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Old Sep 26, 2015, 05:03 PM
Dr. Vork is offline
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Burnelli RB-1 advice needed

My plan is to make a 1:20 scale Burnelli RB-1. I have found some drawings, pictures and data of the plane. With that I went to work in SketchUp and drew it up. I have a pretty good idea of how I am going to construct the plane. It's not a very complicated design. Only the wings with 1 degree dihedral and 3 degrees sweep are somewhat challenging.
The length will be about 600mm (23,5 inch) span about 1100mm (43 inch).

I have 2 questions I want your opinion on:
Will this plane be controllable the way it is now, full scale? I know it is hard to predict the behaviour but experienced scale builders should have something to say about how it will behave and what I can do to make it behave better.
The wing profile is M-2 according to the documentation (see pictures). I found 2 airfoils that listen to the name M-2, first the NACA M-2 a symmetrical airfoil. I'm pretty sure it isn't the one used in the original. And the WORTMANN FX M2 AIRFOIL. Which is an asymmetrical airfoil. I'm pretty sure this isn't the one either because Wortmann was born in 1921 and the magazine that mentions M-2 is also from 1921.
So what should I do? Use one of the "standard" airfoils like Clark Y? Or does anyone know what M-2 stands for?

Thanks in advance for your help.
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Old Sep 26, 2015, 06:06 PM
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Michael Max Munk designed air foils for NACA in the 1920's so the M-2 is one of his foils. As far as predicting flying behavior? Not a clue.
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Old Sep 27, 2015, 07:17 PM
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a 'genuine' Clark Y will likely meet ALL your expectations and some.
Scale aerofoils... especially Century old ones don't 'scale down' :-) well at all.
But Hey! half the fun is in trying.
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Old Sep 27, 2015, 08:13 PM
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+1 with Bare on trying scale airfoils! I have a 1/4 scale 1921 Vampyr sailplane that uses a Go 441 foil (scale) and it is amazing how well it flies!!!
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Last edited by ARUP; Sep 28, 2015 at 07:22 PM. Reason: ... uses a Go 441 foil not 451.
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Old Sep 28, 2015, 01:53 PM
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At the size you want to build this the airfoil is not going to be critical. I think the tail size is going to be a problem. you dont have much vertical area and a lot of area that is forward. You may want to over size all of the tail surfaces. Any thing close to scale on the airfoil will work. keeping the build lite will be the most important thing.
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Old Sep 28, 2015, 04:24 PM
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Hi, just to add some variety, there is another aerofoil section of about the same vintage that might be reported as an M-2. It is the Glenn Martin 2 section found here:

http://airfoiltools.com/airfoil/deta...lennmartin2-il

The photos of the RB-1 reminded me of that section, which I think was used on some Navy aircraft to evaluate thick cambered aerofoil sections in about the same time frame. I have superimposed the Glenn Martin 2 section on the convenient photo from the first page of the Flight article and I think the shape is a pretty good match. I think that this may be the section and it is a pretty important visual feature of the aircraft.

I think your choice of subject is very interesting and I look forward to seeing how your model turns out, regards John
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Old Dec 11, 2015, 07:44 PM
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Here is the Wortmann FX M2 airfoil... http://airfoiltools.com/airfoil/details?airfoil=fxm2-il

The RB-2 is almost a copy of the RB-1 except that Burnelli redesigned the tail section to gain more control. Having no similar aircraft to copy from, Burnelli had to make his way work by trial and error. Out of 9 unique planes, over 25 years, he made no major errors in design.

Here is a pdf that shows the RB-2 plans by Alan Heim... http://www.aircrash.org/burnelli/pdf/mod_rb2.pdf He built and flew this design for years. At twice the dimensions, you might have better luck in the control of this very early lifting fuselage design. Being so similar, you may want to consider the RB-2 since the RB-1 was Burnelli's first try with his design. It was said to be a little sluggish in rudder control.

As for your concerns for flight control, Alan says "this subject is gentle and well worth modeling." Here's his story and several flight pics... http://www.aircrash.org/burnelli/mod_rb2st.htm

Hope to see yours soon. All the best, Larry
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Old Dec 12, 2015, 03:42 PM
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Hi, looking back at the comparison of the photo of RB-1 from an article in a 1921 Flight Magazine and the Glenn Martin 2 aerofoil section that I posted in September, I can see that I should have blown the photo up to the scale of the aerofoil section I had, rather shrinking the section to fit the photo. Doing it properly, one can actually see the aerofoil section and that it is a pretty good match for camber and thickness and general shape of the aircraft wing. It is especially apparent in the nose area. You need a bit more imagination toward the trailing edge where there is an aileron and its balance and the section of the wing tends to merge with the visible part of the upper surface as well. One thing that is obvious is the great thickness of the section near the trailing edge.

I think that there was a lot of interest in using very thick cambered sections when the RB-1 was designed, probably prompted by the success of various Fokker aircraft. The Martin aerofoil section was one of many available at the time - in fact the RB-1 wing section is not too different from that of its fuselage. Although the Wortmann section suggested in the last post has the same sort of camber in the nose region, it is much thinner than the Martin section - especially at the trailing edge. Besides I think that Dr Wortmann might have been a bit young to design a section for this aircraft, since I think he was born in 1921.
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