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May 17, 2021, 10:50 PM
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Dumas Dragon Rapide


The DeHavilland DH.89 Dragon Rapide is a short-haul dual-engined biplane airliner from what is rightly called aviation’s “Golden Age” — the 1930s. It was a development of the DH.83 single-engined cabin biplane, and if you’ll look at the picture below you’ll see the shared DNA.

I don’t know that a more elegant airliner was ever built.

Well here we go. This looks to be a fine kit. Step one is fine-point-Sharpieing all the sheet wood parts, which are identified on diagrams in the back pages of the instruction booklet.

I’ve got all the wings framed up, which thanks to laser-cut parts goes fast. In “dry fitting” the upper wing assemblies I noticed a little discrepancy between the plan and the parts; As the ribs of the upper wings “jig” themselves into the spars, there is left a gap of perhaps 1/32” laterally between the forward spar and the root rib. With this gap filled with a sliver of balsa, the rest of the upper wing agreed nicely with the plan, and this problem and its solution were the same for both upper wings.

With the lower wings, there was a similar issue: The main spar was about 1/32” too long at the wing root. Again the discrepancy was symmetrical wing-to-wing, and the tip ribs ended up where they were supposed to be so I just built them out with a few ribs sliding over their lines.

Now, I am dangerously ignorant when it comes to electricity. I think that with a pair of Park 250s this 42” wingspan plane will be hilariously overpowered. I have some experience with the 180-sized brushless motors you get with the UMX foamies, and I suspect that a pair of them would be overtaxed pulling a draggy biplane of this size, however lightly built.

If any of you can offer advice on a good power setup, I’m all ears.
Last edited by jmlamb; Oct 31, 2021 at 03:27 PM.
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May 18, 2021, 01:53 AM
Viceless no longer :)
fairweatherflyer's Avatar
What a great project - its a very elegant plane. My Dad as a boy on the Isle of White had to help weigh passengers and their luggage before they went on their flights - Some of the more matronly looking ladies gave him 'looks', that he still remembers today for when he used to shout out the weight for it to be recorded.
May 18, 2021, 08:01 AM
Still the "Pro"-crastinator...
Steve85's Avatar
I have one of these on the shelf for building "one day", so I'm keen to see yours come together. As for power, the original brushed IPS geared motors put out a maximum of 20-25 watts each, so you're not looking for too much more than that, especially as Pat Tritle suggests overpowering the model leads to squirrely flight. I'd be tempted to use something like a Suppo 2204 or the Hobby King Silver Wonder on 2s as a brushless replacement. I may also have a couple of the originally-spec'd IPS geared motors and brushed ESCs in my stash, and they're yours if you want to go old school.

Steve
May 18, 2021, 04:20 PM
Registered User
I've got this kit in my big pile of kits. It was going to be my next model, but now it's a toss-up between this one and the Moustache model works Beaver. In any case I'll be watching this build with interest. i'm thinking of putting mine on floats, and powering it with two e-flite park 250s, which I found to be a very good motor in the 35" Tiger moth.
May 19, 2021, 06:58 PM
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Thank you, Steve, for the offer and suggestions, especially the tip about the wattage of Tritle’s intended motors.

Can I assume that wattage is a good measure of expected thrust, or is there some weird “horsepower vs. torque” thing with brushless vs brushed motors?

The Park 250’s supposed to be 55 watts, and the little Park 180 is 30 watts. Maybe 180s would pull it ok after all?

The mission for this model will be to look pretty and do lazy touch-and-goes, and so the lighter the hardware the better.
May 19, 2021, 09:41 PM
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AntiArf's Avatar
1811 prop data here: https://web.archive.org/web/20160424...otor-H-560.htm
You can run an 1811-2000kv at around 40W, if not more. I've ran them on 3s with 5030 props. Very capable motor.
As for the old brushed setups, I have a Guillow's DR1 that flew well with an IPS geared BL Feigao setup. I stole the motor for an EDF and replaced it with a brushed motor. The model was built back in my heavy days at over 6oz. It just had enough power to fly with a brushed motor on 3s with a 7030 prop on A gearing if I remember correctly, and that's abusing the setup. Same prop on 2s with a 1811 would probably be fine in the model. Might want to check the cowling size also, as I know an 1811 would fit. Larger motors with larger mount sizes may have an issue.

If you could find and wanted to run the GWS IPS gearboxes, this could be a possible motor choice, although the 6730kv would require working out an idea ratio/cell count. I bought one for 40mm EDF on 3s.
https://www.ebay.com/itm/201370331296
Nothing wrong with it, although I believe the 4100kv Feigao is what people commonly used in the model years ago. For all the hassle and money though, I wouldn't bother with the IPS brushless route.
May 19, 2021, 09:54 PM
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Alright. That HURC motor looks good. Two at full chat should approach a pound of static thrust, which is surely enough.
Thanks!!

