Washout with double wing-fold

[Dave Cooper]

Hi All

Just read Alan Cantwell's thread on Washout - very informative...

I'm wondering about how best to deploy it on the 1/4 scale Wyvern which has a double wing-fold. The first fold occurs at about 1/4 span and, although the wing bottom is horizontal, it has 1 degree of anhedral due to spanwise taper. The next section has 6 degrees of dihedral but also incorporates a second fold (also inwards) of the extreme wing tip.

I was planning to build the inner wing section integral with the fuselage and up to the first fold with no washout. Two possibilities then exist for the remainder : (1) just apply washout to the tips (2) build in washout gradually from the first wing-fold outwards. Instinctively, I'm drawn towards the second option but, have no previous experience with wing folding models.

Thanks for any practical experience here.

[Alan Cantwell 1131]

http://www.internetmodeler.com/2005/nov ... -Color.jpg

complicated wing, isnt it? are the wings going to be folders, or just standard 3 piece, with plug in outer sections?
if its plug in outers, then, for my money, i would incorparate the washout in the VERY large outer panels, what do others think?
just as a matter of interest, how do you intend to do the sliding flaps?

[Dave Cooper]

Hi Alan

The wings will be folders (probably electric for the first fold with a pushrod /bellcrank set-up to fold the tips). The inner section will carry the linkage for the Youngman (Fairey) flaps - on the full-size, they hinge /extend from a cantilevered arm off the rear spar /trailing edge. The outer section carries a separate, more conventional, split flap /dive brake assembly together with the ailerons. I hope to replicate this on the model.

I think it makes sense to build the folding tips (the extreme outer 6" of span) in line with the outer wing and jig it all as if it were one single length of washout...

From a fail-safe point-of-view, is it a good idea to 'interlock' the wing-fold with the main retracts such that the mechanism will only activate when the gear is down, locked and compressed (I will be having about 1" or so of oleo travel) ?

Open to all ideas...
Dave

[Phil Clark]

I've seen models with washout built only into outer panel and they look very odd..................depending on how the washout is added (LE down, or TE up) you either get a slight kink in the TE or LE when viewing it down the span of the wing (uuggghhhh ). Better visally to build the washout in over the full span. If you're using a wing rib plotting programme such as Profoli, you can add the necessary jig tabs & it'll do it for you..........

I'd keep washout progressive from root to tip unless the full-size says otherwise.

Phil

[Alan Cantwell 1131]

Phil, would it not be a tad difficult to get the twist along the wing, what with the flap mechanism this design has?

[Chris Lane]

I found lots of pictures here but still can't work out how the flaps work or whether there is any washout!
http://www.primeportal.net/hangar/howar ... php?Page=1

This appears to be Yeovilton since it has a Concord in the background?!? Chris

[Dave Cooper]

Thanks for the replies so far - looking through my full-size tech file, the root incidence is set at +1degree. By visual estimation of a 3-view, the tip TE looks to be about 1 to 1.5 degrees above fuselage datum. So, I estimate about 2-2.5 degrees of overall washout. The test pilot's reports (Harald Penrose) say the S4 variant was very benign at the stall. The only (known) remaining full-size is the one in Chris's post (FAA museum, Yeovilton). This is the H-24 R-R "Eagle" engined prototype and not, the Python turbo-prop S4 which came later.

Flaps: as far as I can tell, the inboard and outboard flap mechanisms operate independently (the outboard incorporates dive brakes as well), although, in the operational photos, you nearly always see them deployed together. Effectively, in frontal elevation, the wing is 'cranked' at the first wing fold. I think it should be possible to build in about 0.75-1 degree of washout to the inner wing with the remainder outboard if I use a ball joint or two as part of the flap hinge /actuator to take up any 'out-of-plane' movement. These would need to be fairly small, high-quality joints to take the considerable lift /drag loads - perhaps a 'helicopter' joint or something similar ?
Dave

[Phil Clark]

If you don't want to built in mechanical washout, why not consider a wing section change root to tip......something with less camber at the tip will give you aerodynamic washout even if they are both set at 0 degrees.

