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-   -   DH4 Biplane Build advice from enlarged DUMAS plans (http://www.rcuniverse.com/forum/scratch-building-aircraft-design-3d-cad-174/5426496-dh4-biplane-build-advice-enlarged-dumas-plans.html)

tenacious101010 02-16-2007 07:08 AM

DH4 Biplane Build advice from enlarged DUMAS plans
I want to build a DH-4 Biplane. I purchased a Dumas DH-4 kit and enlarged the plans by 200%. It will have a 70 inch wingspan.
I realize I will have to change several things, the engine mount, fuel tank area, wing attach, landing gear strength, etc. What is a good way to make shock absorbing landing gear? I was wondering what range engine size might be appropriate for this size and type plane. I realize built weight will have an impact, but I have no experience with biplanes. I am not sure if I would use a 2 stroke or 4.
Any inputs as far as wing incidence, or anything I should take into consideration would be greatly appreciated. One area of concern is attaching the wing struts between the wings, what are good ways to make this connection since they need to be removeable?
Thanks, Denny

kdc 02-16-2007 06:56 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
There is a plan for an 84 inch DH4 which uses a 80 or 90 four stroke. Weight was 12 pounds.
Plan is by Gary Sunderland who used a Laser 90. Was published in England by Aviation Modeller July 1997. ( I think the designer is from Australia )

I have this mag and I provided this info to another enquiry on rcuniverse some weeks back.

kdc 02-16-2007 07:42 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
I looked back and found that it was your enquiry previously.

Frankly if you have never built a scale biplane before you should build from someone elses plans (of similar size ) to get all the detail construction.
Find another WW1 biplane plan in the same size and copy the detail construction, if you dont want to buy this plan. ( why dont you want to buy this plan, it looks detailed and is (I think ) by a well known modeller and magazine columnist )

Even an experienced builder would have great difficulty in producing a decent scale model biplane in a few weeks even with a good plan. It is normally many months work, maybe a year.

BMatthews 02-17-2007 03:40 AM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
The engine you need will depend a lot on how you intend to build the model. If you go for very light construction you can easily get away with a 60 4 stroke. If you go very heavy you'll need a 90 or perhaps even a 1.2. If you tend to stay fairly faithful to the small lightweight structure and perhaps opt for functional rigging you can keep it very light. It'l suffer on windy days but that light a model would look super impressive on calm days as it floats around. If you were to use a similar structure as the old free flight gassies then there's no reason your DH-4 cannot come out at the 7 to 8 lb range. At that weight a 60 4st would do fine.

Mind you if you're after a full on scale model then it will tend to come out heavier if you're not extra careful. But if you were after a full on scale model then you would not have started with a Dumas plan for a starting point.

tenacious101010 02-18-2007 08:30 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
Thanks for your input kdc,
I love challenges and this sounds like a fun one. I feel confident I can make this work. I spoke to a guy that told me it took 4 months to get those plans, I cant wait that long. I see no reason that this will be that tough. I have built many things and feel I am up to this once I work out some details.
I could be wrong, but I am up for it. Your inputs really are greatly appreciated.
Thanks, Denny

tenacious101010 02-18-2007 08:36 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
Thanks for your insights, I would like it light and it seems the wind is always blowing here. I suppose with my lack of experience it will be a bit heavier than some would make it but I can use design methods I have seen in other kits. I have built 2 Top Flite kits and a few other smaller simpler ones. I have a Saito 90 4 ST that I would like to use, it should have plenty of power for this plane. I just have to work out basic construction for shock absorbing landing gear that looks scale, wing strut attachments since the wings have to be removable. Any help with designs of these areas would be greatly appreciated.
Thanks again, Denny

kdc 02-19-2007 02:55 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
I cannot see any reason it took 4 months. It might be the US Mail (by sea ?) that is slow.

Have you just doubled the thickness of every piece of wood?

tenacious101010 02-19-2007 04:03 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
kdc, I plan on doing a lot more than doubling the sizes. I will make interlocking bulkheads and solid dides at the front for strength. The landing gear, engine mount, wing attach are the main areas that will need to be beefed up. I will need to make ailerons also. I will modify the cockpit location too, on the American DH4, the front cockpit location was swapped with the fuel tank that was between the cockpits on the British version. Since it will be so much bigger, I will also have to make it so I can disassemble it. All this will add weight along with the details I am going to add.
Thanks, Denny

kdc 02-19-2007 05:53 PM

RE: DH4 Biplane Build advice from enlarged DUMAS plans
No! I meant it is probably necessary NOT to double the sizes of most materials!
Double the sizes means 4 times the cross section and this is probably too much. (too strong, too heavy )
I have examined the AMI plan and it looks ( not certain ) as though the longerons are 5/16 square.
What sizes were the main longerons and uprights on your original kit?

Actually that is not really relevant, you need to follow good practice for the size and type of model you are building.
Too strong means too heavy and the landing speed will have to be higher. Slowed down a heavy model will fall out of the sky & crash heavier, while a light model will still be flying OK. You should build to fly, not to survive crashes! Light models crash less often.

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