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Geoff's Jet Provost - Build Log

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Geoff Gardiner26/02/2020 21:31:08
483 forum posts
832 photos

All done.






Has anyone added tip tanks to theirs?

David P Williams27/02/2020 17:27:53
874 forum posts
286 photos

Looks great Geoff. Yes I'm working on tip tanks - I think it looks so much better with them. I fired up Fusion360 and the 3D printer and made these. They weigh about 10g each without paint, just need to make sure not to add too much weight when I paint them. Need to decide whether to glue them on or use magnets.



Geoff Gardiner27/02/2020 23:47:05
483 forum posts
832 photos

Yours also looks great David.

I have also been playing with Fusion360. My first attempt weighs in at 16g unpainted, which I think may add too much weight.

I haven't figured out attachment yet but my feeling is to make them detachable in case they adversely effect flight.

Maybe magnets or simply friction fit.

Keep us posted how you get on.


Geoff Gardiner01/03/2020 11:34:15
483 forum posts
832 photos

I have had a weigh-in, I always hate this bit.

Total weight without battery is 612g.

With a 2200mah battery weighing 180g, it needs 30g of nose weight to balance.

Giving a total of 822g or 29oz.

I have ordered a couple of 2700mah which weight 235g and should mean I won't need any nose weight.

This would give an AUW of 847g or 29.9oz.

Sounds a bit heavy.........again angry 2

adrian garnham01/03/2020 12:45:59
22 forum posts

Looks great.

I built one a few months ago and it too came in on the heavy side ... about 800g inc 2200 mah.

I used the powerfun 50mm fan running on 4s ... should have given given around 765g thrust which I think would have been ok I feel.

However, when I measured the thrust coming out the rear end of the provost I was only getting around 370g thrust. That's why it wouldn't fly

I removed the fan and tested it on the bench and was getting near to the 765g.

I then added a thrust tube of the same dimensions as in the provost and the thrust went down to around 400g on the bench.

Fitting a constant 50mm tube brought the thrust back up to near the 765g mark.

I am currently finishing off my home made CNC router but once done I plan to revisit the provost and re-designing it around a constant 50mm tube. Hopefully it will still look like a provost

Philip Barrett 201/03/2020 13:52:24
14 forum posts
5 photos

Adrian, before taking any drastic measures have you tried increasing the size of the cheat hole on the underneath. I got around a 100g of extra thrust by increasing the size of the cheat hole to around 25 sq cm. It now is 4.5cm deep and 5.5 cm wide. Worth a try!

adrian garnham01/03/2020 14:29:25
22 forum posts

Thanks for the input Philip.

That was the first thing I tried before taking the fan out to bench test .... not much improvement at all.

With my bench setup I had the equivalent of an unlimited cheat hole and it was the thrust tube that was causing the loss of thrust.

In hindsight I should have bought the FMS unit .... although at the time there wasn't a 4s version available to purchase and the powerfun appeared to be more powerful than the 3s FMS version that was available.

I may purchase an FMS unit and do some bench testing with my existing airframe before going too far though !!

Philip Barrett 201/03/2020 17:07:58
14 forum posts
5 photos

I can understand why an EDF unit installed gives significantly less thrust than on the bench, given it has to breathe through nacelles and cheat holes. However, I can’t understand why running a parallel thrust tube gives such a better thrust than the slight taper used by Tony in the Jet Provost.

Can any contributor out there explain this???

adrian garnham02/03/2020 12:55:07
22 forum posts

I found this video on YouTube .... gives a live demo of the effects of thrust tube taper ....


Geoff Gardiner05/03/2020 11:39:00
483 forum posts
832 photos

Here's something weird and rather annoying.

Before I installed the EDF unit I ran it up to make sure it was working, but not up to full power, and all seemed OK.

Now that it is all finished, it's time to test the thrust that I am getting. So I put the model nose down on my scales and ran up the motor. I got to about 300g of thrust at just over half throttle and then the motor stopped. Tried again and anything over about half throttle and it stops. For the third attempt I wired in my power meter to see what was going on.

I found that it was getting up to 58amps at about 700watts and then cutting out, accompanied by a faint smell of hot electrics. The fan seems to be turning freely and I am using a 3s 2200mah battery and 40amp ESC.

