STOLSPEED Vortex Generators Performance Enhancement for Light Aircraft
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New Prop Test Comparisons
From top to bottom 66" Bolly
For these tests, the props were pitched to give 5200 rpm at best climb rate of 57 kts. The test flights using manifold pressure as the reference, gave incredibly equal results for all props – all within one knot of each other! One knot is less than the tolerance of the measuring ability. Engine power is RPM x Torque, so any testing that only compares at RPM settings isn't testing at the same power output. ie- If the prop is pitched for 5500 WOT rather than 5800, then cruising at 5000 will show a higher speed, but of course that's at a much higher percentage of total power than if WOT was 5800. Ideally we should test at equal fuel flow rates, because that truely indicates engine power, but that's difficult to determine accurately in real time. I've tried fuel flow meters, and don't find them accurate enough, at these flow rates, to be useful for good test comparison. The only way I've found to get truely accurate fuel flow measurement is to measure the fuel used on a three hour flight at a constant power setting, which gets a bit time consuming for multiple tests. As I understand it, manifold pressure is quite a good indicator of actual engine power output, provided altitude and air density are equal. So I've done the cruise speed comparisons at equal manifold pressures, all at 2000' QNH, and all at very similar atmospheric conditions.
Flight Test Results
Kool 69" Kiev 71" Bolly 70" Bolly 66" AonProp 69" WOT (rpm) 5900 5900 5810 5800 5800 Pitch 16.5 16.25 19 20 15 Time to Climb 60 60 60 76 60 RPM 5170 5170 5200 5240 5230 Static Thrust (kg) 164 162 163 ??? 173 Static RPM 4930 5070 5230 ??? 5240 MAP @ 2000ft kts / rpm kts / rpm kts / rpm kts / rpm kts / rpm 26" 92 @5610 92 @5490 93 @5500 92 @5500 93 @5500 25" 85 @5160 86 @5160 85 @5030 85 @5230 86 @5200 24" 79 @4910 80 @4840 79 @4800 79 @4850 79 @4800 23" 74 @4660 75 @4640 ??? 75 @4630 75 @4500 It's interesting to have a look at the differences in profile and helix between different props, but the performance is very much equal.
AonProp Kiev Kool
Analysis Just as in the earlier prop tests, I could find no real difference in cruise speed between any of the props tested, when equal power was carefully applied to each. So it would seem that when someone claims a big difference with a different prop, they are probably depending solely upon RPM, and are actually applying more less power. The only difference found was that the smaller diameter Bolly was considerably degraded in climb.
Kool
It runs as smooth, and stops with much less jolt than the Warp. Ground observers noted that the noise produced at cruise and full power at 800ft AGL was considerably less than the Warp. Kool also produces a version with anti-vortex tips to reduce noise even further. I know of a
The hub is fairly plain, with a matt black finish. It uses the standard 75mm bolt pattern. For 5200rpm in climb, the pitch at 600mm from the centre measured 16.5º. I've decided that this is my favorite prop. Very strong and smooth running. Very good L/E protection. The Kool is US$890 plus $120 shipping direct from Canada.
The Bolly props are an Australian design and well-known here as a high quality prop. They tried having them made in China, but weren't satisfied with the quality, so are now manufacturing in Australia again. They're now under new ownership with big plans to become a world prop manufacturer.
Hans started with a Woodcomp on his 701, but it snapped off cleanly at the junction to the hub when it nicked the ground while taxiing through a dip..... (The butt of the blade was seen to be hollow!). He used his first Bolly for about 600hrs and loved it, until dropping the nose wheel into a rabbit hole destroyed it..... He immediately replaced it with a new Bolly. The Bolly blades are considerably lighter than the Warp Drive blades, so the rotational inertia is noticeably less. This makes it smoother running, and considerably less jolt on start and stop. The blades are wider than the Warp and a more rounded shape as seen in the photos. The 'Duratuf' leading edge protection is a heat-cured polyurethane, moulded into the leading edge. It’s resilient and very effective protection against chipping. The Bolly hub also uses the 101.6mm bolt pattern and drive lug system, particularly suitable for the 100hp engine. It's very nicely machined, solid, and attractive so it doesn't really need a spinner.
The labelling of this BOS range of Bolly props is a bit strange..... The tips of the Bolly aren’t flat, so can’t measure pitch at the tip. So I used the standard 600mm (2ft) out from the centre, where it measured 19º for 5800rpm WOT.. Kiev I don't have photos of the Kiev, but it's a slim, elegant prop. There can be a delay in getting one, as they can't seem to keep up to demand. AonProp light.avia@gmail.com
....................................................................................................................................................................... Earlier Prop Comparisons This is from an earlier prop test comparison.  Peszke
Bollie
Warp Drive
 Warp Drive
Kool
Testing Procedure
I’ve long wanted to find some head-to-head comparisons of different propellers. There are many accounts of someone trying a new prop and reporting amazing results but I never found any tests that had been well-controlled to get the base line equal.
