Dickw Posted June 16, 2020 Share Posted June 16, 2020 Hi Colin Our respective results surprised me so much that I have just run my tests again to see if I made a mistake. Latest test results using the same setup as before - (electric data from telemetry log and thrust figure from scales):- Thrust 355 / 360 gms, amps 20.65, watts 210, volts 10.19. On the face of it I am getting similar thrust to you at approx 66% of the amps. If I had a decent 3s battery with the right connectors, it looks like my 4s unit running on 3s would outperform your 3s unit. Something is definitely wrong. Dick Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 16, 2020 Share Posted June 16, 2020 OK. not a fair test this time, but I just tried a 3s 5000 Lipo at storage charge, but since it won't fit in the model I had to do it with the battery hatch off. Thrust 460gm, amps 24.1, watts 275, volts 11.35. Definitely something strange going on with some of the 3s units. Mine is an FMS unit are the problems with the FMS or the PF unit? Is there any difference? Dick ps just noticed Colin confirmed his is an FMS unit. Edited By Dickw on 16/06/2020 15:32:00 Quote Link to comment Share on other sites More sharing options...
John Roberts 9 Posted June 16, 2020 Share Posted June 16, 2020 Has anyone returned their low thrust FMS units to George at 4-Max for testing? He seems to generally have a good reputation in the model flying community and I feel certain that he would want to assist in identifying the problem especially if there is a 'rogue' batch of dodgy or mislabelled FMS units in circulation. I know this won't be of any use to those who purchased direct from Banggood etc. but certainly worth a try for those who bought from 4-Max Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 16, 2020 Share Posted June 16, 2020 Both mine were from Banggood so that may be where the problem lies, although they did look to be genuine FMS units. Not giving up though as I intend to build either the Gnat or Phantom and this time will buy from 4-Max. And who knows, once we are released from shielding, I may find that the Provost flies fine! Quote Link to comment Share on other sites More sharing options...
David P Williams Posted June 16, 2020 Share Posted June 16, 2020 I have three of these 50mm edf units ordered from Banggood as 'FMS 50mm 3S', in two seperate orders. I didn't inspect them closely. The two that came together are marked FMS and have 5400kv motors, and one of them is fitted in my mostly built Provost and untried as yet apart from checking that it actually runs. The one that came on its own is actually a Powerfun unit with a 4900 kv motor. Hmmmmm Quote Link to comment Share on other sites More sharing options...
brokenenglish Posted June 16, 2020 Share Posted June 16, 2020 I'm following this thread, as I really like the models but, honestly, flying a sport plane shouldn't involve all this high-tech (for me!) research and testing. RTF EDF planes seem to fly without too much hassle, so where's the problem? Has Tony gone too far in the "small, solid, quick-build" concept? Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 16, 2020 Share Posted June 16, 2020 I don't think it is a problem with the planes, but there does seem to be an issue with some of the EDF units. The Gnat is my first attempt at an EDF and not knowing anything about it I just bought the suggested bits from 4-Max and they work fine. The Gnat flies great. Dick Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 16, 2020 Share Posted June 16, 2020 Hi all, I dropped George at 4-max a line and he came back very quickly with the following points: Have you done the cheat holes? These are imperative, without them they won't fly. Try enlarging the cheat holes, the size Tony puts on the drawing is the MINIMUM size Have you made sure the ESC is on "High" or "Hard" timing? You must have a good quality high C rated battery Have you got the exhaust outlet diameter correct, again this is critical Did you use the inlet ring on the fan? again very critical. The thrust figures we supply are with the fans in free air. As soon as the fans are fitted in a model the thrust will be reduced and this will vary from model to model. Unfortunately - i've already checked all of these points, but nevertheless I hope it helps someone! In desperation i've ordered a 2200 4S pack to see how the thrust compares. Is this likely to blow up the motor? Edited By Alex Body 1 on 16/06/2020 18:11:29 Edited By Alex Body 1 on 16/06/2020 18:12:06 Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 16, 2020 Share Posted June 16, 2020 I said that I would test my Provost so here is how it did on a slightly discharged Zippy Compact 2200 3s, FMS fan and suspended on luggage scales: Amps, settled down at 24. Watts, about 240-250. Thrust, 460g. Battery hatch covered as much as I could. Watt meter disconnected and hatch cover fitted, thrust 450g. What do you all reckon to this? Will it go? Cheat hole is 50x50mm. Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 16, 2020 Share Posted June 16, 2020 Well done Alex - there are certainly a couple of points there I'd like to check. Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 16, 2020 Share Posted June 16, 2020 Must confess I only just checked my exhaust diameter and it is a couple of mm too small. Is this really likely to cost me 100g of thrust!? Quote Link to comment Share on other sites More sharing options...
