Nigel R Posted July 17, 2017 Share Posted July 17, 2017 One thing I've seen done in the full size world is to laminate the solid section. That way, if a weak point causes a failure, it is restricted to a single lamination and the structure as a whole survives to get you down. Although the aim there is really to save your life more than anything else, as the spar structure is at that point defunct and needs replacing. I wouldn't laminate a 1/4 plank tail, but my route would be a hard 1/4" x 1" wide strip along the hinge line, it does a decent job to provide a spar-like element to the tail without much weight gain over a med-soft plank. Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted July 17, 2017 Share Posted July 17, 2017 Absolutely guys - I've used 1/4" sheet for years on anything up to 46 powered models with no problems - maybe even 61, can't quite remember what my old Gangster 63 was. I used medium to hard sheet, made up of 3 pieces, one rectangle and two triangles for the LE, so if I had a bad joint between the two triangles there is the potential for a stress concentration there Certainly I will be looking for stress concentrations due to careless trimming. It occurred to me I did have trouble with errant cyano locking my pushrods and fairly brutal surgery was required in the are below the TP to sort it - it maybe the mount has failed rather than the Tailplane itself - it's not loose exactly, it just seems that one side can be moved up and down a little rather more easily than I would expect. Let you know what I find. Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 17, 2017 Share Posted July 17, 2017 Maybe you got into some odd resonance situation where the tailplane was able to buzz about? Out of interest, I presume the crack was external to the fuselage? Keep us posted anyway! Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted July 17, 2017 Share Posted July 17, 2017 There was no hint of flutter or anything like that Nigel, just a sharp crack.. And there is no obvious crack external to the fuz either, although I have yet to cut into it - been a bit down from the Radiotherapy I'm going through, TBH, kind of drained and lacking in enthusiasm for anything. Ends this Thursday though, so onwards and upwards.... Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted July 23, 2017 Share Posted July 23, 2017 So.. the plot thickens I removed the rear fuselage floor and had a good look at the tailplane. The TP itself was sound, the problem seemed to be a crack in the fuz sides - so, amendment, anyone building one of these might like to consider fitting Tailplane seat doublers or a bit of reinforcement under the TP mount. I flooded the area the area with cyano, then filled it solid with block balsa - nothing is moving down there now boys. So, took it up to the field yesterday - beautiful afternoon, no wind, clear blue skies. Took off fine, but t needed a lot of down trim, and at speed, flutter could clearly be heard, so landed and diagnosed a slightly loose elevator horn, nipped the bolts up and tried again. Again, massive down trim was required, to the extent I ran out of trim and felt I needed to land as a matter of urgency, there being no wind I elected to come in on the short strip, having made my fellow flies aware, and commenced the approach. As I cleared the fence (as I thought...) I cut the engine, but missed the switch, looked down, and well, we all know what happened next. The barbed wire caught it, stopped it , and flung it a couple of yards back into the adjacent field. On recovery it looks fine from the top, but the underside of the wing looks like its been hit with a shot gun. The feeling was thats its a simple repair, but I don't like repairing... I can now only think I had a problem with my elevator linkage, maybe the (metal) clevis jumping on the threads? Let you know when I am sure. To top off a perfect weekend I took my 80% Challenger out today, and managed to sieze the engine.... I guess I've had better weekends, but I'm sure I've had worse ones too. Quote Link to comment Share on other sites More sharing options...
Martyn K Posted July 24, 2017 Author Share Posted July 24, 2017 Err Regarding the Fus, a doubler is shown on the plan from just to the rear of F6 to the tailpost.. I agree - dont skip it Regarding your clevis. Just check you havent put a UNC (Goldenrod) clevis on an M2 rod... Martyn Quote Link to comment Share on other sites More sharing options...
Nigel R Posted July 24, 2017 Share Posted July 24, 2017 re: doublers on tailplane; some vertical grain balsa was always my poison, usually dug out from the scrap box. re: crack, was the crack in both fuse sides or only one? re: flutter on the elevator, could be all sorts - let us know what you find... Edited By Nigel R on 24/07/2017 09:42:30 Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted July 24, 2017 Share Posted July 24, 2017 Posted by Martyn K on 24/07/2017 09:22:01: Err Regarding the Fus, a doubler is shown on the plan from just to the rear of F6 to the tailpost.. I agree - dont skip it Regarding your clevis. Just check you havent put a UNC (Goldenrod) clevis on an M2 rod... Martyn My mistake Martyn, don't know how I missed that - I guess I proved it's necessary! My pushrod is a carbon rod with M2 threaded rods bound and cyanoed to both ends, M2 clevises and appears to be perfectly solid and slop free, but I did have an issue with one of these clevises slipping on the threads once before - thought I had dumped the entire batch of clevises and rods, but maybe not. Once I have my models properly trimmed I usually lock the clevises with a drop of Cyano too, but I hadn't got round to that either. Challenger is now sporting a nice, new Irvine 36 and the KF is being prepped for surgery after I do a bit more on my Bullet. Quote Link to comment Share on other sites More sharing options...
