Applewood Posted January 9, 2023 Share Posted January 9, 2023 Hi can you help please. I'm not sure if I've got the right setup for this model, struggling to rotate WOT from grass strip. I have the Sebart Mini Avanti S composite EDF which uses a 90mm fan. I have the Wemotec Midi 90mm fan with HET 650-68 1500kv running 8S. However it doesn't seem like it’s enough power taking off from grass strip WOT, you can't get it to lift it's nose and rotate. I mainly fly IC warbirds so this is something completely new to me. Have I got the wrong motor/fan combination? Or do I need to persevere and tweak/modify the setup. My setup: Sebart Mini Avanti V2 3.8kg with 6S lipo JP Hobby retracts with brakes (powered by 3S 450mah lipo 55g) Wemotec midi Evo 90mm 11 blade fan partnered with HET Typhoon 650-68-1500 36mm motor. (8S -80a 2368W 3.69KP, 10S - 5.0 kgs (10S 37V) @100A.) Hobbywing HV (5-12S) 120amp ESC (opto) FrSky TD R18 and 2x 1100mah life flight batteries (132g) X20 Radio Hitec HS-5085MG servos Turnigy 5000mah 25-35C 4S LIpos x2 in series, 8S, in good condition not puffed 980g weight combined CG 145mm from the front of the wing - as per manual On the bench I've measure WOT 8S lipos : 25C Turnigy 2271W 80A 10S. 109A 3874W I did measure thrust, but didn't record results, I think they were not far off spec. Grass strip 110m (360ft), at the time grass was bone dry, not long but could have done with a cut. At the time there was 10mph cross winds so no lift being offered to help. Observations. Taxing at WOT it won't rotate, full up elevator wouldn't get it to lift it's nose. Take off flaps used. The last run, I reduced power towards end of the strip and it shot up off the ground 15ft without warning. The combination of grass, small front wheel, and down thrust, looks like its pushing the nose down. Maybe reducing throttle, reduced the down thrust and was the explanation for it shooting up. A few things I’m going to try: 1) Get that grass cut nice and short, take off when wind is favourable 2) Read somewhere that WOT induces some down thrust, so I'm going to extend the front nose leg so that it will help with the rotation, found a chat on YouTube who did the same to make it rotate. 3) Better batteries - I would rather stick with 8S, than move to 10S due to expense of new batteries and additional weight 4) Worst case change the fan/motor / batteries I've spent quite a lot on this, and I'm at the point of either investing it it further or selling it. If I need to change motor/fan/batteries, I'm probably going down the sale route. anyone had similar experience and can offer any advice. My club mainly fly's IC so no advice is available locally. Quote Link to comment Share on other sites More sharing options...
john davidson 1 Posted January 9, 2023 Share Posted January 9, 2023 We use a roll of carpet, once the model gets air under its wings it it usually away 1 Quote Link to comment Share on other sites More sharing options...
Denis Watkins Posted January 9, 2023 Share Posted January 9, 2023 As John says And avoids hiking it off before the wing is flying, Let the wing lift it off, all under control. Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 9, 2023 Author Share Posted January 9, 2023 1 hour ago, john davidson 1 said: We use a roll of carpet, once the model gets air under its wings it it usually away Are you using carpet for the entire strip, or just short piece to get the model moving. Sorry if this is a stupid question, all my three clubs have just been grass strips. Thanks Quote Link to comment Share on other sites More sharing options...
Shaun Walsh Posted January 9, 2023 Share Posted January 9, 2023 Is the CoG correct? Can you fit a slightly larger nose wheel to increase the angle of attack on the take off run? Quote Link to comment Share on other sites More sharing options...
