New EDF Mini Jets- Jet Provost & Folland Gnat

[Stephen Belshaw]

Finished the Gnat, my 3S version came out at 22ozs but I need to add some sort of battery tray so it will creep slightly over Tony's designs weight. I fitted the wing in two halves as recommended by others, the build I found very straightforward using the laser cut kit by the covering was a challenge! I also fitted two servos for the elevators as I couldn't get a satisfactory linkage with one servo. Hatch is retained by magnets but not a huge amount of grip so I may need to add another (more weight)! Not sure when I will maiden this as my usual flying space is a bit too rough and as a predominantly glider guider I think it's going to test my nerves! Anyway, here she is:

[David Hazell 1]

Stunning!

[Lucas Hofman]

Looking good!

Go for an open area for your first flights I was surprised at how quikly it becomes a small dot in the sky, and since the glide is flat you should not have to come in for landing over trees or hedges. Good luck.

Lucas

[John Roberts 9]

I also had a successful maiden with mine a couple of days back. Initially the model displayed pronounced 'Jeremy Corbynism' (leaning strongly to the left!) but a few correcting trim clicks soon resolved that issue.

I have left the aileron deflection at the recommended 3mm with plenty of expo (45% on Spektrum) which keeps the changes of direction smooth, flowing and twitch free. As for elevator I settled on 8mm up and 6mm down with 30% expo. Model glides nicely making landing a breeze.

Thanks to my friend and clubmate Richard for the photos.

[Stephen Belshaw]

Nice flying shots John and useful info on the control throws. Is everyone landing the Gnat dead stick?

[Dickw]

Posted by Stephen Belshaw on 04/06/2020 05:10:39:

................. Is everyone landing the Gnat dead stick?

Yes and no!

I used low throttle to bring my Gnat round to final approach but shut the motor off a few feet above ground. If you have the motor running close to or on the ground you would risk sucking dirt and grass etc. through the cheat hole into that lovely fan.

It can be kept flying surprisingly slowly using low throttle.

Dick

[Mike Bell]

Martin M, I have recently got to fly my Gnat and to answer your question on launch, a good, flat, firm throw is all that is needed. I am a mode 1 flyer too and have had no problems, the model stayed on track with no appreciable sink while I got my thumbs back to the sticks.

I had too much aileron movement in initially which was a mistake but when dialled down a bit it is fine. As others have noted I have found that the elevator movement can be increased over the plan recommendation. I found on a couple of occasions that pull out from a dive could be a bit too slow for comfort. CG is as per plan.

Mike

[Martin McIntosh]

Thanks for that. I now need to pluck up courage and increase my carrot intake.

[Dickw]

Two more flights with my Gnat today.

Self launching is no problem, and as others have said a good firm flat throw gets it a way nicely. I am a mode 2 flyer and launch with my right arm, so the plane is on its own until I get my hand back on the sticks, but so far that has not been a problem.

One thing I have done, which may be helpful, is to have a launch mode with both ailerons down a mm and the elevator up a couple of mm. As soon as my hand is back on the sticks I switch that off.

The other thing I noticed was that on both flights the maximum height flown was between 145m and 150m, so that seems to be my "chicken out" altitude for what is quite a small model - perhaps when visibility is a bit better..........

Dick

Edited By Dickw on 04/06/2020 23:29:08

[Trevor Crook]

Still waiting to try my Provost. I had an unsuccessful attempt pre-lockdown when it wouldn't climb away from launch, but that was with a 25C battery. I now have a couple of 40C packs, which boost the thrust from about 450g to over 500. Haven't been able to try it yet as I don't want to self launch for a maiden, and musn't use anyone else at present.

[Lucas Hofman]

Trevor, I gave my launcher a pair of disposable gloves to avoid contact contamination. Keeping a distance is not a problem.

Good luck, Lucas

[Steve Jones 2]

Great Job John and lovely pics.. knew you would enjoy .. looks so great in the air this model . Smooth flyer too

steve

[Dickw]

Posted by Trevor Crook on 05/06/2020 07:47:56:

Still waiting to try my Provost. I had an unsuccessful attempt pre-lockdown when it wouldn't climb away from launch, but that was with a 25C battery. I now have a couple of 40C packs, which boost the thrust from about 450g to over 500. Haven't been able to try it yet as I don't want to self launch for a maiden, and musn't use anyone else at present.

If you can warm up the packs before flying - e.g. on the car dashboard under the windscreen on a sunny day for an hour - that should noticeably increase thrust. I usually heat my battery packs to about 35 degrees C for certain competition flying and it really does make a measureable difference.

Dick

[ken anderson.]

hello dick...I've been using lipos for a long time now c/w all the advice about storage etc,and have never come across any saying put them" on the car dashboard under the windscreen on a sunny day for an hour"!...not been funny or telling you whats right/wrong...... but I would have thought that would have been the recipe for an accident-hope i'm wrong...

ken anderson...ne...1.......right/wrong dept.

[Dickw]

Hi Ken

I actually use a thermosticaly controlled heater box to heat my Lipos to around 35 degrees C in a controlled way, but I have observed others at competitions using the "car dashboard" method instead without any problems.

I think Lipos are safe up to about 45 degrees C while charging, and 60 degrees C just sitting there.

After a flight I put them straight back in the heater box and back on charge ready for the next flight, and have been doing this for about 10 years.

I don't think any of this is good for long battery life, but if you need a bit more power for a competition or getting a difficult model in the air, a bit of heat makes a big difference.

Dick

[Steve Nash 1]

I agree with the warm lipos idea. I was sceptical about it until I tried it myself.

There were four of us down our club field last autumn, and we were all flying edf models. Everyone was flying with cold battery packs and they were all getting about 2 minutes less flight time and a noticable reduction in power, myself included.

