Mark Kettle 1 Posted January 22, 2015 Share Posted January 22, 2015 Nice Simon, nice model good luck when you fly it. Quote Link to comment Share on other sites More sharing options...
Electriflier Posted January 22, 2015 Share Posted January 22, 2015 Another work of art from Mr Chaddock - good luck on the maiden Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 24, 2015 Author Share Posted January 24, 2015 I was concerned that the paint weight would have shifted the CofG aft so I taped on 0.3g of nose weight to bring the CofG to 30%. It was calm enough this morning for its maiden. Just two short circuits as it was still seriously tail heavy. Rather than add more weight which would effect the performance it was obvious that the battery just had to be moved and quite a bit at that - about 3". At the moment the battery slides forward from the hatch and is almost completely 'buried' in a box. Technically it would be possible to extend the box so the battery could be pushed forward still further but obviously it would have to be puled out by its leads! . A bit of surgery. A big hole in the lower skin where the battery has to end up. The battery box extended 3" carefully matching the existing. The cut out fuselage skin glued back in. A bit of filler and a paint touch up and its done! The CofG is now at 27% with no nose weight. That's 2% further forward than it was for its maiden with the nose weight. Hopefully a video next flight. The only real disappointment so far is the 3 axis stabiliser. Even with the sensitivity turned right up it only moves the control surfaces a very small amount (less than the 10% trim movement) even with the most violent movements. It can be switched off from the Tx so once I have the Canberra flying properly I can see how effective it really is. Quote Link to comment Share on other sites More sharing options...
Toni Reynaud Posted January 25, 2015 Share Posted January 25, 2015 This video might be of interest. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 27, 2015 Author Share Posted January 27, 2015 I also wondered about its decalage - the angle between wing and tailplane. Following scale I set the tailplane parallel to the fuselage datum however the wing has significant incidence. I fear the CofG would have to go a lot further forward to compensate. Perhaps it would be simpler to fly with less wing incidence. To physically alter the wing incidence would require virtually rebuilding the whole plane but the tailplane incidence could be changed by cutting it free from the fuselage, increasing the size of its the slot and making good with tapered inserts. The tailplane leading edge has been raised by about 3 mm. Now just need some suitable weather. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 28, 2015 Share Posted January 28, 2015 I am not sure there is a problem, other than if the incidence/angle between the two surfaces is to large, you either need to trim the tailplane with up or down trim to achieve level flight. Not good news I agree, in that the drag from the tail surfaces are now higher than ideal. Perhaps the one incidence that matters a little more, is the wing to body, as this determines the sit of the model in the direction of flight, either being nose high or low. Again with a drag penalty. But as we know, the ideal sit occurs only at one speed. As long as we are not extreme with our incidence, more an academic point on a model aircraft, than a major issue. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted January 28, 2015 Author Share Posted January 28, 2015 Erfolg My concern was not so much the drag from the down elevator required but the fact that the tailplane becomes an under cambered lifting surface. The wing on the other hand is a truly symmetrical section. In this sort of condition there is a real possibility it can become longitudinally unstable with speed hence my desire to get it to fly with the elevator 'neutral' with the tail plane but without adding weight. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted January 28, 2015 Share Posted January 28, 2015 From real experience of flying models, many of which you will have seen with the elevator either pretty much permanent up or down trim permanently set, have any caused pitch problems from observation. I have experienced problems from poor linkages with gliders at speed, where the push rod has deflected, allowing more down trim due to the deflection, hence even more speed. I do not think I have been aware of pitching moments due to camber and speed on the tailplane being an issue with RC models. Although we did see many what appears to be now strange tailplanes with FF and in the early days of RC, from cambered tailplanes, as per the wing or inverted. Of course i have to ask how fast do your DF models get? Now having changed clubs, I see a lot of fast DFs, non of which seem to have any control issues at speed, or when slower. One of the nicest I have seen, is a U2, which flies like a glider. I think you are possibly overly concerned, due to your experiences with the rearward CG, which we all know causes heart stopping moments, particularly if not dead calm. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 3, 2015 Author Share Posted February 3, 2015 Weather was calm enough this morning to give the Canberra another go with the tailplane incidence altered. Still a bit tail heavy as I had not pushed the battery as far forward as it should have gone but it seemed to fly reasonably well. The rather erratic approach was to do a pancake landing to minimise damage to the battery hatch which had opened and was hanging down. It seems to have sufficient thrust and should be a bit less twitchy with the battery in its most forward position. Quote Link to comment Share on other sites More sharing options...
