|Now and then one digs deep down into one’s own archives of decades of modelling. Maybe out of curiosity or boredom. And sometimes one can find real treasures. Doing so I detected copies of an article which had been published years ago in the German Control Line newspaper “LASSOGEIER”. The article had been written by Christoph Holtermann, one of the best German F2B pilots. The contents of this story was high quality information for flyers who have just left the beginner status, who know how to build a decent model able to fly stunts, can fly all or most of the FAI schedule manoeuvres and show some deeper interest in serious aerobatic flying now. Alas the article with its first class information is no longer available. It would be a pity if this information would be lost forever. That’s why this story is repeated here. Some additional information about the development of my Messerschmitt Me 109 design has been included. At first let me repeat Christoph’s original wording.|
1981 Claus Maikis had published a plan for a Me 109 model in the German
magazine “Modellflug International”. It was a simple profile
model intended for the then popular 35 size engines . Claus recommended
this design as a good trainer model and suitable entry for serious stunt
Actually I had made big progress with this design. The reason is the solid construction with a wing without front sheeting, thus a light and flexible construction with decent sweep. The fuselage made out of 10 mm balsa is very high. That’s why it has high rigidity yet is flexible enough to withstand minor crashes. One disadvantage then was the unsatisfying torsional rigidity of the fuselage. But you cannot have everything.
In 1988 I have tried a second attempt with this model because I considered it a suitable beginner stunt design. Also I wanted to find out how well I could build, trim, and fly this airplane with all the experiences gained over all these years. The result was overwhelming. About 10 more or less experienced pilots have tested this design.
Amazing: all of them have performed a very nice schedule on their first flight. Even team race legends like the Metkemeijer brothers (who haven’t flown the FAI schedule since more than 25 years) performed very well. Also Serge Delabarde (European Champion), Henk deJong, Willi Schmitz, Richard Kornmeier, Eric Leupold, and Frank Kuckelkorn were highly impressed by this model. Now what does this model have what other models don’t have? The answer is: everything fits quite well.
OS LA 46 with stock venturi but with later installed spraybar instead of the original crankcase mounted needle. The control line version of the OS LA 46 is not available in Germany, but you can get the original venturi and a 3,5 mm spraybar in the US or in England. As an option the pictures show the system with stock spraybar arrangement.
Original muffler with the end tube increased to 8 mm (=Millimeter) diameter. When drilling be careful here in order to not break the end tube. This is best done with an awl. I’ve used a rubber exhaust deflector 50 mm long , inner diameter 8 mm. I’ve kept the small cone within the muffler.
wood propeller 12 X 4 reduced to 11,5 diameter. I haven’t tried other
120 ( 4 oz ) plastic tank with one clunk. The Uniflo tube should end at one third of the tank length at the tank outer wall. Don’t forget the overflow tube. The tank is fastened with an aluminum strip. A soft rubber sheet is mounted between tank and fuselage.
For side thrust one washer is placed under the front engine flange holes. With a forward located center of gravity much side thrust is not required. Just try it without!
engine runs like a clock, very constantly at a lean four stroke. On the
OS it’s not easy to detect the switch from four to two and vice versa.
Doesn’t matter: just control the airspeed with the needle. This 46
engine can even power much bigger airplanes at about 1800 Gramm. So it’s
not a bad choice for this light model. You can easily control it with the
needle. I cannot recommend other engines because I haven’t tried any.
And I’m not going to try just because the LA 46 fits perfectly; regarding
weight as well as power.
Should you think about any other engines please consider the weight: without muffler they should be around 250 to 260 Gramm.
I have installed a big (100 mm) bellcrank. It’s made from 1,5 mm epoxy plate. The output arm is 25 mm. The flap horn pushrod is a bicycle spoke with carbon tube which is connected to the 25 mm plastic flap horn. Then again a carbon tube pushrod is connected to the 25 mm elevator horn. So we have a 1 : 1 control ratio. After many flights I have found this system to be the optimum. The model flies very stable yet enough sensitive. Here the low wing loading is a big help.
With the cloth hinges the movable surfaces deflect easily and there are no hinge gaps. I wouldn’t recommend plastic hinges. Installing these is much more work and they don’t offer any advantages for this construction with bolted on horns.