Ron Gray Posted January 9, 2023 Share Posted January 9, 2023 13 minutes ago, Shaun Walsh said: Is the CoG correct? Can you fit a slightly larger nose wheel to increase the angle of attack on the take off run? Both things the OP has already checked / done or will be doing (see his original text!). Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 9, 2023 Author Share Posted January 9, 2023 41 minutes ago, Ron Gray said: Both things the OP has already checked / done or will be doing (see his original text!). Yes I'm going on COG recommended by the manual and others on forums. As described, one recommendation I picked up from a German youtube channel, was to increase the front strut by 2cm to lift the nose when the gear is down. I'm awaiting a new longer strut pin for the front landing gear. Quote Link to comment Share on other sites More sharing options...
john davidson 1 Posted January 9, 2023 Share Posted January 9, 2023 2 hours ago, Applewood said: Are you using carpet for the entire strip, or just short piece to get the model moving. Sorry if this is a stupid question, all my three clubs have just been grass strips. Thanks Longer the better but it is surprising how much a ten foot strip helps to get speed up and the weight off the wheels, that is what we use, kept in the shed, two strips can be overlapped of course to give twice the length if necessary. Fun is to be had trying to land back on, could start a comp! Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 9, 2023 Author Share Posted January 9, 2023 6 minutes ago, john davidson 1 said: Longer the better but it is surprising how much a ten foot strip helps to get speed up and the weight off the wheels, that is what we use, kept in the shed, two strips can be overlapped of course to give twice the length if necessary. Fun is to be had trying to land back on, could start a comp! I'm really intrigued about this, I wouldn't have thought such a short length would make a difference. We have a roll of quite stiff plastic/rubber matting I'm wondering if that would work, I'll have to go and measure it. Quote Link to comment Share on other sites More sharing options...
Colin Carpenter Posted January 9, 2023 Share Posted January 9, 2023 I’ve got the 70mm foamie and have had to buy some high C lipos for it. I normally fly at 9 am and the grass is always wet despite warm nights. If I wait till 11am and use the whole strip I can usually just get it off ! Lovely flyer once it’s up ! Colin Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 9, 2023 Author Share Posted January 9, 2023 Just checked the internal resistance and the batteries are fine, very low IR. But they are not that special just Turnigy Blue 25-35C 4S 5000mahs. Quote Link to comment Share on other sites More sharing options...
Trevor Posted January 9, 2023 Share Posted January 9, 2023 I don’t know that model so can’t really help. However, if you do give up on it, I can thoroughly recommend the Freewing Avanti - copes very well with grass and flies beautifully. Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 9, 2023 Author Share Posted January 9, 2023 33 minutes ago, Trevor said: I don’t know that model so can’t really help. However, if you do give up on it, I can thoroughly recommend the Freewing Avanti - copes very well with grass and flies beautifully. It should fly similar (https://www.nexusmodels.co.uk/sebart-mini-avanti-s-1-42m-jet-white-red.html). Apparently Sebart licenced the Avanti design to Freewing to produce their foam version. Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 10, 2023 Author Share Posted January 10, 2023 On the bench I've measure WOT watts/apps on two types of 8S lipos when running up the edf. With the esc’s default medium timing 15deg. Measuring at WOT 45C Graphene 2023W 75A (26.97V/ 3.37 per cell), 25C Turnigy 2271W 80A (28.39v/3.55 v per cell) With lower 7.5 deg timing, 8S Graphene 70A 1934W (27.62v/3.45v per cell) 8S Turnigy 75A 2138W (28.5v/3.56v per cell). Quick test with 10S 109A 3874W 35.54v/3.55v per cell). I think that means with the best battery (surprisingly the turnigy) the voltage under load is 3.55V which could be quite low, although I’m not an expert. Would you agree? Does that mean the lipos are capable enough. Quote Link to comment Share on other sites More sharing options...
Alan Hilton Posted January 10, 2023 Share Posted January 10, 2023 Try measuring static thrust using a spring balance attached to the tail group you should get about 4 kg Quote Link to comment Share on other sites More sharing options...
Applewood Posted January 10, 2023 Author Share Posted January 10, 2023 3 minutes ago, Alan Hilton said: Try measuring static thrust using a spring balance attached to the tail group you should get about 4 kg Thanks, I’m planning on doing some static thrust tests. According to the spec the best I could get on 8S is 3.69kg, or 5Kg on 10S. Wemotec midi Evo 90mm 11 blade fan partnered with HET Typhoon 650-68-1500 36mm motor. (8S -80a 2368W 3.69KG) Quote Link to comment Share on other sites More sharing options...
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