John Laverick Posted June 18, 2010 Share Posted June 18, 2010 HI Guys, bit of help needed if you would be so kind. I have a Ripmax mustang which I've been flying for two years. No problem with the flight characteristics, however I increased the size of my battery which is abviously heavier so I adjusted the battery to get the correct C of G, but when I took her up yesterday the flight was exactly the same apart from when she was in a loop. when she got to the top of the loop she rolled out to the right, try as I might I couldn't get her to do the other half of the loop without her rolling out. is this due to her being a bit nose heavy, or tail heavy? thanks in anticipation John Quote Link to comment Share on other sites More sharing options...
John Privett Posted June 18, 2010 Share Posted June 18, 2010 Sounds to me as if it's stalling, though the top of a loop seems a slightly odd place for that to happen unless you're deliberately pulling a lot more "up" at the top. One wing is stalling before the other - hence the roll. Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted June 18, 2010 Share Posted June 18, 2010 John could it be stalling there because it's heavier? Being heavier the stall speed will be higher. Can you carry any more speed through the loop? Quote Link to comment Share on other sites More sharing options...
Allan Bennett Posted June 18, 2010 Share Posted June 18, 2010 I agree; heavier battery may spoil the flight characteristics to the extent that it's failing to make it over the top of the loop, and stalling. Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 18, 2010 Share Posted June 18, 2010 It could be just the extra weight as Chris says....alternatively if the COG has shifted slightly, then it could be perhaps nose heavy requiring too much "up" elevator to pitch. Conversely,maybe its tail heavy, and snapping out at low speed as it were.Whatever the cause, Its worth noting your other comment about there being no real difference in flight performance. In my experience many electric models really benefit from being kept light, and I have a few that simply do not like /need the extra weight that even a slightly higher capacity battery brings. Of course the power to weight ratio also alters, so in some cases you end up "chasing your tail" the extra weight needing more power to move it, so flight duration is not noticeably better - flight characteristics however could end up a lot worse.I reckon as Chris says...its just got heavy and is complaining - how much extra weight has been added through the larger battery ? - and is the AUW now more than designed? Quote Link to comment Share on other sites More sharing options...
John Privett Posted June 18, 2010 Share Posted June 18, 2010 Remember that the stall is caused by the angle of incidence of the wing exceeding a crtical angle - it's not just a question of speed. Heavier battery, more weight, it all needs more lift from the wing for the same flight. So that means either higher speed (but from the same motor power and with probably higher drag?) or a higher wing angle of incidence. And so a flight where the angle of incidence remained "safe" with the lighter battery now needs a higher angle with the heavier setup and at some point stalls. My only surprise is that it happens at the top of the loop where less elevator is needed. Maybe John is pulling in more elevator at the top to try and "hurry up" the loop and get back to safe, level flight? Quote Link to comment Share on other sites More sharing options...
kiwi g Posted June 18, 2010 Share Posted June 18, 2010 John was the loop a fast tight loop or a big aerial sky breaking loop.?? Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted June 18, 2010 Share Posted June 18, 2010 Just to always try the simple things first - are you sure the model's lateral balance is OK? Could the battery be off-centre adding weight to one side rather than the other? Try checking the lateral balance by supporting the model using a loop of cord at the crankshaft - behind the spinner - and the tail. A small error in lateral balance shows more at slow speed just as at the top of a big loop. Does it drop the same wing when slowing to land? BEBEdited By Biggles' Elder Brother on 18/06/2010 22:26:49 Quote Link to comment Share on other sites More sharing options...
Myron Beaumont Posted June 18, 2010 Share Posted June 18, 2010 Don't think its the longitudinal C of G for what must ge only a relatively small increase in weight .Maybe you just need a change of approach .Then again I don't know the model Not a very useful comment ,I do realise that Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 19, 2010 Share Posted June 19, 2010 BEB says..."Try checking the lateral balance by supporting the model using a loop of cord at the crankshaft"Spoken like a true IC / petrol head LOL Quote Link to comment Share on other sites More sharing options...
Tim Mackey Posted June 19, 2010 Share Posted June 19, 2010 Incidentally, I shall be test flying one of these for a mate tomorrow.Edited By Tim Mackey - Administrator on 19/06/2010 00:13:48 Quote Link to comment Share on other sites More sharing options...
