Simon Chaddock Posted January 19, 2016 Author Share Posted January 19, 2016 Still calm and very grey this morning so try again with just a touch of nose weight (0.3 oz) with the object of getting some better video shots. All going well until......... Despite the high speed impact the Depron monocoque did its usual energy absorbing 'crumple'. You could tell the electrics are OK as the EDF was still running! Repairs already under way. Quote Link to comment Share on other sites More sharing options...
McG 6969 Posted January 19, 2016 Share Posted January 19, 2016 Amazing planning, construction & results, Mr Chaddock. And thinking that I'm just trying to put a Hybrid Depron Ballerina together... Have a quick repair, Sir. Cheers Chris BRU - BE / CTR Depron Gurus Control Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 19, 2016 Share Posted January 19, 2016 I reviewed the video a few times Simon, and it is still not at all obvious what happened. Other than it seemed to simply screwed around in an apparently dive? Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted January 19, 2016 Share Posted January 19, 2016 It was almost as if the c of g was still a bit too far back, although you've already looked hard at that. It is very short coupled, any possibility of the tail being blanketed in some attitudes? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 19, 2016 Author Share Posted January 19, 2016 To be honest I am not too sure myself what happened and I was there! It certainly seemed to roll in to the left and it was actually upside down when it came to rest suggesting a control issue of some sort. As an aside I am not that happy with the radio as I have had to rebind it twice but I suppose it could also be the Tx as it is new and the A4b is the only model in the memory. It is well on the way to being fixed. So - note to self - never mind the camera keep it high until you have really got a handle on its characteristics! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 20, 2016 Author Share Posted January 20, 2016 I made a 1/5 speed a 'slomo' of the actual crash but I am not sure it helps diagnose the problem any, even at full screen! But you can hear the fan hit the casing as a result of the impact! Edited By Simon Chaddock on 20/01/2016 13:27:52 Quote Link to comment Share on other sites More sharing options...
J D 8 Posted January 20, 2016 Share Posted January 20, 2016 You can see aircraft is well banked over just before final decent so wings would have not been giving much lift at that point.John. Quote Link to comment Share on other sites More sharing options...
Stephen Jones Posted January 21, 2016 Share Posted January 21, 2016 It is very hard to see it clearly with the sky being same color as the model .Disorientation maybe ? . Listening to the audio 9 seconds onwards i understand you're disappointment . Steve Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 21, 2016 Author Share Posted January 21, 2016 The structural repairs now virtually complete. One advantage of the stressed skin monocoque is that the stresses at any point are low, it has to be as it is only 2mm Depron, so provided the glue is adequate all the cracks in broken structure can simply be glued back together again. Whilst I cannot be sure the crash was not due to 'thumbs' two of the servos gear trains are a bit suspect. Did a surface stick in an off set position? As all the surfaces move with aileron input any fault is bound to leave a rolling tendency. As the torque effect on launch is not as severe as I expected I decided to simply remove the the lower fin servo and fix the surface. This is no bad thing as the lower fin and 'rudder' gets all the hammer in the belly landings An additional advantage is the loss of the servo wull move the CofG a bit further forward with no increase in weight. A win/win situation! The other suspect elevon servo was replaced. Not exactly a simple jib as the servo and its long wire were completely built in. The next completely new problem was that the Orange RX3SM rx refused to bind at all! This was half expected as it had 'lost' its bind twice already. To remove the Gyro Rx required a further hole to be made in the top of the fuselage. Under test with a non gyro Rx. Nearly ready just needs a touch of lightweight filler and a lick of paint! At least the A4b is doing what was intended - finding out what works (and what doesn't) which should make life that much easier if and when I build another one........... Edited By Simon Chaddock on 21/01/2016 22:19:16 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 24, 2016 Author Share Posted January 24, 2016 Things did not go quite according to plan! I made two very basic errors. 1. After the first rather short flight with minimal control which ended successfully - just! - I did not pack up and go home to ponder on what was wrong but had had another go! 2. With a bit of a breeze and marginal control I made the decision to "bring it back" rather than to get it down immediately before it got too far away. Of course went beyond the range of the 'park fly' radio and it glides remarkably well. It ended up about 500 yds away on a golf course but it does stand out quite well on a fairway! So what was wrong? I strongly suspect it was a mistake to couple the upper rudder as an aileron as it create a positive adverse aileron yaw effect which coupled with the EDF torque meant it would not really turn right! It would probably would have been more controllable if the rudder had been set to be just a rudder! I also suspect some of its control difficulty comes from the fact the symmetrical section wing and tail plane are set "0/0" so the combined surfaces act like a single surface but without the deltas natural longitudinal stability. The 3 axis gyro used in the earlier flight likely gave the illusion of stability. The nose cut back to the original construction joint. Apart from the badly damaged nose all the rest is fine so it will be rebuilt - again - and but a gyro will be included!. Edited By Simon Chaddock on 24/01/2016 23:25:19 Quote Link to comment Share on other sites More sharing options...
