View Full Version : Variable wing area quiz

Onan the Clumsy
31st Oct 2003, 09:59
Here's one for you chaps from a quiz I read in a magazine...

"There are numerous modern airplanes with variable geometry wings. What airplane allowed its pilot to increase wing area by more than 50% without using leading or trailing edge devices?"

I'll give you five points for their answer and ten points if you can think of another...

31st Oct 2003, 10:37
:confused: The only one I can think of is Tornado. As the wings sweep back, part of them disappears into cuffs on the sides of the fuselage, but as much as 50%... I doubt it.

Onan the Clumsy
31st Oct 2003, 12:26
Nope. We're talking pre WWII.

Good try though

31st Oct 2003, 14:58
There was a 1931 design with variable wing span, but that didn't double the wing area. Neither did that Russian biplane design with a retractable lower wing 'more than double' the wing area.

31st Oct 2003, 15:28
In more recent years there have been a couple of German (and possibly one in the UK?) gliders which had telescopically extendable wings - the pilot could extend or retract them by pushrods as required...

The only other candidate I can think of was that jobbie that had an inflatable wing - think there's one at the Army Air Corps museum at Middle Wallop, can't remember who built it...

Then there was the "slip wing" Bi Mono and Hurricanes, but it can't be that surely...

31st Oct 2003, 15:45
Sounds like the telescopic-winged devices developed by Yvan Makhonine in France. His Lorraine-engined Mak-10, first flown at Le Bourget in August 1931, had a wingspan of 13 to 21 metres. The BMW 801-powered Mak-123's span could be varied from 19 to 33 metres. If memory serves, it came to grief at Toussus-le-Noble in 1947.

Another possibility is Russian Grigorii Bakshayev's RK/LIG-7, flown in 1937. It had five telescoping airfoil sections that stowed against the fuselage and could be hand-cranked outboard, extending to about mid-span over the constant-chord main wing. Total area increase on that was more like 70%, though. On Bakshayev's unflown RK-1 fighter it would have been around 240%. The RK-1 had tandem wings over which the telescopic sections were extended hydraulically right to the tips.

31st Oct 2003, 16:34
Didn't RTFQ, did I! The Mak-123 increased wing area by 83% with the wings 'telescoped' to their maximum span.

Still can't remember the name or nationality of the biplane whose lower wing could be retracted into the upper wing - or even certain when it flew, if at all? Polikarpov, perhaps?

31st Oct 2003, 16:58
BEagle: There were several of them IS-1, IS-2 and IS-4 all by Vaselli Nikitin. The lower wings folded into the fuselage sides transforming biplane into cantilver shoulder-wing monoplane. The IS-4 was a great looking beast, tri-gear, resembled a biplane Airacobra.

31st Oct 2003, 21:54
That's the one!

So the answers are:

Mak-10, Mak-136 (Telescopic wings) about 83% increase in wing area

Nikitin IS-1, IS-2 and IS-4 with retractable lower wings and an increase of about 60% with the wing extended.

Nikitin IS-1: http://ww2photo.mimerswell.com/air/su/nikitin/is-1.htm

Onan the Clumsy
31st Oct 2003, 22:42
Very good. I'll award equal points all around.

"The 1931 French built Makhonine monoplane had telescoping wings. The outer portion of each wing telescoped in and out of the inner portion on rollers. With wings outstretched to 69 feet, the 480 horesepower single had a top speed of 155 mph. Rolling in the wings to 43 feet increased that top speed by 32mph."

And yes the Nikitin mono/biplane was the ten point answer. Now if only they had designed it to retract the upper instead of the lower wing, it would have looked a lot like an F4 Corsair.

Not many people know that the Russians deployed the Nikitin on the Eastern front against the Luftwaffe with considerable early success. This didn't last long however as once the tutonic masters of engineering realised all they had to do was remove the guns and cover their airplanes in patches and they no longer had a problem with Nikitin. :ouch:

Excellent answers chaps. btw, I grew up making model airplanes and reading books about them and I thought I knew quite a lot, but after reading this forum for a while, I realise how little I really do know :ok:

31st Oct 2003, 23:01
I don't suppost that the Mercury-Maia really counted as a method of 'increasing the wing area'? Nor the addition of a B-36 to the XF-85, B-29 to X-1 or B-52 to X-15?

Aren't things so much more boring now??!!!

31st Oct 2003, 23:39
BEagle: Thinking along those same lines, if it were about increasing volume rather than area, I suppose attaching a Curtiss Sparrowhawk to the airships USS Akron or Macon would take top honours?

Reflecting on the Nikitins has got me thinking how good the Laird Super Solution racer would have looked with a retractable lower wing.

31st Oct 2003, 23:48
speaking of things variable, extendable etc; does anyone have any further information regarding the Sigma project of a variable geometry high performance sailplane (glider) that Slingsby were developing in the late '60's?

