Basil Posted March 28, 2021 Share Posted March 28, 2021 Danny, forgive me but firstly why are you doping the frame prior to covering? Secondly, is there only shrinking dope or are there more types.? Thirdly,as a mature returnee who has only heard of solvent based dope for shrinking, I see that there is now water based dope advertised are the water based dopes as effective as the solvent types, or have they specific uses. I assume the moderator may reallocate this to a seperate thread !! Thanks in advance Bas 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 28, 2021 Author Share Posted March 28, 2021 Hi Bas, there are two types of cellulose based dopes in modelling, shrinking and non shrinking. And if you include full size dopes there is also low taut, which is what I am using here. You may hear of banana oil which is basically a none shrinking dope with additional plasticers such as castor oil. The polyester covering i am using is Ceconite, which is a lightweight covering used on full size aircraft. The weave is very fine and as I am using dope to stick the fabric down it does not soak through as well as an open tissue or silk. So you need the dope to soak through from the airframe side too. The prior coats do two things, fluffs up and locks the balsa fibers so that some 800 grit will make the wood super smooth. The other reason is dope applied on the top soaks through and softens the underlying dope. Giving a better chance at sticking it down. I must say i am not finding the Ceconite is shrinking much with heat, the LAS instructions say 114 degrees max, but I am unable to get creases out at that. 120 its better, but would be curious what others are using? I have not tried water based dope, as I am sticking with what I like. Solvent based can be lifted and re stuck ? Cheers Danny Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted March 28, 2021 Share Posted March 28, 2021 Doping the framework and reactivating it with fresh dope through the fabric was how I was instructed to attach covering to a full sized glider open structure. 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 28, 2021 Author Share Posted March 28, 2021 For certain close weave tissues it is also the only way, Esaki for example ? Well the Ceconite does work, but it is much slower in the long run than an iron on covering. It also leaves a bit of a frayed edge. I remember a control line friend showing me nylon covering, and they said you can sand the frayed edges no problem, but do not bring sandpaper near the surface until at least three coats of dope!! So that's what I will do..... But the rear flappy bits are covered. Cheers Danny 2 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 28, 2021 Author Share Posted March 28, 2021 (edited) So four coats of low tautening dope mixed 50/50 with thinners..... Cheers Danny Edited March 28, 2021 by Danny Fenton 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 My Polyester resin arrived so I used the supplied tape to join the two halves, I believe the later kits come with a one piece cowl. I am not sure how well the bandage will hold the shape without some internal structure, we will have to see, when/if the resin sets...... I also covered one of the ailerons. The 4 coats of dope have created a lovely drum tight finish, and the edges can indeed be safely sanded. If you sand before enough dope is down the threads will fluff. Cheers Danny 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 Its been 30 minutes and the resin should have started to gel after 20, did I say I hate polyester? Fingers crossed..... Quote Link to comment Share on other sites More sharing options...
Basil Posted March 29, 2021 Share Posted March 29, 2021 19 hours ago, Danny Fenton said: Hi Bas, there are two types of cellulose based dopes in modelling, shrinking and non shrinking. And if you include full size dopes there is also low taut, which is what I am using here. You may hear of banana oil which is basically a none shrinking dope with additional plasticers such as castor oil. The polyester covering i am using is Ceconite, which is a lightweight covering used on full size aircraft. The weave is very fine and as I am using dope to stick the fabric down it does not soak through as well as an open tissue or silk. So you need the dope to soak through from the airframe side too. The prior coats do two things, fluffs up and locks the balsa fibers so that some 800 grit will make the wood super smooth. The other reason is dope applied on the top soaks through and softens the underlying dope. Giving a better chance at sticking it down. I must say i am not finding the Ceconite is shrinking much with heat, the LAS instructions say 114 degrees max, but I am unable to get creases out at that. 120 its better, but would be curious what others are using? I have not tried water based dope, as I am sticking with what I like. Solvent based can be lifted and re stuck ? Cheers Danny Danny, thanks for that. Info on the subject of doping and finishing seems a bit thin on the ground, for the likes of me. Would you reccomend Banana oil under say the laminate that we've been able to bulk buy here on the forum in the past week , in order to improve the finish, or is it only for use under doped finishes. Bas Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 Hi Bas, for under the film it isn't needed, however if you are going for a really nice finish then I would use sanding sealer on the wood first. You can make sanding sealer by adding a little talc to dope, I would use non shrink but whatever you have. Just be careful if it is a shrinking dope as it may distort un-supported sheeting. The sanding sealer will dry with a really coarse feel to it. I really light sanding with 600/800 will have it really smooth and ready for your final covering. The beauty of iron on films is that you don't need to do much preparation, in fact you don't want it too good, the film seems to grip better to the less than perfect finish. And you are less likely to get air bubbles trapped underneath. Banana oil is used as the final coats, after dope, when you want to do more sealing without risk of distorting the airframe with more dope. Once you have achieved the required tautness, then switch to banana oil ? until the surface is airtight or slightly glossy, ie has a slight sheen. Hope that helps? Cheers Danny Quote Link to comment Share on other sites More sharing options...
David Holland 2 Posted March 29, 2021 Share Posted March 29, 2021 Sorry to jump in but I would not recommend dope under laminate. It adheres far better to bare balsa and you stand a good chance of air bubbles under the film if you seal the wood. David Quote Link to comment Share on other sites More sharing options...
