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Nov 07, 2013, 10:12 PM
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Klemm Kl 25

Klemm L.25, later Klemm Kl 25 was a successful German light leisure, sports and training monoplane aircraft, developed in 1928. More than 600 aircraft were built, and manufacturing licenses were sold to the United Kingdom and the United States.

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Nov 07, 2013, 10:13 PM
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davidterrell80's Avatar
I see the seeds of the great WW2 fighters in this design.
Nov 08, 2013, 08:14 AM
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The Klemm KL-25 has been a favorite of mine for many years. It was build in many variations in several countries. There was a Graupner (I think) kit for brushed Speed 400, and a larger Krick kit. A plan appeared in Flying Models maybe twenty years ago. Since then, nothing.

There was a full-size Swiss design, the Erla 5, and the British Dart Kitten. Both were low-wingers, but single-place. Both were similar to the Klemm.

I saw the remains of the Klemm at Old Rhinebeck in June. Sad, but maybe some day...

I see below this thread references to five other Klemm threads. Must investigate!

Jim R.
Last edited by JRuggiero; Nov 08, 2013 at 08:28 AM.
Apr 06, 2014, 04:22 AM
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Klemm 25 Drawing

Apr 07, 2014, 11:14 AM
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from wikipedia

With low cantilever wing, fixed landing gear, and two open cockpits, the aircraft was developed by Hanns Klemm who used his previous design, the Klemm Kl 20, as a starting point. It first flew on a 20 hp (15 kW) Mercedes engine. About thirty different versions of the Kl 25 were made, and these were equipped with engines ranging from 32 to 70 kW (43 to 94 hp). The fuselage was covered with plywood.

Depending on the model, the aircraft's weight was 620 to 720 kg (1,367 to 1,587 lb), and it had a 10.5 to 13 m (34 to 43 ft) wingspan. Take-off was achieved at only 50 km/h (31 mph) and the maximum speed was between 150 to 160 km/h (93 to 99 mph).

General characteristics

Length: 7.5 m (24 ft 7 in)
Wingspan: 13.0 m (42 ft 8 in)
Height: 2.05 m (6 ft 9 in)
Wing area: 20.0 m² (215 ft²)
Empty weight: 420 kg (926 lbs)
Max. takeoff weight: 720 kg (1,587 lbs)


Maximum speed: 160 km/h (99 mph, 86 kts)
Range: 650 km (404 mi.)
Service ceiling: 4,800 m (15,748 ft)

A Pilot's Hand book with a couple drawings can be found here:
Oct 21, 2015, 03:59 PM
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Jim.Thompson's Avatar

Tug plane.

I have just been introduced to this fine old model. I've been looking for designs for a glider tug, and I think this will be just fine for the task.
Perhaps a 25% scale model. I have a 100 cc two stoke engine.
I am interested in any available details someone might have about the aileron hinges. It looks like the stab hinge is a centre hinge. Correct?

Any more build details would be most welcome.
Oct 21, 2015, 05:12 PM
Registered User
Originally Posted by Jim.Thompson
I am interested in any available details someone might have about the aileron hinges. It looks like the stab hinge is a centre hinge. Correct?

Any more build details would be most welcome.
Does this photo help out with the aileron hinges?

Oct 21, 2015, 07:05 PM
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Build method considerations.............

Yes it does to some degree. It shows that they use a pintle and gudgeon type hinge which is outboard, or behind, the aileron leading edge. There is a name for this type of hinge, but the word eludes me.
Probably not necessary to replicate in a model. A simple conventional top skin hinge or centre hinge would suffice I imagine. Much depends upon the wing construction method I choose.
The simplest and most obvious for a composite builder like me, is to cut a low density white foam core and vac bag a light layup over that. A slot for a 3 mm ply shear web could be hot wire cut through the foam cores and glued in place. The spar caps could then be included in the skin lay up and consist of a tapered strip of 200 gsm uni-carbon.

A somewhat more scale like method would be to use a hybrid built up composite type construction. I try to avoid using balsa unless necessary as I have an allergy to it and it is becoming far too expensive.
For this second alternative, the ribs could be made in one of two ways. The simplest is to use foam/fibreglass sandwich, using depron or similar thickness in XPS foam hotwire cut into sheets. Light glass layed up either side. Then the ribs can be cut out with lightening holes and for the required spars etc.
Or: They could be built up, using light timber like some Spruce, Baltic Pine or Pauwlonia that I have in the shed. Similar in fact, to the full size original.
Then the skin could be a pre-made light fibreglass skin instead of the more conventional commercial covering of some type.

I plan on doing some small test layups to get an impression on the relative weights of the two different approaches. Weight projections will be pretty much a deciding factor, but at this stage, I have a preference for the second method in my comparative ignorance, mainly because it is new territory for me and might look a bit more authentic. More work for sure, but that is ok. The simple vac bagged wing over foam would be much quicker and easier.
Oct 21, 2015, 08:31 PM
Registered User
IIRC, the name of ailerons where hinge is aft of LE are called a "Frise type" (pronounced freeze type) aileron. This configuration allows the forward portion of aileron LE, ahead of the hinge, to stick below the lower wing surface, creating a bit of drag, contributing to the decrease of adverse yaw effects. While turning, a down angled aileron produces more lift and subsequent drag on outside of the turn. The inboard up angled aileron produces considerably less drag, and an imbalance occurs where aerodynamic forces tend to react opposite to desired turn direction.
Oct 22, 2015, 02:01 AM
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Frise type ailerons.

Yes, that's it.
A couple of rough sketches of some here:
Sep 23, 2016, 12:03 AM
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Jim.Thompson's Avatar

30% scale Klemm finished, registered and maidened.

Some pictures here:

Flight video here:
RC Klemm Aerotow and flight (9 min 18 sec)
Last edited by Jim.Thompson; Sep 23, 2016 at 03:09 AM.
Sep 23, 2016, 08:34 AM
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Klemm L-20
Drawing © by AEROMAX & Hans-Jürgen Fischer
Sep 24, 2017, 02:11 PM
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Here is the drawing from post #1, resized, touched up and set on 36-inch paper in a 300-dpi zipped pdf..
Apr 24, 2018, 03:50 PM
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I've got a 1:10 scale Graupner kit of the Klemm L25 I'm going to put in the classifieds...
Oct 07, 2018, 10:38 PM
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I am planning on building another smaller one after the loss of my 30% scale Klemm.
This time, half that size @ 15%. 30 cc engine.

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