Quote:
Originally Posted by Roarks
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?
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Well I dare say almost everything under the sun has been tried with props, but maybe you have a better idea. However the standard is hydraulically controlled "constant speed" prop with a prop governor. This is not new, been around for a half century. There are variable pitch props both in flight and on ground but those have given way for the most part to either "constant speed" or fixed props. Not to say having the ability to vary the pitch of your prop does not have benefit, but I am saying go all the way to constant speed. If you love simplicity and lower cost than FIX prop is an excellent compromise.
As I understand it you want a mechanical link to prop pitch that is simple but allows you to set the prop pitch in flight for low pitch (high RPM) for high pitch (low RPM) and maybe something in between... like shifting a 3 speed manual transmission. There have been variable pitch non-constant speed in-flight adjustable pitch props. Navion and Bonanza have had them. The Navion used hydraulics I recall and the Bonanza electric. These would not be cheaper today and most owners have converted their Navion or Bonanza to hydraulic constant speed props.
Moving blade pitch to a mechanical control in the cockpit (no electrical or hydraulics) on a spinning prop requires some kind of swash plate and linkage (like a helicopter). I don't know of anyone accusing helicopters of being simple. Again hydraulic is the standard because it has proven to be the best design.
ELECTRICALLY controlled both available pitch and constant speed props have been done from the early days to present. You can buy electric props but cheap they are not. A slip ring and brushes provides power to the electric pitch motor in the hub. Again hydraulic is the standard and has replaced electric exclusively for certified planes. If low cost and simplicity is your goal while having control over blade pitch, the path of least resistance is hydraulic constant speed prop.
The compromise is a fixed prop. This is a very good compromise giving good TO and climb and efficient cruise.
In general fixed pitch props are cheaper, lighter and smoother and can't get more simple. For the experimental plane builder/owner having one or two spare fixed props for STOL or Speed or general purposes is doable. To swap a prop is about an hour or two. Wood fixed props are wonderfully smooth. If you love simple FIXED PITCH is the way to go.
There are also fixed pitch ground adjustable props but I don't care for them for high powered Lycomings, based on poor history from some manufactures in the past. Things may have changed. Ground adjustable props are fine for small engines on ultralights, and in the past ground adjustable props didn't do well on the Lycoming with strong power pulse. I'm not up on the latest greatest props. I much prefer a fixed prop as mentioned above. Simple, reliable, cheap, light. If you want a different prop it's pretty straight forward swap.
Cost? You can find a serviceable used Hartzall CS Props for $4000 and a governor for $1000.
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