1919 AVRO biplane scratch build in foam board

by alibopo | December 9, 2013 | (7) Posted in Projects

1919 AVRO 539B Biplane

UPDATE 16/01/2015 - Here's the plans for this build; 1919AVRO539b


  

Though the plane appears here as a tail dragger it was originally designed and built as a seaplane to compete in the 1919 Schneider Trophy event held in the UK at Bournemouth. Given my present flying skills, building it with floats would be a disaster waiting to happen - so I stuck with the wheels.

 

 It all starts with a plan…. courtesy of the interweb. 

Next – how big to build it? So that I could make the wings in a single piece I re-scaled and printed the drawing to make use of the longest edge of my A1 foam board sheet (841mm). Using the Baby Blender for comparison - the wing chord of the AVRO 539 is less, but the wing span is greater. Doing the sums it turns out the wing area is almost identical - so the wing load will be very similar to the Baby Blender.
 

This wingspan decision dictated all the other sizes. I cut out the pieces from the scaled print-outs and transferred the outlines and hinge detail etc. to the foam board.
 

I used the plan and elevation to help lay out a typical FT style fuselage – top and two sides. To create the gradual curve on the rear of the fuselage I took the top panel all the way to the tail.
 

Here it is with all the basic components added – tail, servos, power pod, turtle deck formers and top wing support. I added a double-layer cross piece at the front to rest the undercarriage against. Note – the servos are mounted well forward to help with balance.

 

The top wing support is screwed into 4 tongue depressors – 2 glued on the top and 2 trimmed ones on the inside. 

The wing support frame is made-up of two identical pieces of bent wire that are bound together with thread and CA glue.

I hoped the frame would be stable enough to support the wing but it was a bit too springy, so I added thin bracing wires to create stiff triangles. The top ‘skid shaped’ wires are for attaching the wing elastics. 

Knowing the chord and wingspan, I was able to lay out a typical BB2/Cruiser type wing. The only addition to the basic design are anchor points for the struts. I described them as ‘brace’ points in this drawing. This is the bottom wing, which isn’t as wide as the top wing – that wing goes right to the edge of the foamboard.

After I cut this first wingtip, I used the offcut as a template to draw the other three. 

I use spare servo arms as the attachment points for the struts. These poke through holes I cut in the foam, and are glued on the inside of the wing with a short length of skewer through the end to spread the load. The bit that sticks out has useful holes for fitting wire to. I didn’t intend these to be too structural, just help maintain the spacing between the wings - and they’ll definitely add character.

The upper wing is flat and the lower wing has dihedral. To make-up the lower wing I bent a piece of 2mm wire to the correct dihedral angle and embedded this in my wing spar. This made assembly much simpler as the spar helped to produce the correct dihedral as the wing was assembled. The wire will add some strength, but was mostly just an aid to assembly.
 

The aileron servos were sunk into the wing during assembly. 

The bottom wing centres using a pad glued to the top of the wing, which fits between the fuselage sides. The back rests up against a stiffener running across the fuselage.  

The top wing centres using this rectangular pad, which fits inside the wire frame. 

I used thin wire to make-up the struts that space the wings. I left the ends at the top a bit longer to make it easier to get them in and out just now. 

Here’s the tail detail. I added a strengthener inside the fuselage, and included a little cut-out to help stiffen the rudder keel. I also added a steering tail skid. 

Here’s a test fit of the paper templates for the turtle deck. I later included a hole above the servos to avoid the need for a removable section. 

The undercarriage is held on by elastics. At the back I use an extra loop in the wing elastics and at the front a dedicated elastic/skewer. The wheel axle is sprung by passing it through two twisted prop saver rings. The landing gear frame is made-up from two mirror-image parts bound together using thread and CA. 

I like the overall look of the plane - here it is in comparison to the original.

Almost there - the whole plane has been sprayed with clear matt varnish and is ready to maiden. In this picture you can see the servo access opening hidden under the top wing. I blanked out the wheel spokes with foamboard and card for a better look.  

Foam radiator and headrest fitted - just the windscreen to add to the cockpit, and a final paint job.

I'm very pleased with how this plane has turned out; compact, classy and stylish.  

Here she is with a headrest, windshield, paintjob and a pilot. Those are bigger wheels on the front, which have mostly allowed 'proper' landings. I filled-in the spokes with foamboard using the method from my "Olde-style wheels for olde-style planes." article. You might notice the nose is slightly remodelled. I had a prop-saver fitted, and the prop got knocked off-centre without me noticing - next time I powered-up I 'shaved' the front end down. A little outline plate cut from pizza base foam has neatend it up a bit.

You can see the little beast fly if you follow the Flite Test links below.