I have googled it, but only came up with a reference to it, saying "Chosen because the Sigma was designed to incorporate the sum of knowledge about sailplanes up to that time." Designers are listed as Irving, (persumably Frank) Venon and Welch (Anne?).

It is mentioned in passing in Wally Kahn's book, 'a glider pilot bold', and one of Phillip Wills' books (can't remember which).

Also, the history of Slingsby gliders (Martin Simmons) makes reference to it, as well as some other far-fetched projects the company was involved with in the context of the catastrophic fire at the factory, which was one of the nails in the coffin of the Company. Granted, it says the fire destroyed all records, but wondered if anyone could add anything more?



1st Nov 2003, 00:49
YP, I have Janes "All The Worlds Sailplanes" at home which includes the Sigma project - when I get back from the pub, I'll try an remember to put the book aside for tomorrow, bring it to work and scan the pic and post some details... Unless someone beats me to it of course! I know there's a pic, cos it had the Greek Sigma on the fin...

1st Nov 2003, 01:31
I recall a TV item about the Sigma. The pilot had to pump the full-span flaps in and out by pushing back and forth on the rudder bar assembly.

I vaguely recall being told that the lift dependent drag coefficient was way in excess of estimates and that the hoped-for L/D ratio was never achieved in practice?

henry crun
1st Nov 2003, 05:12
Someone will no doubt correct me if I am wrong but I think the Sigma went to Canada.

To who and for what purpose I cannot remember.

1st Nov 2003, 07:14
BEagle and Henry, correct!

Treadders reporting, back from pub, pi$$ed but - hopefully - digitally coherent!

The variable geometry of the Sigma project was based on the flap system rather than extendable span... As BEagle says, rudder pedal power operated the hydraulic flap and u/c system...

Project passed to Prof David Marsden at University of Alberta in 1977 - my book published 1978, so no outcome...

If possible will include a pic and the narrative tomorrow evening...

Incidently, West German effort ...

Akaflieg Stuttgart FS-29 had telescopic wing sections with variable span from 13.3m to 19m.. flew in 1975...

henry crun
1st Nov 2003, 09:20
For those who are interested I found this article by Nick Goodhart about Sigma.

It has a detailed description of the aircraft and what it was like to fly.


4th Nov 2003, 16:12
thanks for the research all, very interesting. The Jane's article sounds good Treadders, if you're able to post it, or link to it....

The article sounded like they were in the process of building a prototype; did it ever fly (as BEagle says), and what became of it?


ps. where / how did you find the article Henry? - my googling skills appear to have deserted me!

4th Nov 2003, 20:53
Betcha thought I'd forgotten... Er, I had!

Here's the pic:


Hopefully the description in Henry's link covers the design and ideas, here's the postscript.

The prototype first flown in September 1971 by Nick Goodhart, Handling and performance proved satisfactory but there were problems with the "flexible closure plates" which were used to seal the gap between the fowler flaps and the wing on the under surface of the wing.

In 1977 passed to Prof David Marsden in Alberta who proposed replacing the original flaps with "simple slotted flaps in the course of his research on variable geometry sailplanes."

There's also a pic of the FS-29 mentioend in my post above if anyone is interested...


henry crun
5th Nov 2003, 03:50
yellowperil, Use Advanced Search in Google, enter sigma in the 2nd box and glider in the 3rd box.

Answer was, I think, on the 2nd or 3rd page of results.

5th Nov 2003, 22:39
thanks for the advanced googling tips Henry, futher multishirking at work has led me to this postscript to Sigma:

Marsden Gemini


Span 18.5 m./ 60.75 ft
Area 11.52 sq. m. / 124 sq.ft.
Aspect ratio 29.8
Airfoil Wortmann FX-61-163/35SF mod.
Empty weight 356 kg. / 785 lb.
Payload 220 kg. / 455 lb.
Gross weight 576 kg. / 1,240 lb.
Wing loading 50.0 kg. / sq. m. / 10.0 lb. / sq. ft.
Structure all metal except for GFRP forward fuselage; stainless steel ribs, fittings and control system.

L/D max. 40 119 kph /64 kt / 74 mph
Min. sink 0.63 m/s / 2.08 fps / 1.23 kt
76 kph / 41 kt / 47 mph

Country of origin Canada
Designer David Marsden
No. of seats 2
No. built 1
No. in the U.S. 1
The side-by-side two-place Gemini, which flew in 1973, has a genuine variable geometry planform. Marsden, who successfully modified the British Operation Sigma Type C variable geometry glider, used a number of the Sigma features in his design. It has full span 35 % chord Fowler flaps which are extended when climbing and retracted when cruising. When extended, a high maximum coefficient of lift of 2.2 is achieved, giving a good climb performance. The flaps also deflects to 80 degree for approach control. It has slotted ailerons for improved roll control. During the 1970s the Gemini set 7 Canadian multi-place records, 3 of which it still holds, including the 500 km speed triangle.

(obtained from http://www.sailplanedirectory.com/zwfnw.htm where there's a picture too)