Solid wings

[Simon Chaddock]

In threads elsewhere the benefits and disadvantages of solid "plank" wings has been raised.

A long time ago now I built this very high aspect ratio (31:1) free flight 72" (1829mm) span glider with a solid plank wing out of 1/4 (6mm) balsa. It has a fully profiled wing section with a constant taper. 3" (75mm) chord at the root to 1.5" (37mm) a the tip. Actually the wing is made up of two pieces, the leading 30% is harder stock & the rest soft. The tail and fin are 1/16" (0.8mm) sheet and the rear fuselage is 1/32" (0.4mm) sheet rolled into a tapered tube.The glider weighs 4.5 ozs (128 gms) ready to fly.

The wing (when new) was surprising flexible - in a static load test I got the the tips to nearly 45 degrees!

Although it looks impressive it does not really fly that well. It is fine in a straight line but with over 75% of the total airframe weight in the wings and with short tail moments, once it starts turning a spiral soon develops but fortunately the wing is pretty crash resistant.

I did actually start building a double size RC version (still with solid balsa wings) but chickened out & went back to building "proper" balsa structures!

[Tom Satinet]

I've got a 60" plane that is machined out of poplar.........

[Former Member]

[This posting has been removed]

[Erfolg]

Was the "Spiral Death Dive" a record by Napalm Death or Mega Death?

Your problem is almost certainly "Aeroelasticity". Perhaps a spuce spar, and some outer skin to prevent twisting (I mean aeroelasticity) could make the wing viable.

Expect a post by Eric shortly.

As a addendum, I regularly fly a model of 42" span, 3/8" thick approx. (made up of two 3/32 spruce apars with a 3/32" plank shear web ). the rest of the wing is a georidic 1/16 balsa profiles, the lot coverd with Solar film. Section MH 32 ish. Does not flutter, twist, no obvious bend due to flight loads, and is very light.

Erfolg

[Slopetrashuk]

It does look a little underfinned.

[Andy Green]

I remember the mini phase, I build one years ago, designed by Chris Foss, kitted by Morco Mold I think.

Got the plan somewhere.

Andy

[Alistair Taylor]

  Simon - what's the dihedral on your model? The wing lokos very flat to me - this might be causing an initial adverse roll on application of rudder (plane banks the wrong way initially), followed by the nose dropping into the turn, with insufficient control authority once the turn has started to pull out - although I may be talking out of my hat of course..... try bending the wing joiners a bit to see if this helps.

I remember the mini-phase too. I aquired a plan and the wings (but no fuselage) some time ago, and so built a fuselage for it.

The wing is all balsa (no spruce spar) but the LE is supposed to be hard, the TE soft (light), and washout is sanded into the tips.

The plan also shows an aileron wing with standard (for the 1970s) radio gear (big heavy DEAC and substantial servos).

Mine flew very well with a Cox Babe Bee 049 on the nose, although it wasn't really a park fly plane - the glide is very flat and quite rapid, so you need a decent landing area. i think it was intended to be a slope soarer, with the requisite ability to penetrate. On the flat it would go up very well when in a thermal at height, but bungee launches using a football field length bungee only gave quite short flights.

Sheet wings have appeared on lots of models - but were probably not popular in the very early years (1930s-1940s) due to the cost of balsa.

AlistairT

[Former Member]

[This posting has been removed]

[Erfolg]

In past Aeromodellers there are are numerous examples of balsa wings, some quite elaborate, being made up of several carefully prepared planks, and finally sanded on both surfaces to an aerofoil. At that period mainly under-cambered.

Later the "Jedelsky" ? wing had some vogue, Being made up of two pieces jointed. This then had a few quasi, wing ribs to help maintain shape, the top surface only being sanded.

Many of these types had one thing in common, and that was a relatively deeper section than apparent, from a casual glance, due to the camber. The relative importance of this was both to give a better "second moment of area" or "I" (do you not love engineering speak), which improved the bending strength as "I" is greatly influences by depth^3. The width is less important than where it is located. They also benefited from a better torsional resistance, same reason, but I will not further bore you with engineering speak.

I am not really sure what the problem is, but I have found that, flat wings even on a glider do not seem to cause a real problem, when turning. Had a Ridge Rover (still have) by Chris Foss? something like 120" span, primary control was by Flapperons yet was just as happy using the rudder for turning, no dihedral at all.  Lack of fin/rudder area has though, as mentioned, certainly need it for turning initiated by rudder and to stop that dreaded Napalm Death, "Death Spiral" .

