New EDF Mini Jets- Jet Provost & Folland Gnat

[Tim Ballinger]

My first time with a hot glue gun as well, seems to be the goto tool I’ve never found a need for before!

Tim

[Tim Ballinger]

Fan installation went well as did the acetate jet pipe. I did find that a piece of foam pipe insulation was exactly the right size for holding the acetate tube tight against the inside of the former thereby leaving two hands free to apply tape and glue.

[David P Williams]

Good tip with the pipe insulation Tim. Bit of a three-handed job isn't it?

[Steve Jones 2]

Something to think about chaps for the elevators.. they are only held by the outer 3mm sheeting at the back of the intake duct and I thought it was a little weak for vertical bending.

I added some extra reinforcement strips the inner fuse as shown in Tims pic. This allowed me to glue the root of the elevators to something..

I used hot glue on the fan of my Provost but it broke free on the maiden as a blade shed !! I re-glued with epoxy after roughing the fan cowl. On my Gnat I epoxyed from the start (its not coming out !!) and if i have a fan motor issue i can remove them and leave cowl in place..

[Tim Ballinger]

Test run the EDF. Certainly makes a potent desk fan!

Thanks for the thoughts Steve, I’ll certainly have a look at the tailplane mounting. I must admit I used more than the recommended number of blobs of hot glue to hold the fan in so I’m fairly confident it will stay in place🤞
Tim

[alan barnstable]

I initially only glued the motor in with a few blobs of hot glue and it broke loose after a hard landing. I have now glued it in more comprehensively.

[Tim Ballinger]

Perhaps even a few more blobs then......

Tim

[Tim Ballinger]

Steve,

see what you mean about the tailplane attachment relying on the intake skin . Got to be careful not to build a battleship but I think you are right, it is probably worth an extra gram of balsa each side.

Tim

[Dave Chatterton]

Hi guys. Just thought that I would let you know that I used mirror ply for the tube and therefore had more glueing area . Dave

[Tim Ballinger]

A handy byproduct of changing from the acetate Dave. I still have the cut outs from the inner fuselage sides which provide a handy template to insert an inner tailplane seat so I’ll just trim a piece out of those for each side.

Tim

[Steve Jones 2]

Yes Tim,

If I build another... really would like to do the Red Arrows version before they changed to Hawks.. then I would not cut such a large rear hole in the inner fuselage sides - using this as the inner elevator mount. There is no air flow there and the additional wood weight would be insignificant.

Steve

[Tim Ballinger]

Steve,

here’s what I did. I left a gap so I could still key in with the triangular section at the top. Bit more of a jigsaw but it seemed to finish up the same.

[Steve Nash 1]

Anyone weighed their Jet Provosts yet?

tried maiden flight at the weekend but seemed a little heavy. My hand launcher didn't quite give it enough oomph and it didn't fly off, just settled onto the grass.

have done bit of work to it to try and lighten it. I've cut some lightening holes in the underside rear fuselage and changed a few things. I've taken out about 1.5 oz.

mine now weighs in at 26.5 oz with a 2200 lipo but needs additional 1.3 - 1.5 oz of lead in the nose to achieve the C of G, making a total of just under 28 oz. I might try a 2700 lipo as that should come out the same but no lead needed. This time I will make sure lipo is at room temp to make sure it gives proper power.

if I was to build another I would cut lightening holes all round the rear fuselage and also the tailplane and fin. None of this would be seen after covering and would help take away a bit of the tail heavyness.

any thoughts ?

[Steve Jones 2]

Hi Tim,

Looks better and the elevator would be in double shear... curious you have left the top right corner open as the hinge line is at the rear so I would have made the triangle go the other way - I am sure it will be fine though

Steve, Not sure on the weight of my Provost with its 2200. Will measure tonight and post.. It does need a hefty shove to launch, a coupe of times in low wind it failed to get away and belly flopped.. The Gnat on the other had goes away like a missile ..... Will check its weight and maybe its a less draggy frontal area.. It needs much less power to cruise too.

Steve

[Tim Ballinger]

Steve,

I did to start with then decided I wanted the Triangular fillet to locate the rear intake side securely. seems solid and the half’s fitted squarely without any fettling.

Tim

[Steve Nash 1]

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 barnstable]

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 1]

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 2]

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 barnstable]

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 2]

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 barnstable]

Useful feedback Phil, will give this a go. cheers

[Tim Ballinger]

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 1]

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 1]