Simon Chaddock Posted June 17, 2015 Author Share Posted June 17, 2015 A period of really calm weather allowed a 'real' endurance test. With the 5000 mAh battery balance charged to full (charger cut off) I flew the Endurance II for 66 minutes power on all the time. It took 1280 mAh to balance charge it back to full again. This gives an average current consumption of 1.16A which is remarkably close to the figure I obtained with the first shorter test. Still a bit short of the 1A figure I obtained with the first Endurance but not too bad. Remember this is the total power - motor, servos,and radio. The battery is a 2s so it is flying on about 8.6W. The Endurance II weighs exactly 15 oz which means 9,2W/lb. This now poses the question that despite my best efforts what aspects of the first Endurance airframe made it that little bit more efficient given that It had the same wing span, motor and prop? I shall have to think about that. . Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 25, 2015 Author Share Posted June 25, 2015 My thoughts turned towards its swept and up turned wing tips. Although they look nice I have suspicion they are really aimed at providing a degree of stability and reducing any tip stall. There is quite a bit of the area that creates drag with little or no lift benefit. Fortunately the up turned portion of the tip is beyond the aileron so it can be simply cut off and replaced with virtually no weight penalty. The replacement tip is similar to the design I used on the first Endurance. Swept back but with a bulged trailing edge to avoid any discrete point. As i am after efficiency the underside is flat and with no wash out. Early yesterday morning it was absolutely still so another hour long endurance flight - actually 65 minutes. The battery needed 1023mAh to recharge to full. 1.023 x 60/65 = 0.944A average consumption meaning in theory at least a full 5 hours duration from the 5000mAh battery. The tips do seem to make a difference. However this flight was made in absolutely ideal conditions where the plane could be left for quite long periods (up to a minute at a time) without any input so saving on servo loads. I don't know what the proportion of servo & radio current actually is but at such a low total current it is probably significant. I am also not convinced its V tail is ideal. Being out of the slip stream will reduce the drag but it does not seem to provide the same degree of stability as the equivalent size cruciform type. I think that will be the next modification. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 25, 2015 Share Posted June 25, 2015 Watching with interest... My aerodynamics isnt what it should be, but surely a percentage of the lift the (old) upturned tips produced would be wasted as the direction of lift would be canted into the centre of the plane rather than vertical so having the effect of increasing the wing loading which will require more power for the same lift - is that right ???? Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 26, 2015 Author Share Posted June 26, 2015 Dave That is correct although its actually slightly worse than that as the up turned bit of the tip is at zero incidence and virtually symmetrical in section so simply creates drag. It does have advantage is when the plane is yawing as the 'leading' tip will now have significant positive incidence and thus lift the wing (and the opposite for the lagging wing) but because it is acting right at the tips the effect is stronger than it would be for the same amount of dihedral. It seems that the high wing, low battery configuration of the Endurance has adequate roll stability with virtually no dihedral. Quote Link to comment Share on other sites More sharing options...
Dave Hopkin Posted June 26, 2015 Share Posted June 26, 2015 Thanks for confirming my analysis of what was happening Simon, tricky stuff this Aerodynamics..... So what other experiments are you going to try? Perhaps a Turbulator... Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 26, 2015 Author Share Posted June 26, 2015 As the Endurance has been set up with very limited natural stability for maximum aerodynamic efficiency obviously any sort of turbulence raises the number of control inputs dramatically. Was the lowest power flight so far simply the result of the absolutely still condition and the reduced servo inputs? This poses the question just how much power do the servos actually take. The first test is to put on a Watt meter and leave the plane static for say 15 minutes and see how many mAhs are recorded. This would represent the 'standing' power required by the radio The repeat the test but including the typical stick movement s. The difference between the two figures (multiplied by 4) would represent the power required by the servos for an hour flight. The results are very interesting. The 'standing' power consumption came out at a whopping 194 mAh over an hour. This represents nearly 20% of the total power consumed during the flight! Adding the typical stick movement made very little difference adding just 11 mAh. over an hour. It thus seems that the benefit of the still conditions was not the servo load but the fact the Endurance could be better trimmed for constant minimum power flight. With such a large proportion of the power being 'fixed' any further improvement is going to be increasingly difficult. One solution would be to make the plane rather bigger say twice the size (96" span) so the 'standing' power drain would be a much smaller proportion (about 5%) of the power to required to fly. . . Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 28, 2015 Author Share Posted June 28, 2015 Still perturbed by the big (or in my case the relatively enormous!) 'standing' power consumption it occurred to me that the original Endurance used 35 Meg rather than 2.4. So the Watt meter went onto the 35 meg Super Cub which also uses a 2s LiPo. Its standing power consumption was just 96 mAh over an hour. 2.4 may be brilliant but not at everything! So my last spare miniature Corona 'full range' 4ch 35 meg rx goes in place of the 6ch Orange 2.4. This does present a problem as it currently uses 'dual aileron' with the sub trims used to individually centre each as well as allowing differential movement. With only 4 channels the ailerons will have to go on a Y connection and there can be no differential. Unfortunately this has resulted in both ailerons being drooped at their centre position. Not ideal for a plane with no dihedral. no washout and limited natural stability! I did fly it in this condition and it showed 'interesting' handling characteristics. So the ailerons have to physically re-centred by repositioning the servo horns. A bit brutal but when filled and painted it should be as good as new - I hope. By changing to 35 Meg its endurance should be increased by a substantial 10%. Edited By Simon Chaddock on 28/06/2015 13:15:41 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 1, 2015 Author Share Posted July 1, 2015 The first 'endurance' flight with the 35 meg radio did not go too well. No problem with the plane it flew very well. Clear blue and puffy clouds (it is quite hard to see at altitude in these sort of conditions) with much thermal activity. The Endurance thermals very nicely such that I lost sight of it and only recovered by putting it into a spiral dive so the sun reflected of its bright white wings! This happened twice so I came down much lower! With no timer on the 35meg I have to use a watch. Getting close to an hour I glanced at my wrist and when I looked back up the Endurance was nowhere to be seen! Tried a spiral again but being lower I knew I only had a second or two to spot it. I didn't! Fortunately a dog walker did and said " it dived in behind the trees". Given the hight of the them I could only hope he was right. He was but it did not come out unscathed! But at least I got it back! A bit of a major rebuild required. