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EProp Testing Comparison                                                                   October 2020


Well, the EProp sure is different, with it’s very slender blades and all carbon fiber construction, including the hub. Weighs nearly nothing. Feels delicate but I guess that carbon fiber can do it if the builders know the material. Right away notice that it starts and stops without the jolts of heavier props; that’s really sweet! And runs very smoothly. It comes with a nifty digital protractor for setting the pitch.



Contrast the difference in width of those blades! The EProp has the narrowest blades I have ever seen on a power prop. My Kool would have one of the widest blades around. The thickness is also in the same ratio but I couldn’t get a good photo of that. This is sure going to be an interesting comparison test!

The instructions with the EProp mostly stress to set the WOT (wide open throttle) to 5500 rpm, but a special note recommends to set for 5800rpm for the Savannah. That’s the setting that I found to be the best for the EProp on my Savannah, as detailed later.



Testing at WOT 5500 rpm

But first I set it for 5500 which I found to require a pitch angle of 24.6 degrees.
First of all tested the EProp and a Bolly head-to-head both set to 5500 rpm WOT.


EProp 69”

EProp 69”

Bolly 66”

Bolly 66”


MAP

RPM

Speed

RPM

Speed

Fuel burn

(approx.)

WOT

5500

98

5500

98

26

26”

5200

89

5180

90

20

25”

4880

84

4910

85

17

24”

4580

78

4580

78

14

23”

4400

75

4420

74

12

Climb

5250

2000-3000 ft

950 fpm

5000

2000-3000 ft

860 fpm



This demonstrates that both props performed exactly the same in speed when the engine power was exactly the same for each. The Bolly was way down in climb, just as the 66” Bolly that I tested years ago performed well in cruise but lagged in climb. (The 68” Bolly also tested back then climbed as well as any other prop, so diameter is important for climb.)


The lesson here is that if you re-pitch your prop to 5500 WOT then it will probably perform just as well as the EProp at that same setting, but I don’t recommend that you pitch any prop on a 912uls to 5500 WOT (more on that later).

But I really do like the EProp when pitched to 5800 WOT, as the data will show.



Testing at WOT 5800 rpm


The instructions with the EProp insisted on setting WOT to 5500 rpm, except when it later stated that for a Savannah that should be set to 5800 rpm…..
So I set it to 5800, which turned out to be a pitch angle of 22.6 degrees.
Then tested the EProp and a Kool head-to-head both set to 5800 rpm WOT.


EProp 69”

EProp 69”

Kool 69”

Kool 69”


MAP

RPM

Speed

RPM

Speed

Fuel burn

(approx.)

WOT

5800

98

5900

97

26

26”

5540

92

5640

91

20

25”

5250

86

5250

85

17

24”

4930

79

4980

78

14

23”

4710

75

4740

73

12

Climb

5520

1000 fpm

5200

1000 fpm



This demonstrates that both props performed almost the same, difficult to measure the difference. With any single measurement I ignore one knot differences as being within the margin of error. However when I have done multiple tests with consistent repeatable results I think the margin of error can be taken as less than one knot. These results are from multiple tests in good conditions head to head and were very consistent. So, from these results I think I can conclude that the consistent one knot faster speeds with the EProp indicate the greater efficiency of that prop. That would be expected with the thin narrow blades of the EProp compared to the wide thick blades of the Kool.

But it is really remarkable that the performance is so similar despite the vast difference in form. Very much like the surprising results of those earlier tests at https://www.stolspeed.com/nid/46

I really liked the EProp when set at 5800 WOT.


Analysis:

When I did that earlier prop comparison testing, I started the analysis with this comment:


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.


That’s exactly what’s happening here. If the EProp is pitched to 5500 rpm rather than the Rotax specified 5800, then flown at the same RPM as a prop that had been pitched to 5800, then of course it will fly faster because the engine is producing more power, maybe 85% instead of 75%. It’s not the new prop itself that’s giving the higher speed, it’s the increased power applied.