If the wings do twist (by a noticeable amount), when held at the tip, when applying a torsional force, I am pretty sure that "Flutter" at a speed above pedestrian is an ever present danger, plus directional control will be compromised. Even heavy weight tissue doped on will improve things, without any more exotic glass epoxy skinning.

I think we should recognise that most of the free flight models were not expected to cope with the forces/speeds that RC modellers expect their models to handle as routine.

Erfolg

[Simon Chaddock]

I did say I built it a long time ago.

The wing is probably rigid enough as the plane only weighs 4.5 ozs and in the static test it was loaded to the equivalent of well over 12g! The problem is, as already spotted, a lack of dihedral (it has some 8 degrees when flying), washout (it has none apart from the very tip) and fin area for the aspect ratio (31:1) of the wing. Even the most extreme full size modern gliders are only up to 28:1 and they have very clever wing designs and a pilot!

The last issue concerns Reynolds numbers and the boundary layer. I understand that any normal type of wing section does not work as well in very small sizes and low speeds. In these conditions air is more like treacle.  As the wing on my glider is only 1.5 inches wide at the tip and has a wing loading is just 4 ozs per sq ft, I doubt it is ever going to work as well as it might in a bigger, heavier model.

Now double the size  - 12ft span, 4 channel, micro servos, 2lbs AUW.......oh no not that again...... I got a Junior 60 type thing to build for my 5cc!

[Alistair Taylor]

Eh? What? Free flight? Wot no rc?

Wossat then?

 Sorry, haven't had my coffee yet. Must pay more attention, go to back of class, 100 lines etc etc

That Reynolds bloke really is a party pooper.....

Simon - the plane does look quite stunning. You might find that at larger sizes you can make use of materials other than balsa (e.g. blue foam) to achieve a similarly robust wing at lower weight. I remember seeing a chuck glider with blue foam TE and balsa LE that flew very well (well, OK I saw it glider across a small hall...), and was resistant to finger marks thanks to a light coat of something foam friendly (PU varnish? - not sure). Just an idea.

I really like sheet wings as the part counts for quite substantial structures are very low, I find building much easier, and all the sheet wing planes I've flown so far have performed admirably.

AlistairT

[Erfolg]

The Reynolds number is a dimensionless unit, ie it is a number, it gives a clue if the flow is laminar, supercritical (could be either laminar or turbulent, dependant on factors such as are you moving from the laminar towards the turbulent eyc.), or tubulent. It has no units such as pascalls a force per unit area, or density kg m-3..

The number is often part of scaling process in modelling Euler Numbers, you can bring in Stokes law for fluids etc. But we often talk a lot of nonsence when we modellers start talking about molecules, viscosity of fluids.

It just happens that we modellers choose a wing chord and flying speed that puts us in this super critical region. So we often see apparently different behavior from apparently the same conditions. This is the reasoning behind the turbulator strip  on many free flighters. The boundary layer is made to be turbulent and the model trimmed to optimise this induced regime.

I would not let Reynolds numbers get in the way of model flying.

Erfolg

[Alistair Taylor]

Hiya Erfolg

I'm impressed at your grasp of foreign languages - now what did all that actually mean?

I tried to get my head round Reynolds numbers a while back.

My brain boundary separated and I went into full turbulent flow.

A quick flying session soon had me laminar again.

AlistairT

Cool! Over 500 posts!

[Erfolg]

Alistair

All we modellers need to know, is that our models fly, and  we get pleasure from the experience.

If you are a professional engineer you may need to know more. You may bring it into your modelling in understanding what is or has happened. Yet at the end of the day, innovation, observation, experiments come first. The theoretical explanation comes later. Engineers take the theoretical facts to predict to an acceptable level of how systems will perform, for most it is how ythey make a living.

We modellers are interested in fun, so my cals are confined to CG placement, tailplane area and very occaisionally comparing one beam with another (but only on a comparative basis).

Know I am  thinking about the divergant, hysteris loop and electron spin and how it relates in the re-installation of my outrunner. Perhaps a screwdriver is all that is needed.

Erfolg

[Erfolg]

Just looked at the moment arm it appears to be about 4 chords or 12". Does not seem that wrong to me.

Anyway I would bung in a couple of mirco servos, micro receiver and a small brushless with lipo and fly to the wings come off. 

Erfolg

[Simon Chaddock]

Reynolds number and boundary layer - I thought that might stir up a few things!

One day I will try again: same size, same weight (4.5 ozs!) but including 3 channel RC and no foam!