Donnyjue Posted May 26, 2015 Share Posted May 26, 2015 This is the first scratch built model I've made. I was really impressed with the finished product and spent hours on the detailing (panel lines, rivets etc). Only trouble is the flying, or lack of it. Lined it up on the club field for its maiden and was pretty confident it would fly beautifully but it didn't want to get its nose up in any hurry. After it gained a bit of ground speed the tail lifted and shortly after I put in some elevator, and some more elevator... eventually it lifted slightly but lost control and flipped. Ended up on its roof and ripped the stab and rudder off. I think it may have tip-stalled, but not entirely convinced. I didn't think this model would suffer from this unless it was put into extreme conditions. All-up weight was 4.5 kilos and C of G checked against plan. Is it too heavy on wing loading. I'm looking at putting some more throw into the elevator and possibly finding weight savings. Any other ideas? Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 26, 2015 Author Share Posted May 26, 2015 Some photos to put meat on the bones: Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted May 26, 2015 Share Posted May 26, 2015 Here's a bit more meat for your bones, this model won our winter build folks he made a superb job of building and finishing it. And here's the man himself John Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted May 26, 2015 Share Posted May 26, 2015 Been thinking about this my myself Jules, I tried to pick a good spot on the strip because of the retracts and I reckon I gave you too short a take off run so yes it tip stalled and it's my fault. John Quote Link to comment Share on other sites More sharing options...
Tony F Posted May 26, 2015 Share Posted May 26, 2015 Firstly, beautiful mate Secondly, what's the setup. Electric? Specs of motor esc and battery? And prop siz? Don't let it put you off it look fantastic. Tony Quote Link to comment Share on other sites More sharing options...
Engine Doctor Posted May 26, 2015 Share Posted May 26, 2015 Sounds like you pulled it off the ground before it was at flying speed causing the tip stall. What power train are you using ? Is there enough power ? Try changing the three bladed prop for a two blade as they are more efficient . Edited By Engine Doctor on 26/05/2015 22:00:07 Quote Link to comment Share on other sites More sharing options...
Martin Harris - Moderator Posted May 26, 2015 Share Posted May 26, 2015 It does seem a little heavier than the advertised design weight (4.1kg) and your description of pulling lots of up elevator would certainly suggest the possibility of a tip stall. Have you checked that any washout designed into the wing is correct? More elevator throw is likely to make the situation worse! With a model like this, you do want the tail to come up on the take-off run - taking off in a tail down attitude is a likely recipe for a tip stall and what you should find is that as it accelerates with the tail up, it's quite likely that the model will fly itself off but if not, the gentlest application of up should result in flight when the model is ready. Try to avoid a sudden pull-up and allow the model to climb gently before starting the first turn. Watch how full size do just this - here's a good example (or 20) Note how the B at around 1.19 corrects a slightly over enthusiastic rotation and levels off before retracting his u/c and accelerating to climb speed. Seeing a scale model climbing out at 45 degrees or so is a pet hate of mine - not only does a steady climb look far more realistic but it increases your chances of not having an incident if you hit some turbulence or lose power at an inopportune moment. One tip, assuming scale type ailerons, is to set them both up a few degrees - this introduces a little extra washout and can help if a model is prone to tip stalling. Hope this helps you to have a happier flight next time! P.S. Silly question I expect but you did check for reversed ailerons? It's amazing how often people get it wrong so it's always worth asking. Edited By Martin Harris on 27/05/2015 00:06:21 Quote Link to comment Share on other sites More sharing options...
Tony Nijhuis Posted May 27, 2015 Share Posted May 27, 2015 The mustang is a balancing act between holding elevator just enough to stop nose over and not get the model to rotate too early. The model needs very little elevator to rotate when she reaches flying speed.....it sound like you reached it with too much elevator applied and she flicked. If you have a simulator and a Mustang model, try taking off with holding up elevator and then accelerate.....guess what happens..... Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 27, 2015 Author Share Posted May 27, 2015 Posted by Martin Harris on 26/05/2015 23:42:55: It does seem a little heavier than the advertised design weight (4.1kg) and your description of pulling lots of up elevator would certainly suggest the possibility of a tip stall. Have you checked that any washout designed into the wing is correct? More elevator throw is likely to make the situation worse! With a model like this, you do want the tail to come up on the take-off run - taking off in a tail down attitude is a likely recipe for a tip stall and what you should find is that as it accelerates with the tail up, it's quite likely that the model will fly itself off but if not, the gentlest application of up should result in flight when the model is ready. Try to avoid a sudden pull-up and allow the model to climb gently before starting the first turn. Watch how full size do just this - here's a good example (or 20) Note how the B at around 1.19 corrects a slightly over enthusiastic rotation and levels off before retracting his u/c and accelerating to climb speed. Seeing a scale model climbing out at 45 degrees or so is a pet hate of mine - not only does a steady climb look far more realistic but it increases your chances of not having an incident if you hit some turbulence or lose power at an inopportune moment. One tip, assuming scale type ailerons, is to set them both up a few degrees - this introduces a little extra washout and can help if a model is prone to tip stalling. Hope this helps you to have a happier flight next time! P.S. Silly question I expect but you did check for reversed ailerons? It's amazing how often people get it wrong so it's always worth asking. Edited By Martin Harris on 27/05/2015 00:06:21 Some great points Martin. Where ever possible I try not yank n' climb. I was running out of field at the time of trying to rotate and think I must have panicked a bit. The wind had dropped to almost dead calm and therefore would have added to lack of air over the wings. All pointing to the stall. I'll make sure there is a bit more field to gain some more ground speed next time. I check the control surfaces before every flight and usually make a note of aileron orientation but I will definitely double check when I have her back together again. I'll look at adjusting the ailerons both up a couple of mm - nice tip - never thought of doing that to create wash out. It does have flaps but don't think I'll use these for take off until I see their effect 100 metres up. Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 27, 2015 Author Share Posted May 27, 2015 Posted by Tony Nijhuis on 27/05/2015 00:19:38: The mustang is a balancing act between holding elevator just enough to stop nose over and not get the model to rotate too early. The model needs very little elevator to rotate when she reaches flying speed.....it sound like you reached it with too much elevator applied and she flicked. If you have a simulator and a Mustang model, try taking off with holding up elevator and then accelerate.....guess what happens..... Thanks Tony, I'm sure this one will fly perfectly once the pilot gets his act together. I think your right about letting it climb on its own and I might have a look at the sim to see if I have one on there. Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 27, 2015 Author Share Posted May 27, 2015 Posted by john stones 1 on 26/05/2015 21:50:12: Been thinking about this my myself Jules, I tried to pick a good spot on the strip because of the retracts and I reckon I gave you too short a take off run so yes it tip stalled and it's my fault. John Hey John, don't put the blame on yourself. You didn't have the sticks. Pilot error would have been down to me. The grass was a bit long really and would have slowed it down, then add in the lack of head wind and it just wasn't ready to rotate. We'll take it from the other end of the field next time and see if Gary's got his mower handy. Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 27, 2015 Author Share Posted May 27, 2015 The model has an electric set-up, pretty much as the recommended. Roughly 1200w of power with 4s 5000mah battery and 100amp esc (I like to have a bit in reserve). It shows about 65amps on full throttle. Motor is a Turnigy Aerodrive 5060. Quote Link to comment Share on other sites More sharing options...
john stones 1 - Moderator Posted May 27, 2015 Share Posted May 27, 2015 Grass gets cut this week, get your finger out John Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 27, 2015 Share Posted May 27, 2015 Hi, looking at your data you don't seem to have anything like 1200W. 65amps from a 4s is about 950W. Given the weight of 4.5Kg (9.9lb) that about 97W/lb. Now it should fly on that - but your wing loading is very high and that means you need a high airspeed to fly. So you don't have a lot of power in hand I suspect - and even at nearly 100W/lb, given the "need for speed", you might be a lot closer to the margin than you imagine. Give a high drag on the undercart, the high wing loading demanding a high take off speed, and the fact that you don't exactly have loads of power to push through the barrier - its possible to see how this model might struggle a bit. Once in the air, and the undercarriage drag dissapears, it would probably be OK - its just a matter of getting there! BEB Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted May 27, 2015 Author Share Posted May 27, 2015 OK, I made a cock-up with the figures etc. I gave earlier today. The LiPo is a 6s (22.2v) and the motor is an NTM Prop Drive Series 5060 360kv. So, in fact, I made an under estimate of the power at full chat (65amp) which was actually 1443w - 145w per lb. Should have enough power there, but I will be looking to lighten the load by a lb or two. Quote Link to comment Share on other sites More sharing options...
Biggles' Elder Brother - Moderator Posted May 28, 2015 Share Posted May 28, 2015 Yes, you're right, with that sort of power you should be able to get it off. It will still have to go at a fair old lick because of the wing loading - so the idea of sheading a bit of weight is definitely a good one. BEB Quote Link to comment Share on other sites More sharing options...
Danny Fenton Posted May 28, 2015 Share Posted May 28, 2015 Looks great and I am sorry the first flight didn't go as planned Tony F asked a good question earlier on, what is the prop diameter and more importantly in this case pitch? Cheers Danny Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted July 6, 2015 Author Share Posted July 6, 2015 Sorry it's been a while since I last posted, been busy with repairs etc. Danny, the prop is a 3 blade, 16x8 electric. Quote Link to comment Share on other sites More sharing options...
Donnyjue Posted July 6, 2015 Author Share Posted July 6, 2015 In the following fortnight I had a couple of failed attempts which involved a bit of struggling with ground handling and landing gear collapses, but I was not deterred. I gave up on the HK retracts that I bought with the kit as they were constantly collapsing just on the ground when turning so I couldn't trust them to withstand a landing. I ended up buying some electric Eflite 120's which were a solid as a rock. I also dialled in loads of expo for the rudder to stop the twitchy ground handling (I think the position of the tail wheel being closer to the centre of the airframe gives it this twitchy habit). The maiden flight was just a few days ago on a beautiful sunny evening. 10mph headwind ensured an easy takeoff but I did give it a long run even after the tail lifting before rotating. What a different experience it was this time, I expected a real battle but, in fact, it handled like a pussy cat. I had to trim the elevator quite a bit to stop it climbing and a little aileron to the right but after that it was great. The first landing attempt without flaps showed a tendacy to tip, so I powered away and did the second with flaps and a bit of power which made it so much easier. Hopefully the Club open day will be rearranged after it was cancelled due to inclement weather and she will take pride of place. Quote Link to comment Share on other sites More sharing options...
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