Cheers to all in the Flite Test community, all those shared ideas and enthusiasm have helped make this build possible. alibopo.

UPDATE; the plane had a 1700KV 28A motor to start with, but current draw was quite high with the 9x3.8 prop I was using. Time in the air wasn't really that good. I tried a smaller prop, 8x4, to allow the motor to use its revs to produce the thrust - hoping for more efficient use of the motor - but I think too much thrust was lost pushing air against the blunt nose. A bigger prop pushes more air out beyond the blunt nose, so not so much thrust is lost. With all that in mind I decided to try a slower revving motor, better suited to turning a bigger prop. I went for an EMAX GF2215/20 1200KV which theoretically draws about 20A with a 10 x 4.7 slow flyer prop. I only had 9 x 4.7 prop around, so tried the plane with that. It flew fine, with plenty of get-up-and-go for the take-off. I'm guesstimating my max current draw from this 'under-propped' setup is somewhere around 15-16A. This should give me much better flight times, though I've still to get a chance to confirm this. Last outing, with the new motor and prop, shortly after I got the plane in the air the wind picked up and I was happy (relieved) just to get it down without mishap!

COMMENTS

808aerosquadron on December 10, 2013
That is cool. I especially like your wing and cabane struts ideas. Very cool.
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808aerosquadron on December 10, 2013
Alibopo - What motor are you using for this? She looks to be about the size of the Baby Blender.

Not having access to Adams foam board, I am also having power-to-weight issues with heavier foam boards and am looking for alternate motors. Have you found a "beefier" set up that works well?
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alibopo on December 11, 2013
Hi 808aerosquadron, I do fly planes on those original Blue-wonder motors but I quite quickly moved-on to more powerful ones. I look at the current rating, which, if you munge-the-maths and allow for efficiency losses, you can multiply by 10 for a 3S battery setup and get a watts (power) value. You then use that power value in comparison to your plane weight to work out what kind of performance you'll get. Read-on to see what I mean. In this instance I've reused the motor from my Baby Blender build. It's a Mystery A2212-1700KV which is rated at 28 amps - (that's 215W on a 3S) - it's listed as suitable for a 300-800g plane. My BB had an AUW of 726g. I'm using 1000mah 35C batteries which in theory can output 35A. On my heaviest plane I'm getting about 8-9 minutes of flight, though some of my planes are carrying ballast weight which could be replaced
with more battery weight. I decided to standardise on that 1000mah size as I can use them on every plane I have, and with the 35C rating there's enough current for my larger draw motors. Also when I worked out a cost per mah for various batteries around
this size, the 1000mah came up much cheaper for some reason. I was able to buy more time in the air for my money - though I don't get super-long flight times. I'd actually have preferred a lower KV motor, 1200-1500 is a good range for these size of models due to the size of props they can swing, but it was an Ebay bargain that was too good to miss :)

Referring to this reccomendation chart, I'll go through my 'heavy foam board' planes;

50-70 watts/pound: 11-15 watts/100g Minimum level of power for decent performance
70-90 watts/pound; 15-20 watts/100g Trainer and slow flying scale models
90-110 watts/pound: 20-24 watts/100g sport aerobatic and fast flying scale models
110-130 watts/pound: 24-29 watts/100g Advanced aerobatic and high-speed models
130-150 watts/pound: 29-33 watts/100g Lightly loaded 3D models and ducted fans
150-200+ watts/pound: 33-44 watts/100g Unlimited performance 3D models

My now deceased BB (726g) came in at 29.6watts/100g - putting it at the top of the Advanced aerobatic range (in theory).

My GeeBee has an AUW of 825g with a GT2210/13-1270KV 17A motor recommended for 600-800g planes - from the chart that's 22.7 watts/100g which is sport aerobatic and fast flying scale. Which sounds about right for how it performs.

The Tribewt has an AUW of 680g and flies on the Emax CF2822 1200kv 15A - rated at 160w - that's 23.5 watts/100g - sport aerobatic and fast flying.

The Morphocoupe Bush Plane weighs in at 938g and the motor is rated at 210 watts - that's 22.4 watts/100g - sport aerobatic and fast flying. It probably would do that if I hadn't accidentaly built-in a permanent flap/undercamber on the wing. The plus side of that mistake is it can coast around quite slowly if I want it to.

The Avro has an AUW of 925g with the 215w motor - 23.3 watts/100g - sport aerobatic and fast flying. But that includes 40g of ballast. I might lose some of that once I work out a final CG - just now it's on the 25% point, but it could shift back. I'm expecting a fairly wide flight envelope, but no extreme top end speed.

