Propeller questions

[FLS]

Thanks PJ but I meant it was interesting that the weight loss and CG change weren't modeled in AH.  I was asking if, in the case of a wingtip loss, only the drag and lift difference was modeled.

[Oldman731]

I'm thinking the potential for overspeed does exist. 

I'm sure it does.  Governor can take care of a lot, but I'm sure that it can't take care of everything, particularly in Jug Dives.

- oldman

[PJ_Godzilla]

Thanks PJ but I meant it was interesting that the weight loss and CG change weren't modeled in AH.  I was asking if, in the case of a wingtip loss, only the drag and lift difference was modeled.

Okay. I wasn't sure of your basis. There seems to be a wide range of technical knowledge in this place. Of course, I know you're training staff so I figured you're technically clued in anyway but might like to see those EoMs.

[Stoney]

In real life I've never had a prop gain RPM.  When hauling jumpers we used a low RPM setting with high airspeed (well, high for a Cessna -- 170 +/-) and didn't notice any RPM change.

My Grumman had a climb prop and a 160HP conversion on it, and I would have to pull throttle during decents to keep the RPM under redline.  Not quite a dive, but once I was showing 150-160 mph IAS, the prop was wanting to turn around 2900 rpm.  That being said, I really don't know the overspeed potential of the Jug, just seems like a prop optimized for 300-350 mph wouldn't tolerate that kind of speed.  I could be totally wrong though.  Bodhi works on them--perhaps he could tell us...

[hitech]

Stoney: Ever take it to a prop shop and have it adjusted?

I had similar problem when I got my RV. It had a Areo/ pitts prop on it that never had it's min and max pitch stops adjusted. Min would over speed at cruise speeds and I would have to back off on power.

Ah has both min and max pitch stops. So they can over speed.

HiTech

[FLS]

Okay. I wasn't sure of your basis. There seems to be a wide range of technical knowledge in this place. Of course, I know you're training staff so I figured you're technically clued in anyway but might like to see those EoMs.

I always appreciate your responses but my brain isn't wired for math. I get F=M*A but that's probably just based on experience.

[colmbo]

My Grumman had a climb prop and a 160HP conversion on it, and I would have to pull throttle during decents to keep the RPM under redline.  Not quite a dive, but once I was showing 150-160 mph IAS, the prop was wanting to turn around 2900 rpm.  That being said, I really don't know the overspeed potential of the Jug, just seems like a prop optimized for 300-350 mph wouldn't tolerate that kind of speed.  I could be totally wrong though.  Bodhi works on them--perhaps he could tell us...

Since you said "climb prop" I'm betting you had a fixed pitch prop in which case RPM will increase with an increase in airspeed.

[moot]

I've seen overspeed in AH but never damage from it.

[Stoney]

Since you said "climb prop" I'm betting you had a fixed pitch prop in which case RPM will increase with an increase in airspeed.

Yes, but its the same principle.  Once the blades on a constant speed prop hit the stop, any increase in speed beyond that will create an overspeed condition.

And I didn't get it re-pitched.  After I had two cylinder base nuts shear from the high-compression pistons (long story), I overhauled it and put low-compression pistons back in.  That dropped the power enough that I couldn't get it past 2700 RPM much at all.