inflite adjustable props

[Russ]

chasing hints on how to operate these things............to "cruise"

 

2.5 efi subaru, prop pitched at full fine to limit engine to 5500revs

 

soobs rev all day around 4000...........4300

 

craft has............manifold vacuum, fuel flow,tacko, and all the other normal instruments

 

so.............setting up for "cruise" is best achieved how, getting conflicting advice from some folks, hence asking here.

 

 

[facthunter]

Consider it to be a variable "top" gear. if you have it too "tall' it will not work well . Your engine will "slog" and you won't get the horsepower you need, and the prop may be at a higher angle of attack than optimum.

 

If the pitch is too fine you will over rev. Play with it over a period of time. Will be good having a fuel flow meter so you can get airspeed/fuelflow figures. convert to true airspeed if you fly over a fair range of heights.

 

At what height would you use full throttle normally for cruise? At low levels you might consider not using too low a rev setting with full throttle.

 

With a certified set-up the MP/ RPM limits would be specified. You have to use a bit of commonsense and be sensitive to the engine. ( as you do when driving a manual car).

 

You may find there are rev ranges to avoid. Thes are not easy to determine and relate to harmonics in the drive train. Seek advice from people using a similar prop and redrive and engine. Nev

 

 

[Russ]

thanks for this.........................being the first to set up this type combo, seeking that info is not avail first hand. Suck and see seems to be the go, monitoring MP and fuel flow might be the key to what's the best settings. ............again...thanks

 

 

[bones]

Russ, surely there is someone in your local area up there with a VP prop on something, they should be able to tell ya how it should be done.

 

What i would do though is, set the prop to hold the RPM to your max you want static, then read the MP, that would be my max MP i would use when in flight, for when your triming the prop.

 

I thought it be flying by now? and i only realised it was you at the Atherton airport a few weeks back as you drove out, i was driving the double deck cow taxi, getting av gas.

 

 

[Russ]

they refer to their cessna manuals for the settings.............that means jack sh!t to my application.

 

Prop makers attached manual tells me to refer to engine makers specs for best settings ...........( subaru would go in a spin if i sought that )

 

Suck and see is going to be the go i think ( WOT at 5500 shows 29 inches MP ) my thinking is, that is 100% power........so if i set that MP to around 75%........20MP thereabouts then crank on some prop pitch , monitoring fuel flow, revs, etc......then i should be getting results ?????????

 

Maybe i may be able to even drop that MP even more to achieve an engine just loafing along................will know in 3 weeks, coze that's when i take delivery.