Simon Chaddock Posted November 18, 2012 Share Posted November 18, 2012 A couple of days ago I managed to fly my 40" Depron 'Endurance' for 2 hours and 5 minutes. (see Field Tales) I felt it had a bit more to give but repeated 2+ hour flights to find out would be tedious and extremely boring to do so I created my 'ballast' battery. The same weight and size as the 5000mAh one but only 1/5 the capacity. Flew this afternoon, took it right down to the LVC and it managed an amazing 38 minutes! This would suggest, all things being equal, the 5000mAh one should be good for 38x5 = 190 minutes or just over three hours. And that's without the possible aerodynamic improvements I have in mind. So what are they? First the prop. The chances are small that the basic 7x6 'slow fly' prop I am currenttly using is the most efficient there is, particularly at the very low power levels being used (<15W!) Second the airframe. The fuselage is already light and just battery 'size' and with its pod and boom layout it has about the minimum practical cross section and surface area. Little scope for improvement The wing is also very light so any further weight saving is likely to be marginal. The wing section is a standard Clark Y. Whilst on paper other sections are more efficient there is evidence that at very low Reynolds numbers the aerodynamic streamlining and thickness to chord ratio are the predominant factors rather than its detail profile to achieve the maximum lift to drag ratio. Next is the wing tip shape. The Endurance has simple square cut tips with a small fairing. The current trend is for significantly raked and up swept tips which, in theory at least, improves efficiency by reducing the size of tip vortex. It will be relatively easy to add and test this sort of tip extension. Heaven forbid I should get close to 48 minutes on 1000mAh as this would represent an endurance of 4 hours! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 19, 2012 Author Share Posted November 19, 2012 The ballast battery. During the endurance test flights the 1000mAh battery will be always taken to LVC. This will likely shorten its life quite quickly (just as well its cheap!) so it is only held in place in the pack by double sided tape. The current prop, a very slightly trimed 8x3.8, has been replaced by an 8x4.3 again with 1mm taken of the very tip to clear the boom. The slightly coaser pitch should improve the minimum power cruise but I fear any benefit may be so small that it will be difficult to measure against all the other variables that could effect the duration of a 38 minute flight. The new raked wing tip alongside the original simple tip fairing. I am not sure about this. The tip adds 4" to the span, looks nice and in 2mm Depron only weighs 3g but that is still 7 times that of the original fairing! Its all going to come down to drag reduction versus weight. I will resist adding these tips until I can confirm any benefit of the new prop - only change one thing at a time! Edited By Simon Chaddock on 19/11/2012 13:21:26 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 21, 2012 Author Share Posted November 21, 2012 Pretty calm this afternoon so another go with the 'ballast battery' in the Endurance but with the coarser pitch prop. Launch 15:11 Land 15:54 43 minutes Thats equivalent to 3hrs 35 minutes with the full 5000mAh battery. At 43 minutes the average discharge is 1.4A. If we say the average voltage is 8.2V then it is flying on 11.4W. It must be nearer 11W when the radio and servo loads are taken into account. If the raked tips are as effective in improving performance my 4 hour target could really be in reach! Edited By Simon Chaddock on 21/11/2012 17:07:17 Quote Link to comment Share on other sites More sharing options...
Radge Posted November 21, 2012 Share Posted November 21, 2012 Well done Simon! Very interesting. 4 hours? You'll really have to do some prep for that, weather forecast, etc. Quote Link to comment Share on other sites More sharing options...
fly boy3 Posted November 21, 2012 Share Posted November 21, 2012 Might have missed it but any pics. of this model, and do you use a deck chair for these record attempts. Congratulations Quote Link to comment Share on other sites More sharing options...
WolstonFlyer Posted November 21, 2012 Share Posted November 21, 2012 Nice design of plane for long flights Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 22, 2012 Author Share Posted November 22, 2012 I very much doubt I shall actually attempt a 4 hour flight. I will be happy if I can demonstrate the potential for such a thing by flying for 48 minutes on the 1000mAh ballast battery. It might then be interesting to go back down again and see what performance can be achieved within a 1 hour duration. Quote Link to comment Share on other sites More sharing options...
