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DH89a Dragon Rapide

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David P Williams31/03/2020 16:03:40
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902 forum posts
309 photos

I am contemplating starting the build of a 1/6 scale 96inch span DH89a Dragon Rapide.

I have two plans - the Jerry Bates one (which is actually the Bob Sweitzer one from 1982 that Jerry bought the rights to), and the Martin Tuck one from the old Nexus Plans. I also have the canopy and fibreglass cowls from Jerry Bates.

The Bates/Sweitzer plan is very detailed and quite complex - the Tuck one much less detailed and much simpler, although missing quite a bit of vital information. The Bates one has one piece wings (tricky to transport 8ft wings even in my large-ish estate and the Tuck one has wings that detach outboard of the nacelles (still a tight fit in the car !). I thought I might be able to use a combination of the two. I'm not aiming for a super scale competition model - just a good standard club scale one.

I've built quite a few kits, and a handful of builds from plan only, but they have been smaller and less complex than this, so this is a nice daunting challenge. Any online build blogs I can find (all of them a few years old) seem to end in unfinished models, which is a bit worrying.

I have one main question for you more experienced builders and designers and that relates to the wing aerofoil profile. Both plans show this to be undercambered, but all photos and info I can find about the full size aircraft appear to show a flat-bottomed section, albeit with a hint of reflex toward the trailing edge.

Somewhere online I found a set of Pilot's Notes, which stated that the aerofoil section is RAF34(Modified).

Below are ribs/section from both plans, a rib drawing from the full size servicing and repair manual, RAF34, and photos of a full size during restoration.

The Jerry Bates plan -

jerry bates plan rib.jpg

The Martin Tuck plan -

martin tuck plan rib.jpg

Rib from Maintenance and repair manual -

rib.jpg

RAF34 -

raf34.jpg

Full size restoration -

dh-89 2012-16.jpg

wing section2.jpg

Some of the historical builds from the Bates plan that I found online stuck to the plan profiles, others filled in the undercamber to give a flat bottom. So few of these made it to flying models with flight reports that it's unclear which version worked.

What would you do?

MattyB31/03/2020 16:37:46
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2029 forum posts
31 photos

No reason why a flat bottom wing shouldn't work, and it will be easier to build. As a glider guider I always agonised over the wing sections of models I might build or purchase, but for powered model like this pretty much anything with some decent thickness and camber should do the job, though you might want to blend it into something semi-symmetrical and lower camber at the tip with a smidgeon of washout.

Edited By MattyB on 31/03/2020 16:37:57

Martian31/03/2020 17:05:20
2479 forum posts
1163 photos

Well, whatever way you build I'm onboard. if you are not after accurate scale fidelity I would opt for the simple wing rib approach

Chris Walby31/03/2020 17:52:09
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1199 forum posts
299 photos

Watching with interest and I once spoke to a chap that makes foam veneer wings about a replacement for my mossie. His response was which wing profile (for mossies) out of a choice of 5 did I want as each designer picked a profile to suit their design. My point is that its designers that select profiles to suit their designs for their reasons and unless to can discuss with the designer why they made that choice its best sticking with the original design.

All the best

PS Don't ask my why sad but if you consider two or more piece wings make sure the wing tubes are set up in the design stage (far easier) for the ribs and then there is no chance or getting them slightly non parallel at a later stage.

David P Williams01/04/2020 16:53:39
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902 forum posts
309 photos

Thanks chaps. It will be a while before I get going on this I think - maintenance on existing fleet, a couple of repairs, and a couple of other builds to finish first. I want to assemble a 'kit of parts' before I start, so cutting ribs and formers will be something I do a little at a time amongst other things.

Matty - yes, the Bates plan calls for 3/16" washout at the tips.

Chris - the whole wing joiner thing needs quite a bit more thought. It's a very thin wing section and the lower wing has slight anhedral to outboard of the nacelles, then dihedral to the tip, so not much room to fit tubes of any size in. The Tuck plan indicates 10SWG wire joiners but no detail. I don't have much experience at designing stuff like this, as I said above my building experience has been kits and plans with good detail and explanation, but I'd really like to give this a go.

cymaz01/04/2020 17:23:34
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9196 forum posts
1186 photos

Have a think about a flat bottom wing, not a bad thing and easier as you’ve 4 to build.

What about a steel or aluminium strip edge on in a ply slot. Works on some 1/3 and 1/2 scale Spacewalkers.

This chap may have some useful ideas and tips

Manish Chandrayan01/04/2020 20:01:55
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631 forum posts
73 photos

Jamie Cuff flies a red DH 89 (Sweitzer/Bates design) that was featured in April 2019 RCM&E. The model has detachable wings that separate at the inner struts. His model is powered by a pair of ASP 52 or 60 four strokes 

I think Jamie is here on the forum, please, some one correct me if I am wrong on that account

 

Edited By Manish Chandrayan on 01/04/2020 20:03:57

Manish Chandrayan01/04/2020 20:15:42
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631 forum posts
73 photos

And have you seen this build? he uses the same split method

Polish Dh 89

Chris Walby01/04/2020 20:41:22
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1199 forum posts
299 photos

David, If you are struggling with the split wing you could always have a chat with Chris at SLEC. He designed in wing tubes on a one piece wing (now three piece with tips and centre section with nacelles). Best bit was everything lined up although the ribs are not equally spaced and the tips have dihedral compared with the centre section.

Good luck whatever you decide smiley

David P Williams03/04/2020 16:12:39
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902 forum posts
309 photos

Hi all - sorry, had a day away from the PC yesterday.

Cymaz - I agree, flat bottomed wings will be much easier, and I will investigate strips on edge.

