Bucker Bu 131 Jungmann

[Rod]

Well after the Su29 I built a vintage Lanzo bomber using traditional balsa, spruce, silk and dope. This has given me such a good time I have decided to build an IMAC model of the Bucker Bu 131 Jungmann using the same materials and with the vintage theme (prototype flew in 1934).

Normally I would start the thread after the design was finalized and construction started to give impetus to the thread. But this time I would like to include you guys in the design process as well. I am hoping to get some feedback on the aerodynamic and structural design details.

[Rod]

Here is the scale drawing that I will be working from.
Here are the final laser cutting DXF files.
Here are the PDF vesions of the cutting files.

[Rod]

I have a ZDZ 120 I will use for this model. I have measured the exhaust timing so I can design a tuned pipe system for the model. The exhaust timing is 148 degrees which is a bit low for pipes but the motor will still respond to them.

[Rod]

Dick Hanson designed a Jungmann for the TOC and has posted his design strategy on FG. That is to reduce the wing span by 9% (thereby staying within the 10% rule). My usual method is to increase the tail moment by 9% but Dicks plan achieves the same result but has the advantage of negating the rather narrow chord of the Jungmann. You cant get the same span/area/tail moment aerodynamic advantage as a 20-300 Ultimate but it is still pretty good.

Like the Carden Ultimate I want thin 10% airfoils one piece wings and no flying wires. Hopefully I will be able to avoid their test flight results!

[Rod]

OK so how big should this model be? I suppose the best place to start is an estimate of the weight. The ZDZ 120 is not particularly light at 6.5 lb add on a couple of pipes, complicated landing gear and 2 wings however I think I can design and build quite a light airframe, well I would be very happy at 29lb AUW.

If I knew the optimum wing loading for this size biplane and 29lb AUW is correct then I would have the exact size to build it.

[rcpilot82]

This should be a great build!

[Rod]

Here is a preliminary drawing. All I am looking at now is size and general layout. At 2050mm (80.5") the area is 1803 Sq in, maybe a bit small as this would give a wing loading of 37oz/sq. ft at 29lb. If I go up to 86" the wing loading comes down to 32.5 oz/sq. ft.

Don't expect professional standard drawings, I will be doing just enough to build the model. However I will put up the DXF files for anyone interested.

[brusty]

Okay, I'm on board. Nothing to add, just watching in awe. I'm sure this will be a great forum. B.

[dm8221]

Always in awe of designer built planes,liked the full scale color scheme.Will be watching your built thread.Have a special bond,as I was fortunate to have lived in New Zealand for a time met a lot of great modelers. Don

[forgues research]

I"m with Barry, nothing to add at this time but it will be refreshing to see something different for a change....

Roger

[stevep]

Make it big as possible, light as possible, big light planes fly great, go for it

[MX304]

Very cool project!

[Rod]

I have plenty of spruce which I want to use in the construction of this model. What do you guys think the size of the fuselage longerons should be, bearing in mind that this is a 100cc+ class of model. My feeling is 1/4" or 5/16" square.

[forgues research]

	Quote: Originally Posted by Rod
	I have plenty of spruce which I want to use in the construction of this model. What do you guys think the size of the fuselage longerons should be, bearing in mind that this is a 100cc+ class of model. My feeling is 1/4" or 5/16" square.

That would depend a lot on the design and the amount of stringers used.

Roger

[Rod]

That's right Roger. There is a single stringer on each side and on this version a 7 stringer turtle deck.The fuselage will have the vertical and diagonal (balsa) bracing between the longerons as shown in this sketch.