ken anderson. Posted June 15, 2020 Share Posted June 15, 2020 hello alex,someone did have a problem with their Mig when they eventually found out their fan was designed for a 4s battery...and they had been trying with a 3s one.....not giving enough thrust...changed to 4s...model flew.... ken anderson...ne.1..long shot dept. Edited By ken anderson. on 15/06/2020 13:13:56 Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted June 15, 2020 Share Posted June 15, 2020 Eddie, Apologies I misread your post as about a Gnat not the Provost! Have not built that one but I think the same is true only more so. You need max thrust and lightest airframe you can. Maximising ( and I mean as big as you can possibly make it) the cheat inlet right next to the fan entry I think should be your next step. Up the battery c rating and measure the thrust before you try to fly. Tim Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted June 15, 2020 Share Posted June 15, 2020 Ken has a good point and we have had one person who actually had a duff fan! Definitely best to measure before you try to fly. Tim Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 15, 2020 Share Posted June 15, 2020 I am also only getting about 300g thrust from my FMS fan in my Provost. I had the same with the fan in the Sabre which I posted about in that topic. I was hoping it may have been a case of a bad fan, but the Provost is exactly the same. I have tried various batteries including a 40C graphene, but 310g was the best that I got. No idea how anyone is getting these 600g figures! Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 15, 2020 Share Posted June 15, 2020 I am also only getting about 300g thrust from my FMS fan in my Provost. I had the same with the fan in the Sabre which I posted about in that topic. I was hoping it may have been a case of a bad fan, but the Provost is exactly the same. I have tried various batteries including a 40C graphene, but 310g was the best that I got. No idea how anyone is getting these 600g figures! Quote Link to comment Share on other sites More sharing options...
Lucas Hofman Posted June 15, 2020 Share Posted June 15, 2020 What ESC are you using? I am using one from FMS that was recommende with the EDF unit. I think I have read somewhere about someone having to change an ESC to get good results? Quote Link to comment Share on other sites More sharing options...
Steve Jones 2 Posted June 15, 2020 Share Posted June 15, 2020 Alex, your model is a stunner - I nearly did that scheme and if i build another i will do. As others say, its not the model , these is clearly something wrong.. the 3s fan has a 5400KV motor, the 4s much lower Kv so if on 3s would be low thrust. check yours.... If me i would try other batteries and esc in turn.. MY model has no issues on 3s, good luck Steve Quote Link to comment Share on other sites More sharing options...
Geoff Gardiner Posted June 15, 2020 Share Posted June 15, 2020 My Provost was only giving me 300g of thrust and the motor cutting out above half throttle. It turned out to be a faulty (new) ESC. Quote Link to comment Share on other sites More sharing options...
Geoff Gardiner Posted June 15, 2020 Share Posted June 15, 2020 Still yet to maiden. Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 15, 2020 Share Posted June 15, 2020 Thanks all. EVERYTHING in the model is stock from the 4-max 3 Cell setup. I've just ordered a couple of new Overlander Batteries - one 50C one 80C. It will be interesting to see if these can get the fan spinning any faster... Does anyone have any other suggestions if that doesn't yield results? If it is a faulty ESC, is there a way to tell? Is the 4-max stuff decent or should I be going with a different type? All my previous models have been off the shelf, which has been great for learning to fly - but useless for building my own; so any advice is really really appreciated! Quote Link to comment Share on other sites More sharing options...
