Sopwith Pup replica

nomma · 25 April 2004, 09:34 AM

Hi all,

I have been encouraged by so many fellow builders that I can't refuse any more...

I am at least going to proceed with the planning of a Sopwith Pup replica in Sweden.

I will, of course, have a lot of questions, and I hope that you don't mind me bothering you with these in the future. I have already received great help from Wolfenbill and others. I have built the Pup in 1/4 scale using Jim Kiger plans, so what I will do is basically to repeat the process in full scale and with aircraft quality material.

I am right now producing CAD drawings of all metal fittings, which is a huge effort. And I already have one question - I have not been able to find any table of minimum bend radii for steel (4130) in the AC 43.13, only for aluminum. Where can I find this info? Or what radii do you use for steel?

Attaching a CAD of one of the spar boxes. No 90 degree bends there, of course...

Best regards,

Magnus Lord

nomma · 30 April 2004, 09:16 AM

The work producing CAD drawings of the fittings is well under way. Thanks Arno at Memorial Flight for your help!

A parallel step is to produce the rib web templates. I want the airfoil to be as correct as possible, so I have compared the Replicraft original airfoil with one found in Flugsport 1919. There are differences - you can see them in the picture below. It is mainly the upper curvature that differs. The Replicraft profile has a flatter start and a rather flat area between the spars.

Do you know any other source of coordinates or templates for the Pup airfoil? It would be great to be able to confirm with another one.

Cheers,

Magnus

Brad · 30 April 2004, 09:58 AM

Quote:

Originally posted by nomma@Apr 30 2004, 03:16 AM
[b] The work producing CAD drawings of the fittings is well under way. Thanks Arno at Memorial Flight for your help!

A parallel step is to produce the rib web templates. I want the airfoil to be as correct as possible, so I have compared the Replicraft original airfoil with one found in Flugsport 1919. There are differences - you can see them in the picture below. It is mainly the upper curvature that differs. The Replicraft profile has a flatter start and a rather flat area between the spars.

Do you know any other source of coordinates or templates for the Pup airfoil? It would be great to be able to confirm with another one.

Cheers,

Magnus

Hmmm... I'm not sure I'd want to fly either of them. Looks like they'd have a very abrupt stall, due to the sharp leading edge contour. If you want a museum quality replica, then by all means use the correct airfoil. If you want a sport aircraft, I suggest a more modern airfoil for the sake of safety.

Brad

nomma · 30 April 2004, 11:01 AM

That is an interesting question! I have read some reports from pilots who flew them, and they claimed that it actually has rather good and pleasant characteristics. The leading edge indicates an abrupt stall, but I don't know what happens aerodynamically in a biplane. The wings will probably stall at different angles, due to the disturbances between them, and that could perhaps broaden the stall curve. I don't know. But I know that the Pup was known to be one of the best flyers of the WW1, although under powered.

Cheers,

Magnus

mossie · 30 April 2004, 11:35 AM

The data I have indicated that RAF 16 was the airfoil profile. I have coordinate data for this profile, please PM me with your e-mail and I send you a contempory profile and NACA report with the coordindate data.

jumpinjan · 30 April 2004, 01:43 PM

Undercamber airfoils have good lift at "slow" flying speeds and high drag at higher speeds. I would consult with an experienced builder before I would film up the design with that airfoil.
Jan

baldeagle · 1 May 2004, 03:56 PM

Use the original airfoil. Tiger Moths had a similar one, and they trained thousands of student pilots with them.

jumpinjan · 2 May 2004, 10:29 AM

Well, that's fine if he can find an original LeRhone and full size prop to pull it.

nomma · 2 May 2004, 10:39 AM

Thanks Baldeagle!

Yes, I am going to use the original airfoil - changing it has never been an option.

Thanks also to Gerry Mos who sent me the ordinates for most of the RAF airfoils. I noticed however that it wasn't the RAF 16. The Pup profile looks like a modified RAF 18 - the rear section is almost the same, but the front is thicker. The LD curve for the RAF 18 looks surprisingly good, actually. No abrupt stall there.

I am not doing much visible work yet, so I have no pictures to post this time. I am trying to decide whether to use 4130 steel or not. According to a table I found, the minimum bend radius for an 18 Gauge 4130 sheet is 4 mm (about 5/32"), which I think is a lot. I will do some testing next week. Another solution is to weld the sides together instead of bending the parts.

I am looking at the possibility to "water cut" (don't know the English word) instead of laser cutting the brackets. The technique produces perfect edges, without subjecting them to heat which sometimes can cause cracks when bending.

Cheers,

Magnus

William · 2 May 2004, 11:33 AM

Magnus et al,
We are making slow progress on our Pup with the sternpost finished, most fuselage brackets cut and awaiting bending and the front engine plate underway. We will use the original airfoil per Sopwith plans and are still looking for an 80 hp Le Rhone. It is still possible to find them but requires patience. Below is an ad that ran on Barnstormers today for the Rotec radial for those that prefer modern alternatives. We have also considered water-jet cutting but have less access to it. We have suffered no ill effects from heat crystallization at the edges from laser cutting and had no bending problems,so far. Our logic to present has been to save the complicated spar boxes for last so as to work our way up the learning curve with the other bits. Although the original builders may have used more primitive techniques/tools at times, they were truly master craftsmen.
Good luck with your project and let us know if we can be of assistance.
Best regards,
William
canvasfalcon@msn.com
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