The control system MUST move absolutely free of friction. Pushrods must never rub, surfaces MUST move easily. When covering with film take care to not iron even over the hinge gaps, thus limiting deflection.
Center of Gravity
To check CG just hold the model at the wing tips with your fingers. Preferably put the model upside down because of the CG being located high on the fuselage. CG location is much more forward than shown on the plan. This position makes for an excellent stability and saves line tension in all overhead manoeuvres.
Since the Me 109 is a low winger I have used heavy Graupner 50 mm (2 inch) wheels to bring the vertical CG down. You need not care much about weight. Construction of the Me is very light and you will easily end up at 1050 to 1100 Gramm.
I have used “Oracover” film since this will absorb some of the energy should the airplane ever crash. Also beginners will learn quicker to work with it and to master this material than to handle silk span and dope. Even the fuselage is covered with film. I recommend to cover the edges around the engine and the fuselage-to-wing joint with some epoxy. I also recommend fabric film.
To achieve very stiff fuselages and wings the traditional silkspan covering is still the accepted method. However since this Me 109 profile model surely will not be the ultimate contest machine for World Championships, the small gain in (expected) performance is not worth the trouble. For myself I would never try it.
|Warped wings can be ironed out later. Because you can never get this done perfectly, I have added a small aluminum trim tab. This is bent up or down untill the wing sits exactly horizontal.|
I have lengthened the “flap-hinge gap to elevator-hinge gap” dimension to 330 mm. I have also increased the tailplane area up to 20% of the wing area. This will make for very nice round manoeuvres and for good straights in the square manoeuvres.
I have slightly changed construction of the main spar to avoid the covering sag too much at the wing center. Span is 1230 mm. The size of the tailplane should be increased to about 20% of the wing area. It is important that the fuselage is cut from strong 10 mm Balsa. The balsa plank should weigh at least 130 Gramm. You can find this kind of wood everywhere, even at the building center. Flaps and tailplane are cut from solid 6 mm balsa (70 to 80 Gramm the sheet). Ribs are made from strong 3 mm balsa (40 Gramm). Spars and leading edge are strong balsa. However when buying you should look very careful that these are not bent or warped.
Flap horn- and elevator horn- wires are 2,5 mm piano wire. Flaps and elevator need not be stream lined with a thin trailing edge. This is a lot of work, you’ll lose stability, and you will hardly save any weight. Only the leading edge of these parts should be rounded carefully in order to reduce tension on the fabric hinges and to avoid gaps.
Because of the changed spar construction the bellcrank is mounted in a different manner than shown on the plan. The bellcrank is held between two 3 mm ply bearers (25 X 50 mm). These are glued to the main spars and strengthened additionally.
Location of the front line guide is 20 mm forward of the plan location; the rear guide is 20 mm aft of this. A 15 Gramm tip weight is glued to the outer wing tip. This is the correct weight for 015 lines at 18,2 Meter line length ( 60 inch).
The pushrods are made with carbon tubes. You can also use glass fiber tubes. This way the length of the pushrods can be adjusted easily and precisely. On the front end I’ve used a ball link, on the rear end there’s an M3 clevis.
As you can see: there are not many changes. The main topic is the engine. It runs fast and consistently. On Schnuerle- type engines please quickly forget the 6 inch pitch propellers. You’ll get all kinds of problems when trying to set the engine.
At last: I’m sure you can change still more details on this design. For instance adjustable line guide, stiffer fuselage, more rigid wing, etc. But this was not within the design envelope of this airplane. Those who want to have a serious contest machine should build a bigger full fuselage design. However who is looking for an absolutely competent trainer model to practice the full F2B schedule - and with very low efforts - this Me 109 will fully serve this purpose. She will give a lot of fun to beginners as well as to experts - and to those who want (in a sense of “back to basics”) to relive their experiences of the past.