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 2, 2015 Author Share Posted July 2, 2015 Rebuild complete and now with a conventional cruciform tail. The new tail has slightly greater area yet is fractionally lighter. The elevator servo is built into the thicker base section of the fin. A further 64 minute flight this morning in nice calm condition (its fifth 1 hour flight in six days!) required 1050 mAh to recharge the battery to full. This represents and average consumption of just 0.98 A . That's about 9 W from its 5000 mAh 2s LiPo. The battery has a pretty easy time as it is being discharge at just under 0.2C! I need to do another flight just to prove the power consumption figure is repeatable but it is so boring to do. Edited By Simon Chaddock on 02/07/2015 21:40:45 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted July 4, 2015 Author Share Posted July 4, 2015 Just to complete the story I managed 66 minutes this morning in pleasant but slightly bumpy conditions. It required 1030 mAh to fully recharge the battery giving an average current consumption of 0.94A. So it is now reasonably safe to claim that the Endurance II can maintain height on just less than 1A. Whether this really means it could fly for 5 hours by fully discharging the battery I do not intend to find out! Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 24, 2016 Author Share Posted February 24, 2016 I noticed HK (UK Warehouse) were selling these. 6Ah 4S for £10.61 ! Only rated a 2C (12A) but that would be no problem for the Endurance II as it would not take that even at full power and 'cruises' on less than 0.1C. The Endurance only uses a 2S so if I could split the 4S I would have two batteries. According to the spec the 4S weighs 364 g so 'half' would come in at 179 g The 5000mAh 2S I current use weighs 209 g. So a 6Ah 2S Multistar has 20% more capacity yet weighs 15% less ! This I have just got to try! Edited By Simon Chaddock on 24/02/2016 21:04:12 Quote Link to comment Share on other sites More sharing options...
Robert Armstrong 2 Posted February 25, 2016 Share Posted February 25, 2016 New to this thread, but wonder if you have considered using just one aileron to reduce the control power load? I know some pylon racers used to be built with only one aileron. I also had a clevis disconnect in flight from one aileron on my Acro Wot and if was still quite controllable to a damage free landing. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 25, 2016 Author Share Posted February 25, 2016 Robert I suspect it could be flown with one aileron (I too have done so in very similar circumstances!) but to improve the Endurance's efficiency its wing has virtually no dihedral, no washout and coupled with small tail surfaces its stability is pretty marginal so the adverse yaw from a single aileron could well create bigger problems that any benefit. It is however just stable enough on a calm day to circle without attention which of course is the best way to keep the servo load to a minimum! Even when control is required it is only the tiniest of inputs, quite frequently just a 'click' of trim.. I can assure you it not a very exciting form of RC flying! You are of course quite correct that with a total current draw of only 1A the servo & radio requirements do start to become significant.. Indeed this was one of the reasons I changed from 2.4 to 35 meg as it only needed 2/3 of the standing current. I now have two 6Ah 2S batteries. From this. To this Because of the much smaller leads and connectors each battery weighs just under half at 175g which at a 26% reduction over my current 5Ah 15C LiPo is actually rather better than expected. So if it does indeed deliver 6Ah this battery would then represent as big an improvement in performance (but only in this application) as the LiPo did over NiMh! I do have my doubts about the claimed capacity. Edited By Simon Chaddock on 25/02/2016 11:57:12 Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted February 26, 2016 Author Share Posted February 26, 2016 Just for the record the cut down 6Ah 2S Multistar does fly the Endurance II quite nicely and I managed a 32 minute trial flight this morning. Stopped only because it was very cold! It has no problem supplying the 7.5A (48W) required for full power. The only issue at the moment is a very low charge rate (about 1A) which is regardless of the rate set on the charger. At such a rate charging anything like the full 6Ah would take a very long time!. Edited By Simon Chaddock on 26/02/2016 00:58:59 Quote Link to comment Share on other sites More sharing options...
Dave Bran Posted February 26, 2016 Share Posted February 26, 2016 Interesting. I took the other way, light and small cell pack. Years ago, for the school club I run I took a couple of the range of Slovakian "Fik" EPP chuck gliders, just rough raw foam, no covering, and used the 100 (1 metre) wing on the 80 Fus/Tail. RET control, two 9g servos. Power was from a tiny 800mAh 2S via a 8A ESC into a 1000kV Blue Wonder, 8x4.3 slowfly. This used to manage without problem what it was intended for, 40 plus minute flights with novice none too smooth pilots, power on all time, often excessively, and was nowhere near drained at the end, able to loop consecutively. From this it was pretty obvious that it would have managed around the hour pioss more if flown carefully power on all time That was on 35MHz, powered from the BEC. No way was I about to try though, I was bored to tears watching the kids do 40 mins. Quote Link to comment Share on other sites More sharing options...
Stephen Jones Posted May 17, 2017 Share Posted May 17, 2017 Well Done, Simon, In getting a write up in the BMFA News . On page 42 of the June 2017 issue "Just How Long Can You Fly?" A nice read Even if i did read it here 1st, Steve Quote Link to comment Share on other sites More sharing options...
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