David Holland 2 Posted March 29, 2021 Share Posted March 29, 2021 Sorry, Danny, you beat me to it!! Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 Just now, David Holland 2 said: Sorry, Danny, you beat me to it!! No worries, I can be a bit polar with my opinions, it is really good that others respond too, the more the merrier ? fortunately we agree ? Cheers Danny Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 I have been on the full size Auster forum, and they seem a friendly bunch. I wanted to know how the full size was covered around the fin/fuselage area. There is no real structure to form that curve, simply the fabric stretched between the fin leading edge posts and the fuselage top longerons. DB suggested an underlying balsa structure, and that is an obvious way to go, however you know me..... Anyway the good fellows in the Auster group rolled out some fascinating pictures showing how they do the fabric. And I was a little taken a-back at how many ways there are to skin a cat!! Some join fabric in a seam down the fin post. Some fabric the fin post and fus fairing as one piece. I wont bore you with them all, however one chap caught my eye as somebody that has been round the block, and he said you do the entire side, including the fin in one piece! I thought about it and that was a challenge I could not refuse. So...... 2 Quote Link to comment Share on other sites More sharing options...
jrman Posted March 29, 2021 Share Posted March 29, 2021 (edited) That's exactly the way I have covered 3 Piper Cubs (2 1/4 scale and 1 1/5 scale) Easier than it sounds, isn't it? Avatar is one of the 1/4 scale. I used the same technique on a 1/4 scale SpacewalkerII. Edited March 29, 2021 by jrman Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 3 minutes ago, jrman said: That's exactly the way I have covered 3 Piper Cubs (2 1/4 scale and 1 1/5 scale) Easier than it sounds, isn't it? Avatar is one of the 1/4 scale. Lol easy was not the word that sprung to mind, certainly not with Ceconite and dope! I know my errors on this side hopefully put them right on the other ? may even do this side again, have to see how it goes..... Quote Link to comment Share on other sites More sharing options...
Dwain Dibley. Posted March 29, 2021 Share Posted March 29, 2021 Looks like I added a sliver of wood to take the bottom of the covering. You seem to be missing the ply part underneath part 300, apologies if I missed that bit earlier, where you didn't use it . ? D.D. Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 I didnt want the line to show, so didnt use it, its not present on the full size. Quote Link to comment Share on other sites More sharing options...
Dwain Dibley. Posted March 29, 2021 Share Posted March 29, 2021 gotcha. ? D.D. 1 Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted March 29, 2021 Share Posted March 29, 2021 Fascinating stuff. There’s always something to learn. 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 29, 2021 Author Share Posted March 29, 2021 Managed to do the other side, did a better job than the first. But corrected the error on the first, by running another strip of Ceconite from the lower stringer to the bottom. Once tapes are added hopefully it wont be noticeable. Added the first coat of dope. I am concerned about how little this Ceconite is shrinking, and more alarming perhaps is how it is relaxing as soon as it cools. The dope gets the tension back into the fabric, but its still strange. That gap between the tail-plane and the fuselage (as per the full size) has taken a great deal of effort to achieve, but I think it will be worth it. So that's a bit of a milestone I guess, still a long way to go...... 2 Quote Link to comment Share on other sites More sharing options...
Dwain Dibley. Posted March 29, 2021 Share Posted March 29, 2021 Hats off to you old bean. ? D.D. 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 30, 2021 Author Share Posted March 30, 2021 So the polyester resin used to join the cowl halves finally set. It was still a bit tacky last night, but this morning is completely dry. I was nervous that a single layer of tape and resin would be enough to hold its shape, but when the former was removed the shape was nice and rigid. I will add blocks to the front bulkhead so that the entire engine bay area can then be fuel proofed. The single coat of dope has shrunk the Ceconite nicely, I guess that's the way it is best used. And not to worry too much about the soft tension after heat. Three more coats should be enough to fill the weave. I will spray some primer on one of the tail surfaces first and check for pin holes. Cheers Danny 2 Quote Link to comment Share on other sites More sharing options...
Murat Kece 1 Posted March 30, 2021 Share Posted March 30, 2021 (edited) Looks good even without te paint. My Ceconite arrived on a long roll.. I am following you Danny.. I will use it on my next plane.. Edited March 30, 2021 by Murat Kece 1 1 Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted March 30, 2021 Author Share Posted March 30, 2021 35 minutes ago, Murat Kece 1 said: Looks good even without te paint. My Ceconite arrived on a long roll.. I am following you Danny.. I will use it on my next plane.. Thank you ? It has been an interesting exercise for sure. It definitely suits larger airframes, but you will eat your dope supplies. I buy that from LAS by the gallon. Because it uses heat to shrink, and I am using dope to stick, the two do not interact, ie heating/shrinking doesn't loosen the glue, and doping doesn't alter the shrink (until it dries) it doesn't sag the covering at first is my point. I will be interested to hear how you get on. And remember if you want to shrink AND stick (wing tips for example) be very careful using an iron around wet dope ? Cheers Danny Quote Link to comment Share on other sites More sharing options...
Dwain Dibley. Posted March 31, 2021 Share Posted March 31, 2021 Danny, I found this old footage of my auster, and I thought you may like to see it. By all means get the mods to delete it if you don't want it on your blog, I won't be offended. Hope you like it. D.D. 5 Quote Link to comment Share on other sites More sharing options...
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