Gemma Jane Posted June 19, 2010 Share Posted June 19, 2010 Hi John, I get this on a GWS P-38 it gets to the top of the loop and then seems to drop out on one side. I'm pretty sure it's a form of accelerated stall and most likely in your case coming from the increased weight. In a way your post kind of confirms what I suspected as it appears the only thing you have done is increased the weight of the model to cause this. Certainly my 38 is way over the recommended weight and does exactly the same thing. I kind of exhausted other explanations such as the airframe not being true etc. I guess what is happening is that one wing goes into the stall which is what causes it to kind of 'flick roll' out of the loop as the other wing is still producing lift. It's certainly weird flying a model that does this with no control inputs! If anyone has a better or more precise explanation of what is happening I would love to know as I've yet to solve it on the 38. Quote Link to comment Share on other sites More sharing options...
ken anderson. Posted June 19, 2010 Share Posted June 19, 2010 john - i would go along with all of the above and add that the weight of your model-the direction of travel/wind speed...and the speed of your model will all contribute to it falling off the top of a loop...try directly into the wind.....bit more speed and gentle on the elevator........at the top...and then let the momentum of the model carry it on it's way out of the loop...... ken anderson....ne 1..... Quote Link to comment Share on other sites More sharing options...
John Laverick Posted June 19, 2010 Author Share Posted June 19, 2010 Many thanks for the replies guys, Seems that the general consensious is that the extra weight is causing her to roll out. However I took her up this morning and got the fright of my life. I slowed her down for a landing and at about 50 foot she flipped over on to her back with no input from my controls what so ever, luckily I had my wits about me and she was going fast enough to rectify it, but it didn't half put the willies up me. guess it was just a glitch of some sort but it wasn't nice. Regards John Quote Link to comment Share on other sites More sharing options...
John Privett Posted June 19, 2010 Share Posted June 19, 2010 John, I'd say that flip on final approach is part of the same issue. To fly slowly with the additional weight you'll be flying with the wing at a higher angle of incidence to the airflow than before. If you exceed the critical angle then the wing - or part of it - will stall. Sounds like one of the wingtips has stalled first (a common occurence with tapered wings) and the sudden loss of lift at one end of the wing can cause a dramatic flip such as you experienced. That's what my 2p is on anyway! Quote Link to comment Share on other sites More sharing options...
John Laverick Posted June 19, 2010 Author Share Posted June 19, 2010 Thanks John, I thought she would just drop a wing and stall, didn't realize that a tip stall could be that dramatic. John Quote Link to comment Share on other sites More sharing options...
Chris Bott - Moderator Posted June 19, 2010 Share Posted June 19, 2010 I tend to agree with John P. Have you tried it again with the lighter battery? Quote Link to comment Share on other sites More sharing options...
John Privett Posted June 19, 2010 Share Posted June 19, 2010 Posted by John Laverick on 19/06/2010 15:00:13:Thanks John, I thought she would just drop a wing and stall, didn't realize that a tip stall could be that dramatic. John Yep - I can assure you that a tip stall can be quite dramatic - and traumatic too! Quote Link to comment Share on other sites More sharing options...
Former Member Posted June 19, 2010 Share Posted June 19, 2010 [This posting has been removed] Quote Link to comment Share on other sites More sharing options...
John Laverick Posted June 19, 2010 Author Share Posted June 19, 2010 Chris, gonna try the old battery tomorrow, Thankfully I've another plane I can use the two new batteries on so it's not a waste of money. John Quote Link to comment Share on other sites More sharing options...
Chris Channon Posted June 19, 2010 Share Posted June 19, 2010 Hi John, I have a Kyosho Spit .40 ic model that does exactly the same thing, i have checked and balanced, bit it still flicks out if i pull a touch too much elevator. Regards Chris. Quote Link to comment Share on other sites More sharing options...
Simon Chaddock Posted June 19, 2010 Share Posted June 19, 2010 JohnJust how much extra weight did you add and what is the total weight? For the reasons already pointed out a relatively small increase can have quite an impact on aerobatics where the plane can approach the stalling speed.Extra weight increases the stalling speed. Extra weight and pulling g increases it a bit more. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted June 20, 2010 Share Posted June 20, 2010 Posted by Tim Mackey - Administrator on 19/06/2010 00:12:37: BEB says... "Try checking the lateral balance by supporting the model using a loop of cord at the crankshaft" Spoken like a true IC / petrol head LOL Oppps! Guilty as charged m'lud! BEB Quote Link to comment Share on other sites More sharing options...
John Laverick Posted June 20, 2010 Author Share Posted June 20, 2010 Tim did you manage to do your test flight? does a CRANKSHAFT not belong to a car?? BEB Don't want to put the cat among the pigeons, but surely the petrol heads have had their day? Electric has to be the way forward. Had a petrol head over to my house today and he gave the best he could for and Against, but he went away knowing he was beat! John Quote Link to comment Share on other sites More sharing options...
David perry 1 Posted June 20, 2010 Share Posted June 20, 2010 No a crankshaft is the bit wot holds the cranks! Regardless of the veehickle. As for tip stalling, I don't know the model in question, but could you not set some washout into th wings? Or perhaps try deflecting the ailerons UP a smidgeon, which gives the effect of washout. Both these things can help reduce tipstalling. D Quote Link to comment Share on other sites More sharing options...
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