537-1024x768.jpg
 
I am going to make a shroud and do the same on my engine, and will be making the shroud soon.

The O-360 with a CS prop is going to pull 300-370 kg of force at full power. I doubt the RV tail wheel/fuselage section was designed to handle that force, in the direction it is applied.
 
Force on tailwheel

I am going to make a shroud and do the same on my engine, and will be making the shroud soon.

The O-360 with a CS prop is going to pull 300-370 kg of force at full power. I doubt the RV tail wheel/fuselage section was designed to handle that force, in the direction it is applied.
I was not sure it would handle the force of a thrust test, but the factory assured me that it would.

What's your plan? Tie off at the gear?
 
The gear mounts are made to handle a great deal of force. I will also somehow tie the tailwheel to the straps going to the main gear mounts, to keep it centered, and down. But the tension will be on the main gear mounts. Maybe just a spreader bar between the straps, with the tailwheel strapped in the middle. I will see how it looks when I get to it.
 
ground run

I made a shroud and ran engine per Mahlon's brake in part 1. All looks good and I have a static rpm about 2350. I can't seem to figure out what rpm will give me 75% power for the next phase. I have a fixed pitch prop and no fuel flow so not much help there.

Can anyone tell me what static rpm will give 75% power? I can't see how to get this out of the available power curves?
 
I made a shroud and ran engine per Mahlon's brake in part 1. All looks good and I have a static rpm about 2350. I can't seem to figure out what rpm will give me 75% power for the next phase. I have a fixed pitch prop and no fuel flow so not much help there.

Can anyone tell me what static rpm will give 75% power? I can't see how to get this out of the available power curves?
Any chance you can install FF? It's included with most engine monitors. If you don't have a good engine monitor you will have a much more difficult time diagnosing issues, and tuning your engine. Today FF almost seems like a mandatory bit of information, like altitude and airspeed.

The RPM that gives 75% power will depend on density altitude, prop pitch, and probably some other variables. Kevin Horton wrote a really good article discussing this here: https://www.kitplanes.com/determining-engine-power/
 
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