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New EDF Mini Jets- Jet Provost & Folland Gnat

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Steve Nash 110/12/2019 14:14:31
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52 forum posts
11 photos

Hi Steve,

thats what happened to mine - a belly flop. Definitely a good throw needed.

I really wanted to stay with the 2200 lipo as I've started to build the Gnat too, and wanted the batteries to be for both planes instead of buying more different ones, so will prob settle for a bit of nose weight instead of bigger batt.

Steve

alan barnstable10/12/2019 17:43:09
19 forum posts
2 photos

Mine (Provost) is also 29oz, including the 140g I had to add in the nose to balance.

Unfortunately it is virtually impossible to launch even with having someone else throw it. The only time we were successful was when there was a strong headwind. On all other occasions it has belly flopped, and on one occasion it resulted in the motor breaking free, and on another it cartwheeled and broke the tail. I've fixed it now, and will try a bungee launch.

I think the problem is that it's to heavy for the wings/motor, and the design results in it being tail heavy and having to add weight in the nose. Without the nose weight it flies horribly.

Edited By alan barnstable on 10/12/2019 17:43:39

Steve Nash 110/12/2019 18:15:28
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52 forum posts
11 photos

Alan,

were you also using a 2200 lipo?

I definitely think the plane needs seriously lightening at the back end. I have cut lightening holes in underside as it is easy to just cover with film, but doing sides, fin and tailplane means disturbing the finished stickers etc.
It could be altered during the build if I was to build another, with plenty of lightening holes in the rear. Maybe the wing could be moved back about 5mm or so if the intakes would still work out ok, that would hopefully take away the need for nose weight.

Steve

Steve Jones 210/12/2019 18:40:02
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586 forum posts
431 photos

Alan

As we all know the building of a model and the resultant weight can differ significantly between models. Wood selection is critical and can have a large effect.

i am not the lightest builder but try and I suspect the provost being a little more bulky is prone to over weight if not careful

the model is a great flyer once away but needs a little more airspeed to fly than the gnat. If I was building again I would take more care on wood selection and maybe reduce some sections carefully.. lower weight, better flyer .. it’s simple I guess..Don’t give up but keep at it and when you do take to the air enjoy

steve

alan barnstable10/12/2019 18:52:40
19 forum posts
2 photos

Hi Steve/Steve,

I use a 2650 3 cell battery. I do have smaller batteries but then I'd have to add even more nose weight.

I bought the wood pre-cut from Tony Nijhuis, so assume it was the right weights for the model.

It's a shame, it's a good looking model, and all at my club think it's it's great, until they see us trying to launch it !

I agree that taking weight off the back half would help, but it would weaken the airframe and I wouldn't want to risk it.

Unfortunately I'm running out of people willing to throw it, they dislike seeing it crash as much as i do.

I have fitted a tow hook underneath, and I just need to make up a launch ramp and elastic to try and get it to a higher launch speed. But weather pants at the moment so unlikely to get this done soon.

cheers, Alan

Philip Barrett 211/12/2019 09:51:35
18 forum posts
5 photos

I have had the same problem trying to get my Jet Provost away with a hand launch. This puzzled me, as the weight was around 26 ounces only. Admittedly on all occasions the breeze was very gentle. I decided to take the fan unit, a FMS 50, out of the model and test it. I was only getting around 330 g of thrust installed, against the 600 promised.

Out of the model and in a test rig I got 620g, so what was happening in the model? I decided it had to be a breathing problem. I increased the size of the cheat hole on the underneath to a maximum by taking it to the wing trailing edge, then tried it with the top hatch off. Amazingly, was now getting around 480g of thrust.

As it spoiled the look of the model I drilled 12 holes in the top hatch and opened them up top 12mm diameter with a Dremel coned grinding stone. Checked the thrust again, now got around 430g. It feels totally different now, and I am sure it will get away whenever our patch dries out.

Worth a try if you are struggling!

alan barnstable11/12/2019 11:11:53
19 forum posts
2 photos

Useful feedback Phil, will give this a go. cheers

Tim Ballinger11/12/2019 11:27:39
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796 forum posts
290 photos

Useful feedback indeed. Perhaps the airflow to the gnat is better which is why that is reportedly having no problems. I know it’s not the whole story but is total intake openings on the two designs any different. ( I’ve not got the JP plan to check).

Tim

Steve Nash 111/12/2019 18:36:47
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52 forum posts
11 photos

Just had successful maiden flight of the Provost.

I did a few things to lighten the plane and it now weighs in at 27.6 oz including 2200 lipo and 1.3 oz lead.

i didn't have anyone to hand launch for me so I thought I would give it a go myself. There was a moderate breeze and I had kept the battery nice and warm in my pocket. I launched it just above head height with a firm chuck slightly upwards and it just flew away no problem, it didn't even sink a bit. The only thing I gave had to change is that I didn't have anywhere near enough elevator travel, but other than that it flew ok. I got about 5 mins from the 2200 which left 24% in the pack after landing. The landing was a bit firm due to the lack of elevator authority.
this was a total contrast to last weekends attempts to fly which resulted in belly flops onto the grass. Definitely better now it's lighter. I have a small piece of sandpaper glued each side of the underneath to grip better and had one finger in the entrance of the cheat hole to help push it forwards.

Steve

Steve Nash 111/12/2019 18:38:17
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52 forum posts
11 photos

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Steve Nash 111/12/2019 18:39:39
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52 forum posts
11 photos

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.

Steve3bac01dd-cc2e-4df9-a4f2-f5ac1d13cb0e.jpeg

Edited By Steve Nash 1 on 11/12/2019 18:43:21

Ray Wood 411/12/2019 20:32:09
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221 forum posts
44 photos

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 Rayimg_20191211_202654.jpg

Steve Nash 111/12/2019 21:08:07
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52 forum posts
11 photos

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

Steve Nash 111/12/2019 21:18:23
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52 forum posts
11 photos

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

Steve Nash 112/12/2019 17:04:37
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52 forum posts
11 photos

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

martin collins 112/12/2019 19:36:18
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429 forum posts
199 photos

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

martin collins 112/12/2019 19:46:37
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429 forum posts
199 photos

Anyone used the 4500kv motor on 4s?

Steve Jones 220/12/2019 09:17:13
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586 forum posts
431 photos

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

Barry Buxton21/12/2019 15:56:29
18 forum posts
12 photos

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.

Tim Ballinger21/12/2019 18:57:24
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796 forum posts
290 photos

ec7b0161-fbb5-47ab-831d-fd50b15c1030.jpegBarry ,

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 ).
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