This is exactly what we did on our Valkyrie sport jet kit......from memory, NACA 2412 at the root and a NACA 008 at the tip......no mechanical washout, an easy wing to build but giving very benign handling.

Phil

[Dave Cooper]

Thanks for the tip on aero' washout Phil. I had considered this but, don't yet know enough about the selection criteria for the two different sections - root and tip. I'll have to start reading "Abbott & Doenoff" again ! On my Phoenix RC flight sim' there's a Bearcat (nearest I can find to a Wyvern) - I've scaled this to 11 feet span and 55lbs. The default wing section is an Eppler 374, root and tip, and this gives very nice handling near the stall. Changing the tip incidence to give 2 deg's of washout, made not much difference to the low-speed handling but did make spin recovery a lot more difficult especially when the spin was fully developed - 6 turns.

However, I will try some different tip sections, with less camber, just to see what results - not sure though how representative this will be of the Wyvern's wing. The Bearcat's wing is similar in planform but doesn't have the cranked dihedral of the Wyvern. Will also try some NACA pairs as these seem to feature a lot on the warbirds.
Dave

[Chris Lane]

David Lednicer gives NACA 23018 at the root and 23010 at the tip. Incidentally have you seen this nice cutaway of the geartrain?

Chris

[Dave Cooper]

Hi Chris - the two NACA sections that you mention - were they for another Wyvern model or, the full-size perhaps ?

(The gearbox info' is very useful. I also found this a while ago...it incorporates the reduction gear as well as the main prop drives and reversing gears. I also have a cutaway of the Rotol pitch change mechanism to work with. Needless to say that mine will be a simplified version ! The two turbo-prop units I've looked at so far come with a reduction box so I will just be adding a reversing planetary gearset and main drive shaft assemblies.)

Cheers, Dave

[Chris Lane]

Sorry - complete goop. I read Fairey Gannet data in error. It actually comes from http://www.ae.illinois.edu/m-selig/ads/aircraft.html. Westland Wyvern sections are NACA 65-212 root and 65-214 tip.
Chris

[Robin Woodhead]

If you look at the LINKs section on this forum, item 6; goto Aircraft Wing section Database, scroll down for Wyvern, you will find that the Westland Wyvern sectiuons are as follows.

Wing Root NACA 65-212
Wing Tip NACA 65-214

I am surprised that more people do not use this resource, which was put there by me some years ago.

Robin

[Dave Cooper]

Thanks Chris, Robin - I see that I shall have to make myself more aware of the contents of the LMA website !

Quick question : In the Public Domain Aerofoil listings (Abbott & Doenoff), it shows two sets of ordinates for the 65-212 section (which are quite different) and none for the 65-214...do you think this could be a miss-print and the second set is actually the one for 65-214 ? Is there another source I could cross-check with ?

Cheers, Dave

[Robin Woodhead]

Dave,

You are correct, the 65-214 is missing, but using the following info you should be able to work out the section.

The NACA five-digit series describes more complex airfoil shapes:[6]

The first digit, when multiplied by 0.15, gives the designed coefficient of lift (CL).
Second and third digits, when divided by 2, give p, the distance of maximum camber from the leading edge (as per cent of chord).
Fourth and fifth digits give the maximum thickness of the airfoil (as per cent of the chord).

For example, the NACA 12018 airfoil would give an airfoil with maximum thickness of 18% chord, maximum camber located at 10% chord, with a design lift coefficient of 0.15

The reference for the aerofoil picture is shown as a gif file, the data file needs opening as a Excell file when prompted.

By the way, the programe called FOIL is a very useful bit of software; it allows wing sections to be drawn and multipul wing ribs to be produced, with or without washout, taper etc.

Hope this helps. Robin

[Dave Cooper]

Robin - thanks for demystifying this. I knew that the last 2 digits related to thickness but was not aware of the meaning of the others.

I will certainly look at, and study, the other programs and files that you mention...
Dave