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-   -   Manual Pitch prop (https://vansairforce.net/community/showthread.php?t=175110)

Roarks 09-10-2019 04:49 PM

Manual Pitch prop
 
I'm honestly a low time pilot. I have a hard time wrapping my brain around constant speed propellers for some reason. I've flown aerobatics with one... I understand it helps keep from overspeed doing maneuvers... but adjusting one for cruise flight is something I've never done... thus ignorance. Tried one in flight sim... and seems like I even touch the prop lever I end up lagging the engine and loosing airspeed.

That said... I am a helicopter pilot too... and those make perfect sense to me. Engine RPM is governed or set with throttle, and we control pitch directly.

So while sitting in a Propeller class (A&P) I learned about 2 position props. Sounds amazing. Apparently spitfires were like this and there is a company Hoffman that makes one.

So this all comes down to $$$. a nice CS prop costs what $15k? Now there are oil seals, a prop governor and a whole bunch of other stuff that needs $ maintenance. I'm honestly okay with a fixed pitch prop, but this two speed prop business sounds cool! So thinking about the mechanism... Why not make the pitch infinitely variable so you can tune it in? Seems mechanically simpler than a discrete "two position".

The mechanism is fairly simple. It could be a simple lever in the cockpit... maybe even a collective/throttle like a helicopter... which really is instinct now.

Takeoff and landing would obviously be low pitch... probably even rig up a low throttle+not low pitch=alarm. Apparently some spitfire pilots had issues with this.

I like mechanical simple things. I bet I could make it fairly easily=cheap...This sounds amazing to me what am I missing?

bkervaski 09-10-2019 05:24 PM

Quote:

A nice CS prop costs what $15k?
$7K-$8K for a Hartzell CS prop.

BobTurner 09-10-2019 05:24 PM

Quote:

Originally Posted by Roarks (Post 1372868)
I like mechanical simple things. I bet I could make it fairly easily=cheap...This sounds amazing to me what am I missing?

Well, for starters, the hub forces. With a fixed pitch prop, the prop is one piece, and the aluminum prop carries the centrifugal load. Once you want the pitch to vary, you need two separate prop blades, and a hub attachment to keep them from flying off. The force on that hub is measured in TONS. And, while being held against those forces, the blade has to be able to rotate. Not totally simple.

The other stuff (governors, transfer collars, etc) generally go to engine TBO with little or no maintenance.

Roarks 09-10-2019 10:52 PM

Quote:

Originally Posted by bkervaski (Post 1372873)
$7K-$8K for a Hartzell CS prop.

Really... I'll have to look again.

Quote:

Originally Posted by BobTurner (Post 1372874)
The force on that hub is measured in TONS. And, while being held against those forces, the blade has to be able to rotate. Not totally simple.

CS props do it. Helicopter Tail rotors do it. Huey tail rotor is almost 200hp. it's mechanical.

N941WR 09-11-2019 06:00 AM

My old I-290d2 was set up for a "controllable pitch propeller". It was neither a constant speed nor a fixed pitch prop.

On the nose of the engine, there was a lever, about where the prop oil line goes in on some engines or where the forward mount goes on others.

From what I understand, and I could be wrong, my O-290d2 came off an agriculture version of the Super Cub. (Think crop duster.)

There was a cable that would run to the cockpit which allowed the pilot to manage the RPM's by adjusting the prop pitch.

When I called Lycoming years ago, they connected me with a gentleman who had experience with this engine (he must have been really close to retirement). He sold me the NOS part I needed to convert the engine to a fixed pitch prop and told me about how the original prop would have worked.

The original props were wood with metal shanks and apparently didn't last very long. Still, it would have been a cool prop to put on my RV.

smokyray 09-11-2019 10:04 AM

Constant Speeeeeed....
 
Quote:

Originally Posted by Roarks (Post 1372868)
So while sitting in a Propeller class (A&P) I learned about 2 position props. Sounds amazing. Apparently spitfires were like this and there is a company Hoffman that makes one.
I like mechanical simple things. I bet I could make it fairly easily=cheap...This sounds amazing to me what am I missing?

RS,
Great question, one that has been multum disputatum on this site in the past. :) My Dad owned a 65HP 1945 Taylorcraft BC12D and shared a hanger with a 1946 65HP Luscombe 8A. The 8A ragwing was equipped with a Beech Roby manually adjustable wood prop.
https://www.notplanejane.com/beechcraft.htm I flew both aircraft extensively in my youth and was able to compare them it every arena including STOL, formation flying and cross country. The bottom line was the Luscombe has a slight edge but not a huge one yet the Beech Roby always intrigued me.

Twenty years later my first sport-plane, a Van's RV4 was and still is a marvel of aviation prowess. It had ALL the qualities I required in a personal aircraft. At 925 pounds with a Wood Sterba prop and salvaged 0-320 I could take off from my 400 meter rough turf strip, clearing 50' pine trees on a hot, muggy FL day, climb at 1500 FPM and cruise at 180 MPH at 8500'. I could perform aerobatics, fly formation with and dog-fight my F16 bros in their RV's and travel from Idaho to FL in one (albeit long) summer day. I didn't want to add weight or cost so I kept it as is for many years. However comma, I kept my eye out for a lower cost, albeit lighter weight alternative CS propeller. My search yielded nothing I could either afford or wanted to compromise in additional weight.

