Adjustable-pitch vs. constant speed prop

D

DMD3.

Pre-takeoff checklist
Joined
Nov 8, 2014
Messages
474
Location
Tifton, Ga
Display Name
Display name:
DMD3.
I’ve heard that some experimental aircraft have in-flight adjustable props, yet they are not constant-speeds. Like a c/s, the blade angle is adjusted to give better takeoff & climb performance and then adjusted for cruise. But yet like a fixed-pitch, the rpms will increase during a dive or as the aircraft builds speed, and decrease during climb, etc.

Are a/p props any less expensive than c/s props? I realize that a c/s can cost several times more than a f/p, AND they have to be overhauled more frequently. Would a/p’s need to be overhauled as frequently? Also, are a/p’s lighter than c/s’s? A c/s prop is heavier than a f/p if I’m not mistaken.
 
Frankly, I don't seem to recall a single adjustable pitch prop application that's not constant speed, in significant numbers out there. Experimental airplane or not. Which is to say, it's a moot point. Your choices on a cost basis are effectively c/s or f/p. Reminds me of the pressure carb applications: "Poor man's fuel injection...no carb icing! well okay some too....but less!" :D
 
hindsight2020 said:
Frankly, I don't seem to recall a single adjustable pitch prop application that's not constant speed, in significant numbers out there. Experimental airplane or not. Which is to say, it's a moot point. Your choices on a cost basis are effectively c/s or f/p. Reminds me of the pressure carb applications: "Poor man's fuel injection...no carb icing! well okay some too....but less!" :D
Click to expand...

Apparently they exist, but are fairly uncommon. Someone else has asked this question in the past:

https://aviation.stackexchange.com/...-constant-speed-and-variable-pitch-propellers
 
hindsight2020 said:
Frankly, I don't seem to recall a single adjustable pitch prop application that's not constant speed, in significant numbers out there. Experimental airplane or not. Which is to say, it's a moot point. Your choices on a cost basis are effectively c/s or f/p. Reminds me of the pressure carb applications: "Poor man's fuel injection...no carb icing! well okay some too....but less!" :D
Click to expand...

They exist, I’ve owned a couple in the past. Youll mostly find them on antique aircraft. I don’t know of any installed on common e/ab aircraft in significant numbers however.
 
Ivoprop makes some. They're a homebuilder's prop. They started out as a ground-adjustable, but later adapted an electric motor to them and fed it through slip rings and brushes, to change the pitch.

https://www.ivoprop.com/inflightmagnumodel.htm

Ivo's props don't have blades that rotate in a hub. They are a composite prop that has steel rods inside the blades that are rotated to warp, or twist the outer portion of the blade. It's much less efficient than rotating the blade: a truly efficient prop would change the pitch at the hub much more than at the tip. Do the trigonometry and see.
 
hindsight2020 said:
Frankly, I don't seem to recall a single adjustable pitch prop application that's not constant speed, in significant numbers out there. Experimental airplane or not. Which is to say, it's a moot point. Your choices on a cost basis are effectively c/s or f/p. Reminds me of the pressure carb applications: "Poor man's fuel injection...no carb icing! well okay some too....but less!" :D
Click to expand...
Our club has an inflight adjustable electric pitch empty prop

The control box Fort is extremely homemade looking, looks like someone purchased a project box at RadioShack with a few off the shelf knobs and dials but seems to work well

It has two modes, Auto and Manual. On auto you dial in the RPM you want with a knob and on manual you toggle a switch from course to fine
 
Dan Thomas said:
MT prop.
Click to expand...
I knew what he meant. I have a 9 year old at home, phonetics work just fine amongst knuckle-dragging pylets. You know you're among the hooked on phonics crowd when you're called the uppity one for daring to use trisyllables..... :D
 
Thanks. I hate touchscreen typing but wrestle often with the disastrous speech to text..

Yes, 'MT' prop
 
Stewartb said:
Maybe thinking of Aeromatic?
Click to expand...
I've got some time flying behind a Russian knock off of the Aeromatic prop.
PXL_20220627_021339963-01.jpeg
It's actually a genius design which changes pitch based on airspeed (wind load on the blades) and rpm (it has counterweights which get adjusted for the specific application). No knob inside. Works well enough to make me wonder why there isn't a modern version.
 
There is. Aeromatic is in business.
http://www.aeromatic.com/

My exp Cub has a Whirl Wind constant speed. My fixed pitch-constant speed threshold is 200 HP, and my Cub engine exceeds that easily. Below 200 HP I’d choose a ground adjustable prop.
 
Here you go https://www.propellor.com/
Adjustable, but not constant speed. Has settings for takeoff, climb, cruise and hold. Also has a feather setting.
 
