Gap for Biplanes?
 

I have purchased a Dynaflite SE5a kit. Although discussed many times on here and other WW1 websites and forums, nobody seems to have actually modified this kit to make it more real looking. Everyone agrees the wing gap is to much on this kit. My estimate is the top wing may be 1 to 1.5 inches too high. This is a 1/5th size model. I don't know what the reasons the manufacturer would have for increasing the wing gap. Yes, the model is designed as a fun-fly model. I may, or may not modify the plane by lowing the upper wing. I've built other stand-off scale WW1 bipes with scale wing gap and could detect no problems with doing so. Most stand-off scale and scale bipes I see have scale or close to scale wing gap.

What possible problems might occur with lowering the top wing on this kit?

RE: Gap for Biplanes?
 

Measuring the gap on the SE-5 in a Wylam drawing, the gap is 1.125", the chord is 1.21".or the gap is .93:1.
Most bipes have gaps above .7 or so.
The relatively slim fuselage of the SE-5 makes the gap look larger.. I'd have guessed over 1:1 before I measured it.

RE: Gap for Biplanes?
 

All well and good, however, the Gap on the Dynaflite SE5a still appears out of proportion, when compared to the real plane.

I'm going to sit down with the plans and other information I can find to determine what the real gap was in comparison to this model.

Back later!

RE: Gap for Biplanes?
 

Scaling from various reference information and books I have I estimate the gap on the SE5a to have been around 4 feet 9 inches. The plans with the Dynaflite SE5a at 1/5th scale show the gap of the model to be around 5 feet 6 inches. The gap between the cords of the two wings on this model as it is designed work out to be 13 3/8th inches. Scale gap @ 4 feet 9 inches works out to approximately 11 and 5/8ths inches.

RE: Gap for Biplanes?
 

If you use Sparky's ratio and multiply the wing chord on the kit by 0.93 what do you get for a gap?

Of course this doesn't mean that the designer didn't cheat on the chord as well. Also many model makers are somewhat shocked at how large a true scale fuselage is when they draw it out. It may well be that this designer reduced the fuselage width and height because of this If he then kept the wing planform and spacing scale the skinny fuselage will make the wing gap look wrong as well.

RE: Gap for Biplanes?
 

Probably a dumb question; but, where does the .93 come from? What are you saying? Is Gap is suppose to be 93% of cord? Or is it suppose to be no less than, or the opposite, no greater then 93 %?

Mark

RE: Gap for Biplanes?
 

Measure the chord of the wing.
The gap on the full-scale SE-5 is .93 of that dimension.
For a 10 inch chord, the gap would be 9.3 inches.

RE: Gap for Biplanes?
 

One of the reasons I did not understand the .93 question is I have the Wylam Drawings of the SE5a and there is no place on my drawings were the aircraft has a wing gap of 1.125, or cord 1.21. My drawings show a plane with a wing span 13.375, so my drawings are a much larger scale. However, at 1/5th scale, my calculations of what the wing gap should be, of around 11.625, compares with Tall Paul's: Cord equals 11.875 X .93 equals 11.04. If I average the two answers for gap, I come up with approximately 11 5/16ths inches. As drawn, the Dynaflite SE5a has a wing gap of 13 3/8ths inches. I find that the model has 2 inches too high a wing gap.

Now, back to the question I originally asked: "What possible problems might occur with lowering the top wing on this kit"?

RE: Gap for Biplanes?
 

Providing you've done the math properly, lowering the wing won't make anything worse.
It will probably improve the glide power-off by reducing the amount of down elevator needed to keep the nose down, a condition I've noted with my Nieuport and Camel.. the upper wing creates drag well above the c.g, creating a nose-up condition when gliding.

RE: Gap for Biplanes?
 

All else being equal the smaller gap will produce more drag and steepen the glide slope. The material I've read in the past indicated that a smaller interplane gap results in more drag due to more airflow effects between the wings. A larger gap reduces this effect. Like most things it's a sliding scale with no one totally correct answer. After all some of the last racing biplanes actually had very small interplane gap ratios so there must have been other factors at work as well.

RE: Gap for Biplanes?
 

Bruce, It's good to see someone unafraid of contradicting their own hypothesis, all in the same paragraph! Isn't aerodynamics fun!! This was meant with humor!

I guess the next question would be; Why would Dynaflite make the gap so unsightly large?

RE: Gap for Biplanes?
 

Well, I suspect it was meant as a "fun sport sort of stand way back and squint scale model that was designed more from memory and maybe a couple of pictures because the designer didn't like to do the math that would be needed to draw up the plans accuratley" sort of scale model.... :D