For instance, normal cruise at 5200rpm burns 3 litres/hr more fuel when pitched at 5500 rather than 5800, for an increase in speed of 5 kts.
Using Rotax’s Specific Fuel Consumption figure of 0.276L/hr/hp, that 3L/hr figures to about 11hp, which is considerable. Actually it’s getting close to Maximum Continuous Power specified by Rotax. That 5500 RPM for max continuous specified by Rotax is only valid if the WOT is pitched at 5800. So if 5500 is 300rpm down from 5800, then 300rpm down from WOT at 5500 is 5200 for max continuous. (I realize that it’s not necessarily linear, but close to it.) This is confirmed by the test data that shows that if the EProp is pitched to 5800, 26” MAP gives 5500rpm which is max continuous specified by Rotax, but if the prop is pitched to 5500 WOT then that same power setting of 26” MAP gives 5200rpm. So if you pitch your prop, any prop, to 5500 WOT, and cruise at 5200 you are at max continuous and flying about 5kts faster. If you fly any 5800 prop at max continuous of 5500 it will also fly at least 5kts faster than usual cruise.

A max continuous recommendation is determined by internal heat dispersion factors, not the actual RPM. Components such as exhaust valves and pistons need to transfer heat to the outside cooling system through valve guides and piston rings, and at continuous high power they can overheat due to the limits of that heat dispersion rate.

I realize this confusing, but I don’t know how to explain it better. It’s comfortable for me because I was testing engines for power and torque and specific fuel consumption in engineering school in the ‘59…..


MAP and actual engine power

Manifold Absolute Pressure (MAP) is an excellent measurement to determine actual engine power produced. It’s an easy instrument to fit and is accurate. Fuel burn is also an excellent measurement of actual engine power produced, but I don’t have a fuel flow gauge that has the precision to be definitive, but is still a good general indicator.

MAP doesn’t indicate actual engine output, but is very repeatable to set the same actual power output for each run, and thus good for comparison testing. I fly each comparison test at 2000 QNH in stable atmospheric conditions as similar as possible to the previous run. Then I fly a 4-way GPS orbit at constant power and altitude for every speed figure. Nearly get dizzy going round and round. Many test runs over the years have produced very repeatable consistent results with this method.


I find it very difficult to explain to flyers that the same engine RPM is NOT always the same power output. RPM is only half the formula; the other half is Torque.

Rotax specifies that for an engine pitched to 5800 WOT, the max continuous is 5500rpm.
That 5800 figure specified by Rotax is based on their assessment that it will run the engine in the most favourable rpm range for normal operation.
Testing showed that max continuous of 5500 when pitched to 5800 WOT equated to a power setting of 26” MAP at 2000ft.
However, with a prop pitched to 5500 WOT, 26” MAP gave 5200rpm.
Power = RPM x Torque, so at 26” for example, a reduction of RPM from 5500 to 5200 has increased the torque by about 11%.
Then the question is, do you want to run your engine
- at higher RPM and lower Torque
- or lower RPM and higher Torque??
Taken too far, the lower RPM and higher Torque becomes ‘lugging’ the engine…..


25” @2000ft is my usual cruise power, and with the prop pitched to 5800, that gives an airspeed of 85kts at 5200rpm. But if the prop was pitched to 5500 WOT then the RPM would be 4880 which I consider slower than best RPM, and somewhere I believe I saw a caution from Rotax that it was inadvisable to cruise in the 4800rpm range. (Can’t find that caution now)
And cruising at 5200  with the prop pitched to 5500 puts the MAP at 26”, which I have already indicated is near maximum continuous power…..
I don’t feel comfortable at either of those situations so wouldn’t ever pitch to 5500.

Probably doesn’t hurt the durable Rotax 912uls, but I heed Rotax specifications for this very expensive engine.

There are many aircraft flying with props pitched to 5500 – 5600 rpm for many years, so I guess it can be done. But if you want to run a prop set to 5500 WOT on a 912uls then I reckon you should contact Rotax for their advise. Not any third party…..

5800 WOT is excellent in all regards, and that is where I would pitch the EProp.
Small wonder Rotax stipulates WOT 5800.




Now here’s an interesting result!
Comparing the speeds produced by the EProp
when pitched at 5800 as compared to 5500,
each for the same amount of power produced by the engine as measured by the MAP.


EProp

 5800

EProp

5500

Fuel burn

L/hr





26”

92   @ 5540

89   @5200

20

25”

86   @5250

84   @4880

17

24”

79   @4930

78   @4580

14

23”

75   @4710

75   @4400

12


Note that the EProp when pitched to 5800,
actually cruised FASTER than when pitched to 5500,
for the same power applied and same fuel consumption.
Many won’t believe that, but these are the results of careful testing.