Trevor Posted August 16, 2017 Share Posted August 16, 2017 It's gone a bit quiet here. Has anyone else got one of these on the board at the moment? Ive just printed off the plans for the IV-40 and am aiming to build the electric version over the Winter. I'm getting the shopping list together at the moment but have a rule that Winter builds can't start before September so I'll have to restrain myself for a few more weeks! The build will be documented on my website (Bartonhewsons.uk) but I'll put a posting on here when the project gets underway. Cheers Trevor Quote Link to comment Share on other sites More sharing options...
Trevor Posted October 3, 2017 Share Posted October 3, 2017 Okay, the Kwik-Fli build is now underway. As promised, here is a link to my build diary: http://www.bartonhewsons.uk/home/modelflying/sport/kwikflidiary.html My thanks to Martyn for making this available. Trevor Quote Link to comment Share on other sites More sharing options...
Martyn K Posted October 3, 2017 Author Share Posted October 3, 2017 Nice build blog Trevor. Are you building the KF3 or KF4 variant? Quote Link to comment Share on other sites More sharing options...
Trevor Posted October 3, 2017 Share Posted October 3, 2017 I’ve gone for the tapered wing, on aesthetic grounds. I’m just hoping that, with the added weight of the retracts, it won’t be too ‘flicky’! Whilst the main gear has gone in okay, fitting the nose retract in ahead of the wing and under the battery tray is going to be a bit of a squeeze. I’m not sure yet where the ESC and steering servo are going to fit! Trevor Quote Link to comment Share on other sites More sharing options...
Martyn K Posted October 3, 2017 Author Share Posted October 3, 2017 Should be OK. I would be inclined to lock the nosewheel. Mine will steer quite adequately for take off an landing although taxiing is a bit difficult. You will need a bigger battery than I used, the 3000 4S I used is too small, a 3800 4S would have been better Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted October 3, 2017 Share Posted October 3, 2017 Good Luck with it Trevor. Mine - albeit just under 3lbs has absolutely no bad habits at all, certainly no flickiness. It's back up and running again, well enough to get 3rd at the Huddersfield meet a few weeks ago. Build it as martin drew it and I'm sure you will love it. It does have a rather large elevator and I think it is worthwhile paying attention to the security of the wood and linkages. Mine now has ply spreader plates top and bottom for the horn, and if I were building another I would think about twin pushrods too. Sure you'll love it! Cheers Tim Quote Link to comment Share on other sites More sharing options...
Trevor Posted October 3, 2017 Share Posted October 3, 2017 Thanks for the feedback. 3lb seemed an ambitious target Tim, then I looked back a page and noticed that in July you gave the weight as just under 4lb. Is 3lb a typo or has it been on a crash diet? Martyn, I'm surprised at your comment about battery size. 4s x 3300mah is one of my 'standard' battery sizes - see Stearman (58in, 5lb 4oz), Comet (80in, 6lb 4oz), Capiche 50 (56in, 4lb 3oz), Chorus Gull (62in, 5lb 14oz), Chipmunk (75in, 5lb 11oz) and Aquabird (60in, 4lb 3oz) - all of which give reasonable flight times without running the battery too low. Admittedly, none of these has quite such a thick section as the Kwik-Fli, but I still would hope to be able to set the flight timer to at least 8 minutes. Am I being too optimistic? Quote Link to comment Share on other sites More sharing options...
Martyn K Posted October 3, 2017 Author Share Posted October 3, 2017 I have a 3000mAH battery in the nose of mine - and quite a lot of lead to get the CG right.. I would rather go for a heavier battery and take the lead away. I use a 11x8 prop. This seems about right for the model and I get 5-6 minutes of throttle % timer with that. I would prefer to use an 11x10 prop (if the system will cope with that without letting the smoke out) - in which case a higher capacity battery would be essential. A lot depends on how you fly though. With my setup, its not a fast model compared with the ic powered KF3-40 but it has reasonable vertical performance. Dont worry about the thick section. Surprisingly, it adds very little to the drag bucket Quote Link to comment Share on other sites More sharing options...
