Steve Nash 1 Posted December 11, 2019 Share Posted December 11, 2019 These are the lightening holes I made. The fuselage is still very strong and can't be flexed at all. Other changes were reducing the length of the esc wires, removing the aileron y-lead and plugging the servos straight into two seperate channels in the receiver, removing some blobs of hot glue that were holding wires, and removing the top hatch spring catch and fixing the hatch in place. Steve Edited By Steve Nash 1 on 11/12/2019 18:43:21 Quote Link to comment Share on other sites More sharing options...
Ray Wood 4 Posted December 11, 2019 Share Posted December 11, 2019 Hi Steve, Wow that drastic !! I'm just covering but could add some lightness holes, was your Lipo right up the front? And still needed ballast? Regards Ray Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 11, 2019 Share Posted December 11, 2019 Hi Ray, your JP is coming along nicely. yes my battery is right up the front and also the 1.3 oz lead as far forward as I can get it. Before I lightened it it had an extra ounce of lead in the front, so I've taken that out as well as everything else I changed. other flyers have reported the same tail heaviness and needed lead, or a bigger heavier battery (2700 ish). If I was to build another I would add more lightening holes than I did on this one. I had already finished it all so didn't want to have to re-do all the stickers again. Lightening holes are ok as long as the structure is still strong. I always do round holes or at least square holes with rounded corners. Just remember that every gram too heavy at the back usually needs double at the front to counteract it. I've grabbed the fuselage and tried to twist and bend it and its rock solid still. If you decide to try it just don't overdo it. Steve Edited By Steve Nash 1 on 11/12/2019 21:20:36 Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 11, 2019 Share Posted December 11, 2019 Hi Philip, very interesting results from your edf thrust tests. If only we could utilise all of that 620g thrust, the JP would be a totally transformed beast ! Based on your results I might increase the cheat hole a bit more niw. Steve Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 12, 2019 Share Posted December 12, 2019 Have just done some thrust tests on the JP. I have enlarged the cheat hole a little bit by 10mm in width and 15mm in length. the thrust with a fully charged battery was 530g, so I'm quite pleased with that. I did do jt with the top cover off and the result was about the same, so I wont bother making any extra holes in the top. Steve Quote Link to comment Share on other sites More sharing options...
martin collins 1 Posted December 12, 2019 Share Posted December 12, 2019 Watching Tony`s videos the performance on 3s seems very tame, anyone upgraded theirs to get a performance boost? Anyone used the 4500kv motor on 4s? Edited By martin collins 1 on 12/12/2019 19:47:45 Quote Link to comment Share on other sites More sharing options...
martin collins 1 Posted December 12, 2019 Share Posted December 12, 2019 Anyone used the 4500kv motor on 4s? Quote Link to comment Share on other sites More sharing options...