Joe
May 19, 2021, 10:09 PM
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AntiArf's Avatar
I just ordered one today from this guy: https://www.ebay.com/itm/324307748721
He has a web site too, which requires a signup for login. Been dealing with him for a some time now. https://www.buzzardmodels.com/bm1811-2000
Saving a few dollars ordering from places in China has proved not worth the hassle for me.
May 19, 2021, 10:24 PM
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Cool. Iíve probably given Horizon enough money. Thanks for the input.
May 21, 2021, 12:51 AM
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Well, the tiny DH. 84 is already doing its job of keeping my mind occupied all hours with ingenious ways of saving weight, any or each of which are probably hare-brained and backwards.

In the Rapide’s day, engine power-to-weight ratios were lacking to modern (read: 1950s) air-cooled boxers and cutting-edge (1970s) turboprops that now pull short-haul people carriers. It was this ratio, I think, that guided the designers to wooden biplanes and not the fact that nobody at DeHavilland knew how to build a metal cantilever monoplane — if you’d shown up at their door with a pair of Pratt & Whitney PT-6s, I’m sure they’d have put together a perfectly good King Air-type-thing around them.

Given the limitations of the 1930s motors, though, the wire-braced biplane probably was, and probably still is, objectively the best engineering solution to the problems of making an airliner light enough to carry a profitable load and strong enough to do it daily on 1930s airfields.

So, it follows that if the points at which the flying and landing wires (made from that indestructible braided fishing line we have now) attach are all strong and rigid, then other mechanical means of attachment might be reduced or eliminated. I guess I’m thinking here of the aluminum tubes that run through the fuselage and inner wing ribs, but could you make a lighter engine mount, for example, by letting wires in tension do the work?

I think I’m going to lean into this wire bracing idea and see how light I can get this thing.
May 21, 2021, 07:54 AM
Still the "Pro"-crastinator...
Steve85's Avatar
Quote:
Originally Posted by jmlamb

I think Iím going to lean into this wire bracing idea and see how light I can get this thing.
Well, this is definitely going to be interesting!

Steve
May 22, 2021, 05:24 PM
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AntiArf's Avatar
I've used individual bracing cables on biplane struts with aluminum tubing crimps, where you can always open them up then recrimp, or cut off a crimp if necessary to adjust the wires and then use a new crimp. Good for adjusting wing panel straightness and/or washout. The nylon coated beading wire looks good, but requires a bit of pre stretching so it doesn't stretch out after installation. Got my 1811 motor yesterday and it came with a real prop adapter. I don't know if the vendor always includes them, but when I've gotten them from other places they only come with the useless prop saver adapters.
May 23, 2021, 01:10 AM
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My kids are hard at work on their Wittman Tailwinds. Good kits for a kid’s first build, and they’re really doing good work.

I’m thinking about using blocks of soft balsa to do triple duty holding carbon tube motor mounts and the landing gear, and serving as anchor points for the rigging for the DeHavilland. Tiny carbon rods, soft balsa, and CA all love each other, in my experience, and don’t ever want to be torn apart.

The kit calls for some pretty hefty piano wire for the gear, and I’m starting to come around to the opinion that metal wire is a good strength-to-weight solution for gear. It seems to work a treat on my kids’ Tailwinds (it does for the real ones too). Even so, I built my Wedell-Williams with soft balsa gear reinforced with tiny carbon rods. Freeflight thrust bearings in the sides of soft balsa wheel pants held 1/20” (ish) aluminum tube axles that were never given enough room to bend. I crash that thing PLENTY, and the gear soaks it up.

Hopefully I can get back at it next week and start in on the tailfeathers.
Last edited by jmlamb; May 23, 2021 at 01:22 AM.
May 23, 2021, 01:18 AM
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Quote:
Originally Posted by AntiArf
I've used individual bracing cables on biplane struts with aluminum tubing crimps, where you can always open them up then recrimp, or cut off a crimp if necessary to adjust the wires and then use a new crimp. Good for adjusting wing panel straightness and/or washout. The nylon coated beading wire looks good, but requires a bit of pre stretching so it doesn't stretch out after installation. Got my 1811 motor yesterday and it came with a real prop adapter. I don't know if the vendor always includes them, but when I've gotten them from other places they only come with the useless prop saver adapters.
Wow. That is a mighty fine toy seaplane. Wow again...

I like the aluminum crimp idea. I assume you freeze it where you want it with thin CA? Or does that defeat the point?
May 23, 2021, 06:41 PM
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AntiArf's Avatar
Thanks, I saw the full scale Curtiss America at the Glenn Curtiss Museum's website on Keuka Lake in New York state, and had to build one. Could have done a better job with the drawings Roy Tassel sent me after the build got going, along with a 1914 news article from the London Times that he sent along with the drawings.

I simply crimp the tubing with tweezers. Sometimes you can use tweezers to get the crimp to open up enough to adjust the wires, where if not I just cut them off and use a new one. I leave a good inch of extra wire to grab onto if I need to adjust them, and then cut it off when I'm finally happy with the entire job. Thanks to a number of Sterling kits, I have a stash of tiny brass flange bushings like GWS used to supply with their Pico servos, which are perfect for embedding in wing struts for cable through and tie off points. Small brackets are nice if you're really going scale, but are more work.

Good to see your kids building Peck Polymers kits. I remember when the LHS reached the point where they almost couldn't give them away, as everyone wants LC stuff with molded parts now.


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