I did these tests with all care and attention, and based on lots of experience in such projects.
No doubt many will disagree with some opinions, and I respect their right to disagree.
But facts are facts, and I must present the results that the test data produced.

 - John Gilpin                                                                                                            


Further thoughts……
I don’t quite understand the drive to fly a Savannah faster than the 80-85 kts range….

That is the design speed of the aircraft, and at those speeds the aircraft is very smooth, stable and easy to trim hands off for hours at a time.


When flying those tests at 90kts, I found the aircraft to be less stable, didn’t retain trim as well as before, some buffeting, and a feeling that it was being pushed harder than it wanted to go…..


Maybe the S model handles 90kts better, but it feels to me that the VG model doesn’t really like to go that fast…..


Just for interest, an increase in cruising speed from 85 to 90 kts
makes for a time saving of only 3.5 minutes per one hour travelled…..


............................................................................................................................................................................ 

 

 

Even more props comparison testing…..


‘Stump-pulling’ this time


Previous prop testing had surprisingly shown that all props have very much the same efficiency, with no measurable difference for cruise speed and climb when pitched to the same actual engine power setting. Earlier test results below explain that fact.

The real difference that I was wanting to test this time was the static pull. Previous testing had found that static pull gives no indication of cruise or climb performance. But of course it does make a difference in short takeoff performance. That initial thrust makes a big difference in how quickly the aircraft gets rolling and up to flying speed. With the popularity these days of seeking impressive STOL performance that could be significant.

So I purchased a digital load cell and set up a ‘stump pull’ arrangement to give all props equal conditions. I tested and re-tested to ensure consistent results. The differences in ‘grunt’ are significant.

Of course such results are also effected by atmospheric conditions such as Density Altitude. So I tested and re-tested to compensate for different conditions and selected an average that gave the most fair comparison.

This time testing a couple of new props from Meglin, being imported from the Ukraine by https://www.bushaero.com.au

Meglin used to be named Luga before some reorganizations over there. It seems there are three factories over there, which work together and compete.

The Kool prop that I’ve used for 11 years was also made in one of those factories, using the same techniques and materials and profiles, and all fit the same hubs. Kool was the name that a distributer in Canada re-branded the prop that I bought. I love that prop and now have 1100 hrs on it and it still looks like new, despite many ‘adventures’ operating off dirt strips and off-field landings outback. It’s mowed some tall grass and shrubs and kicked up sand and dirt but the stainless steel leading edge just gets more polished. All those props are very strong and smooth-running. They have thick sections and high-lift profiles which makes them completely rigid and stable. That stainless leading edge is very superior, being very strong and well-bonded with through rivets. The gelcoat is excellent quality and keeps its good appearance for many years. The butts of the blades are 50mm in diameter compared to the smaller butts on other popular props. All in all, they are very sturdy props.


The Meglin factory is the only one that manufactures the scimitar-shaped blades. They also make a wide range of props for different uses as shown in the website.
https://www.bushaero.com.au/composite-propellers

 The three models that I tested are:

The scimitar-shaped SR-107 3-blade 72”,
The scimitar-shaped SR-106 3-blade 70”
and the scimitar-shaped SR-107 2-blade 72”.

My 69” straight-blade Kool would be the same as the CR-104 listed.
I included the Kool in the testing as a reference, having been through many tests over the years.

Spinners are available for these props but I didn’t want them in the way for all the bolting/unbolting of prop changing and re-adjusting.
(Besides, I figure spinners on STOL aircraft are like hub caps on a 4WD…)

To do this thrust testing I purchased an electronic load cell and tied it off to a stump as below. Then placed the wheels on boards on level ground to eliminate rolling resistance in the grass.







Meglin 3-blade 70”


Meglin 2-blade 72”


 

Static Thrust Testing Results  


Prop / Diameter WOT rpm Static rpm Thrust kg
Meglin 3-blade 72" 5800 4900 196
Meglin 3-blade 70" 5800 5200 195
Meglin 2-blade 72" 5800 5220 190
Kool 69" 5800 5050 190
Bolly 68" (Average 5 props) 5800 5200-5300 165
Kiev 5800 5230 165
EProp 5750 5750 155


So there is a considerable difference in static thrust, and this was noticeable when flight testing, in that the Meglin props had more immediate ‘grunt’ when the throttle was opened and takeoff roll was reduced.
30 kg thrust makes a big difference.
It’s not really practical to measure actual takeoff roll at this airstrip due to changing grass length, strip not level, and varying wind conditions, but a Savannah owner who tried the 72” 3-blade from his very short strip with tall trees at the end, noticed a considerable improvement compared to his Bolly.

