In flight variable pitch props

[Bennie Vorster]

Is it really worth the money spend to fit an in flight variable pitch prop to my Bush Baby and what do they go for lately. Will I have to replace my E Box 3.47 as well. What performance can I expect ?

[Bennie Vorster]

Morph Help.

[Aerosan]

Bennie, the question is what do you want to achive

[Morph]

Bennie,

I never got mine to work properly as I couldn't get the prop balanced.

However the BB is a high drag plane with a fairly limited cruising range of 70 to 90mph. All of these speeds are readily achieved using a fixed pitch prop and varying the rpm, as well as adjusting your angle of attack using the flaperons

If you take something like a CTsw which is very slippery and capable of speeds from 65kts to 129kts then variable pitch props make more sense. a fixed pitch prop might not be able to give you the whole speed range without running out of rpm. You could find the engine screaming at max before reaching 129kt cruise. By increasing the pitch on the variable pitch prop, the cruising rpm could be reduced to a more comfortable level, say 5000rpm on the 912S motor.

[Morph]

The concept behind the IVO inflight prop is to take off at max rpm, say 6500 to 6800 on a 582.

Then with wide open throttle start increasing the pitch. Your rpm will drop as will the rate of climb. Stop when you are climbing at about 100fpm. Now reduce the throttle marginally to get straight and level flight.

You are severly limited by the BB wing which will not be able to be adjusted to fly straight and level beyond 90 to 95mph. except if you apply forward pressure and full thottle, but then it's not comfortable to cruise at that speed.

As a result I don't really see the point of a variable pitch prop.

However Mogas has one in his BB. Perhaps he can give a better answer

[Ian]

I went through the same 'investigative movie' as Morph with the Savannah.

What really dissuaded me:

1. The C of G has to be re done, the VP mechanics weigh quite a few Kgs right on the nose of the aerie.. may have to carry some ballast to get the envelope acceptable
2. The torque demand on the motor increases so I dont think there is much fuel saving.
3. The cost outweighs the 'earlier arrival'. The Neuform VP is really nice, but not much change from 35K otherwise I may have bought one with the kit
4. Higher compexity = more maintenance and higher reliability risk IMHO
5. Less to do at take off and landing times

I know John Waterson has an IVO VP (relatively simple) on his demo Sav and that seems to work ok...



Cheers ian

[ICEMAN]

Bennie,

Read this for some insight to make your choice:

http://www.auf.asn.au/groundschool/propeller.html

[Mogas]

I concur with all said above but must point out that the main advantage of a VP in this airframe is that you can use all the available HP at take-off thus making it a nice STOL plane. I get airborne in 75m, close to MTOW, airfield 500' elevation, temp 25C.
I got my prop cheap. New cost is about R30K.
Would I buy a new one for my next BB? No.
Average runways I use are about 400m. Ample length to get in the air with a cruise prop at MTOW.
My 2c worth.

[Boet]

Bennie, nie die moeite werd nie. As jy nog nie een het nie, laat Pieter de Necker vir jou n 72" X 52" prop maak. Jy sal NOOIT weer n ander prop koop nie. :D