The prop I had been using for 400hrs was performing well enough, but I wanted to see if I could do better. Then I had the opportunity to borrow and try several quite different brands of props. I enjoy experimenting, and testing for real results, so took on the project. It’s not as easy at it would seem to get fair comparisons – first, lots of short flights and pitch adjusting to get WOT (Wide Open Throttle) straight and level rpm exactly equal for each. (I sure don’t like thundering along at full throttle, with the ASI off-scale, 100+kts, just under Vne for this
My aircraft is a Savannah, originally with leading edge slats but now with the slats removed, and VGs on the original airfoil. The engine is a Rotax 912ULS, 100hp. All test flights were at 2000’ QNH, about 1600’ AGL here. I installed a digital tacho to get repeatable rpm. Had a manifold pressure gauge calibrated by an instrument shop. Flew 4-way GPS legs with a VSI for level flight (the only way to get true speed comparisons). Kept the fuel weight very near equal. Temperature and atmospheric conditions very near equal (approx 23ºC). Did the comparison runs at first light for most stable air. Swapping the props took only minutes so the conditions were very much equal. Did the whole procedure over and over again to eliminate anomalies and averaged the results. Then found that the results were so much the same for each that I didn’t believe them, so did it all over again. But they came out the same yet again....... After a fuel bill of $500 in one month, I was satisfied with the results as being true and fair.
Some will immediately say they get higher climb rates and better speed than this, and often I seem to get those indications as well in general flying, but repeatable results under same conditions is what I’m after here.
Pitch was measured with a Warp Drive protractor – a very good instrument, worth getting whatever prop you are using. It’s very easy to use and gets repeatable results right down to a quarter of a degree.
Results
The results obtained are very interesting and quite surprising. And somewhat disappointing as well - I had hoped to find some dramatic differences that would get me a prop that’s far superior to others. Not so, the results show that there is very little difference at all between quite different props. When I first got those results that are so much the same, I thought it must have been a coincidence, so had to do it all over again, and then again. It just seemed unlikely that that they could come out so much the same!
A couple of times when I first tried a new prop I got excited by a considerably higher indicated air speed, but each time when the pitch was adjusted to the same WOT reference of 5800rpm, the 4-way GPS speed at 5000rpm came out pretty much equal to the others.
The test flights using manifold pressure as the reference gave even more equal results – all within one knot of each other! As I understand it, manifold pressure is a very good indicator of actual engine power output. Effectively each prop gave exactly the same speed for the same power setting! That’s one test that I just had to do once again last weekend, and the result was the same yet again.....
The only real differences showed up in the static thrust tests. The biggest difference was between the Peszke and the Kool, and still only 12kg out of 190kg, about 6%. But yet, time-to-climb to 1000ft AGL for all of them was very much the same. Time-to-climb from take-off is difficult to compare precisely because it’s so much effected by variations in getting stabilized at climb speed, more chance of variations in lift or sink in the surrounding air, and of course air temperature (even at first light there are often layers of different temperature air at these levels). But after many climbs, all the props showed the same range of times, and averaged about 60 seconds.
Of course many other users out there will claim they get different performance with their props - some of them almost magical...... But this is what I found, after really careful testing. I have no reason to promote or demote any one prop against another. It's been a lot of effort for no dramatic results, but at least it measures some realities.......
Warp Drive
Warp Drive Warp Drive hub with drive lugs
The Warp Drive props are so widely distributed and known that I’ll use it as the standard for comparisons. I’ll keep referring comparisons to the Warp because it’s the best-known prop of the lot.
The Warp Drive is certainly the strongest of the lot – as others have said, “You could chop wood with them!” I have a broken one from a wrecked 701 that we re-built, and can see that it’s solid carbon fibre and resin all the way through. The lighter props will have foam cores. Of course this makes the Warp Drive heavier and much greater rotational inertia. It takes noticeably longer than lighter props to ‘spool up’ on opening the throttle, and stops with an almighty jolt on a 912S. In my Rans S7 with the older flat-bed engine mounts this is alarming, but there have been lots of Warps on S7s for a long time so it doesn’t seem to cause any structural problem. I believe the newer ‘focalized’ engine mounts on the S7 are much smoother, just as they are on the
Those squared tips are very strong and functional, but probably cause the greater noise that we noticed compared to the rounded, tapered ends of the other brands. This strength and durability, and with the nickel leading edge makes the Warp a popular prop on float planes and dirt field use.