Steve Jones 2 Posted December 20, 2019 Share Posted December 20, 2019 Nope Martin, cant see the point as it would be heavier , need to fly faster at launch and the 3s setup is plenty fast enough once in the sky .. too fast in fact to be scale. 3s with a light model is a great setup Steve Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 21, 2019 Share Posted December 21, 2019 I fitted the FMS 4S fan into my gnat, very disappointed with it currently, using a 4S 2200 battery. The fan claims a 960g thrust but my basic testing in the gnat is only showing 500g thrust, drawing 30A current. I tried to maiden it but it just headed to the ground and I couldn’t get it to fly at all, total weight including the 4S battery is 26oz, how have others done with the gnat, I wondered about swapping to the 3S fan but I’d only save 2oz in weight and not sure if this would help at all. This is my first edf build so wasn’t too sure if I’d built too heavy or not or where to start looking to get it flying. Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted December 21, 2019 Share Posted December 21, 2019 Barry , Thats disappointing. Some others have had issues with the Provost being overweight but not the gnat. Tony’s original was 24 oz . Certainly at theses weights we can not afford to go over by much but it sounds more like you have an airflow problem more than anything else. If you read back in the threads an enlarged cheat air intake worked miracles for a sluggish Provost. My gnat only has the 3S setup and although I squandered 0.25oz on cockpit furniture today it is still only 20.5 oz ( including everything except covering ). Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 21, 2019 Share Posted December 21, 2019 Thanks Tim, without the access hatch I get about another 60g of thrust but I’m not convinced that’s going to be enough but I will add more access holes, not too sure how to shave 6oz off it though to get to your weight, I could lose 2 oz moving to a 3S setup but sacrificing thrust. I tried to see if I could upload a photo from my iPad but not too sure how to do that, do I have to create an album first then share from that ? Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 21, 2019 Share Posted December 21, 2019 Found out how to add photos if these help Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted December 21, 2019 Share Posted December 21, 2019 See you sorted the photo album out. So thats an extra 10 % thrust based on the 3s fan but still sounds well down on the 4s spec. Grasping at straws are you sure you have the throttle calibrated for the ESC so that you achieve full throttle. Only way to shed weight at this stage is to cut lightening holes as is shown for the Provost a few pages earlier. What did you cover it with ? Tim Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 21, 2019 Share Posted December 21, 2019 Yes, I calibrated the throttle and measured 36A / 500W at full throttle. I painted the plane after giving it a coat of eze-kote, grey primer rubbed quite well down after applying and 3 tins of humbrol enamel thinned out for spraying. Must admit I am thinking that the paint has added more weight than covering. I’ll put some extra vent holes in it and when / if the weather improves I’ll give it another go, would like to sort this out as I’ll be getting the Phantom kit for Christmas. As a matter of interest what is the best way to measure the static thrust, I basically hung it from a set of luggage scales and powered her up Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted December 21, 2019 Share Posted December 21, 2019 Fingers crossed for the next attempt. as for thrust measurements, I guess you will find not many folks bother. I have used a spring balance in the past. Perhaps deserves a thread in its own right . I am certainly no expert.! Tim Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 21, 2019 Share Posted December 21, 2019 Barry, lovely looking model you've made there, I've just started building mine. I measured the thrust on my Provost using a digital hanging scales. I suspend the plane from the tail using a string loop around the tail and zero the scales. Then just open up the throttle and see what you get. I got 530g thrust on the Provost with a freshly charged battery that had been kept warm in my pocket for a while, otherwise the lipo's don't perform very well this time of the year when they are cold. That 530g is on a 3s fan using an Overlander 3s 2200 battery. After a while the thrust dropped down gradually to around 515g. I would have thought that your 4s fan should perform better than that. You say that you would only save a couple of ounces by swapping to 3s, but on an aircraft that should weigh around 20-22 oz that is 10% of the weight, so it will make a difference. On a 40 size IC plane a couple of ounces wouldn't even show a difference, but on models like this weight is the enemy. Steve Edited By Steve Nash 1 on 21/12/2019 21:13:02 Quote Link to comment Share on other sites More sharing options...
i12fly Posted December 21, 2019 Share Posted December 21, 2019 Just an idea...... As air intake seems to be a limiting factor, maybe if you use a 4S set up you need to open the cheat hole area a 'corresponding amount' to get the extra air throughput? This could affect some of the model types but not others of course, depending on how the air is balanced of cheat versus intakes. In reality axial fans (which effectively EDFs are), move air and generate relatively little pressure, so much so that they soon stall when restricted on the inlet or outlet. On the other hand centrifical fans (not practical for EDF) generate a more significant pressure, increasing right up to the point where the outlet is blocked completely. Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 22, 2019 Share Posted December 22, 2019 Another idea is to check the timing of the esc, as I read that this affects the performance of the motor. My esc was from another plane which had an outrunner swinging a prop. In that plane I had the esc set to low timing. In the Provost I have set it to medium timing due to the high rpm required. Steve Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 22, 2019 Share Posted December 22, 2019 Thanks for the ideas guys, I’ll try retiming the esc later and add extra breather holes, failing that I’ll order a 3S fan. It as it’s a nice day here in Stoke on Trent I’m going to take the Riot out for a fly today and get back on this after Christmas. Have a good Christmas all Quote Link to comment Share on other sites More sharing options...