stuey Posted June 16, 2020 Share Posted June 16, 2020 If you have a smaller diameter exhaust, you end up with less static thrust put higher efflux speed. A bigger diameter gives more static thrust, but lower efflux speed. This is what I understand to be correct for older lower blade count fans, I think higher blade counts do need a slightly bigger exit. I thought the Provost was supposed to be a 4s setup BTW? I tried powering up my Hunter yesterday before covering and final fit out, it had just below 1:1 thrust ratio on a 45% charged 25c 3s pack. Not hooked it up to the watt meter yet though. FMS fan from 4-max. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 16, 2020 Share Posted June 16, 2020 Further to my post above I have checked it on a 4Max 2600 at 70% charge. 475g thrust with the battery hatch fitted. Model weighs 710g or 24oz with this. Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 17, 2020 Share Posted June 17, 2020 Posted by Martin McIntosh on 16/06/2020 19:21:46: I said that I would test my Provost so here is how it did on a slightly discharged Zippy Compact 2200 3s, FMS fan and suspended on luggage scales: Amps, settled down at 24. Watts, about 240-250. Thrust, 460g. Battery hatch covered as much as I could. Watt meter disconnected and hatch cover fitted, thrust 450g. What do you all reckon to this? Will it go? Cheat hole is 50x50mm. Martin I am new to EDF so am not perhaps the best person to comment, but have a look at Tim Ballinger's test results for a known good FMS 3s fan on page 9 of this thread. His current and thrust data is way above yours. Now compare your data with that of my 4s unit running on reduced power (3s instead of 4s) and it seems too similar to me:- Thrust 460gm, amps 24.1, watts 275, volts 11.35 My 4s unit running normally on 4s would be taking about 40 amps which is similar to Tim's 3s unit. I would be very suspicious of a 3s unit running at 24 amps full throttle. Dick Edited By Dickw on 17/06/2020 10:02:24 Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 17, 2020 Share Posted June 17, 2020 Hi all, George at 4 Max has once again helped me out here and contacted Tony Nijhuis himself. Tony emailed be back directly with the following: There will be approximately 30% loses due to the install….That is expected and taken in to account in the design I have just checked all my prototypes and the Gnat, with a 3S 2200 and the FMS 3S 50mm fan produced, 406g dropping to around 370g. The Power fun thrust will be slight less as the motor KV is less. So in short you are not struggling to get the static thrust…YOU have achieved it…..now go out and fly the bloody thing…..LOL Hope that helps! Cheers, Quote Link to comment Share on other sites More sharing options...
Colin Bernard Posted June 17, 2020 Share Posted June 17, 2020 Taking George's comments on board I have had an interesting morning in testing the various suggestions. The tests were done on my Provost using a freshly charged 3S 75C Graphene LiPo. The outlet diameter matched the plan so no further testing on that. Looking at the other points, my default timing was 'medium', I had omitted to fit the inlet ring and the cheat hole was standard, so I looked at each of these in turn. For the cheat hole I initially simply took off the top hatch to see if it made any difference. The results are summarised below... So a 45% increase primarily due to adding the inlet ring and increasing the size of the cheat hole. I was surprised at the difference the inlet ring made but thinking about it I guess the original abrupt entry would create a lot of turbulence which the ring eliminates. So a fairly happy bunny now. (Will be happier once shielding relaxes and I can get to the field!) Hope this helps you guys. Quote Link to comment Share on other sites More sharing options...
Martin McIntosh Posted June 17, 2020 Share Posted June 17, 2020 Well, from Tony`s comments it looks like my 450-475gm is in order so I shall stop worrying. I shall carry out the same tests on my Gnat and enlarged Hunter. Tried a test taxi with my Concorde the other day but although it ran for a few yards on the not as short as it could be grass it suddenly went round in circles, only to find that my fishing line steering had broken so a rethink needed. This needs to be held back on the ground for a fair time whilst the PF fans get up to speed. Not sure if using 10 wheels causes more or less friction with the grass. Quote Link to comment Share on other sites More sharing options...
eddie frudenberg Posted June 17, 2020 Share Posted June 17, 2020 I must have made the first Jet Provost wrong somehow. Really wanted one. So I have ordered another wood kit to build another, using my original hardware. Which should be ok according to tony's reply to 4Max. Looking forward to covering my lawn in wood shavings again. once I have a working Provost I like the look of the the Hunter. Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 17, 2020 Share Posted June 17, 2020 Got a new 50C rated battery and i'm now getting around 450grams thrust, and the 4 Max battery has jumped to about 400... really strange! Will hopefully get it in the air with the 50C pack this weekend! Quote Link to comment Share on other sites More sharing options...
Philip Barrett 2 Posted June 17, 2020 Share Posted June 17, 2020 I flew my Jet Provost successfully for the first time yesterday. I had previously tried hand launches, but with no success. For the record the model weighed 760 g and I was getting 440g of thrust on 3 cells. The game changer was the use of a Graupner bungee cord doubled up, with a static length of around 20 feet. I screwed a tow hook on the C of G position to the hand hold block in front of the cheat hole. This had been enlarged as previously discussed. With a good pull before release and full power the JP climbed out strongly, pitching up slightly before the tow line disengaged. It then continued to climb out, and looked fantastic. So the message is don’t give up, a good bungee will sort it ! Quote Link to comment Share on other sites More sharing options...
stuey Posted June 17, 2020 Share Posted June 17, 2020 If you want to fit a catapult hook, a good position to start is 2/3 of the distance back from the nose to the cg. For example if the tip of the nose to the cg is 60cm, fit the hook 40cm back from the nose. This helps pull the model forward, you don't want to zoom upwards like a hi-start. This is from my own experience and info gained from RC Groups EDF forums over time. Quote Link to comment Share on other sites More sharing options...
Dickw Posted June 18, 2020 Share Posted June 18, 2020 More flights with the Gnat today, and for the first time someone with a camera to take some in flight photos. Thanks Chris - superb shots. (but looks like I need to get my hair cut!) Dick Quote Link to comment Share on other sites More sharing options...
eddie frudenberg Posted June 18, 2020 Share Posted June 18, 2020 Some great info on here now for any TH jet builder. Including me on my current Jet Provost build. Quote Link to comment Share on other sites More sharing options...
chris larkins Posted June 18, 2020 Share Posted June 18, 2020 A few more pics of Dick's lovely Gnat Quote Link to comment Share on other sites More sharing options...
Alex Body 1 Posted June 18, 2020 Share Posted June 18, 2020 That's a beauty Dick! Lovely scheme. Where did you get the decals? I trust no issues launching then? Quote Link to comment Share on other sites More sharing options...
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