I flew a Hartzell prop on the Navion that was controllable but not constant speed. The Gopher engine on my plane lacked the accessory pad necessary to drive the governor. Often when we flew together the PNF played prop governor and adjusted the blue knob to keep the RPMs in line.
 
The B35 Bonanza had one for something like 9 years.

https://www.bonanza.org/globalassets/migrated/pdf/electricpropelleroperation.pdf

Not sure how many are left that haven't been converted, but here's one on eBay.
https://www.ebay.com/itm/284708811226
s-l1600.jpg
 
Last edited:
My Bonanza F35 has an electric prop. You can select manual or constant speed mode.

Early Beech Roby props were on some aircraft...maybe Cardboard Connies...early Bellancas. They had a hand crank on the panel for changing pitch.
 
I flew a J-3 way back that had an A-75 with a Beech R-003 prop. AKA, a Beech-Roby. Controlled by a hand crank installed aft of the throttle. The prop control kinda looked like a window crank for a 1947 Desoto. Shafting ran fwd to the prop where a pinion turned a six inch dia gear on the prop. Pre-take off was to crank it backwards (low pitch) to the stop, then blast off. When the wheels left the ground, crank 1/2 turn fwd for climb out. Level off and crank fwd for cruise. It turned that (kinda heavy) Cub into a heck of a STOL plane. I picked up a wrecked Luscombe years later and a R-003 was thrown in. I installed it and flew it for a couple of years. She had a lot of "dig" on T.O. & climb. This prop had an annual requirement for a hub tear-down and non-destructive test. The hub was repacked with grease for another year. Took about a year for it to stop slinging grease on the windshield.

When I was a kid, the Old Ones would rave about the Aeromatic prop. Auto shifted from low pitch on T.O. then high pitch in cruise. It was a factory option for just about everything from Ercoupe to Cessna Airmasters and everything in between. Many Stinson, Tripacers, Belancas, Globe Swifts, etc were delivered with them. The FAA killed them when one slung a prop blade. The controversy arose when a broken fence post was found among the wreck. FAA said the prop failed. The Aeromatic fans said it hit the fence on T.O. There is a guy in Fallon, AZ that has the TC, had/has a supply of hubs & blades, that only could be used on an Exp. Art Scholle had Aeromatic props on both of his airshow Chipmunks. It certainly qualifies as a ground adjustable prop. Once you set it up and flight test it, it does all the work. Hint on operation principle: Centrifugal force does all the pitch changing. Ingenious.
 
Last edited:
DMD3. said:
Are a/p props any less expensive than c/s props? I realize that a c/s can cost several times more than a f/p, AND they have to be overhauled more frequently. Would a/p’s need to be overhauled as frequently? Also, are a/p’s lighter than c/s’s? A c/s prop is heavier than a f/p if I’m not mistaken.
Click to expand...
Some info from the TCDS for Piper PA-22's. Could be a helpful starting point. Example.
Fixed pitch wood prop: 11 lbs (Sensenich)
Fixed pitch metal prop 25 lbs "
Koppers Aeromatic prop 34 lbs
Hartzel C/S prop 54 lbs (My guess is that governor and controls would be in addition to this wt
and be counted against the airframe, not the engine/prop)
 
Look closely at the nose of the plane behind me. I got a Beech-Roby. Love it!
 
DMD3. said:
I’ve heard that some experimental aircraft have in-flight adjustable props, yet they are not constant-speeds. Like a c/s, the blade angle is adjusted to give better takeoff & climb performance and then adjusted for cruise. But yet like a fixed-pitch, the rpms will increase during a dive or as the aircraft builds speed, and decrease during climb, etc.

Are a/p props any less expensive than c/s props? I realize that a c/s can cost several times more than a f/p, AND they have to be overhauled more frequently. Would a/p’s need to be overhauled as frequently? Also, are a/p’s lighter than c/s’s? A c/s prop is heavier than a f/p if I’m not mistaken.
Click to expand...

I have an electric MT on my Lancair.
What plane?
Would a/p’s need to be overhauled as frequently? yes
are a/p’s lighter than c/s’s? yes mostly but there are some lighter c/s on the market like the whirlwind.
Catto is also starting to make c/s blades which fit a Mccauley hub.
I would choose f/p if choosing based on cost.
I would choose c/s if weight and diameter is not a problem.
 
My Taylorcraft had a Beech-Roby on it at one point. The guy that installed it filed a 337 for the install. (not needed, per TCDS it only needed a logbook entry) Now it no longer complies with the LSA rule.
 
You must log in or register to reply here.
Back
Top