Are our wings over-engineered?

[J D 8]

Chris, I liked your story as I had some experience in the late 70's in Grasstrack racing in 1300cc saloon class where allowed engine modifications were very limited.

Looking for an edge at a time when everyone in Grasstrack was running with Castrol R I switched to a synthetic oil [ it was expensive ] but allowed the motor to rev freely from the start and remain clean inside [ races were short only five or six minute's] With little warm up time before the start.

Made the national final in 1980 only to have my only puncture in three hard years of racing.[ Twice a week April to September. ]

[Bob Cotsford]

As I recall years ago the leading edge sheet was recommended to maintain the wing profile over the more important leading 30% or so up to max camber with the benefit of adding torsional rigidity, webbing to increase the resistance to spars folding in under high G and allowing smaller section spars. A combination of these two produces your full D box adding together the benefits of each of the two components to produce immensely (for that time) strong and rigid wings with the minimum material content. This was well illustrated when you watched different thermal soarers going up on a bungy launch. My, how those wings bent!

So, no it's not over-engineered, though in my view material sizes are often chosen to resist manhandling as much as to cope with flight loads.

[kc]

I thought the Chapman principle was if it didn't fail it was too strong, so build a lighter part.

To return to the subject - my point is an Ugly Stik wing is proven so don't beef it up and don't change it. One could make a similar wing for a low wing version rather like the photo on the Outerzone preview of the Ugly Stik.

Lots of early Boddington designs use a slotted main spar made from balsa. see Ghost Rider, Sky Rider, Herr Flick etc. I never liked this idea although it saves the bother of adding webs and also locates the ribs plus keeps them vertical. Notching the spar to me causes a built in weakness and balsa is so variable it's easy to get some too soft. However it seems to me that by laminating the spar - top half spruce lower half balsa which is notched - it would be a better and could be practical. Anyone tried this?

[kc]

All this started because Geoff put some info about building a Liddle Stik ( 46 inch scaled down Ugly Stik) and I compared the Liddle with my 50 inch version which used D box plus cap strips and took a lot of time! I think I over engineered it although all up weight is 3.5 pounds - 50 inch with lipo.

Geoff mentioned 1/8 spars and of course he meant the extra spars not the main spars.

What I didn't mention is that both the Ugly and Liddle Stik use riblets together with this additional smaller spar. This must all help if no LE sheeting is used. Ugly Stik uses 1/8 ribs while Liddle uses mainly 3/32 ribs. Again this helps if not using capstrips. So everything together produces a satisfactory wing, leaving out any of these items might not. Don't change a proven design!

Note that the Liddle has a comment about adding webs - some people did some didn't and no reports of problems ( in 1968....) And that the Ugly Stik has comments about using covering that stiffened wing, while later comments said film was sufficient.

[Bob Cotsford]

kc, I've built models using the eggbox method, most memorably the Mercury New Jr Monitor control liner. The big problems with the method is that the slots need to be very accurately cut, too lose and the glue contracts pulling the spar into a banana, too tight and the ribs push the spar into a banana the other way. Get it just right and you are relying on glue strength to hold things together under negative G. Used with small section spar caps top and bottom though you get a very quick build yet strong wing. Leading edge sheet could be used to form the spar capping creating a quick build strong and stiff wing.

Eggbox worked well enough for c/l wings which were low aspect and often used very large section leading edges, and for lightly loaded single channel/REM models in the 60's and 70's not subject to -ve G. As with everything, model structures have moved on using the experiences (and folded wings) of the past to show us what NOT to do.

[Bob Cotsford]

also, in the 60's there were no internet forums to provide feedback on the ones that failed!

Riblets are a compromise, adding extra wood to maintain the nose of the wing section without going as far as fully sheeting that area. Unfortunately it doesn't help with torsional rigidity, though on a model like a Stik this won't be an issue.

[kc]

I found that making egg box construction for DIY projects ( pigeon hole storage etc) was dependant on accuracy as Bob says - so i avoided planes that used that method. However nowadays laser cut rib sets are avaible for Ghost Rider, Herr Flick and Sky Rider. But Boddo who used it in lots of early designs himself seems to have changed away from that method for almost all of his later designs ( Herr Flick was an exception ).

[Geoff S]

Posted by Peter Christy on 03/05/2020 11:02:21:

Posted by Simon Chaddock on 03/05/2020 10:18:42:

 

"To improve performance - add lightness" as Colin Chapman used to say.

Which is why Lotus came to stand for Loads Of Trouble, Usually Serious!

