Prop questions

[Karmutzen]

VariEze O200, I’d like a little better climb and acceleration on takeoff. Before going too far down the rabbit hole, is it as easy as a new prop? I see ballpark static rpm target numbers of 2350. Anything else? Relative merits of an extension (how long?), spinner?

[Kent Ashton]

What are you seeing in cruise at 8000-8500 MSL?   Generally we would prefer to max out the rpm at that altitude when leaned to peak power which requires relatively more pitch.   A prop pitched for climb will leap off the ground but overspeed the engine at the cruise altitudes.   You could sacrifice cruise speed for more climb—depends on your priority.  Maybe have two props.    Try to borrow some props and compare them.

IMO your static number is about right for a cruise prop.   I would expect a climb prop to yield a higher static.   I usual test them at 8500 leaned to peak, trying to get one that maxes out the engine and accept lower takeoff performance.   On an EZ I had a climb prop that was quite a kick but it would overspeed the engine at higher speeds, however it was just fine as a spare prop.

I think spinners on a pusher are a waste.

Edited January 11, 2021 by Kent Ashton

[Marc Zeitlin]

16 hours ago, Karmutzen said:

VariEze O200, I’d like a little better climb and acceleration on takeoff. Before going too far down the rabbit hole, is it as easy as a new prop? I see ballpark static rpm target numbers of 2350. Anything else? Relative merits of an extension (how long?), spinner?

Not nearly enough information to make a recommendation. What prop is on the plane now? Do you have wheel pants? If so, what type? What RPM do you see static? What RPM do you see on the takeoff roll, just as you rotate? Is the 2350 RPM you mention what you've seen recommended, or what you actually get? What RPM do you currently see in cruise, and at what DA, throttle and mixture setting? What RPM do you see at WOT, leaned for max power, at what DA?

What I like to see in an all-around climb/cruise propeller is the ability to exceed maximum engine RPM (which, for an O-200, is 2750 RPM) by 50 - 100 RPM when at WOT, leaned for max power, at your usual cruise altitudes (call it 8500 ft.). So in this case, you'd want to see 2800 - 2850 RPM (you won't hurt the engine) in those conditions. If you get less RPM than that, you've got more of a cruise prop, and if you get more RPM than that, you've got more of a climb prop. But these #'s will also be dependent on aircraft drag - no wheel pants will decrease cruise speed by ~120 KIAS and RPM by ~100.

Also, if the prop is not matched to the airframe well, you can have good static but lousy cruise, or vice-versa.

Everything is interrelated - without more information, no recommendation can be made.

[Karmutzen]

Marc and Kent, thanks. I’m just in the process of mounting wheelpants (fitted, now need to glas the cuff to the leg) picture attached. Don’t know what they are. I’ll get that done before any further cruise tests. 
 

I was getting 2350 static with the old tach and thought all was good, then I put a new tach in and it only shows 2150. Need to crosscheck with an external optical tach to see which tach is right. WOT at 2000’ without wheelpants was 150 knots at 2580. 

Prop on there now is a locally made 63-72.

[Kent Ashton]

Those pants will be nice.   A run at WOT at 2000 feet does not tell you much.  You're probably at full rich so it's not realistic.  With regard to Lycomings (I know you have a Conti), Lycoming says you cannot hurt the engine leaning when below 75% power so I think it is better to get up to 8000-8500 feet, where the engine can only produce 75%, lean it to peak power and see what you get.  It is a consistent way to check a prop.  I expect Conti says something similar.  Static can vary depending on the atmospheric conditions or whether the aircraft is sitting in a little headwind or tailwind.

However, you want better takeoff performance.  Sometimes the the nose strut height can be a little low making the fuselage deck-angle flatter.  Also make sure you're getting full elevator-down travel.  These airplanes cannot lift off until the canard develops enough lift to raise the nose.  Flatter fuselage and less elevator travel would increase the rotation speed.  Also front-seat weight can be a factor.  😞

[Karmutzen]

Progress, cross-checked the new T-30 with a TruTach, and it is accurate to 1% throughout the range. Next to finish the wheelpant install, though that won’t change the 2150 static, or the doggy takeoff performance. Preference still to glass the transition to the gearleg, instead of to the top of the pant?