Engine choice for 30% scale Klemm KL25

[Jim.Thompson]

I have just finished building a 30% Klemm for the purposes of aerotowing.
I am looking for suggestions for an engine for this model. The single cylinder Sthil engine that I converted for use in it causes far too much vibration.
Currently short listing several 110 - 120 cc two strokes including BE124, DLE120, DA120 and 3W110. Also do a bit of pipe dreaming about the very impressive Valach VM120, but my budget will not extend that far.
This will be my very first internal combustion powered aircraft in over 50 years. I fly gliders, mainly slope but have become increasingly interested in aerotowing/thermal flying lately.

So, please post any suggestions, experiences and reports etc.

[Jim.Thompson]

Oops, forgot the picture. Here it is now.

[JimD]

Jim,

What is the wing span and weight of this aircraft?

Tow pilots in our group have had a lot of experience with DA-100, DA-120, and DLE-111 engines on various airframes. The DA-100 seems to be the most user friendly (meaning easy to start and adjust), but the DLE-111 and DA-120 engines are a bit stronger on tow.

The DA-100 likes a 26x10 prop for maximum towing performance. Both Xoar wood and Falcon carbon props have used with good success.

The DLE-111 does well with either a 26x10 or 27x10 prop. On this engine, our experience has just been with Xoar wood props.

The DA-120 does really well with a 27x11 Falcon carbon prop. Mejzlik 28x12 carbon prop has also been good. Mejzlik 3-blade 27x12TH carbon prop works okay and is the quietest, but has less top end power.

So far, we have not had any experience with the DLE-120 engine.

Hope this helps.

JimD

[Xroadie]

Jim.Thompson...I assume this is the Schlundt Klemm L25....correct? I have been eyeing that airplane for a while on Vogelsang's website and have talked with Götz about the very same thing! As you know the model flies very well with just a Zenoah G38. Schlundt's website mentions a G38 on a 22x8 prop but Vogelsang mentions a G38 with a gear drive which swings a 32x18 prop....but I am not sure there is enough room to swing a 32" prop. They claim it will tow a 3 meter glider with the G38.

Do you know what the max prop you can put on the Klemm that won't hit the ground on take off or landing?

I have thought about building it with the cowl on and trying to keep the engine inside, either using an inverted single or even and inline twin, like the new Da100 inline twin, which swings a 26" to 28" inch prop....it's more expensive than the DA100 opposed twin, but the cylinders would not stick out and it is cheaper than the Valach VM-120 inline twin, by about a thousand dollars! I have not seen the plans so I do not know if the cowl is long enough for an inline twin are tall enough for and inverted single like the DA85 single. It all depends on how much prop clearance you have and how big of a sailplane you want to tow with it. I thought about building it to use as a same scale tug for a 1/3 scale Minimoa that I'd like to build, and not for general towing duties. It looks like you are not using a cowl in your photo so a cheaper opposed twin could be used.

JimD, The model is a little over 170" and is said to weigh about 32lbs.
Pete

[Jim.Thompson]

Jim,

What is the wing span and weight of this aircraft?
..................................................
JimD

JimD,
Thanks for the reply with the engine details. Much appreciated.
My aircraft has a wing span of 3.9 mtr. Wing area is 200 sq. dm. The AUW with the engine fitted in the picture is 22 kg.
The DA 100 would seem to be very suitable from your assessment. They have some 4-40 threads though, which is a deal breaker for me. I live in Australia.
I have started to look at the 3W, which is all metric.

Pete,
My plane is a model of the Klemm KL25, as indicated in the title.

[Xroadie]

Pete,
My plane is a model of the Klemm KL25, as indicated in the title.

Yes Jim.....I saw that...my questions was, is it the Klemm L25 kit made by Schlundt or something you built from scratch? Just trying to help as there is a lot of information about that model and power for it on a few websites. Also...if it is the Schlundt kit, the biggest prop that allows clearance is 30"....according to the manufacturer. The power requirements to tow are limited by prop clearance and how big a glider you plan to tow.
Pete

[Steve P]

FWIW! I was very happy with the 3W 120 installed on my Pegasus. One tough, strong motor.

Thanks for sharing your project with us!

[Jim.Thompson]

Yes Jim.....I saw that...my questions was, is it the Klemm L25 kit made by Schlundt or something you built from scratch? .............................
Pete

Oh, I see now what you meant. Sorry for my ignorance, but I know next to nothing about kits. I avoid them at all costs and build only scratch, usually from 3 view drawings. That way, I know what I have got and can tailor the construction method for my gear etc.. Interesting to know that there is a kit out there available for this plane though. I will look it up for interest sake. Full build thread here if you are interested:

http://www.rcgroups.com/forums/showthread.php?t=2523079

Ignore the size mentioned in the title. The model grew during the design process.

[Jim.Thompson]

FWIW! I was very happy with the 3W 120 installed on my Pegasus. One tough, strong motor.
.................................................. ........

I have the 3W 110i B2 at the top of my short list at the moment. Of the many cheaper Chinese engines, I am looking closely at the BE124.
However, the German engineering quality of 3W appeals to me. All metric threads too - the use of some 4-40 threads on DA is a deal breaker for someone like me who lives outside the US.
I live in Australia. (I have been unable to fill in my location details on my avatar yet, anyone tell me how?).

[ARUP]

Pete- I have this kit in my stash. The Schlundt Klemm nose bowl and cowl is one piece and measures 330mm in length. The rear of the cowl is about 210mm wide x 310mm and at the nose bowl to cowl separation line measures about 140mm wide x 250mm.
Jim- sorry for the hijack. Welcome to the forum!

[Jim.Thompson]

No problem ARUP, any discussion is welcome. Thanks.

[Jim.Thompson]

..................................... The single cylinder Sthil engine that I converted for use in it causes far too much vibration.
.................................................. ..

I have greatly ameliorated the vibration problem by fitting a rubber engine mount. This was despite the advice from more than one of my mentors that it would not work. i had mentioned it way back in the build thread and allowed myself to be argued down. I figure I should have followed my instinct and experience in this regard; after all, internal combustion engines have been fitted with rubber mounts since the engines were invented to the best of my knowledge.
Accordingly, I have prepared the plane to take out to our coming festival to meet up with our large model inspector for its permit to fly inspection. Subject to that, we plan to maiden the plane.

Video of the engine temporarily mounted on the plane for initial testing with some details are in the post below. The engine has now been positioned higher and the carburettor mounted securely.

http://www.rcgroups.com/forums/showp...&postcount=770

[Jim.Thompson]

The plane was test flown by a couple of my far more experienced flying companions. Some video here: https://www.youtube.com/watch?v=wwYrNwiMv2I

And more pictures and details on the build thread here: http://www.rcgroups.com/forums/showt...523079&page=52

So the good news is that my self converted big single cylinder engine is suitable for this plane after all. All who flew it commented the engine/prop/plane combination was just about ideal.
And I no longer have to look for a replacement engine.
If only I had listened to my own intuition on the matter of using rubber mounts in the first place, instead of allowing myself to be persuaded that it would be counter-productive!
Thanks for all the contributions anyway. It helps towards further understanding of this aspect of the hobby which is new to me.