Manish - I have the RCM&E article on Jamie Cuff's model. According to that, he didn't build it, it was built by someone called Len Stevens from the Martin Tuck plan rather than the Bates one. I had also seen the Polish Bates plan build before, and it does show quite clearly how he did the lower wing break with 5mm and 6mm carbon tubes, so thanks for the reminder of that.

Chris - thanks for the encouragement.

The Jamie Cuff model apparently flies on a pair of 52FS engines, the Polish one on a pair of OSMAX 61 2 strokes. I have a decent pair of SC70FS engines, but I'd really like to use a pair of Lasers. Need to do some careful measuring on the plans though to see if I can squeeze fuel tanks down low enough in the nacelles. The taper and wheels might get in the way. I also need to do some careful measuring of the car - might need to buy a vansurprise

Manish Chandrayan04/04/2020 08:01:14
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631 forum posts
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Hello David, yes I am aware that the particular Rapide wasn't built by Jamie. And that's the reason I wrote 'Jamie flies' instead of built etc. But from what I remember him writing was that it was powered by a pair of ASP/Magnum 60's. He does have few other from the Dragon family that are powered by different engine combinations and one of them being OS 52. The wing fixings on the Rapide he has is very simple, there are no tubes/rods etc, just a spring loaded catch and a tab. The flying/landing/bracing wires are all functional thereby not needing any wing tubes/sleeves etc.

I have a the Bates, kit and parts that will go on the build table once the TN Wellington is done. My initial plan was to use a pair of Laser 80's. I had one and thought of getting another one. But this was shot down by Jon who advised on using a matched pair and also said that the 80's may be too much. Given the engine mount design and the issues involved I gave up idea of using lasers, and settled for 2x70 Saito's instead.

I purchased the short kit from Belair and the glass and plastic parts from Jerry

David P Williams04/04/2020 12:32:16
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902 forum posts
309 photos

Hi Manish - I was just going off the RCM&E article by Alex Whittaker about Mr Cuff's Rapide. It states that it is from the Tuck plan, weighs 16.9lb and is powered by ASP52FS with Graupner 12x5 props. I was surprised as my Dual Ace has two SC52FS and flies well but not ballistic, and it is lighter and much less draggy than the Rapide.

I agree that Lasers will probably be too difficult to fit, particularly with the tank location problem, so if this goes ahead I will probably use the best two of the three SC70FS that I have.

I have the glass and clear parts from Jerry Bates also, but didn't buy the Belair short kit as I will probably go with flat bottomed ribs.

I have recently found out that there is a dismantled full size Rapide in a hangar at a microlight airfield about 50 miles away so will be visiting that as soon as the restrictions are lifted (I guess it doesn't count as essential travel).

Good luck with your build

Manish Chandrayan04/04/2020 18:16:51
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631 forum posts
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Good luck with your visit to see the Rapide and I am sure we could use some of the pictures you might take there

kc04/04/2020 19:17:16
6423 forum posts
173 photos

It's interesting that the models use an undercambered wing but the full size didn't. It seems unlikely the models used the difficult to build undercambered non scale section for no reason. Maybe the models fly better undercambered? It doesn't seem worth buying a plan and then disregarding the wing ribs unless you KNOW for sure flat bottom would be better.

Of course it is just possible that the undercambered wing was just copied from some completely different model for convenience on the Rapide and then second designer just copied the first!

Alan Gorham_04/04/2020 19:24:18
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1247 forum posts
145 photos

I wouldn't necessarily take Alex Whittaker's word as gospel on someone else's model. This is the man that in his column in the magazine a few months ago would have us believe that Duncan Hutson the designer of many scale models was also responsible for the Flair Hannibal and Magnatilla! When it was obviously the work of Dudley Pattison of Flair...

David P Williams15/04/2020 14:49:46
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902 forum posts
309 photos

Well - after poring over the plans and reading through every build thread I can find on various forums, I've decided to tackle something a little more straightforward than this for now. I'll come back to this at a later date. Thanks everyone for your contributions, all noted for the future.

Manish Chandrayan04/05/2020 20:17:02
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631 forum posts
73 photos
Posted by David P Williams on 04/04/2020 12:32:16:

Hi Manish - I was just going off the RCM&E article by Alex Whittaker about Mr Cuff's Rapide. It states that it is from the Tuck plan, weighs 16.9lb and is powered by ASP52FS with Graupner 12x5 props. I was surprised as my Dual Ace has two SC52FS and flies well but not ballistic, and it is lighter and much less draggy than the Rapide.

I agree that Lasers will probably be too difficult to fit, particularly with the tank location problem, so if this goes ahead I will probably use the best two of the three SC70FS that I have.

I have the glass and clear parts from Jerry Bates also, but didn't buy the Belair short kit as I will probably go with flat bottomed ribs.

I have recently found out that there is a dismantled full size Rapide in a hangar at a microlight airfield about 50 miles away so will be visiting that as soon as the restrictions are lifted (I guess it doesn't count as essential travel).

Good luck with your build

Looks like the RCM&E information may be correct after all. At least in terms of design. Yesterday Jamie did post on his FB page that the model was built by the original builder from Martin Tuck plans.

Where did you order the Martin Tuck plans from?

Edited By Manish Chandrayan on 04/05/2020 20:17:55

David P Williams05/05/2020 10:20:56
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902 forum posts
309 photos

Hi Manish - the Martin Tuck plans were from the old Nexus Planse Service, now Sarik Hobbies here.

They are not very detailed at all - little more than a three view with some framing drawn on, fuselage formers outlined and wing sections from which you have to derive the ribs by deducting sheeting, rib caps, etc. plus a sketch of the nacelle construction. Would build lighter than the Bates/Sweitzer plan I guess.

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