|So far this was Christoph’s original text. His information and what he said is still valid today. His first class help is exactly what flyers need who step up to this kind of airplane. Especially if the popular and easily available OS LA 46 is chosen. However there’s much more which is worth mentioning about the development of this Messerschmitt-profile- airplane.|
|All this has started with a kit, a price won at a local contest. For several years a German model airplane company had tried to sell control line kits of the American Midwest company. Among these kits was one Me 109 profile model for the then popular 35 size engine. I won such a kit. Since I’ve always had an inclination for simple designs and for this engine size this kit was the right impetus to start construction. Alas wood quality was not quite what I can accept. Many parts had to be replaced.|
|Since I had to produce new parts anyway I decided to shape them more to my liking. For instance the airfoil thickness was increased slightly, the leading edge cross section (a complicated milled product) was changed to a simple 10 X 10 mm balsa spar, the tailplane was slightly enlarged, plus some other minor changes. This model was flown several times to test the flight characteristics but it wasn’t flown continuously.|
|At that time (1979) I had planned to spend my holidays in England and to visit the British National Championships. At the same time my friend Stephan Raetsch had planned a motorcycle holliday. So we decided to meet at Barkston Heath. Since he couldn’t take a model with him on the bike, I took the Me 109 with me so he could take part in the contest. That’s what he did. Stephan liked the airplane. However in a sharp corner the weakness of this design showed up - on pullout he touched the asphalt. No big problem, with a little epoxy the wounds were easily healed. It was quite obvious that the (still too thin) airfoil and the narrow flaps just couldn’t produce enough lift.|
|Around that time the editor of a German magazine had asked me whether I had another control line design for publication (imagine that: he asked me ! How times have changed !! ). Many of us still flew 35 size models then. So my Messerschmitt was a suitable object. It was powered by a Super Tiger 35. I just drew a plan with the overall dimensions of the Midwest kit but including the modifications I had done to the design. Wing design was changed for easier construction, thickness of the airfoil was again increased on the drawing and the tailplane was enlarged again.|
|Pictures below show this kit based and modified airplane. All these modifications were included in the new drawing. The article was published in “Modellflug International” in 1981. When Christoph Holtermann was looking for a suitable airplane to start his stunt carrier he found this plan and built the model. As we can see now it seems that it was not a bad decision for him. The plan is still available today from this magazine.|
|The Me 109 fell into oblivion. Many years later Christoph found himself in a situation to help beginners who wanted comtetent help in improving their flying skills. Again he chose this design and built it with the experience and knowledge he had gained over all those years. He even produced four kits for his beginners. The outcome can be read in his own story (see above). Years later Christoph even converted this model to electric drive. I’ve seen him fly this version and the airplane behaved quite convincing.|
|This was - so to speak - the forth version of the original layout. The sketches below will show some of the changes made in comparison to the original layout. What appears to be subtle changes can sometimes come out as drastic improvements in flight characteristics.|
1) The original kit design as produced by Midwest
2) My modified kit model
3) My modified plan published by FMT magazine
4) Christoph’s version for OS LA 46, later electric drive
we’ve not yet come to the end.
For easy access and quick entry into the electric world a simple design was searched. I had no intentions to follow the current (!) streams nor the desire to reach contest level performance. Just fun and enjoyable aerobatics should be possible - plus the possibility to fly outside of the noise limited flight times of my club airfield. Out of laziness - and supported by Christoph’s experience - again the Me 109 design was used. Based on the last (published) plan only a few minor changes were made. The wing airfoil was again thickened to a typical modern section. Tailplane area was increased, too, but aspect ratio is smaller now.
|I was really surprised by the outcome. Now flight performance of the airplane was on a level which definitely allows contest participation (admittedly for some more modest demands) - but nevertheless amazing for a simple profile airplane with electric drive. I actually considered flying this model on contests now and then. That I didn’t do this is another story and has nothing to do with the flight characteristics of this (now) number 5 version of the Me 109. The plan was published in the German magazine “FMT” (Flug und Modelltechnik) . It shows the electric version. Friends of wet power can use IC engines as well; you just need to install longer engine bearers.|
|It is very interesting to follow the development route of a design through several stations and levels. A lot can be learned from this. In the end the metamorphose from a simple kit model to a refined design version has definitely improved the basic layout and its flight characteristics quite noticeably.|
are available. Alas searching on the websites of the publishers is very
demanding. If you are interested try:
For additional information about the electric ME version the link will get you to another page on my website. This story may not provide the latest technology but may serve as a basic starting point into the electric world. Just click the EL button.