Toni Reynaud Posted February 3, 2015 Share Posted February 3, 2015 Congratulations, Simon. That looks remarkably good once it's flying stably. Very scale appearance for something so small. Another masterpiece! Time travelling too - all done six years ago accoring to the date in the corner! Toni Edited By Toni Reynaud on 03/02/2015 06:11:32 Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted February 3, 2015 Share Posted February 3, 2015 It looks the part, doesn't it? Sounds it as well! You keep on proving that you know exactly what you're doing Simon. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 3, 2015 Share Posted February 3, 2015 Congratulations Simon. I was amused at the frantic button pushing (the trims), as I think we have all been there. I think you are spot on that the CG is to far back. I am intrigued at what the wind speed was. Another personal aspect, I could not have coped with a black model, I would have gone for the Orange or yellow striped versions.That is because I have a need to see a model clearly, particularly if it is doing its own thing from time to time, I start doubting that what it should be doing in my opinion (the sticks) is the same as to what is happening. One of our club members must live within a mile of you, he lives near the canal, not far from the cross. I know I missed you last time you came to our club, and I know that the BMFA membership is an issue for you (that is your right), I would still like to see some of your models flying either at I assume the High scholl playing fields or at our club site as a casual learner visitor. Perhaps one of your next outings? I must confess that the Canberra is one of the few (which include the MB aircraft, Helston racer, Spiteful) UK aircraft I have wanted to build and was most certainly outstanding. Although in my case i am attracted to the USA (Martin) version, mainly because the engines being much bigger in diameter and the extra wing area. Well done again, now what you need is more power. bigger battery and strengthened wings. What, It wont fly as well Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 3, 2015 Author Share Posted February 3, 2015 Erfolg Just a point but as a BFMA county member so I do have insurance. I would certainly like to fly as a casual visitor at your club. I will PM you. There was very little wind on the day of that video but then even 2 or 3 mph is quite significant on a plane that can fly at just 5 or 6! Toni My 808 managed to lose the time and date and now stubbornly refuses to reset it despite going through exactly the same routine as I used to set it in the first place! With a bit of nose weight the Canberra is now flying a bit better (video to follow) so I will completely rework the battery box again to move the battery still further forward. Quote Link to comment Share on other sites More sharing options...
Andrew Price 2 Posted February 3, 2015 Share Posted February 3, 2015 Simon. That looks great. The last Canberra I saw was at RAF Marham, probably 5/6 years ago. It looked as good as when I first saw one, at Farnborough, many years ago. They all looked good, as does your fantastic model. Well done You. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 3, 2015 Author Share Posted February 3, 2015 As promised today's video. Better but it still needs the battery moving still further forward. It will mean a new hatch but in some respects it will be structurally better as it will remove the current hatch which creates a weak point in the fuselage.. Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 3, 2015 Share Posted February 3, 2015 Yep, it still seems to have a phugoid (when landing), or is that elevator stick induced? Was this the reason you were considering altering the incidence between the tail plane and wing? I guess you had thought that a inverted camber tail plane was also a potential attenuator? I have seen it on early RC models, although i thought to get planes to self pull out of dives, when the controls were neutral. If it is is a phugoid, the model is not as slow as some FF models that could be seen exhibiting the trait. I do not think i have seen one (if that is what it is) with a RC model. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 3, 2015 Author Share Posted February 3, 2015 Erfolg I suspect the CofG is very close to being unstable, particularly at low angles of attack.. You can see in the video just the slightest touch of up elevator produces a very pronounced pitch up yet at slow speed and higher angles of attack it is nothing like so 'twitchy'. The tiny radius of the loop (and it was not even full up!) would also indicate a rearward CofG. It was a similar problem on landing. The approach was reasonably constant but as it got close to the ground I expect I instinctively pulled back a touch and it ballooned up probably made worse by the ground effect on the Canberra's broad low aspect ratio wing. Modifications under way to provide a new battery position & hatch much nearer the nose. The battery lead will have to be extended and then the old hatch can be sheeted over maybe leaving just a small hatch over the radio just in case it has to be rebound. On 35meg crystal sets I was quite happy to completely build in the rx! Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted February 3, 2015 Share Posted February 3, 2015 Looks to fly o.k. to me Simon, like you say elevator seems sensitive John Quote Link to comment Share on other sites More sharing options...