You can take lightness too far!

--

Pete

 

My cousin was an engineer at Lotus and had quite a bit to do with the Europa. It worried me to death when he went to work for Chapman because he'd driven me for several miles in prototype Hillman Imps and sideways wasn't unusual. Strangley he quietened down when he was in a Lotus I think Chapman's other dictum was that weight was only an advantage in a steam roller - he'd obviously not sailed much because a lump of lead on a keel is quite useful, too.

Chris Walby: Presumably you were grasstrack racing with the JAP engine. The vast majority of my motor cycle competitions were in trials with the odd enduro, usually on totally inapproriate bikes (like my BB34 Gold Star!) but I once rode my 1932 350cc Ariel which was modified for vintage trials in a grass track. I even rode the bike to the event. I didn't do very well and the kidney pain was awful despite wearing a canvas body belt Interesting story.

As regards my Liddle Stik wing, the only modifications I've made to the original design is toadjust the main 1/4" spruce spar angles so that the shear webs glue properly to both lower and upper spars and to fit 2 aileron servos. I don't think it's likely to fold becaue the spar structure is strong but there's llittle resistance to twist. The complete wing including ailerons and servos is about 250 gms before covering.

 

Geoff

 

Edited By Geoff S on 03/05/2020 14:22:53

[Martin McIntosh]

I have not read all of this by any means but do agree that many models are well over engineered. I lot of this may stem from the old days when an airframe had to withstand a bad hand launch; also more recently be novice proof.

I have two 72" Spitfires, the first of which was built as per plan and weighs over 18 lbs. It flies fine on a Laser 180.

Following a mag. article on weight reduction I decided to build another, but this time getting rid of most of the birch ply parts, making the ribs from light balsa instead of light ply and totally omitting any braces on the now three section wing, substituting 1/4 x1/2 balsa spars for the 3/8 sq. spruce ones and omitting wing joining tape, relying only on the glass skin. It lost over 4 lbs compared to the other but when tested it kept climbing alarmingly on full power. Replacing the motor with a 155 cured it.

This gets severely flung around with high G and has not yet fallen apart in the air.

[ken anderson.]

over engineered … … reminds me of my friend who is flying models in the sky now. He decided to "beef" up the construction of his models to make them ding proof!...so one of his models a smith mini plane...he decided to introduce some broom shank(3/4" dia) to each corner of the first few formers as you do as well as fit a 42cc quadra petrol engine..the same time one of our other friends made the same model with a 30cc super tigre motor in...his flew circuits on 1/4 throttle while the over engineered one had to have full throttle or nothing.....and a fair old lick coming in to land before it fell out of the sky....never mind God bless him...

ken anderson...ne..1..over engineered dept.

[kc]

I suppose the comments about Lotus - Lots Of Trouble Until Sold- are relevent, only make it just strong enough to work perfectly. I remember seeing a Lotus Elan crash on the main straight at Brands Hatch, it hit the concrete marshalls post at the top of Paddock Hill and seemed to disintegrate. The largest piece left was about 18 inches BUT the driver just walked away! Much the same with modern ARTF planes - they fly well but when they crash or even have a hard landing they disintegrate and only tiny pieces of perforated ply remain.

We might try the Elan central backbone type construction in planes. Maybe a fretted out backbone of ply or even carbon fibre holding all the main parts and the shape formed from foam sanded to shape. Perhaps it's easier to just buy a foam Wot4 though!

[PatMc]

I once read that Henry Ford sent teams around scrap yards buying up worn out old Ford cars. These cars were then stripped down & all parts examined for wear. Any parts that commonly proved to be still in good condition were made in to less robust standard in future cars if there was any cost saving to be gained. Ideally he wanted all parts of his cars to wear out uniformly.

[Martin McIntosh]

I thought that Lotus stood for `loads of trouble, usually serious`.

A mate recently bought an ancient Elise for which he paid over £19,000. The rest of us are still laughing.

(Sorry, way off topic).

[Peter Miller]

Once,bak in the 50s I had a lift with a Ford test driver.

He told me that Ford had driven one of their cars for about half a million milesand nothing had failed so they took it back and modified some parts so they were less long lasting

[PatMc]

Posted by Peter Miller on 03/05/2020 18:51:52:

Once,bak in the 50s I had a lift with a Ford test driver.

He told me that Ford had driven one of their cars for about half a million milesand nothing had failed so they took it back and modified some parts so they were less long lasting

He did a very thorough job.