Simon Chambers Posted November 23, 2012 Share Posted November 23, 2012 You know what, with that sort of power consumption, I bet your nearly at the level where you could power the whole thing off solar cells. Si. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 24, 2012 Author Share Posted November 24, 2012 Simon C Yes quite likely,but if you look at the price of high power light cells........per Watt about 100 times the cost of a LiPo! Not yet a cost effective alternative - for me anyway! Quote Link to comment Share on other sites More sharing options...
riverlandgirl. Posted November 24, 2012 Share Posted November 24, 2012 Impressive, Cross country electric flights are a reality! I wonder if that duration would even be achievable on a gassie, Might have to look into it... Quote Link to comment Share on other sites More sharing options...
Tony Bennett Posted November 24, 2012 Share Posted November 24, 2012 they crossed the Atlantic with a gassie so i would think yes. simon, what about using 1 solar panel as a trickle charger for the battery while in flight. you could then go for 24 hours during the summer. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 24, 2012 Author Share Posted November 24, 2012 Ideal conditions this morning, calm and cold, very cold! With the new raked wing tips launched at 8:52, landed at 9:53. This means the Endurance now has the capability to fly of not 4 but 5 hours! At such a low current the LVC point is very 'woolly'. I suspect it started to have an effect on the motor after about 45 minutes. You could hear the motor speed fluctuating slightly. At 55 minutes the motor had slowed a bit but even so the planes descent was very slow so I just let it carry on. At 60 minutes advancing the throttle made no difference to the power at all so it really was time to land before the radio & servos started to be effected. The Endurance flies very, very slowly so I suspect any 'cross country' could only be down wind! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 24, 2012 Author Share Posted November 24, 2012 The Endurance always seemed to fly with a slight off set on the ailerons which I had put down to some 'built in' aerodynamic defect although the wings looked true to me. When I held the wing up to the light I noted that the inner ribs were not symmetrically placed about the fuselage centerline. It looked almost as if the one piece wing was fixed off centre. Surely not! Oh yes it is, by 5mm. Oooops! how embarrassing a beginners mistake no wonder it flies with the ailerons off set. I really should put it right but it will be quite a bit of work as the motor would have to be repositioned as well but it does seem to manage ok as it is! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted November 27, 2012 Author Share Posted November 27, 2012 Having though about it for a few days rather than remount the wing in its correct position along with moving the motor by far the simplest was to shorten the 'long' wing! This only required the complete tip section cutting off (taking care not to cut the aileron servo wire!) removing a bit from the centre section and glueing the tip back on. As the tips were only glued and taped on in the first place no strength will be lost doing this and I think I can afford the slight loss of wing area! Not having a permanent off set on the ailerons should decrease the drag a bit. A heading hold gyro? But would the power saved in reduced servo movement compensate for its own power consumption and weight? Quote Link to comment Share on other sites More sharing options...
Radge Posted November 27, 2012 Share Posted November 27, 2012 Good intelligent thought process and solution Simon, hope the adverse aileron problem is solved. Have a Radgepat on the back chap. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted December 2, 2012 Author Share Posted December 2, 2012 I have flown the Endurance twice more since correcting the wing and in terms of how it flies there is not one jot of difference! It does need a bit less aileron off set but a small amount is still required so the wing probably does have a slight 'built in' twist. Both these flight were in more normal conditions with perhaps a gentle 5mph breeze. No real problem itself other than the up wind legs took some time but low down (<100ft) the turbulence certainly was! As it flies at not much more than 5mph and close to the stall virtually every bit of turbulence caused a wing to drop, with an alarmingly slow recovery! Once in the higher smooth air it resumed its docile self - elevator not used, ailerons set to low rate and even then only needing a 'nudge' now and again! I am tempted to fit a gyro to see what happens. I suppose from an endurance point of view would a gyro ovewrall use less power? 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.