Building a B-17 Flying Fortress

by Martinmiha | March 6, 2016 | (15) Posted in Projects

In this article I am going to show how I built a 232cm (7.5 ft) wingspan B-17 Flying Fortress!

Before this plane my friends and I were only flying 100cm wingspan lightweight planes. So we decided to build something bigger. But the idea was to keep the budget low and to use small motors so we can reuse them later. 

We mainly use 7mm depron and 3-4cm isolation board + some aluminium for motor mounts.

The power plant we use is in the links below:

30 Amp ESC | 2200kv Motors | 4S 4500mah 45-90C

I have made the plans myself using an 8 inch prop as a part to compare to get different parts measurements. It took me 5 hours to draw the plans. The next step was to make the motor mounts from aluminium. 

These parts were connected with a 1x1cm 1m length aluminium bar and glued to the wings.

Then we started to build all the other parts: elevator (double layer of 7mm depron + 6mm aluminium tube)

The wing's 4cm isolation board, shaped and then with a tool we call "rašpa" we made the airfoil, glued the second half together, and inserted some aluminium tubes to make the wing demountable.

The main body is constructed of 5-6 layers of 3-4cm isolation board glued together and shaped also with the "rašpa." We used that tool for shaping every big part:

And the motor covers... 4-6 layers of 3cm isolation board glued, shaped etc..

Then we assembled the parts together mainly with hot glue and mitopur glue.

Then we added the landing gear and servos, built the canopy, and taped the aileron, elevator and rudder surfeces on...

Then we made a test flight, crashed it, repaired, painted and now we still keep flying, crashing repairing hehe =D 

And we also covered it with paper and glue just to add some more strength and to make it look nicer when painted...

The entire process took us 60-65 hours of work but at the end it was totally worth it. =D 

We had some problems with the radio. We crashed 3 times due to radio failure, we figured it out only the 3rd time because the first and second time it looked like the plane stalled or something. 

Watch the video and be free to ask anything =) 

 

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COMMENTS

Desert Wings on March 9, 2016
What a build, thanks for sharing.
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Martinmiha on March 10, 2016
Thank you =) sharing is caring =D
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Willsonman on March 9, 2016
First, great build! From the flight characteristics there may be one or both of two things going on. 1) Check your CG. The porpoising (up down up down) may be due to the CG too far aft. If the elevator is super twitchy this is also an indication of that. 2) Airfoil/ incidence. While using a rasping file is great for foam shaping you will find that the airfoil may not be very precise giving you an uneven distribution of lift. I highly recommend using a hot wire to do this but you may not have access to or means to build one. The wing incidence may also be a player in the aerodynamics of this. If you are able to, leave the leading edge where it is and shim the trailing edge just a little at a time, making it sit lower than where it currently is.

You have a great design now... you just need to tweak it to get it more stable. Keep up the great work!
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Martinmiha on March 9, 2016
Thanks you =) I think that the CG is ok but the elevator is just to sensitive. I will fix that for the next time =) yeah i know the airfoil is not totaly simetrical next time I will build a how wire cutter. Thank you for all the sugestions =D
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CMS_1961 on March 9, 2016
Great Design!!! I liked the way you created the engine mount system. I suggest instead of wrecking all that time and work you get a NEW receiver and keep it away from the metal spar/engine mount system, it may be part of the reason for the radio failures!! I have never seen so many radio issues in one flight. Also check your transmitter antenna and batteries. It would be a shame to lose a plane you worked so much on!!!
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Martinmiha on March 9, 2016
Thank you =) we discovered that after about 3-4min the radio or the receiver stop working, but the same receiver and radio used on an other plane works perfectly. From now on we are useing annother radio =)
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Yogenh on March 9, 2016
It is a very nice build. I really think that you should move the CG forward. I know that would help a lot and if you don't have dihedral in it I would put some in. like about 3" for a wing that big. Can you post the planes for it so that I could get a copy to build it??
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Martinmiha on March 9, 2016
Thank you =) I will try to put the CG more forward, but the thing is that a have the battery all the way upfront. But I also think that the CG is good and is only a matter of the sensibility of the elevator ( it is on 100%) I will make it 50% and it should fly better =) The wings already have a small amount of dihedral =)
I can try to make some sort of video for the plans in the near future. Its a little bit of a problem because they are only drawn by hand on a very big paper (app. 2x1m)
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Yogenh on March 9, 2016
That is good and try that definitely having the elevator too sensitive will make it hard to fly.
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HilldaFlyer on March 9, 2016
Great looking plane! Just one question. How do the wing tips stay connected? I would assume they are fastened with more than friction. Thanks!
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Martinmiha on March 10, 2016
Thank you =) I made a 3mm hole from the top of the wing through the aluminium spars and used a pin to prevent every movement.
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Battershell on March 9, 2016
I think others here noted the CG problem. Porpoising up and down is a sign of CG too far rearward. I understand your comment about your elevator buy even 5 - 10mm forward would do wonders. And how about some expo as well around center stick? As for your radio problems ,check to make sure your Tx and Rx antennas are both soldered firmly to their boards. or snapped in place if they are that style. and relocate the Rx away from your motor mount framework of aluminum. That in itself is enough to cause reverb waves of caos for your electronics. Just some helpful hints.
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Martinmiha on March 10, 2016
Thanks for the hints =) I will use all the milimeters left on the front of the plane to corect the CG, I like to fly everythink on 100%, It works for me on smaller planes, but yes, I will use some expo now =)
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Drezed on March 9, 2016
Are you really using a 4 cell battery with a 2200kv motor? I can say from using these motors, a 6X4 prop on 3 cell will pull 30-40 amps. A 4 cell trying to turn an 8" prop will pull WAY more than your 30amp ESC will handle. This is likely the cause of you receiver issues, unless you're using a UBEC of course. :-)

