Multi-engine CS props on Vans Aircraft

[Boomer506]

I am familiar with the difference between multi-engine CS props and single-engine CS props. But I have also talked to aerobatic pilots that prefer their props to go course pitch (instead of fine pitch) with a loss of oil pressure.

Does anyone out there have any experience/opinions on using multi-engine props on our aircraft? I have a line on a couple of Geronimo props with a 12 inch base spinner that might just work.

Thanks in advance

 

[Boyd Birchler]

Counter weighted/Muli engine style prop on RV

I too agree with the idea of course pitch if and when you have an oil interruption to the prop. I plan to do sustained inverted flight with my RV7 and have purchased a Hartzell compact CS prop that is designed for aerobatics.

If the Geronimo props are counter weighted and of recent design (not the old steel hub with blade clamps) they should work fine. The Gernimo may have had one prop that was for a left turning engine. These props will feather all of the way if the engine has a long oil interruption. This may help glide with an engine out.....

The Mooney conversions for the 231 to a Rocket had a full feathering prop and with an engine out got a substantial increase in glide ratio because of that feature.

 

[Boomer506]

I see many views, but only 1 reply (thanks to my responder). Would I be the first to attempt this install? It seems like there are a lot of twins out there that are not getting flown and are selling for cheap. Maybe a good source of engines and props for out fleet. Has anyone attempted this before?
Thanks in advance

 

[BobTurner]

The down side is that there are a few failure mechanisms - governor failure, oil transfer collar leaks, plugged oil line, etc. - where the standard SE prop will let you limp home at a low throttle setting (to keep rpms below red line). With the twin prop you'll be landing immediately.
If you do go this route, be sure to get the 'backwards' governor that goes with the prop.

 

[Boomer506]

Those are good points that I hadn't considered. I was thinking that prop and governor failures would lead to 'course' pitch and not to full feather. And that in course pitch I could still limp home, with throttle back to prevent excessive manifold pressure and not excessive rpm as with the SE CS prop. Are you pretty sure that they fail to full feather? There is a prop shop in Seattle that I can ask too. Thanks for your input.

 

[BobTurner]

The whole point of a prop on a twin is to feather (minimum drag) in the event of engine failure/no oil pressure. I don't know if the coarse (sic) stops can be adjusted to anything other than full feather.

 

[jrs14855]

Props

The light piston twin props do not automatically feather. The prop control must be moved full aft into the feather detent. Turboprops are different, the Garretts and some larger engines have negative torque sensing, which in the event of engine failure drives the prop ALMOST to feather. Complete feather must be done manually.
The Geronimo is an OLD conversion of the Piper Apache. The props are likely very old unless the airplane has been recently upgraded. Almost all of the small twins are old airplanes. The props are typically subject to AD's that are prohibitively expensive. Piper Apache was produced from around 1954 to 1959. A few later airplanes were called Apaches but were completely different airplanes.

 

[Boomer506]

This is an old Geronimo, but the props are the newer, non-500hr AD types. If they are like my old Apache props, they will go to course pitch, but not feather unless feather is selected on prop control AND the motor is still windmilling. I am going to call this local prop shop and ask them about failure modes. I'll let you all know what I find out. Something tells me these old twins may be a potential source of engines/props/insturments for our community.