Propellers: Thrust Test & Fight Performance

N962GT

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Dear Reader:

Rating engine performance is done by coupling a type of brake to the engine and measuring the resultant force. The braking device can be a pump and pressure gauge, a wheel and drum mounted to a spring-loaded torque measuring device, or a propeller with the measurement taken from the engine mounting by a spring scale.

It is a fact the efficiency, or “feeling” of a propeller in flight is not necessarily 1:1 compared to its static thrust results. This may be difficult to understand and even harder to quantify, especially given that in nearly all static thrust testing of the myriad propellers available the results are fairly equivalent. Many folks have tested numerous propellers statically under like conditions and arrived at similar peak thrust numbers with all types of props.

But jump into the aircraft take her for a lap around the pattern and the feedback variation can be more than significant.

Back to static thrust results, it can be concluded that engine power performance can be scientifically quantified & compared – much as any bench brake and dynamometer setup – by simple, static thrust testing. Thus results comparing various power plants, setups, tuning, gearing, propeller speed/ pitch/ diameter are significant and repeatable.

But if you want flight performance to match given static thrust results you’re going to have to talk to others, or do your own expensive trial-and-error testing of various props for your own setup.

When it comes to propeller efficiency and performance in static testing the numbers don’t lie about engine power, but they can be very deceiving for some props when it comes to their actual, in-flight performance reality.

For our purposes, gyrocopters, Warp Drive has a considerable static v flight performance ratio. Add to that its solid composite construction and unlimited lifespan and you have what I personally consider to be the best of the best for pusher gyros where the likelihood of FOD prop strikes is considerable. I’ve had a ½ box wrench go through a prop and it left a 1/8” nick in the leading edge which I fixed in 15 minutes with repeated super glue and baking powder catalyst layers, following by sanding. Have that with a hollow anything prop and you’re replacing a blade.

But my friend Steve Henry has tested way more prop types than I ever will in his constant quest to beat out everyone in the country at STOL events. For his tractor STOL plane he has compared Prince, Warp, NR, and a host of others. He likes NR the best.

NR props have had their problems on pusher gyros, however. One CFI out of Texass flying an MTO lost a blade for no apparently reason (sic). Several of my friends with Tango Gyros have experienced delamination of the gel coat at the blade root.

But they do perform perhaps better than any other prop. Bear in mind they have a life of 700 hrs.

One of my customers reports excellent performance on the Mohawk Aero Co. (MAC) YG2 (Yamaha Genesis Phazer 80 HP) with a 72” DUC prop. It is twice as expensive as most other popular brands, but lighter than Warp and more resilient than NR.

When issues cropped up with NR/ Luga another customer running a MAC YG4 140 HP switched to Aero Prop. His static results were always the same, across the board, regardless of Warp, NR or Aero at 600 lbs. But the Aero Prop was very sensitive to pitch adjustments losing thrust with steep prop-limited RPM changes on either side of optimal pitch, and that flight performance did not match thrust all that well.

My own, personal YG4 gyrocopters have only ever run Warp props – which I have always been exceedingly happy with. I look forward this summer to doing my own comparisons with an NR prop.

(Mohawk Aero has been a Warp Drive dealer for 6 years, and started direct-shipping of NR props to customers in 2018.)

((Please visit www.Mohawkaero.com or email [email protected] for more information.))
 
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wolfy

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western australia
I am currently using an Aero Prop BL1770 3 blade, I haven't done enough yet to comment on durability but I am loving the performance.
I haven't seen a 3 blade yet that has a linear thrust like this prop. I like a fine pitch for climb, but this prop even pitched fine (5800 rpm climb) just keeps pushing even at high air speeds. I have no idea what static thrust It makes but the flight performance is great.

wolfy
 

Brian Jackson

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Thanks for the write-up. I'm curious about similar performance data for the Prince prop mentioned early on. I will be using one with a 503 on a GyroBee (which rhymes by the way :) but the max speed will only be ~70. You also mentioned that your friend Steve Henry was experimenting with STOL performance, where I would think static thrust would be the main consideration due to the low airspeed. Just thinking out loud. Thanks.
 

N962GT

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Joined
Oct 25, 2020
Messages
33
Location
Northville, Michigan
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Mohawk Arrow 140T
Total Flight Time
800 hrs
Added notes: The Aero Prop that was difficult to tune and reported not satisfactory was the straight blade design. The Aero scimitar performance on the other hand has proved to be quite like the NR/Luga scimitar, and comes standard with free metal leading edges.
Thanks for the write-up. I'm curious about similar performance data for the Prince prop mentioned early on. I will be using one with a 503 on a GyroBee (which rhymes by the way :) but the max speed will only be ~70. You also mentioned that your friend Steve Henry was experimenting with STOL performance, where I would think static thrust would be the main consideration due to the low airspeed. Just thinking out loud. Thanks.
Steve's reports include and describes jump take-off performance, extended climb, cruise engine RPM and fuel burn over long interstate trips.
 

MAK

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Sep 7, 2009
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Pretoria
I use a 4 blade Aero Prop with my 154hp Edge Performance engine on my Aviation Artur Trendak Zen gyrocopter and I can vouch for the Aero Prop, great performance.
 

MAK

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Hello Wolfy

The KL-1790
 

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meglin

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Kharkov
Problems with the blades occurred only due to inconsistencies between the manufacturer and the customer. Conventional production blades were mounted on engines with huge torque. With the normal agreement of the terms of the order, the risk is minimized. This is proved by the example of Steve, who has our blades installed on a 300 hp engine. For standard operating conditions, resource restrictions are removed, and the shelf life is doubled.
Best regards, Vladimir Meglinsky
My site: http://propeller.simplesite.com/
 

Resasi

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or a propeller with the measurement taken from the engine mounting by a spring scale.

Greg I’ve only ever seen thrust tests for propellors done by tying a rope to a firmly fixed point, tree, car, hanger, then to a spring scale, then from the spring scale to the gyro.

Then, by varying the pitch of the blades establishing a maximum thrust available...or an RPM at WOT that is a bit under max rpm for the engine so that in flight one does not inadvertently exceed max for the engine.
 
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Resasi

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A process three of us did with the Cricket today.

We were concerned that the gyro had not been thrust tested when we became concerned about the performance under the Brock rotor.

We have put a set of Dragon Wings on and then before test flying did a thrust test. The present pitch of the three blade 52” Arplast on the Rotax 582 allowed the engine to exceed max RPM, while giving around 320 lbs so we have increased pitch on the blades from 19 degrees to 21 and will now repeat the thrust test.

What we are hoping to achieve is a WOT static RPM of around 6200-6300 which would then probably go up to around 6500RPM in flight.
Redline is 6800, 6500 for five minutes, static full power 6200-6400, TO/Climb 62-6400

I seem to recollect a rule of thumb that gave a two degree pitch change as about 400rpm engine change but I may be way out on that one as it will vary from prop type to prop type and for the prop blade length. Be glad for feed back from anyone.

Found a video of someone doing the thrust test.

 
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Jean Claude

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I seem to recollect a rule of thumb that gave a two degree pitch change as about 400rpm engine change but I may be way out on that one as it will vary from prop type to prop type and for the prop blade length. Be glad for feed back from anyone.
This estimate of the rpm drop seems correct to me, except when the addition of two degrees is enough to exceed the stall angle of the blades. Unfortunatly, this case is quite frequent during the static thrust tests
 
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