Andrew Cousins Posted March 31, 2020 Share Posted March 31, 2020 Hello all i need a little help. I have not knowingly built a wing with washout. I am about to embark on a build that requires some wash out in the wing. I have done a little research and just wanted to see if the experts here can confirm if i am correct or not. OK the plan calls for 1.5deg of washout. So i have measured from the route wing rib to the tip. Now using trig i should be able to work out how much i have to lift the T/E of the wing tip rib. So if my wing length is say 95 cm (adjacent) and my angle is 1.5 deg using tan 1.5 X 95cm should give me 2.48 cm. Is this the correct amount i have the lift the T/E of the wing tip rib? It seems a lot!! I have another question but wanted to see if i have this correct before i ask the next question. Many thanks in advance. Quote Link to comment Share on other sites More sharing options...
Martin Gay Posted March 31, 2020 Share Posted March 31, 2020 Hi Andrew, That does not seem correct. The washout is a twist at the wing tip where the trailing edge is lifted. The 1.5 degrees will be in relation to the wing tip chord NOT the span of the wing. I will leave you to your trigonometry, but would expect the washout to only be a few millimetres (3-5mm at most). Martin. Quote Link to comment Share on other sites More sharing options...
jrman Posted March 31, 2020 Share Posted March 31, 2020 No. What you have calculated is 1.5deg dihedral. You should use the tip CHORD to calc the washout. Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted March 31, 2020 Author Share Posted March 31, 2020 Ok looks like i have made bo bo. That does make more sens Told you all i haven't done this before. Ok so with a tapered wing i am going to have to measure the root from L/E to T/E then do my trig calculation. I will then have to raise the T/E of each wing rib by the result. Would i be correct in saying that as i get close to the WING root the rib will get bigger so the amount i have to raise the T/E will increase???? Or is this just done for the tip rib?? Quote Link to comment Share on other sites More sharing options...
Martin Gay Posted March 31, 2020 Share Posted March 31, 2020 Andrew, Measure the tip rib chord. Do your trig calculations on that measurement. This will tell you how much you need to lift the tip trailing edge. Then fit a tapered strip under the trailing edge. The tip end will be the calculated figure and the root end will be zero height. This will give a gradual change in washout along the span of the wing. Check the plan carefully as sometimes washout starts part way along the span. This point would then be the zero height of your tapered strip. Martin. Edited By Martin Gay on 31/03/2020 13:35:46 Quote Link to comment Share on other sites More sharing options...
flight1 Posted March 31, 2020 Share Posted March 31, 2020 because many have explaiined this before me and better here is a link to read to explain it and how to with digrams from vaily aviation this one hope it hepls Quote Link to comment Share on other sites More sharing options...
Peter Miller Posted March 31, 2020 Share Posted March 31, 2020 The simple way that I always use. Take a piece of wood and measure the 1 1/2 degrees on it and cut it out. Wedge that under the tip rib with the LE touching the board. If you do not have a protractor 11/2 degrees is about 1/4" at 10 inches Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted March 31, 2020 Author Share Posted March 31, 2020 Ok the fog is clearing. I know wear i went wrong. Its the root of the rib tip not the wing length i should be measuring. Flight1 Many thanks for the link most helpful. Ok Martin you are correct the wash out is only on the outer half of the wing (rib 7 to 15). Now as the T/E of the ribs do not touch the building board i was thinking of making a tapered strip as you say Martin from the calculated height (at rib 15) to zero. To go from rib 15 to rib 7( rib 7 being zero). Then wear the rib meets the building board i will place the tapered strip. Lifting the ribs to place the strip under. would the following be the best way to build the wing and lock in the washout. 1. fit bottom spar to plan. 2. fit tapered (wash out ) strip to plan wear ribs meet the building board. Then fit ribs and glue to bottom spar. 3. fit top and rear spar then false leading edge. 4. Fit L/E and T/E sheeting to top of wing. Will this then lock in the wash out? sorry for all the questions bit nervous as i have not done wash out before and its a 1/4 scale. My first adventure into large scale. many thanks Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted March 31, 2020 Author Share Posted March 31, 2020 Martin like your idea to. I take it its just the tip rib you do this to? How do you lock in the wash out? I was thinking of using the method in my earlier post. Whats your thoughts. Many Thanks Quote Link to comment Share on other sites More sharing options...