I think the difference between these heavier planes and some that you see is that these ones need to actually fly and be flown - you can't just hang them off the prop like a 3D plane. They stall, they lose speed in a fast turn, they don't leap into the air - a bit like the full size versions.

If you trawl through my articles you'll see all these planes flying. In particular look at my article "Heavy foam board blues?" Heavy foam board is not an obstacle to flying - you just don't get the same performance or flight times, though a lot of the time it's probably not that noticeable.
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808aerosquadron on December 29, 2013
Alibopo, I have been searching for appropriate motors for an airplane in the 34 oz / 960 g range. I checked your articles on the Avro and Morphocoupe Bush Plane but could not deduce the motors you are using. Since they are close to the projected weight, and you seem to be pleased with them, I would be very grateful if you would relay what motors you are using on these airplanes.

Thank you,

808areosquadron
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alibopo on December 30, 2013
Hi, the bush plane is using a D2830-11 1000KV motor bought through Ebay. Here's a link to a page describing the motor; http://www.goodluckbuy.com/d2830-rc-750-850-1000-1300kv-outrunner-brushless-motor-for-multicopter.html (copy and paste in browser)
Max power 210W - suggested prop 8x4 to 10x7
I probably erred on slightly too slow a motor speed here, but it pulls the plane along quite happily.

The AVRO has a MYSTERY A2212-10 1700KV Specifications:
- Max. efficiency current:14 - 22 A (>72%)
- Max Current capacity :28 A/ 60 s
Enough power 22A (at the top of the max efficiency band) x 10v (allows for efficiency losses etc) gives 220Watts - for this plane that's roughly 23 watts/100gram (Sport aerobatic and fast flying from the table above.) I don't regard this as an ideal motor for this plane - I bought it in confusion early on in my RC career thinking the KV value related to power. No big deal - it's still one of my more powerful motors, but I do prefer slower spinning motors.
I've just bought this motor;
EMAX GF Series 1200KV Outrunner Brushless Motors Type GF2215/20
1200 KV - recommended prop 10x4.7 - max current 20.2A - thrust 1125g 2.48lb
I might swop this in to the Avro as it appears to be a more efficient motor and could give me longer flight times.

I know the problem though - manufacturers/sellers use so many different ways to describe motors. I decided to go with slower spinning motors partly to swing bigger props that fit the scale of the models better, and mostly because I hate those high-pitched screamer motors. I think a lot of people start off using 'screamer' motors thinking they are more powerful. I know they work well on pushers with limited prop clearance, or on smaller scaled models, but I can't see the point of using them on larger models.
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alibopo on December 30, 2013
Hi - here's a link to the D2380-11 on ebay; http://www.ebay.co.uk/itm/D2830-RC-750-850-1000-1300KV-Outrunner-Brushless-Motor-Multicopter-e-/251282841052?pt=UK_ToysGames_RadioControlled_JN&hash=item3a819fdddc
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alibopo on December 30, 2013
...and the Emax 1200KV motor on ebay;
http://www.ebay.co.uk/itm/EMAX-GF-Series-1200KV-Outrunner-Brushless-Motors-Type-for-Rc-Airplane-GF2215-20-/300949220874?pt=Radio_Control_Parts_Accessories&hash=item4611f8ae0a
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808aerosquadron on December 30, 2013
Alibopo - Thanks once again.

Like you, I am probably looking at the lower kv rating than the higher, screaming motors. I am also looking at a lower pitch on the propeller, for thrust and scale, instead of a higher pitch for speed. I will be sure and check out these motors.

Once again, this is very helpful.

Sincerely,

808aerosquadron
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808aerosquadron on August 8, 2014
Alibopo -

Following our discussions on motors for our more portly planes, I have had good success with the Turnigy D2836 from Hobbyking: both the 1100kv and 950kv motors. They are not that expensive and received very good remarks from Experimental Airlines in his YouTube review.

I thought I would pass along the information since you were so helpful during our earlier discussions.

As they use to say in the old USAAC: "Keep'em flying',"

808aerosquadron
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alibopo on August 8, 2014
'Portly' - I like that :) I've been thinking about another biplane, an SE5A or similar, something with a bit of length and nose projection to make it more predictable and for easier balancing. Also big enough to fly slow.This could be an ideal motor for that kind of build. Thanks.
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808aerosquadron on August 8, 2014
Funny, I was also thinking of building a 30 inch SE5A, and for pretty much the same reasons. I have been fiddling with drawing out plans for plane, both with an under camber wing and with a kfm2 wing.

I would also like to build a Sopwith Pup or Bristol Scout, but getting the CG correct without gluing a brick to the nose will be problematic.

If you do build your SE5A, or similar, please post photos.

