For the past few months, John Gilpin from www.stolspeed.com has been testing 3 of our Meglin propellers (3-blade 72", 3-blade 70" and 2-blade 72") up against a Koolprop 69", a Bolly 69", a Kiev and an Eprop.
A huge thanks goes out to John for his time, patience, and thorough testing methods he has implemented, and for collating all the data and providing an honest review.
So without further ado, here is Johns review of the propellers.
‘Stump-pulling’
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.
Static Thrust Testing Results are laid out in the table pictured below.
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 testing
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.
PS - 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.