flight1 Posted March 31, 2020 Share Posted March 31, 2020 What 1/4 scale plane is it and what plan is being used could lead to more useful info. The tapered strip placed under the trailing edge of the ribs from the wing tip rib to where you want the twist to start, and with the bottom spare flat on the board is the most common method. Don't forget not to glue the tapered bit of wood to the wing in the build process Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted April 1, 2020 Share Posted April 1, 2020 Hmm - the link provided by Flight1 has the following text which is plain wrong I'm afraid "Aerobatic models are aerobatic by the very fact that they are designed to be inherently unstable or right on the “hairy edge”. Hence, any means of establishing inherent stability is generally not used so it is not uncommon to see aerobatic models not use washout. Scale models on the other hand have a great desire to want to be stable so that the pilot in command stays calmly in command." First, washout has nothing to do with stability. Stability is governed by the position of the CG. The effect of washout is to ensure that the wing root stalls before the tip thus avoiding a sudden wing drop and potential spin when flying close to the stall. A perfectly stable scale aircraft can have a vicious stall if it has highly tapered wings without washout but that has nothing to do with stability. The reason aerobatic aircraft do not have washout is that you spend 50% of your time inverted and then washout becomes wash in! You want the aircraft to perform symmetrically so you don't use washout. Today's aerobatic models do not have dihedral as again it becomes anhedral when inverted and affects the aircraft's yaw stability either way. Second, aerobatic models are not inherently unstable. As far as traditional or precision aerobatics are concerned, the aircraft are always stable. Many pilots though tend to have too much movement on the controls as they believe that for an aircraft to be aerobatic you need large throws. That makes the aircraft twitchy but not unstable. Low control throws transform a twitchy, but stable, aircraft into a very pleasant flying machine that flies on rails. I have buddied beginners to model flying using a 2 mtr competition aerobatic airframe and they manage just as well, if not better, than when flying a trainer. Sorry, but we must correct gross errors when they are made and this is a gross error! Quote Link to comment Share on other sites More sharing options...
SIMON CRAGG Posted April 1, 2020 Share Posted April 1, 2020 Have you tried an incidence meter? I have used one for many years, and it is one of my most valuable aids. Even if you build a model very carefully (even a foamie), wing twist can very easily creep in. I have straightened, and also built in wash out on a variety of models from a fast EDF Hawk, to various pattern ships and several scale models. I would advise getting one and giving it a try...........good bit of kit. Good luck!. Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted April 1, 2020 Author Share Posted April 1, 2020 Hi All and thanks for the input. Flight1. The plane is a 1/4 scale L19 Bird dog. Peter Jenkins. Point taken but do you agree with the information on how to calculate and build in the wash out that is present in this document. Simon Cragg. No i don't have an incident meter but it is on my shopping list as i intend on building a lot more. Thanks for your input much appreciated. Quote Link to comment Share on other sites More sharing options...
flight1 Posted April 1, 2020 Share Posted April 1, 2020 The P J post is only picking out one paragraph of the the text the rest is right enough for our doings. One thing to point out about that paragraph some planes are built unstable to make the more aerobatic/movable take for instance the euro fighter is so unstable a computer flight control is required to fly it. hay ho lets not get distracted, this is about wash out and how to achieve it in the build. The main point of washout is stop the whole stalling at the same time. if the inner part of the wing stalls first you give some notice of it without the dramatic effect if it all stalled in one go. the outer wing has far more 'leverage'. Quote Link to comment Share on other sites More sharing options...
Peter Jenkins Posted April 1, 2020 Share Posted April 1, 2020 Posted by flight1 on 01/04/2020 09:48:27: The P J post is only picking out one paragraph of the the text the rest is right enough for our doings. One thing to point out about that paragraph some planes are built unstable to make the more aerobatic/movable take for instance the euro fighter is so unstable a computer flight control is required to fly it. Flight1 is correct. It was just that para. Only aircraft with a quadruplex flight control system are built to be unstable like the Eurofighter and all other 5th Gen fighter aircraft. We need not detain ourselves with discussion of such esoteric machinery here though. Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted June 26, 2020 Author Share Posted June 26, 2020 Hi all got an up date for you all and another question. Ok I have built half of the wing and I used the wedge method to put wash out in the wing. I have fitted the aileron. Now the hinge point is the same distance from top of the T/E at rib 7 as it is at rib 15. Now if I put a metal rule on the surface of the wing and the surface of the aileron it's all good. See photo. Now if I do the same at rib 15 there is a difference. See photo. This difference is the same as the wash out I put into the wing 5mm. My question is, is this correct. Many thanks in advance Andrew c Quote Link to comment Share on other sites More sharing options...