Notable here is how the EProp produced the lowest static thrust, and the engine revved out to the same as it’s WOT! So it didn’t have nearly enough blade area to couple with the air at that full power setting at no airspeed, and there was heaps of slippage and cavitating. This backs up the observation by an experienced instructor who tried the EProp and noted that when he applied full power in a low speed go-around he got lots of revs but little immediate thrust…. Also noted by an observer off to the side, was that the blades flexed (coned) considerably forward under power. I guess the manufacturer knows what they’re doing, but I sure don’t like the idea of all that flexing going on in such a high revving highly loaded critical component...


 

Cruise performance


These are the results of the recent testing.



72" 3-blade 72" 2-blade 70" 3-blade 69" Kool
WOT rpm 5800 5800 5800 5800

Static pull kg  

196

190 195 190
@ rpm 4900 5220 5200 5220

Climb 

2000-3000ft fpm

910 1034 1000 980
@ rpm 5120 5320 5300 5200





Speed tests



MAP @ 2000 ft Kts @ rpm Kts @ rpm Kts @ rpm Kts @ rpm





26" 92 92 92 92

5650 5660 5520 5610
25" 86 87 85 85

5300 5430 5250 5160
24" 77 80 78 79

4800 4970 4850 4910
23" 73 75 75 74

4700 4800 4650 4660





5000 rpm 79 81 81 80



Interpolating those results to correlate to rpm, which more flyers are used to:

(All props pitched to WOT of 5800 rpm)                                                       Results from earlier testing.             

RPM

Meglin 72”

3-blade

Meglin 70”

3-blade

Meglin 72”

2-blade

Kool 69”


Bolly 68”

Kiev 71”

EProp 69”

5500

89

91

90

89


91

91

91

5200

84

84

83.5

84


85

86

85

5000

79

81

80.5

80


79

81

81

Previous tests of the Bolly and Kiev gave speeds 1-2 kts higher, but those tests were done in winter with cool dense air.
These results reflect more equal conditions.


I know that this consistency is hard to believe, but it’s proven many times over by careful testing.
I’m constantly amazed to see the end results so consistent when averaged over multiple tests.
Not more than 2kts difference between all props!

I would expect that the variation would be greater, considering different prop shapes, atmospheric conditions and measurement variations, but not so.

It’s easy enough to err with instantaneous readings, either by accident or wishful thinking, but averaging multiple tests over time weeds out the variations. Also temperature and density altitude make a difference, as we notice on some days when the aircraft just goes a lot better. These results are averaged from countless tests in varying conditions. All tests done very early morning in steady conditions at 2000QNH about 20°C, over water to minimize thermal activity.

4-way GPS runs are really excellent in that regard. There’s almost always some breeze up there, so the ground speeds for different legs vary by 10 kts or more, but when summed and divided by four the results are remarkably consistent, over and over again. Of course, at the completion of the 4-leg orbit the altitude must still be the same as starting, and that’s an excellent control on flying precision. It’s all too easy when taking instantaneous one-way readings to inadvertently take the indicated speed reading when climbing or descending slightly (seems to happen more often when descending when the ASI reads higher…) a descent rate of only 50fpm makes a considerable difference.

I reckon everyone needs to do some 4-way GPS runs to determine really what speed they’re making through the air.  Also an opportunity to calibrate your ASI. Instantaneous GPS comparisons or even two-way GPS runs are useless. I’ve now done what seems like hundreds of such 4-way orbits, in varying conditions, and continue to be amazed that the averaged result is so consistent.


 

Climb

Also need to do proper climb rate tests. I keep hearing of claims of 1500fpm etc, but I have never measured much above and usually around 1000fpm for a sustained climb behind a 100hp Rotax pitched to 5800 WOT. Once again instantaneous readings are open to big errors due to zoom climb and wishful thinking. I never depend on a VSI, but climb at exactly 60kts for 1000ft timed by stopwatch. I use between 2000 and 3000ft to not annoy residents on the ground and realize that the rate will be a bit less at that altitude than at sea level, but then we don’t usually fly at sea level….