To quote the old RFC, "Per Ardua ad Astra,"

808aerosquadron
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alibopo on August 9, 2014
Regarding the wing. I was very impressed with Flying Penguin RC's recent Flat Shot Staggerwing design. I do like my super-robust folded Armin wings, but dropping to a single layer takes away a whole pile of weight and reduces how much foam board is needed. I imagine an SE5A with that kind of wing design would fly nice and slow.
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808aerosquadron on August 9, 2014
The only concern I have is whether the wing would be strong enough, even with the under-camber wing fold. That is why I was contemplating a KFm2 or KFm5a wing. Check out the "WWI VLF Design Combat Models" thread on RCGroups.com, especially the Sopwith Pup KFm5a wing option.
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808aerosquadron on December 11, 2013
Alibopo - Mahalo nui loa (Thank you very much). This is very helpful.
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Throttle Up on December 10, 2013
Very. very nice! Great work, and nice photos to help the rest of us.
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alibopo on December 10, 2013
Cheers, thanks for that.
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Yogenh on December 14, 2013
I would love to have a set of plans for it. I am thinking of trying to make one of my own. I will have to give it a try

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alibopo on December 15, 2013
Hi Yogenh - I just worked from the 3 view drawing I found on the internet rescaled it and lifted all the sizes from that. I used 'standard' Flite Test Build techniques and construction for the basic elements - wings, fuselage, rudder and elevator. I know that doesn't help you with the wire detail. I can't do anything just now, but I have started on JasonEricAnderson's sketch-up tutorials. Depending on how fast (or slow) I am with learning how to use that software - I should manage a set of plans early in January. If you look at my "Build a Tribewt" article you will see how I have used the basic Flite Test methods in 3 examples; the Tribewt, a single-seater monoplane and the GeeBee X builds.
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c.sitas on December 10, 2013

Ali.; In the start of your build you mentioned water floats and your fear of them.I've found articles of the guys waterproofing the electronics, and to the point of the motor really able to run under water. They claim the only drawback is "saltwater".
they dunkum, dryum out and fly some more.I guess I'm saying ,fear them not!Try um, I did and it's really cool. Makes this old man grin.
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alibopo on December 10, 2013
Hi c.sitas - Art's comments above led me to an article by the late Chuck Cunningham detailing how to do just that. It was intriguing! I'll not say no to giving it a try, but I'll wait until I'm comfortable flying the little beast. I'm not sure how foam board will do in the water. I have flown in fog and rain, but that's quite different. Thanks for the encouragement!
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c.sitas on December 10, 2013
Thanks for the come back Ali. I know what your talking about. I live in Wisconsin, USA and right now the temp is _8 degrees f. Man that'll take the skin off your fingers if not careful. Love your build. Shows great technique.Have a safe winter and fly.
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Yogenh on December 12, 2013
I love it. With you had the plans for it on here

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Art on December 9, 2013
Now that's an airplane - great job - I like biplanes, that's why I like Cunningham's design articles, he took the monoplane basics and had the adjustments for biplanes - I found this 3 view site a long time ago, its by manufacturer but has alot of planes if you need more -
http://richard.ferriere.free.fr/3vues/3vues.html
keep up your great work and great articles :)
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alibopo on December 9, 2013
Thanks, and that's a great 3 views site! Now stored on my favourites.
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Art on December 9, 2013
Yes - I like it too - I see alot of planes I dream of building - if I ever learn how to fly :) I got surprised looking for the SE5a - it was built by the RAF - at that time that meant Royal Aircraft Factory not Royal Air Force - so I learned something on that one :)
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alibopo on December 10, 2013
I've probably been lucky with my flying this summer - I only started after last Christmas, but I've had a lot of good days out. This Flite Test and foam board lark has been a real winner for me - I've been able to move through a series of builds starting with easier planes, and moving on to ones I've designed myself. Still loads to learn though. I'm looking forward to a bit of snow on the ground to try out some planes on skids.
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jess_gordon on June 7, 2015
I like your construction methods. Got some good ideas. Thanks for documenting the build. I just finished a Curtis JN-4D (see article "say hello to jenny") when its approved.
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alibopo on June 8, 2015
Hi Jess, I'll keep an eye out for that, I'm definitely enjoying how these biplanes fly. The Avro was my first biplane, and the wing mounting has evolved from what is shown in the article. See the Polikarpov Po-2 and the SE5 articles. The Avro drawing uses the more recent system, though I'll need to look at it again, I didn't realise it was such a large file. :( I've had a few recent ideas for how to simplify the cabane mount even more, it's massively over-engineered just now (but I'd rather that than it fell apart on the first rough landing). For me the important bit is having a way of holding the wire frame down without gluing it to the deck, to help with landing shocks etc.
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1919 AVRO biplane scratch build in foam board