TIM Shaw Posted October 3, 2017 Share Posted October 3, 2017 Posted by Trevor on 03/10/2017 16:44:10: Thanks for the feedback. 3lb seemed an ambitious target Tim, then I looked back a page and noticed that in July you gave the weight as just under 4lb. Is 3lb a typo or has it been on a crash diet? Oops sorry my mistake, typo it was. Quote Link to comment Share on other sites More sharing options...
Trevor Posted November 4, 2017 Share Posted November 4, 2017 Here we are - another month has gone by. And what an unseasonably good month for flying weather it was - I chalked up twice as many flights for October as in September. As you've probably guessed, that preamble is by way of an excuse about the limited time I've put in at the building bench, but there is nevertheless some progress to report: October Build Diary Entry Trevor Quote Link to comment Share on other sites More sharing options...
Trevor Posted December 3, 2017 Share Posted December 3, 2017 Well, another month, and I could repeat the preamble - another record flying month. Subjectively I don't feel it's been a particularly special Autumn, but the flight log suggests otherwise. Nonetheless, some good building progress has been achieved. The diary entry for November is here: November Build Diary Entry Tim, I'm afraid I'm not going to be able to match your 4lb all up weight. I blame it on the retracts! Trevor Quote Link to comment Share on other sites More sharing options...
Martyn K Posted December 3, 2017 Author Share Posted December 3, 2017 That's looking really nice Well done. Did you put any doublers around the tailplane. It does need them.It will be interesting to see what the AUW ends up like. Keep up the good work. Nice build blog. Sadly, I am sorry to say that Tim passed away last month.Martyn Quote Link to comment Share on other sites More sharing options...
Trevor Posted December 3, 2017 Share Posted December 3, 2017 Thanks for the encouraging words Martyn. I think the tail doublers you mention are visible in the fourth picture on the page, and referred to in the text alongside - unless I’ve missed something?! As of today, the the model weighs just 3lb without battery. I still have the front hatch and cowl to build and the underside of the fuselage to sheet in, plus some bits and pieces to secure the battery, ESC etc. So, with a 4s 3000mah battery on board, I expect to reach 4lb with the covering still to do. Hopefully it will end up around 4lb 8oz AUW. I didn’t know him, but I was very sorry to hear of Tim’s passing. Trevor Edited By Trevor on 03/12/2017 19:18:56 Edited By Trevor on 03/12/2017 19:19:49 Quote Link to comment Share on other sites More sharing options...
Trevor Posted January 1, 2018 Share Posted January 1, 2018 Hello All. The December diary entry of my Kwik-Fli IV build is now online: Kwik-Fli December Diary. I do feel that I’m on the home straight now. In contrast to Martyn’s prototype, my model has come out nose heavy. This has meant that a bit more thought has had to go into the battery stowage and access arrangements but, since the battery sits more or less over the cg, at least variations in battery weight should have little or no effect on the trim. Another benefit is that the ESC, which was displaced from its intended home by the nosewheel retract, can now sit on the vacated battery bay floor, just behind the motor. Happy New Year to all, and may your landings tally keep up with your take-off total all year long. Trevor Quote Link to comment Share on other sites More sharing options...
Martyn K Posted January 2, 2018 Author Share Posted January 2, 2018 Nice progress Trevor Not sure why yours has turned out nose heavy. The retracts will add a bit of weight but I wouldn't have thought that much - and certainly lighter than a LiPo.. You must have used helium infused balsa for the tail surfaces Nice colour scheme by the way Martyn Quote Link to comment Share on other sites More sharing options...
Trevor Posted January 7, 2018 Share Posted January 7, 2018 Martyn, I did relocate the rudder and elevator servos to the wing bay and the firewall did have to move forward a fraction to accommodate the retracted nosewheel so both of these mods will have contributed to the forward cg. However, like you, I was very surprised to see that it had shifted as much as it has. I got the control surfaces hinged today and it's always good to see all the flappy bits moving. I had a quick look over the plans and through the earlier pages of this thread but didn't find any guidance on control throws other than that you felt the need to tone them down a bit after your maiden flight. Do you have any recommended figures? If not, they will be set by the well known TLAR method! Trevor Quote Link to comment Share on other sites More sharing options...
Martyn K Posted January 8, 2018 Author Share Posted January 8, 2018 Ho Trevor, I'll power up the KF IV and measure the throws for you Martyn Quote Link to comment Share on other sites More sharing options...
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