Conclusions


These results indicate that the Meglin range of props showed considerably greater static thrust than all others tested, but still showed the same cruise speeds as all other props. Which makes them well suited for all aircraft, but especially well suited for owners seeking shorter takeoff performance.

The Meglin 70” 3-blade gave the best overall results on a Rotax 100hp.


p.s.-

         I realize that the consistency of these results make it look like they've been 'cooked'.

         If I saw such results for the first time I would be skeptical as well.
         But I guarantee that isn't the case.

         If anyone else wants to do similar tests then please do so.

         But they must be done using the same parameters and care and attention to repeatable detail.






............................................................................................................................................................................





Older Prop Test Comparisons



From top to bottom

66" Bolly
68" Bolly
69" Kool
69" Aon
71" Kiev
(The spots on the blades are for measuring pitch at 600mm from centres)


For these tests, the props were pitched to give 5200 rpm at best climb rate of 57 kts.
Rotax specifies that rpm at climb should not be less than 5200.
This pitch gives 5900 at wide open throttle (WOT) straight and level with two props. 
This is 100 rpm above the red line, but to pitch for 5800 WOT will give a climb at less than 5200.
We never run WOT straight and level anyhow, but we do climb every time we fly, so I'll set for 5200.

 

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.
So effectively, each prop gave exactly the same speed for the same power setting!

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  68"

Bolly  66"

AonProp  69"

WOT (rpm) 

5900 

5900 

5810 

5800 

5800 

Pitch
@ 600mm 

16.5 

16.25 

19 

20 

15 

Time to Climb
2000-3000 ft
(sec)

60 

60 

60 

76 

60 

RPM
@ 57 kts climb
 

5170 

5170 

5200 

5240 

5230 

 






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.
This has been confirmed by two real life cases that I know of, who changed from the 66" Bolly to the 70", and both reported considerably better take-off and climb performance.


Kool

http://www.airtrikes.net/propellers.shtml   

                              Kool                                          Kool hub                                      Kool tip

  
The Kool prop is made in the Ukraine, and is beautifully designed.  It’s like a piece of sculpture, with flowing lines and not a flat spot anywhere.  Even the back surface is slightly concave.  The airfoil is thick and highly cambered, like a high-lift wing, and has a wide chord.  The core must be foam to have this light weight, but the thickness of the section, with the carbon fibre skin, makes a blade with great rigidity and stiffness.  The surface is a mirror-finish gloss black gel coat that looks great when new, but it does mark easily.....  The leading edge protection is stainless steel, moulded into the leading edge at manufacture, with ‘rivets’ embedded in the composite going right through from one side of the blade to the other.

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 Savannah that has that prop, and we’ll do a noise comparison when we can get together.

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.
I have about 400 hrs on it now, mostly on grass and dirt strips, and it's still looking good.

Vasili at http://www.airtrikes.net/propellers.shtml in Canada seems to be the main distributor for America, but several customers I know of have had long delays to get supplied....  

http://www.lugaprop.kiev.ua/catalog_en.html has been mentioned on this forum before, with good service. To order again I would go direct to this Ukrainian supplier. Looking at his catalog I reckon the R104/L104 to be the same as the 69" Kool that I tested and still love.

 

Bolly
www.bolly.com
  
       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 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 labeling of this BOS range of Bolly props is a bit strange.....
The so-called 70" prop is really 68", and the so-called 68" is really 66"???

This because they changed the design of the hub and kept the designations the same.

The Bolly blades do fit in a Warp Drive hub, and when using that hub then the actual diameter is the 70" and 68" as labelled. Is that clear now??
So I've used the actual diameter when referring to them in the test results.
 

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.
Very efficient, and smooth running.  Considered to be a standard as among the most efficient.

A friend has one for 400 hrs on these dirt strips, and it's showing it's wear more than the the Bolly or Kool.
The brass leading edge is considerably dented and tarnished, but still performing well.

There can be a delay in getting one, as they can't seem to keep up to demand.


AonProp

light.avia@gmail.com
The AonProp company sent me this one for testing.  It's made in the Ukraine, to much the same good standard as the Kiev and Kool.
One problem that I found is that the large helix in close to the base meant that I required a 20mm spacer to fit it on my Savannah so that it cleared the cowling.....
It gave the best static thrust, but as a wise guy once said, "....That's irrelevant because you don't fly tied up to a tree anyhow...."  Well, quite right, static thrust doesn't really mean much even in take-off performance.  I've found that it only affects the very initial part of the take-off roll, and as soon as the aircraft is rolling a few miles an hour any advantage in static thrust is nullified.....



