newbie question re prop overspeed with constant speed prop

[mcrae0104]

Yes, ensure that you have adequate cooling for the engine. Maybe a fan in front of the belly scoop to keep things cool.

Just curious, does anyone know what pressure drop is needed across the radiator for an engine like this for ground run?

 

[pantdino]

Imagine your "future self" reading this post again - several weeks from now, post crash, from the burn ward of the hospital.

Would this still seem like a "rational approach"?

Considering what is on the line here, I think a "more" rational approach is spending a few hundred bucks on a used 5.3 from a junkyard, an engine test stand from Summit, and run the PSRU on the ground with a test club until you are satisfied it's going to survive for more than a flight or two.

I remain confused about how I'm told here that with the prop fixed the plane will hardly be able to take off or fly, but the owner with his set for an aggressive minimum pitch says the prop pulls like crazy and the plane climbs at 2500-3000 fpm. He only pulls the prop back to cruise.

Anyway, my plan is to run the gearbox for an hour or so on the ground and change the oil a few times before installing the governor for the first flight. Then change every 2 hrs or so and check the governor for silt,

 

[Voidhawk9]

I remain confused about how I'm told here that with the prop fixed the plane will hardly be able to take off or fly, but the owner with his set for an aggressive minimum pitch says the prop pulls like crazy and the plane climbs at 2500-3000 fpm. He only pulls the prop back to cruise.

The prop will be changing pitch a LOT before he touches the handle for cruise RPM, unless he was an unusual manual-pitch prop?

 

[Toobuilder]

I remain confused about how I'm told here that with the prop fixed the plane will hardly be able to take off or fly, but the owner with his set for an aggressive minimum pitch says the prop pulls like crazy and the plane climbs at 2500-3000 fpm. He only pulls the prop back to cruise.

Anyway, my plan is to run the gearbox for an hour or so on the ground and change the oil a few times before installing the governor for the first flight. Then change every 2 hrs or so and check the governor for silt,

After reading many of your posts, I still don't think you understand how a C/S prop works. My Rocket will climb at 4000 FPM at 85 knots - but if I push the nose over to a faster airspeed, the prop adjusts to maintain the same 2700 RPM I used for max climb. If my prop maintained the same pitch (fixed) that was best for the 85 knot climb, then at 86 knots, the engine would over speed. My airplane will go from 0 airspeed to 220 knots at the same RPM, thanks to the blade articulation of a C/S prop. A fixed blade angle on a fast airplane means you are taking a huge compromise on one end of the performance envelope. Pitch the prop for 80 knots, that's what you get.

 

[pantdino]

After reading many of your posts, I still don't think you understand how a C/S prop works. My Rocket will climb at 4000 FPM at 85 knots - but if I push the nose over to a faster airspeed, the prop adjusts to maintain the same 2700 RPM I used for max climb. If my prop maintained the same pitch (fixed) that was best for the 85 knot climb, then at 86 knots, the engine would over speed. My airplane will go from 0 airspeed to 220 knots at the same RPM, thanks to the blade articulation of a C/S prop. A fixed blade angle on a fast airplane means you are taking a huge compromise on one end of the performance envelope. Pitch the prop for 80 knots, that's what you get.

You are right- I didn't understand the function of a C/S prop well enough. Now I do, thanks to you guys. It's not a mechanical linkage by which you control the actual pitch angle.

I ran the new gearbox for half an hour total and see some tiny, shiny fines floating in the oil. Will do multiple more times then install the governor and plumbing.

Thanks for all your help to this dummy / newbie.

Jim

 

[BJC]

Thanks for all your help to this dummy / newbie.

You would have been a dummy if you had not asked.


BJC

 

[Toobuilder]

You are right- I didn't understand the function of a C/S prop well enough. Now I do, thanks to you guys. It's not a mechanical linkage by which you control the actual pitch angle....

No problem Jim. To add to the confusion, there ARE "controllable" propellers that look just like a CS prop and use much of the same technology, but lack the governor. In these cases you are setting blade angle in flight, but changes in power or speed will change the RPM since the blade angle does not follow a feedback loop.

 

[pantdino]

I think I still need to do some testing to see what the performance characteristics are with the minimum pitch stop set for aggressive pitch. No matter what one does, the risk of a runaway prop from governor failure cannot be fully eliminated.

Would you have to disconnect the governor during tests to be sure it is not increasing pitch?
It sounds to me like a CS prop governor will function to increase pitch and you can't prevent it from doing so.

I guess I'm thinking that power will make up for decreased prop efficiency if the pitch is too high for optimal take off and climb.
Pilots are taking off with 180hp with this plane and it has 270 available for use.
Is my thinking off base?

Thanks again,

Jim