The hub on the Warp Drive is particularly strong. There are four clamping bolts on each blade mounting, and the butt of each blade is reinforced with an aluminum sleeve. The hub uses the larger 101.6mm bolt pattern, with 13mm drive lugs that pass through the engine flange and into the prop hub – very strong, and maybe necessary with that high rotational inertia and those violent rotational jolts on start and stop.... Warp also insists on a squashplate on the front of the hub.
On the
Bolly
Bolly Bolly hub
The Bolly props are an Australian design and well-known here as a high quality prop. They tried having them made in China, but weren't satisfied with the quality, so are now manufacturing in Australia again. They're now under new ownership with big plans to become a world prop manufacturer.
Hans has been using a Bolly on his 701 for about 500hrs and loves it. He went to the Bolly after his Woodcomp nicked the ground while taxiing through a dip and snapped off cleanly at the junction to the hub! (The butt of the blade was seen to be hollow.....).
The Bolly blades are considerably lighter than the Warp Drive blades, so the rotational inertia is noticeably less. This makes it smoother running, and considerably less jolt on start and stop. The blades are wider than the Warp and a more rounded shape as seen in the photos. The 'Duratuf' leading edge protection is a heat-cured polyurethane, moulded into the leading edge. It’s resilient and very effective protection against chipping. The Bolly hub also uses the 101.6mm bolt pattern and drive lug system, particularly suitable for the 100hp engine. It's very nicely machined, solid, and attractive so it doesn't really need a spinner.
The tips of the Bolly aren’t flat, so can’t measure pitch at the tip. So I used the standard 600mm (2ft) out from the centre, where it measured 19º for 5800rpm WOT..
Peszke Peszke hub
The Peszke props are made in
As shown in the photos, the Peszke is certainly the most stylish and sharpest-looking prop of the lot. The metallic silver/grey gel coat really sets it apart from the usual black ones. The blades are slim and gracefully formed, with sexy up-turned tips to reduce vortex noise.
The hub is nicely machined and polished, and matching spinners are available. The 75mm bolt pattern is used.
It’s a very light-weight prop, with the lowest rotational inertia of those tested, which makes it the smoothest running of the lot, and quite noticeably the quickest to speed up on opening the throttle, and less jolt on shut-down. Despite the lesser blade area due to the slim blades, and 68” diameter, it cruised and climbed just as well as the much larger props. Static thrust was 10 kg less than the Warp Drive (but 10 kg out of 190 is only about 5%), so take-off roll was a bit longer, but surprisingly, time-to-climb was very much the same, so the thrust must improve very quickly once the aircraft is moving.
There’s no separate leading edge protection. The factory claims extra strength is built into the leading edge, but extensive dirt-field use might bring some chipping of the surface unless leading edge tape is used....
I’ve lost the pitch settings that I used for the Peszke.....
All in all it’s a very nice prop, and performed really well. I think it's ideally suited for the 80hp Rotax.
This prop is now on a Zenith 701 with 80hp, and performing really well.
Brolga
Brolga
The Brolga is very different construction to the others. It uses a composite hub made by Ultraprop in the
The relatively flat blades give good performance at those speeds, and excellent take-off performance, but I expected that they would run out of puff at higher speeds compared to the high-helix props like the Bollie and the Kool. But testing shows this not to be the case, in that at the same manifold pressure settings, the Brolga performed at 86kts, within one knot of both the Warp and the Kool! The pitch blocks only come in one degree steps. 16º is a bit too fine for cruise, giving WOT 6000rpm, but 17º is over-pitched for best take-off. Since the Brolga is under-pitched, the rpm for the same manifold pressure setting is higher, but the speed was still the same...... I had expected that this large 4-blade prop would be best at take-off and noticeably slower at such speeds, but it seems not to be the case....... At WOT it gave 100+ knots, same as all the others, which was really surprising! I’ve used this Brolga for 400hrs, and the only down-side is that, on long trips alongside a
I originally chose the Brolga because the factory is nearby, the price was right, and I have had good performance from them on earlier ultralights for 1200+hrs. Unfortunately the Brolga is now out of production.......
Kool
The Kool prop is made in
It runs as smooth, and stops with much less jolt than the Warp. Ground observers noted that the noise produced at cruise and full power at 800ft AGL was considerably less than the Warp. Kool also produces a version with anti-vortex tips to reduce noise even further. I know of a
The hub is fairly plain, with a matt black finish. It uses the standard 75mm bolt pattern. For 5800rpm WOT in the
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