Dragon DR I wings

drbubba43 · 15 February 2006, 08:30 PM

I'm not so much a stickler for accuracy these days, just satisifyed if I get a model finished and it captures the feel...

However, what is the deal with the saggy fabric undersides of DML's DR I wings? Did they (I assume) just mess it up, or is there some reason DML made them that way?

I filled the valleys and sanded them smooth trying to maintain the undercamber.

But I was noticing from other builds on the web that almost nobody else did this. Am I missing something?

Ray

Ross_Moorhouse · 15 February 2006, 08:36 PM

Revell in their new 72nd version of this plane did the same thing....

It could in fact be accurate... Have a look at the under wing of this one... http://www.wwi-models.org/Photos/Ger/Fok_DrI/index.html

Footnote. This pic is posted here as a reference point for both the DML 48th and Revell 72nd kits.

drbubba43 · 15 February 2006, 08:49 PM

It is interesting... Look at the photo of the two triplanes sitting side by side. The leading edge of the upper wing on the one closest to the camera looks like the fabric is concave between the ribs. The one furthest from the camera like like the DML kit...

It may be a play of light, but that effect seems consistent on other photos. Neither look a pronounced as the DML kit but it is definately there.

Perhaps instead of sanding an filling, it just need to be sanded down so it is not so pronounced...

What d'ya think?

Ray

Rowan Broadbent · 16 February 2006, 02:36 AM

Hello Ray,

I think sanding should be enough - well that's what I did, so I would say that wouldn't I?

There is no reason that I'm aware of for the Dr I fabric to sag more than any other fabric wing. All the real ones I've inspected (Shuttleworth aircraft mostly) are pretty much drum-tight underneath. To have as much sag as DML protray would have had a markedly deleterious effect on the wing's aerodynamic efficiency.

From my rudimentary grasp of flight theory, the undersurface of an airofoil is subjected to high pressure and the uppersurface to low pressure (in relative terms), thus tending to push up the fabric underneath and "suck up" the fabric above, thus generating lift (the coanda effect??). A floppy underside (OOH Matron!) would "accomodate" or "soak up" the high pressure, thus tending to nulify the lifting effect -wouldn't it???

Be gentle with me, I'm not a real aerodynamicist, you know!

Rowan

drbubba43 · 16 February 2006, 05:51 AM

I think your right Rowan...

On my next DR I build I'm just gonna sand it down a bit so it is not so pronounced.

On that note, in correcting my correction. anyone have any ideas on how to add saggy fabric to the underside of a DR I wing?

(Before you put too much to much thought into the answer, I should inform you that I have no intention of actually doing it. They're staying smooth. The correcting of the correction seems less apealing than the correction, even if it can be corrected.)

Ray

Rowan Broadbent · 16 February 2006, 06:18 AM

Quote:

Originally Posted by drbubba43

(Before you put too much to much thought into the answer, I should inform you that I have no intention of actually doing it. They're staying smooth. The correcting of the correction seems less apealing than the correction, even if it can be corrected.)

Ray

Correct!!!

GSPOINTER · 16 February 2006, 06:19 AM

Most plastic kits have this wrong.

When fabric shrinks when doped, it "shortens" - i.e. tends to want to take the shortest distance between points where it is attached.

On the upper surfaces, the fabric pulls "in" as it shrinks because the direct distance between the leading and trailing edges ( the chord ) is shorter than the distance along the rib tops - thus the "valley" between the ribs. The fabric is trying to assume a straight line.

On the underside of a cambered wing, such as the Brisfit and many WW I aircraft, this effect is reversed - the "shorter" chord distance is below the bottom line of the ribs, so the fabric pulls below this line - giving the appearance of "sagging", although it is taught.

On most kits, the top "sag" is overdone, and the undersides are "reversed" and incorrect.

The Roden Nieuport 28 has this represented almost perfectly.

I've heard this described as a "catenary" curve

Familyman · 16 February 2006, 08:16 AM

Gspointer!

I think you are right! in the DML Fokker Dr. 1 wing undersurfaces this phenomenon is a bit excessive, tho, I think...

Mikko

drbubba43 · 16 February 2006, 10:17 AM

Quote:

Originally Posted by Rowan Broadbent

Correct!!!

Thanks for backing me up.
I was concerned that I was incorrect about correctly correcting future corrections incorrectly... Glad to you feel the same way. So at this point I can rest easy knowing that there is no real need to correct the incorrect correction... Right?

Ray

BTW, when we're done with this I'm going to need to know what color Voss's cowl and wheel covers were.

StephenLawson · 16 February 2006, 07:46 PM

Agreed. Sanding down the undersurface is the best approach.