.......................................................................................................................................................................

Even Earlier Prop Comparisons

This is from an earlier prop test comparison.
Manifold pressure readings aren't quite comparable due to a different gauge used,
but the results are the same, in that all props gave the same speed for the sme power.
Even props as completely different as the Peszke and the Brolga!



Peszke
Bolly
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 Savannah aircraft....)  Then lots and lots of short flights to swap props and compare under equal conditions.  I got really quick at bolting and unbolting props......
 
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.

                Warp Drive protractor                                                     Thrust testing


 
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

Bolly

Peszke

Kool

Brolga

 

70"

70"

68"

70"

68" 4-blade

 

 

 

 

 

 

WOT (rpm)

5800

5800

5800

5800

6000

Pitch at tip (degrees)

12.5*

***

??

11.25*

16* at hub

Pitch at 600mm from centre

19.5*

19*

 

17.5*

 

 

 

 

 

 

 

@ 5000rpm (knots)

81

82

81

82

78

 

 

 

 

 

 

Climb 2000'-3000' (sec)

60

60

60

 

60

RPM  @ 55 kts climb

5180

5100

5350

 

5100

 

 

 

 

 

 

Static Thrust (kg)

194

196

184

196

186

Static RPM

5020

5000

5400

4920

4880

 

 

 

 

 

 

 

 

 

 

 

 

Manifold Pressure

 

 

 

 

 

26" @ 2000' WOT

5800

 

 

5800

6000

25"

86 @ 5380

 

 

87 @ 5260

86 @ 5540

22.5"

77 @ 4780

 

 

76 @ 4680

76 @ 4940


 

 
Warp Drive
www.warpdriveprops.com 
  
                     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 Savannah .  I have the straight blade Warp Drive, as it came on my Rans S7.  The tapered-blade model is reputed to have better efficiency and would have a lower rotational inertia, but I didn’t have one available for testing.
  


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 Savannah , 12.5º at the tip gave 5800rpm at WOT.  At 600mm this measured to be 19.5º.
  
  
  
 Bolly
www.bolly.com
  
                                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
www.peszke.com 


                                 Peszke                                                                Peszke hub
 
 
The Peszke props are made in Poland , and not widely distributed yet, but they are seeking distributors elsewhere.  I found the company very co-operative and easy to deal with.
 
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 USA , but the blades are made in Australia .  The original Ultraprop blades are flat, with no helix at all, but the Brolga blades have some helix – not as much as is optimum, due the limitations of the pitch blocks in the hub.  The pitch is adjusted by changing sets of tapered blocks that hold the blades in the hub.  These blades were designed for the 50-60 knot ultralights and trikes, and have been very popular on those machines. 

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 Kiev on another Savannah , the Brolga consumes one litre/hr more fuel, probably due to the extra drag of the 4-blade configuration, but I can’t measure a difference in testing.  4-blades is necessary with the Brolga because the three-blade cavitates some on take-off.  Of course the 4-blades made for a smooth running and quiet prop, despite it’s rather ‘agricultural’ look. 

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

http://www.airtrikes.net/propellers.shtml  in Canada and USA
 



                              Kool                                          Kool hub                                      Kool tip

  
The Kool prop is made in Russia , and is beautifully designed.  It’s like a piece of sculpture, with flowing lines and not a flat spot anywhere.  Even the back surface is slightly concave.  The airfoil is thick and highly cambered, like a high-lift wing, and has a wide chord.  The core must be foam to have this light weight, but the thickness of the section, with the carbon fibre skin, makes a blade with great rigidity and stiffness.  The surface is a mirror-finish gloss black gel coat that looks great when new, but it does mark easily.....  The leading edge protection is stainless steel, moulded into the leading edge at manufacture, with ‘rivets’ embedded in the composite going right through from one side of the blade to the other.

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 Savannah that has that prop, and we’ll do a noise comparison when we can get together.

The hub is fairly plain, with a matt black finish.  It uses the standard 75mm bolt pattern.

For 5800rpm WOT in the Savannah , the tip was set at 11.25º.  At 600mm from the centre the pitch measured 17.5º.