I need to do some more investigating but does anyone have any ideas.

What sort of amp draw are you guys getting at full throttle?

It is the 50mm FMS (3s) edf unit.

Geoff Gardiner06/03/2020 12:25:43
483 forum posts
832 photos

A bit of good news, or should I say, less bad news.

Leaving the fan unit in situ, I have wired in another ESC and am getting full throttle (32amps 350watts).

So.... a bad ESC.

Just need to dig it out and replace it.

Tricky, now the side inlets are glue on, but better than having to remove the fan unit.

Geoff Gardiner07/03/2020 21:26:25
483 forum posts
832 photos

So, I have successfully removed the faulty ESC and replaced it.

Now I have another dilemma. I purchased a couple of 2700mah batteries to help with achieving the correct CogG without adding any lead. I am surprised, for an extra 500mah, how bigger the batteries are.


I new it might be tight but thought I would give it a try. Annoyingly they are just a bit too wide to fit through the battery hatch.



I now need to decide if it is worth the effort of enlarging the hatch or just sticking with the 2200mah plus lead (which would be 22g lighter than using the 2600mah battery.

What sort of duration are you boys getting with the Provost using a 2200mah battery?

Geoff Gardiner08/03/2020 21:30:22
483 forum posts
832 photos

I have managed to get the ESC a bit further forward - next to the battery. This means I only need 15g of extra weight in the nose with a 2200mah battery. I think I will stick with this setup to start with.

Final weight is 804g (28.3oz) all in.

I have been playing with the cheat hole to maximize the thrust.

1. 49x35mm hole (as per plan) gave 500g of thrust.

2. 49x45 hole gave 525g of thrust. with top hatch removed this increased to 590g

3.49x49 hole gave 540g of thrust with top hatch on.

Tim Ballinger09/03/2020 09:47:36
746 forum posts
277 photos


you are in the same weight bracket as Steve Nash’s JP and he has now got his to fly away so with max cheat intake size you should be ok. Fingers crossed 🤞 for your maiden.


Mark Winstanley09/03/2020 12:04:03
12 forum posts
Posted by Geoff Gardiner on 20/02/2020 20:59:05:

Haven't updated for a while as I have been doing the covering which slows things up a bit.

Printed some control horns.

Printed off a set of decals and cut them with my Silhouette cutter.


This is how I add letters and numbers.

Nearly there!

More later...

Hi Geoff; where did you download the graphics for the provost? The rally finish off the model.

Geoff Gardiner09/03/2020 14:11:40
483 forum posts
832 photos

Hi Mark.

I downloaded each graphic separately using google image search, resized them to scale, then put them all together on one sheet.

Martin McIntosh09/03/2020 15:02:33
3144 forum posts
1133 photos

Now twiddling my thumbs again although not on sticks I am going to build the JP. Got the last available FMS fan on order from the place the Gnat one came from: a very reasonable price. Ordered a FMS 40A ESC from Banggood UK for £12. Just hope that it does not need some sort of programming card.

Useful to know that enlarging the cheat hole creates more thrust.

I have a 4Max 2600 which is the same size as a Zippy Compact 2200 except 1/2" longer so if the model requires nose weight I can use this.

After struggling with the covering film on the Concorde/Hunter/Gnat I may well go for tissue on this since I have a load of water based Ferrari red paint. It would make life a bit easier and I know how to get a good finish.

I shall order the canopy and intakes from TN this time rather than make my own.

Geoff Gardiner09/03/2020 15:37:24
483 forum posts
832 photos

Hi Martin.

Useful info about the 4Max lipo, All the Hobbyking 2700's were of the larger size.

I don't think I put info about weight gained after film covering the fuselage & wings, prior to adding the side cheeks:

Before 522g, After 560g. Thus 38g gained

It will be interesting to see how much weight a tissue and paint finish will add.

Mark Winstanley09/03/2020 16:18:58
12 forum posts
Posted by Geoff Gardiner on 09/03/2020 14:11:40:

Hi Mark.

I downloaded each graphic separately using google image search, resized them to scale, then put them all together on one sheet.

Geoff; Could I impose on you for a copy of the file? They look so good.


Geoff Gardiner09/03/2020 16:23:56
483 forum posts
832 photos

Hi Mark.

No problem.

If you PM me your email, I will send it to you.

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