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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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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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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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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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.mozello.com/
 
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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
 

Chook

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Here is interesting information about the testing of propellers, including very expensive ones:
Vladimir thank you for a comprehensive report. There was obviously a lot of time spent to get your results.
I see that Kharkov is very near the eastern border of Ukraine - stay safe and keep your head down!

Regards.........Chook
 

Resasi

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That was very instructive, contained a lot of good information and would have taken a lot of time. Thank you for posting.

As Chook has said, stay safe, things looking a bit unsettled over there.
 

shootthrees

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Greg,

You are correct on the differences between a static test and performance in the air. I personally experimented with both 3 blade and 4 blade configurations of 68 inch Luga, NR and Bolly Props. The Luga and NR props both had a significant increase in thrust on the static test with the 4 blade when compared to the 3 blade. However, the 4 blade was a complete dog in the are and inferior to the same 3 blade configuration.

I did not do a static test on the Bolly Props, which is an improved version of the Warp Drive Prop. It has the same basic material with a higher quality finish. Plus, each prop is made to the length ordered and not just a cut off shortened version of a longer prop that Warp sells. The 3 blade performance in the air was okay especially at cruise, but, had a lower climb rate when compared to the 3 blade Luga or NR props. The 4 blade Bolly is awesome with both great cruise and take off performance as good as or better than the Luga or NR props along with the solid Warp Drive like material you describe above..
 

N962GT

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To reiterate: There have been numerous prop failures reported of NR/ Luga hollow props on pusher gyros. Why? Most likely because $#!t goes through the prop when it's stickin' out the back. I've come across notes indicating hollow blades should be changed every 700 hrs. Not just Tango, either. Desmond Butts reported losing a prop blade on his MTO in flight. You can have your hollow props, I'm not impressed.

Again, I had a 1/2 x 9/16 double-ended closed box wrench go through my Warp Drive prop on TO, WOT, 145 HP, in 2014. I found the wrench a couple hundred feet to the side of the RW on the edge of the taxiway while taxiing back to the hanger! It put a 1/8" ding in the leading edge of one blade, which I fixed with superglue and baking soda in a few minutes. BFD.

I've been flying the same prop ever since, don't care about a few more FPM of improved prop climb performance since I don't fly Rotax and have far more HP at the same weight from my MAC YG4 than I know what to do with - even with a 250+ lb passenger it still climbs like a homesick angel at 93% power.

To each his own.

As for me, I'll stick with the comfort of knowing that nothing short of a full-blown prop strike on a roll-over is going to take out my solid Warp Drive prop.

Now, let's see some actual GPS data to compare real-world time-to-climb performance, and leave the rest of this BS at home. In fact, start a stand-alone thread for it.
 
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