Jeff
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Martinmiha on March 10, 2016
Thank you for this comment. I know is not responsible to put a 4S on 4x 30amp ESC but we had a low budget.. The 30amp was about half of the price of the 40amp.. And also we tought that the plane will not be heavier than 2- 2,5 kg... The recomanded ESC for the 2200kv motor is an 40amp. I am flying this 2200kv motor with the same 30 amp ESC and a 8x5 prop on my smaller planes and it works perfect, but the heaviest weights 700g (with an 2200mah 3S) , if we multiply it x4 is 2800g but the b-17 weights about 3800g with the battery... I also try to fly it with an UBEC, I would never tought of that, thank you =D
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amcknight31 on March 11, 2016
Pretty sweet! I like your design, especially the motor mounts. Very ingenious!
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Martinmiha on March 11, 2016
Thank you =) and the mount is preaty light weight too, the aluminium parts, the motors, ESC and all the wires weights 600g.
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Kurt0326 on March 14, 2016
Well Done. Great choice for model. I hope to build one about that same size.
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Martinmiha on March 17, 2016
Thank you =) I will publish the plans soon =)
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wolfman2 on March 15, 2016
Great stuff - you guys gave me a whole bunch of ideas with your construction - keep up the good work !!!

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Martinmiha on March 17, 2016
Thank you =)

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Robert4613 on March 26, 2016
All I can say is "WOW!" That is a fantastic build from plan to flight! Great job! Good luck getting the radio issues figured out.
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Martinmiha on April 1, 2016
Thank you =)

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alibopo on March 29, 2016
Fantastic build - well done! Regarding the porpoising - I wonder if it might be because the aft section of the fuselage is too flexible. Just from viewing the video, it did look like the plane was quite flexible. The actual elevator OUTPUT, compared to what you did at the transmitter, will be MAGNIFIED if the WHOLE elevator and rudder assembly can shift above and below its intended position during flight. Maybe on your next build you can insert some vertical stiffening that carries down the length of the fuselage? Thin ply? Regarding radio problems - I would strongly suggest you run a separate SBEC (switching battery eliminator circuit) to supply power to the servos and transmitter. Unfortunately some manufacturers use the term UBEC when the ESC is a simple 'power wasting' linear BEC, so make sure you see the description 'switching' somewhere in the blurb. A non-switching (linear) BEC 'wastes' power to drop the voltage, the more demand, the more it needs to waste. At times of high demand or low battery state, this can create momentary drops in the output voltage, to a point where some receivers actually shut down. At 600grams you should be able to fly a lot slower with that wing area, but at lower speeds you'll need to keep the wings flatter and use a bit more rudder input for the turns. Best of luck with future builds. alibopo
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Martinmiha on April 1, 2016
Thank you for your comment. The fuselage is not flexible, maybe in the video looks like it is but its not flexible at all. The entire plane weights 3800g not 600g, only the battery weights 600g. I will pay atention in my future buying of electronics =) and also I will improve my flying skils =)
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Martinmiha

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Building a B-17 Flying Fortress