Several years ago I flew a Lancair 235 on a pre-purchase inspection. It was equipped with an MT electric constant speed 3 blade prop.
https://www.mt-propeller.com/en/entw/pro_elec.htm
It had a three position setting, needed no oil pressure or assorted lines and was light. I was very impressed at how well the little LA performed with only 118HP and how fast it cruised with the MT electric. The owner informed me that Hoffman also made a similar prop. MT had a service center near where I lived in FL so I flew in for a visit. Not only did they show me an electric CS prop, they allowed me to test a FP MT 2 blade prop on my RV4. That prop still sports the nose of "The Bandit" and the new owner (an F18 pilot) tells me it still performs well against any equally or even higher equipped adversary!
Worth a look...


Bottom line, over the past 25 years I have now flown all the RV models, many with CS props of all the varieties. My own take is a FP prop works well and helps it retain a lighter nose, lower EW and cost with less complexity.
The beauty is like Burger King, you can have it your way...

V/R
Smokey

PS: Another option might be ground adjustable. I have also flown both the Sensy and the Whirlwind. Smooth, capable and not a bad compromise.
https://whirlwindpropellers.com/aircraft/

David Paule 09-11-2019 10:50 AM

Adjusting a CS prop for cruise is easy - Select a desired rpm with the prop control and tach, and select manifold pressure with the throttle and manifold pressure indicator. Done.

The manifold pressure is limited by your altitude on normally-aspirated (non turbo/supercharged engines). At many cruising altitudes, full throttle is an option, since the cruising altitude controls that.

Descents can be interesting. As you descend, the outside air pressure increases and so does the manifold pressure. So you need to reduce throttle appropriately. If you don't, you may find that the manifold pressure has increased to the point that you are no longer descending. It's a form of automatic altitude stability, kind of.

Dave

Roarks 09-11-2019 11:53 AM

Quote:

Originally Posted by smokyray (Post 1372974)
RS,
Great question, one that has been multum disputatum on this site in the past. :) My Dad owned a 65HP 1945 Taylorcraft BC12D and shared a hanger with a 1946 65HP Luscombe 8A. The 8A ragwing was equipped with a Beech Roby manually adjustable wood prop.
https://www.notplanejane.com/beechcraft.htm I flew both aircraft extensively in my youth and was able to compare them it every arena including STOL, formation flying and cross country. The bottom line was the Luscombe has a slight edge but not a huge one yet the Beech Roby always intrigued me.

Twenty years later my first sport-plane, a Van's RV4 was and still is a marvel of aviation prowess. It had ALL the qualities I required in a personal aircraft. At 925 pounds with a Wood Sterba prop and salvaged 0-320 I could take off from my 400 meter rough turf strip, clearing 50' pine trees on a hot, muggy FL day, climb at 1500 FPM and cruise at 180 MPH at 8500'. I could perform aerobatics, fly formation with and dog-fight my F16 bros in their RV's and travel from Idaho to FL in one (albeit long) summer day. I didn't want to add weight or cost so I kept it as is for many years. However comma, I kept my eye out for a lower cost, albeit lighter weight alternative CS propeller. My search yielded nothing I could either afford or wanted to compromise in additional weight.

Several years ago I flew a Lancair 235 on a pre-purchase inspection. It was equipped with an MT electric constant speed 3 blade prop.
https://www.mt-propeller.com/en/entw/pro_elec.htm
It had a three position setting, needed no oil pressure or assorted lines and was light. I was very impressed at how well the little LA performed with only 118HP and how fast it cruised with the MT electric. The owner informed me that Hoffman also made a similar prop. MT had a service center near where I lived in FL so I flew in for a visit. Not only did they show me an electric CS prop, they allowed me to test a FP MT 2 blade prop on my RV4. That prop still sports the nose of "The Bandit" and the new owner (an F18 pilot) tells me it still performs well against any equally or even higher equipped adversary!
Worth a look...


Bottom line, over the past 25 years I have now flown all the RV models, many with CS props of all the varieties. My own take is a FP prop works well and helps it retain a lighter nose, lower EW and cost with less complexity.
The beauty is like Burger King, you can have it your way...

V/R
Smokey

PS: Another option might be ground adjustable. I have also flown both the Sensy and the Whirlwind. Smooth, capable and not a bad compromise.
https://whirlwindpropellers.com/aircraft/

WOW! Roby huh. THAT'S AWESOME! Thanks for sharing

I'm designing an engine for my RV8 and Great lakes... probably for a friends acroduster too... I'm out at the prop... stub/flange. I don't want to fool with prop governor and all that and started thinking of alternatives. I'll have to see if I can get my hands on one of those. I've been eyeballing how Spitfire blades are made... should be a good fit.

Reformed SeaSnake 09-11-2019 01:43 PM

Aeromatic
 
Roark,

It looks like what you may be interested in is an aeromatic. There is a company in Nevada making new ones ($5350 and up according to their web site at www.aeromatic.com). There have been other discussions here at VAF regarding these props. Good luck.

Note, these are not controllable by the pilot. If that is what your looking for, the electric variable pitch and hydraulic CS props are really the only two options available currently. You could buy the aeromatic hub and blades and adapt or build a helicopter Swash-plate pitch control that could be controlled from the cockpit. It would be an interesting engineering challenge (like putting retractable gear on an RV), but I think it would end up costing more than an off-the-shelf CS prop/engine combination and you may have a hard time getting the plane insured.

Roarks 09-11-2019 03:47 PM

Quote:

Originally Posted by Reformed SeaSnake (Post 1373009)
It looks like what you may be interested in is an aeromatic.

Interesting for sure.


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