John Roberts 9 Posted June 15, 2020 Share Posted June 15, 2020 The problem certainly sound like a low thrust issue. Although my model is a Gnat it flies well and doesn't need an especially energetic launch to get it away easily. Full throttle and a firm 'push' and it is away with a nice, gentle, controlled climb out. With a 2150 3S Opti-Power LIPO (35C continuous rating) installed the model weighs 615 grams and, using the 'kitchen scale' test produces around 580 grams of thrust. Fan and ESC both came from 4-Max. I also enlarged the 'cheat hole' by about 20% (pretty much as big as it could go) to help the fan 'breathe'. One final thought occurs to me...……...have you 'trained' the ESC to recognise the correct full throttle point? If not then you might be a long way short of full power even with the Rx stick pushed fully forward Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 15, 2020 Share Posted June 15, 2020 Further to this my Sabre has a Hobbyking ESC and the Provost a Ripmax ESC. And yes, both have had the throttle calibration done. Open to any ideas that don't mean breaking into the model to change the EDF! Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 15, 2020 Share Posted June 15, 2020 Just in case a batch of "3s" fan units have been supplied with a "4s" motor, can any of you with low thrust check the amps or watts at full power. Then someone can compare it with a known good 3s unit. An rpm check would also be good, but perhaps not many would be able to do that. Dick Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 15, 2020 Share Posted June 15, 2020 I decided to try one of my old batteries with the Gnat just now using the kitchen-scales test. The old battery is an Align 40C 2250mAh 3s and gives about 400 grams of power; that's about 60-70 grams more power than the new battery with an appreciable increase in pitch from the EDF. The *new* 4 max battery, not used at all aside from with the Gnat is identical specs aside from being 50mah less, at 2200mah. I can't explain this - I guess it might just be a quality issue! Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 15, 2020 Share Posted June 15, 2020 Hi Dick, would gladly do that if I knew how... i'm afraid I haven't a clue where to start! Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 15, 2020 Share Posted June 15, 2020 Dick - good idea. I'll do that in the morning and report the results. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 15, 2020 Share Posted June 15, 2020 After all these bad omens I shall have to recheck mine for thrust/ weight before venturing out with it. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted June 15, 2020 Share Posted June 15, 2020 Alex, that thrust is way too low . There is a table on page 9 which lists my test results for a 3S set up using various size intake sizes. Although fully charged my lipo was only a 25C zippy. The 600 g thrust I finally achieved was With a peak current of 42A and an rpm of 49000. ( rpm was a factor of 2 out in my table as I used poles rather than pole pairs in my pre test setup!) 4max lipos are usually top notch and are my usual go to lipo. The zippy just provided a better physical size for this model. Not sure what the problem is with your set up but a current measurement would sure help the analysis. Probably worth buying yourself a cheap watt meter. You just connect it in the battery lead and read the values. Tim Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 15, 2020 Share Posted June 15, 2020 Thanks Tim. I've just ordered myself a little watt meter. Given all i've read I simply cannot believe it is an airflow issue as I barely get to 400g static thrust with the battery hatch off. I do wonder if I have a 4S motor. I guess this will be determined by the current draw results using the watt meter? I think the ESC for the 4S and 3S setups are the same - they are just programmed slightly differently. I do at least feel slightly better that it doesn't seem to be my build quality letting it down! Quote Link to comment Share on other sites More sharing options...
eddie frudenberg Posted June 15, 2020 Share Posted June 15, 2020 After another failed test flight I have given up. It was so bashed up I decided to just scrap it. In the process I thought I would look at the thrusts and they were as follow: 3 cell new Turnigy 30-40C 2.2 Ah hi discharge battery. Hobbywing 40 a esc. fully calibrated with throttle on radio. Hi timing. Powerfun 4900Kv on 3s. enlarged cheat hole to inch by three inches. AUW inc battery 700g. Normal---- Bat hatch on. RX hatch on. 350 grams on scales. no chance of flying. With just RX hatch off -------------------------430 grams. Did not fly Here on its me deconstructing the plane No duct tube no RX hatch -----------------466 grams No duct tube with hatch -------------------378 grams No bat hatch no RX hatch no duct --------466 grams No bat hatch, no RX hatch, snapped off fuz/tail and duct. Rear of fan open completely 550 Grams. So 550 grams max but no plane left. I may build another one but keep it lighter and go 4 cell. Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 15, 2020 Share Posted June 15, 2020 That's a real shame Eddie! Did you get to the bottom of why you had low thrust in the first place? It seems strange that you and I are both getting approximately the same thrust and others are not. I do wonder if we were accidentally shipped 4S setups! Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted June 16, 2020 Share Posted June 16, 2020 Eddie, I can not remember if the motors in the Edf unit were stamped with the KV rating or not. Since you have deconstructed yours Can you see any numbers on the motor body ? Tim Quote Link to comment Share on other sites More sharing options...
alan barnstable Posted June 16, 2020 Share Posted June 16, 2020 I also have given up trying to get Provost to fly, have tested thrust and getting very similar figures to Eddie. Am now revising it to have motor and propeller at the front. Obviously doesn't look authentic, but should look ok in the air. My motor was 2627-KV5400 running on 3 cell. Edited By alan barnstable on 16/06/2020 08:41:14 Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 16, 2020 Share Posted June 16, 2020 My Gnat has the FMS 4s Fan unit in it, and this morning I tested it on 3s on the scales. 355 gms thrust at 21.3 amps 220 watts - and that was with an old 3s 2200 connected via a 300mm adapter lead (all I coulkd find at the time) as it had the wrong connectors. In all other respects it was in flying trim with the battery hatch on. It does make you wonder if some units have been supplied with the wrong motor. Dick Edited By Dickw on 16/06/2020 10:45:51 Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 16, 2020 Share Posted June 16, 2020 As per Dick's suggestion I have tested my Sabre and Provost with various LiPo's. All LiPo's were > 85% charged and showing >11v. EDF units are FMS 50mm. The Provost and Sabre both have the standard cheat holes. Edited By Colin Bernard on 16/06/2020 14:08:20 Quote Link to comment Share on other sites More sharing options...
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