I had kept one of the packs warm all the way from home as an experiment, and when I used it the difference was quite literally astonishing. It had bags of power on tap and I got the full usual flight time.

I have also done the same warm lipo experiment with indoor flying and I actually got more than double the flight time than with a cold lipo.

I now have an insulated sandwich bag with a small hot water bottle inside to keep my packs just a bit warm. But NOT TOO HOT as that would be bad.

[Martin McIntosh]

Depending on use, do they not get hot during flight anyway? Some of mine do.

[Dickw]

Posted by Martin McIntosh on 05/06/2020 17:56:18:

Depending on use, do they not get hot during flight anyway? Some of mine do.

Yes, the heat generated in the internal resistance will warm them up, and odd as it may seem that heating effect is greater in cold Lipos than hot Lipos due to the increased internal resistance in cold Lipos.

A double whammy really, power output from cold Lipos is initially lower because of the increased internal resistance, and you use more energy heating them up rather than powering the model.

I have data logs showing the voltage on load increasing as the cells warm up at the same time as the voltage off load drops as they discharge. Overall you are better off starting with warm Lipos - particularly in cold weather.

Dick

[Barry Buxton]

I use one of these from hobbyking in cool weather powered by an old 5000 3S battery

**LINK**

[eddie frudenberg]

I built a TN Jet Provost it eventually weighed 700 g including battery and despite thirteen attempts over a couple of weeks and endless modifications it simply does not fly. Every launch has been a good one even by a bunjee. but it simply wallows and sinks to the ground. the thrust is amazingly good, in that if you hold it upright it almost prop hangs. but it don't fly. I built it from the CNC, wood and cut parts and electronic from THD. But it does not fly. really wanted it to fly. So is there anyone on here that has found the actual secret to making it fly, and has a flying version? As far as I can see, few people ever seem to get one to actually fly! i would build another, that isn't all bashed up once I get this one to work. I did notice the wing span using the pre-cut kit is about an inch shorter than the rcme plan.

[Tim Ballinger]

Eddie , mine certainly flew and there must be half a dozen more successful gnats on the forum (there is another mini jet thread ). You can see u tube video of my first flights at the bottom of page 11 on this thread.

your weight does not seem excessive but I would measure your thrust on a set of kitchen scales. It is crucial you get somewhere near the rated thrust value (600g).
Launch is the critical phase but it sounds like you have that bit under control so I am guessing low thrust is your real problem.

Tim

[Dickw]

Posted by eddie frudenberg on 14/06/2020 21:23:09:

I built a TN Jet Provost it eventually weighed 700 g including battery and despite thirteen attempts over a couple of weeks and endless modifications it simply does not fly. Every launch has been a good one even by a bunjee. but it simply wallows and sinks to the ground. the thrust is amazingly good, in that if you hold it upright it almost prop hangs. but it don't fly. I built it from the CNC, wood and cut parts and electronic from THD. But it does not fly. really wanted it to fly. So is there anyone on here that has found the actual secret to making it fly, and has a flying version? As far as I can see, few people ever seem to get one to actually fly! i would build another, that isn't all bashed up once I get this one to work. I did notice the wing span using the pre-cut kit is about an inch shorter than the rcme plan.

Eddie

There have been several Provosts successfully flown as described in this thread, and the original is shown flying in a video on the first page. However, success does seem a bit harder to achieve than with the Gnat.

As Tim says, it does sound like a low thrust problem, and that mostly seems to relate to incoming airflow and the size and/or lack of obstruction of the cheat hole.

There is quite a discussion around page 8 of this thread that may help. Don't give up.

Dick

[Alex Body 1]

This was my first ever plan build aircraft, so I was pleased that it looked something like the aircraft it was supposed to when finished. Callies graphics did a great job with the Red Arrows scheme.

Flying has been a real pain with only one successful sortie.

The evening of the maiden involved three or four attempts, fiddling with the CG and only finally getting it airborne with a hard throw and a battery a bit further back than I initially planned for, nevertheless - the flight was very good. Slightly poor roll rate, but smooth, fast flying just as promised.

Unfortunately when trying to fly again a few nights ago I could not get it away at all. After five or six very frustrated attempts at a hand launch I gave up and returned home with a bruised ego and a model with far too many bumps and grazes for just one flight!

I think the trouble could be to do with some grass ingestion to the EDF. I removed this and am hoping to try again soon.

The model is a little overweight at about 700g, and the 3S setup gives about 350g/400g with the battery cover on. I'm using a new 40c 2200 11.1 pack, but am wondering if a 50c or 80c may give it a bit more punch on launch. I also wonder if its worth only flying this particular model when there's a breeze to launch into...

Really hope to get this one sorted, as it was a real labour of love putting together!

Any tips gratefully received.

[Lucas Hofman]

350 to 400 gr. of thrust is very little. Mine gives 580 (nose down on a scale). That would eplain any dificulty in getting away.

I do not have much difference with/without battery hatch. If you have the problem might be the air intake. Open up more and make sure all sides are camfered as shown on the plan.

My old LiPo's did not deliver enough, so I had to change. But not to more that 40C.

Try to find why (in the workshop) why you are not getting more thrust and fix it there. That should make a difference.

Regards, Lucas

ps. Impressive to get so good pictures from only one flight!

 

Edited By Lucas Hofman on 15/06/2020 12:59:55

[Alex Body 1]

Thanks Lucas. I actually built in the cheat hole slightly larger than plan (just by a few mm). Given that taking the battery hatch off doesn't get me close to your 580 figure it does suggest its an issue with the power system, though I must admit i'm not especially knowledgable about the electronics and motors side of the hobby at all.

Maybe its a bad battery? Any other suggestions?

Thanks for the comments on the photos - it was a beautiful evening and I had a great photographer on hand.