alan barnstable Posted December 22, 2019 Share Posted December 22, 2019 I've been doing some testing with my Provost whilst it's raining. (note i've only had 2 successful launches out of 8 attempts). Total weight including 2650 3 cell battery and 140g lead weight in nose is 836g (29.5oz). Thrust is 404g with standard cutouts in bottom of fuselage and side ducts. Thrust is 514g with top hatch removed. I'm going to carry out the following steps: 1/ remove weight from rear of plane, and remove some of the ballast weight 2/ enlarge the hole in bottom of fuselage 3/ try flying it without top hatch Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted December 22, 2019 Share Posted December 22, 2019 In light of the queries regarding thrust values I offer my own results for the Gnat using a 50mm FMS fans and 2200 Lipo. Test set up is crude but seems repeatable +/- 20g and is shown below As you can see the model is uncovered and I asked the pilots to step out for the tests on H&S grounds. Next the results What I conclude from this is 1. Although removing the hatch increases the airflow/thrust it is not as effective as providing a clean unobstructed intake right in front of the fan. Hence relatively smaller increases in 'cheat' intake size are very worthwhile. 2. In these static tests the original 'cheat ' intake size is perhaps too small as it does not deliver max thrust. I say perhaps because once in flight with a forced airflow it probably does achieve full thrust. However with folks having trouble achieving flying speed ( ignoring the issues of being above design weight) from a hand launch perhaps max static thrust is a good design point. 3. I achieved 600g thrust with a 60% increase in 'cheat' intake size ( 48mmx48mm). This is pretty close to the spec value of 620g so I will leave it at the new size. 4. My current values of 42A are in excess of the 32A in the spec. Not sure why but are within the ESC spec so I am still happy. I was actually using the Neuron S ESC for these measurements and have not cross checked the values on a another sensor yet but I have no reason to doubt the accuracy of the values. Tim Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 22, 2019 Share Posted December 22, 2019 Tim, very interesting results. The best approach with these models I think is to keep them light and make the cheat holes bigger like you gave done. Its great that you have achieved almost 100% of the thrust quoted in the specs for the fan. Steve Quote Link to comment Share on other sites More sharing options...
Steve Nash 1 Posted December 23, 2019 Share Posted December 23, 2019 The Provost needs a good launch to get airborne, so what I have done is to glue a small piece of coarse sandpaper each side of the underneath just where my fingers grip it. This gives a good grip, and the sandpaper can be painted a matching colour if required. I hold it as shown with one finger just inside the cheat hole to give good leverage when I throw it. I get a really good chuck doing it like this. Edited By Steve Nash 1 on 23/12/2019 10:44:06 Quote Link to comment Share on other sites More sharing options...
Tim Ballinger Posted December 23, 2019 Share Posted December 23, 2019 Good tip Steve, I expect a bit of breeze helps as well. I’m still fitting out the office but covering is not far away. Quote Link to comment Share on other sites More sharing options...
Barry Buxton Posted December 23, 2019 Share Posted December 23, 2019 Following on from Tim’s post, I enlarged the breather hole to ~48x48mm and this has increased thrust slightly to about 520g with the battery hatch closed so a good mod to make, opening the battery hatch isn’t having any major effect, maybe adding ~5-10g extra thrust, I’m beginning to wonder if there’s something wrong with the fan unit so I’ve ordered another one up for trying out, in the meantime I’ll look at how to reduce the weight, I’ll start with a 4S 1800 as that will take 30g off and then investigate making lightening holes Quote Link to comment Share on other sites More sharing options...
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