onetenor Posted January 25, 2016 Share Posted January 25, 2016 I thought deltas needed a reflexed trailing edge or upset elevators to be stable Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 25, 2016 Share Posted January 25, 2016 I do not see a delta. I see a low aspect ratio, swept wing. A short coupled tailplane. I also see a unusually long nose/fore body, relative to the rest. It could be that the inertial effects, could cause issues with respect to extreme manoeuvring, in conjunction with the other features. Then again, it could something completely different. The full size assembly will not have been expected to do anything beyond flying pretty straight and level, I would have thought. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted January 25, 2016 Share Posted January 25, 2016 It reminds me of the shenanigans I had when making my small edf Supermarine Swift. I made a chuck glider first and it had some strange divergent habits. That too is very short coupled with overlap between the swept wing and tailplane. In the end I completely cured it by treating it as a delta. I reflexed the ailerons up by a few degrees and suddenly it was transformed and flew really well, with none of the strange divergent, inertia coupling habits it had previously. I broke the fan a while ago by running it up on the bench and pulling in some f.o.d! One day I'll fix it and fly it again. I think it would be the solution on the V2A4 as well. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 25, 2016 Author Share Posted January 25, 2016 To be fair I did not say it was a Delta but that it has all the surfaces at the same incidence datum like a delta with no reflex. The elevator surfaces do provide some reflex but they are pretty small when compared to the combined area of the wing & fixed tail. The set of the new nose formers. The plan is to add the scale extensions to the elevon surfaces (it adds 50% area) and to connect the rudder as just a rudder. By far the hardest job will be cut the one piece wing free and reposition it with about 2 degrees incidence relative to the tail surfaces. Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted January 25, 2016 Share Posted January 25, 2016 Simon, I can't explain why, but I wasn't able to cure the problem on the Swift with the elevators, I set the tailplane to zero with the wing and adjusted the aileron reflex to set the longitudinal stability. Once I'd done that the elevators still worked as elevators and the ailerons as ailerons, although they were zeroed at a few degrees negative. I know that you're using your elevators as tailerons, you're probably right about leaving the top rudder as just as a rudder because of the adverse yaw issue. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 25, 2016 Share Posted January 25, 2016 The model can be considered to be extreme in its layout, it could be reasonable to accept that the proportions are such that the generally accepted range of manoeuvres are not within the remit of the model. In essence flying in straight lines, making conservative changes of direction are not only scale like, but recognise the characteristic flight envelope of the model. Knife edges, looping are probably not well suited to the model. Just like my PZ does not do inverted flight, preferring to tip stall, with the slightest excuse. Also another model, I would not expect to either knife edge, or prop hang. Just not in its flight envelope or remit etc. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 26, 2016 Author Share Posted January 26, 2016 Colin With a tail plane and elevator (particularly if it is small) it is quite possible to get in a situation where the up elevator required to generate the AOA on the wing causes the elevator to be virtually 'blanket' the tailplane itself. Altering the tailplane incidence so that it is 'normal' to the required airflow restores both the elevator effectiveness and the planes stability. Just as an aside it was not until the Mk4 Swift that a variable incidence tailplane was introduced to cure its unpredictable handling characteristics! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 26, 2016 Author Share Posted January 26, 2016 The Mk3 nose started. This the "wobbly" stage. Very carefully adding the formers making sure everything is lined up true. Eventually all the formers are in so the planking can commence. My intention is to install the ESC and fit the battery box as I go along rather than cutting a big hole and inserting it all afterwards as I did on the previous two noses! Edited By Simon Chaddock on 26/01/2016 17:49:07 Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted January 26, 2016 Share Posted January 26, 2016 Simon, you're right about the Swift Mk4 and all-flying tailplane of course! There's something different here though, the reflex on the swept wing has some stabilising effect beyond my expectations. There's little doubt that if I removed the tailplane completely it would make a perfectly good flying wing, although then the ailerons would have to function as elevons. Good luck with Mk3. Just keep your fingers crossed that next time you land on the golf course, someone doesn't call out Bomb Disposal! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 27, 2016 Author Share Posted January 27, 2016 Colin As far as I can tell the Mk4/5 Swifts still had elevators and used the moveable tailplane just for trim so were able to do away with the elevator trim tabs. Today's modification - altering the wing incidence. The wing was separated from the fuselage top and bottom and both sides, the fuselage cut away below to drop the trailing edge by 6mm. Depron blocks hold the wing down in the new position whilst the glue dries. The skin and the formers above the wing will then be made good. Nothing special about choosing 6 mm - it simply looks about enough! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 29, 2016 Author Share Posted January 29, 2016 Only modest progress as there doesn't seem much rush with what seems like the never ending rain and 50 mph winds! The battery box and ESC installed in the Mk3 nose before the planking progresses too far. In fact to leave access to reconnect the motor wire bullets the nose will have to be glued in place before the planking goes much further. I now have a new stand alone 3 axis gyro which has the ability to be remotely switched between off, rate mode and heading hold mode. If I ever get round to building a true vertical capable version I would hope that full heading hold would provide sufficient stability to allow a scale speed lift off or at least a true scale loss of control and spectacular crash as in the original video! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 30, 2016 Author Share Posted January 30, 2016 The incomplete nose glued on to the remainder of the airframe. Once the electrics are tested (again!) the planking can be completed. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 1, 2016 Author Share Posted February 1, 2016 The next change is to increase the size of the horizontal control surfaces to about scale. These work as elevons in a true 'bank and yank' mode as the vertical surfaces will be fixed.. The final question as yet undecided is whether to risk the next flight without a gyro assist! It is on order but not yet delivered. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 3, 2016 Author Share Posted February 3, 2016 The extended elevons under test. With both the fin servos removed the CofG has moved forward a bit which should help to counter the effect of the 1.5 degrees wing incidence that has been added. Removing the servos, wiring and mixer unit has also saved a bit of weight - about 20g. Not much but every little helps! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted February 3, 2016 Share Posted February 3, 2016 I'm really interested to see what happens next! Quote Link to comment Share on other sites More sharing options...
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