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Overspeed a Ground Adjustable Composite Prop?

dmat

Well Known Member
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Can a light ground adjustable prop like a whirlwind 200GA be overspeed? I am thinking about upgrading my metal prop to ground adjustable but have heard over-speeding can happen on light props. I personally don't see how considering its one pitch and it shouldn't change as its ground adjustable but I figured I ask the peanut gallery.

Thanks,
D
 
Over speeding can happen on pretty much all fixed pitch props - just put it into a full power dive. Of course the airframe might come apart first. With the ground adjustable prop, you’ll need to exercise caution if you put it into fine pitch, or ‘climb’, configuration, and then hope to do high speed cruise.
 
As Bob says

Fixed pitch props are set to absorb all the engine energy before passing max engine or prop rpm.
Ground adjustable props can be adjusted to do be limited the same way.
This doesn't account for the potential to over rev if the throttle is held in while pointing the nose down- no set up can prevent that.
 
Can a light ground adjustable prop like a whirlwind 200GA be overspeed? I am thinking about upgrading my metal prop to ground adjustable but have heard over-speeding can happen on light props. I personally don't see how considering its one pitch and it shouldn't change as its ground adjustable but I figured I ask the peanut gallery.

Thanks,
D

Overspeed is more likely if the propeller is pitched for STOL. Our instructions recommend setting the pitch so that your static RPM is 2200-2300 (gives powerful takeoff and good cruise performance). My RV-6A with O-320 160HP and GA-200L-72" is set to 21.5° with static rpm of 2200 and full throttle level flight rpm of 2700 rpm. If I pitch it to 22.0° or 22.5° then I cannot reach 2700 rpm without diving the plane, but I lose quite a bit of takeoff performance (static rpm of 2150 or 2100 respectively).
 
This is what flight testing is all about. I just replaced a fixed pitch Sensenich aluminum prop, with a Sensenich ground adjustable carbon fiber prop, and can tell you, that the prop speed limit is totally up to you - because you can adjust it. The Whirlwind ground adjustment technique is different than the Sensenich technique, but they both work to the same conclusion - to get you to a pitch setting that best satisfies the performance you are looking for. You want short takeoff and initial climb performance? A fine pitch setting will give you this, but with a degradation of cruise speed, and understand that wide open throttle (WOT) will likely over speed your engine, so control that with your throttle, hence a slower cruise speed. If you want ultimate cruise performance (coarse pitch), your runway and climb performance will suffer, but a cruise performance similar to a constant speed prop (high MP with lower RPM - 2400ish). Think of it like driving your car in overdrive all the time - the ultimate cruise pitch setting. Or driving your car in second gear all the time - short takeoff and climb. It’s a fixed setting, and you get to pick the setting - and you can change it anytime you want - on the ground before you fly.

On mine (Sensenich GA), I’ve chosen a pitch that will give me 2700 RPM at WOT, which is a compromise, allowing decent takeoff and climb performance, and cruise performance better tan the fine pitch setting, but giving up a few knots in cruise. My climb performance suffers a little vs my metal prop, but is still good, and I don’t overspeed my engine at WOT, like I did with my metal Sensenich at any altitude. Cruise power settings are more comfortable (2400-2450 RPM), and TAS at this setting (65%) is 5-7K faster - higher MP, slower prop speed, more aerodynamic blade design, and it’s definitely quieter and smoother.

You can do all of this with a constant speed prop, all of the time, but with triple the cost, increased maintenance, and double the weight. It’s your choice. It was my choice, and I chose the GA option on this, my 5th RV, and I’m satisfied with my choice. Good luck with yours. There isn’t a wrong choice.
 
Overspeed is more likely if the propeller is pitched for STOL. Our instructions recommend setting the pitch so that your static RPM is 2200-2300 (gives powerful takeoff and good cruise performance). My RV-6A with O-320 160HP and GA-200L-72" is set to 21.5° with static rpm of 2200 and full throttle level flight rpm of 2700 rpm. If I pitch it to 22.0° or 22.5° then I cannot reach 2700 rpm without diving the plane, but I lose quite a bit of takeoff performance (static rpm of 2150 or 2100 respectively).

Can you clarify what percentage of the diameter of the prop disc area do you place the gauge (on the propeller) when measuring pitch? 75%? or closer to the tip?
 
Can a light ground adjustable prop like a whirlwind 200GA be overspeed? I am thinking about upgrading my metal prop to ground adjustable but have heard over-speeding can happen on light props. I personally don't see how considering its one pitch and it shouldn't change as its ground adjustable but I figured I ask the peanut gallery.

Thanks,
D

Sounds like whoever told you this was confused. There are people that don’t understand how an engine can spin up quickly but not overshoot it’s peak RPM. The peak RPM will occur based on prop pitch and not vary with the weight of the prop. On a car for instance, the computer limits the RPM by cutting the fuel or spark. It doesn’t matter if you floor the throttle in neutral or gradually approach the limit while accelerating the maximum RPM would be the same.

-Andy
 
Right - it's not the weight of the prop, but rather its pitch, that determines whether or not you can overspeed it with the available engine power.
 
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