Bob Cotsford Posted June 26, 2020 Share Posted June 26, 2020 No, I'm afraid the aileron forms part of the wing section so should include the washout to match the wing. If the aileron is built up you may get away with separating the leading edge and regluing it with the aileron jigged to match the washout. No doubt it would fly as is, but looks? Your choice! Quote Link to comment Share on other sites More sharing options...
John Bisset Posted June 26, 2020 Share Posted June 26, 2020 There were some full size machines where the washout was effectively provided by rigging the aileron appropriately. I have a vague memory that there was some long span aircraft on which the aileron neutral positions could be adjusted in flight for optimum cruise efficiency. Quote Link to comment Share on other sites More sharing options...
john davidson 1 Posted June 26, 2020 Share Posted June 26, 2020 Regarding Eurofightesr and such being unflyable without a computer, why do MODELS of them fly perfectly happily? Quote Link to comment Share on other sites More sharing options...
brokenenglish Posted June 26, 2020 Share Posted June 26, 2020 I haven't read through the thread, but I suspect that you didn't put in the washout correctly. On an aileron wing like this one, it's important to NOT pack up the trailing edge tip, but to build with the trailing edge flat on the board, and get the washout by packing up the leading edge at the wing root. The difference between the two "methods" is not very important on a non-aileron wing but, with ailerons, it's important for the reason that you discovered! Unless the ailerons are only on the outer part of the wing, in which case you can build flat, and set a couple of degrees of up on each aileron. Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted June 26, 2020 Share Posted June 26, 2020 Posted by john davidson 1 on 26/06/2020 21:21:44: Regarding Eurofightesr and such being unflyable without a computer, why do MODELS of them fly perfectly happily? Probably due to having a more forward C of G and/or smaller control movements? Quote Link to comment Share on other sites More sharing options...
Mark Kettle 1 Posted June 26, 2020 Share Posted June 26, 2020 Andrew C, - Brokenenglish - is correct in my book. I control the washout in my designs the way he describes. To help with this let my show a rib set. A 'rib set' for a Avro Vulcan, the longer rib is at the root - the middle of the wing, the smaller rib is the tip. Notice the bottom line of the rib's to the trailing edge are flat, this helps building of the wing and following on with the trim of the model in the sky over a wide range of flying speeds. The washout effect comes from the main bulk of the wing in the middle flying down it's chord line and this makes the tips show washout, the incidence of the tip chord being different to the middle root chord/s. Controlled via my curves, measurements and built flat on the board. Below:- The Root and Tip ribs shown with each other. The main incidence setting coming from the larger rib having the curve come up from the bottom line at the front to the leading edge, and all ribs / wing built from a flat building board. This method I believe makes the model have great stability and control, even left to fly 'hands free' sometimes. See the foam wing in action, using the same wing sections shown above. A nice stable wing, with the model pilot able to place the model where he wants. Filmed March 2015, North Wales UK. Edited By Mark Kettle 1 on 26/06/2020 23:53:26 Quote Link to comment Share on other sites More sharing options...
perttime Posted June 27, 2020 Share Posted June 27, 2020 Posted by john davidson 1 on 26/06/2020 21:21:44: Regarding Eurofightesr and such being unflyable without a computer, why do MODELS of them fly perfectly happily? It is a matter of Center of Gravity. You balance the model so that it has enough stability. Quote Link to comment Share on other sites More sharing options...
brokenenglish Posted June 27, 2020 Share Posted June 27, 2020 Mark, Thanks for the super video. I've never lived anywhere close enough to a possible PSS site to make it a reasonable possibility, so I've never been interested, but that Vulcan flying is superb! Quote Link to comment Share on other sites More sharing options...
Andrew Cousins Posted June 27, 2020 Author Share Posted June 27, 2020 Oh bugger. First things thanks for the help all it's appreciated. I have taken on board all the comments and recommendations. Ok the aileron is only on half the wing. The plane is a L19 bird dog. The plan shows the aileron built separate to the wing and does not mention any wash out in the aileron. I bow to the more experienced builders, but I don't know why it wouldn't show that. It's a Vaily Aviation plan. 1/4 scale Ok before I go cutting and tearing the aileron apart and you all now knowing designer, plane, scale and aileron is only half the wing. What are my options. 1 start the aileron from scratch and build in wash out. Not sure how this would work. Have to have a think. 2 cut the aileron L/E and try and twist it to the correct the difference. 3 leave it as is and trim it out. As mentioned. Mmm don't know. Help... Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.