[Paul Marsh]

Even an airliner was brought down by the pilot over-compensating the control - the rudder in this and sheared the vertical stabilizer off with obvious results. All people on board died when the aircraft spun, ripped the engines off in the spin and crashed.

Flight 587:

[Nigel R]

Full size aircraft are fragile things.

As for our wings, a D-box structure mops up so many of our needs, spanwise strength, twist, keeping airfoil profile, etc, I find it difficult to justify doing anything different for most models. Small & slow stuff excepted, even then I'd just try and look for the lightest of sheets to use, especially if using heat shrink film which adds no strength of note.

The comment on tailplanes earlier in the thread is well justified. Some models that move quickly still carry simple open frame flat structures. Speed and flexibility leads to flutter, flutter is a one time only deal in most cases... Similarly, the fin and rudder, there are big loads on a rudder when it moves, often a large, wide surfacec, it needs to be rigid to transfer all that torque from a control horn right through the whole structure, do we just bolt a horn to a squashy bit of balsa attached to a flexible open frame structure? Or maybe a decent hard point to take load from the control horn into the structure a bit more gracefully and something more torsionally rigid.

YMMV, of course 

Edited By Nigel R on 04/05/2020 09:31:43

[Brian Cooper]

A regime which has worked well for me over (too) many decades is to approach every last detail as though you yourself would actually be inside the aeroplane.

That's EVERYTHING from the basic design, through the build, radio and engine installations, control runs, wiring, etc., etc. . No compromises.

Take the view that "if it CAN fail, then it WILL."

It's amazing how it sharpens the mind.

B. C.

[Nigel R]

Exactly. As the expression goes, PPPPPP, the 6 Ps.

Proper preparation prevents ahem poor performance.

[Plummet]

When I was in education - receiving it that is - we had a Mechanical Engineering lecturer who recommended a book called "The new science of strong materials". Its subtitle was "Or why we don't fall through the floor."

I still have the copy I bought - somewhere!

It discussed why wood is so strong, why fibreglass and resin is so useful and so on.

There are two aviation related bits that I hazily remember. One related to problems with preparation methods for glue joints which failed on the Mosquito. However, relevant to this thread was a discussion about the problems that Fokker (I think it was) had developing one of their WW1 aircraft. The wings were falling off, and the test pilots were then unavailable to answer questions. So they strengthened the wing spars and tried again. Things did not improve, in fact it seemed to make the problem worse. It was eventually realised that the problem was due to the effective centre of lift moving and this causing the wings to twist and disintegrate around the spar. Making the spar weaker and more flexible solved the problem.

Now where did I safely store that book?

Plummet

[kc]

Actually Plummet the same author JE Gordon wrote 2 excellent books -The New Science of Strong Material or why you dont fall through the floor and also Structures or Why things dont fall down. Both very readable and worthwhile. Penguin Science paperback. Should be in any library.

[PatMc]

Posted by Plummet on 04/05/2020 15:23:54:

However, relevant to this thread was a discussion about the problems that Fokker (I think it was) had developing one of their WW1 aircraft. The wings were falling off, and the test pilots were then unavailable to answer questions. So they strengthened the wing spars and tried again. Things did not improve, in fact it seemed to make the problem worse. It was eventually realised that the problem was due to the effective centre of lift moving and this causing the wings to twist and disintegrate around the spar. Making the spar weaker and more flexible solved the problem.

Now where did I safely store that book?

Plummet

I think you're referring to the Albatros DIII & DV/DVa wing spar problems that took some time & several sets of wrong conclusions before they were resolved.

Fokker had QC problems with poor workmanship & cost cutting on materials.

[Plummet]

Posted by kc on 04/05/2020 15:50:26:

Actually Plummet the same author JE Gordon wrote 2 excellent books -The New Science of Strong Material or why you dont fall through the floor and also Structures or Why things dont fall down. Both very readable and worthwhile. Penguin Science paperback. Should be in any library.

Thanks KC. I have both books - somewhere.

Plummet

[kc]

PatMc. Plummet was right it was the Fokker actually D8. See Structures pages 261 to 268.  Actually this book goes against others ( probably what PatMac read) in the Fokker explanation,  ( Urban Myth?)  I would trust Prof Gordon on this as he seems to have been very much involved in such design problems in WW2.   Read his books and be convinced he knows what he writes about.

Edited By kc on 04/05/2020 16:15:24

[Plummet]

Posted by kc on 04/05/2020 16:10:44:

... Plummet was right ...

Edited By kc on 04/05/2020 16:15:24

Ooooh gosh. I must show that to my wife.

Plummet