Propellors

[Asher Carmichael]

I thought I'd start a thread on real world experience with engine and prop combos.

I don't have any verifiable data, I'm wondering if anyone else does. In the old days, Robin Lehman kept a journal of engine/prop RPM's and thrust(lbs) collected via a fish scale attached to the tow release. It is long gone, I guess, and there are a lot more engines and props available so the info would be dated anyway.

From that early information, I have always run a 26x10 on a 100cc size motor. Never had any real reason to change as far as I could tell, so I've pretty much stayed with wood in that size. An occasional CF would slip into the picture but cost was a factor and I also like the fact that wood breaks easier; yes, I know, an odd reason, but I somehow tell myself that it is somehow safer, at least for the engine.

I balance my props but wood just never seems to run as smoothly or spool up the way a CF prop does.

While I was @ Clover Creek, Skip mentioned that he thought a Mejzlik CF 27x10 might be a better match for the DA100 as the blades are thinner and the prop is stiffer and balanced better.

Thoughts overall? What engines/props are you running and do you have any data?

[kjkavaney]

Hey Asher...I have had the same experience as you with 100cc @ 26 x10 and also wood. I have also been told about 27 inch x 10 but as it is I sometimes hear a clip of grass being cut on landings...On DaA-150 I am running 32 x 12 but that is a different story..

[nichda]

Hi Asher,

this is an interesting topic for sure, to share my own experience to date . . .

The model (85% Pegasus) was equipped with a Zenoah 62 which was adequate as a sport flyer but it needed more ponies to be effective as a Towplane.

Now equipped with a well broken in DA100 (not a DA100L) running K&S canisters set long.

Initially I trialed a Biela 25x10 3 blader (which looked cool and was very quiet) but the motor was slightly over propped.
The prop I have settled on is a Mejzlick 27x10 - 2 blader (@ 6000RPM on the ground) and its a perfect match for the airframe and the extra horsepower helps for Towing.

I hope that this helps.

Dale

[pelle_gris]

I have primarily been towing with three different models the last few years.

Most tows have been with a Giant Stinger powered by a piped G-62. This uses an Engel (narrow blade CF) 24x12x2 @ 6600 rpm. Largest model towed is a 40% Nimbus spanning 10,6 m (34,77 ft). Granted this was only possible in a strong headwind, where the tow could be a straight line ahead. Normal 1:3 scale gliders are normally no problem.

The other towplane I have been flying is a PAF 230 (simple trainer not unlike a Pegasus) powered by a piped GT-80. This uses a Mejzlik 22x12x3 @ around 6500 rpm and tows most 1:3 scalers without any problems. Largest model towed is a 1:2 scale Discus.

My current towplane is my own design, This is powered by a King 140RV twin. On this I´m using a Fiala 30x16x2 @ 5300 rpm. This is quite a new model so I have only done a few tows with it, but it pulls anything from 10 lb glass ships to 50 lb vintage ships with ease. It´s quite heavy and the high wing loading makes it very stable during towing and in high winds.
With the current 30x16 prop it´s quite noisy 98 dB @ 3 m) so I´m going to try a Fiala 28x16x3 to lower the rpm´s a bit.
I did the maiden flight with a 3W 32x12x2 @ 5000 rpm, but this seemed to only provide a lot of noise and not much performance. We checked the static thrust with a scale in the tow attachment, and it came to about 52 lb.

In this video you can see my towplane from 4:50 mins.

https://www.youtube.com/watch?v=HZd5Ed_bBa8

When towing I generally like props with at least 12" pitch as lower pitch props, in my experience, provides much lower performance in the air. With 16" pitch there is less chance that the glider will catch up with the towplane in a less than a perfect tow.