Erfolg Posted February 3, 2015 Share Posted February 3, 2015 You could have always have tried strapping some lead on, in various amounts to see what happens. A rearward CG is always a mistake. When I restarted modelling (with electric gliders), I initially tried to fly my models with a rearward CG, (33%) to avoid any lead ballast, as I knew the models had already gained a little wiight. A bad error, as the models would be unstable in pitch with the slightest disturbance. I now fly with the CG no further back than 30%, makes all the difference. I have had something similar, although not on the same scale, when trying to fly to near the stall, when landing, trying to stop it in the air, a little more speed, no problem. Although in my case, the period of one cycle a lot longer, relatively easily killed with a dash of down and adopting a "S" type approach. Although, you seemed quite fast, in the approach, so probably different. I think the CG move will make all the difference. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 8, 2015 Author Share Posted February 8, 2015 The revised battery position. .Just a long thin 'slot' for the battery that is a good 2" (50mm) further forward. There is a small hatch over the radio for re-binding if required. The revised CofG certainly improved the flight characteristics considerably enough to give confidence for so low passes for the camera.. It is still pretty 'twitchy' on the elevator to the point where it seems to want to pitch up or down significantly with even the slightest elevator movement yet it is no worse when more movement is applied. This got me wondering about the substantial scale elevator aerodynamic balance and the effect it might be having on the rather flexible Depron elevators. With the new forward CofG it is flying with the elevators exactly 'neutral' whereas before they were significantly down. Does this now mean that with the slightest elevator input the aerodynamic balance was twisting the outer part of the producing a stronger effect than the actual input from the control horn at the elevator root? I could build new stiffer elevators but the simple test is to simply cut off and fix the aerodynamic portion of the elevator directly to the tail plane. No longer scale but if it has the desired effect (but too foggy at the moment to fly) then it will be worth building new stiffer elevators. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 10, 2015 Author Share Posted February 10, 2015 As I hoped the revised elevator has really made a difference to the handling. It now flies really smoothly especially with the elevator low rate set at 80%. An edited video of this morning flight in cold, damp but almost still conditions. The 3 axis gyro was not switched on. Just a bit of paint touch up and its done! Quote Link to comment Share on other sites More sharing options...
Colin Leighfield Posted February 10, 2015 Share Posted February 10, 2015 Excellent Simon. Quote Link to comment Share on other sites More sharing options...
Ian101 Posted February 10, 2015 Share Posted February 10, 2015 Yes, excellent. Looks like it flies really well now you have sorted it. The way you build is fascinating and very educational. Ian Edited By Ian101 on 10/02/2015 22:04:08 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 10, 2015 Author Share Posted February 10, 2015 Thanks for the kind words. In truth I am rather embarrassed as when I put the Canberra's figures into a CofG calculator the suggested position is more or less exactly where I currently have it!. I could have saved myself quite a bit of bother! Quote Link to comment Share on other sites More sharing options...
chris Ibbotson Posted February 11, 2015 Share Posted February 11, 2015 Simon, I've being following your build with interest. Your videos are a great testament to you and your diagnosis and correction of the flying qualities of the aircraft are superb. As you know I am in the process of building a 74" depron (1/10th scale) Canberra B2 (on hold due to radical surgery on my leg, about 3 months). I have a question to ask if you don't mind. Do you put your "twitchy" Canberra (forget C/G) down to a "flexible" depron elevator that you built or do you advocate adapting/converting the elevator as you did? Thank you for a fantastic build and looking at the last video she flies like a dream. Regards , Chris Quote Link to comment Share on other sites More sharing options...
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