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Geoff's Jet Provost - Build Log


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Trying to avoid divulging this, but with a 3300 plus the nose lead it is, say it quietly, 29oz.

I very carefully selected the balsa and am actually a bit worried that the wing may be a bit too soft and light.

The weight does not really surprise me because compared with others in the range it is rather chunky.

My Gnat is spot on weight wise.

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'printed off a set of decals'. Those look superb, could you quickly run through how you did that? I have the same Silhouette cutter, how did you combine the two processes or was the cutter just used in the lift and place proceedure you showed? I tend to use the Silhouette for larger sized projects as the vinyl is a bit thick, can you recomend a thinner if thats what you used? Thanks, sorry for the interrogation.

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  • 2 months later...

Well, thought I would try for a maiden flight today as I had a flying buddie with me who was happy to hand launch for me.

The first few attempts were failures just straight to the ground.

I then took the top hatch off and after a couple of more attempts we managed to get it away and had a 3 minute flight whilst tinkering with the trim. It does get small very quickly!.

After that we had another half dozen or so attempts with a fresh battery - all failures.

Conclusion - needs a bit more work.

img_1396.jpg

img_1399.jpg

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It's on the previous page Martin.

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.

I was using a 3s 2200mah 50c battery.

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  • 3 weeks later...

Hi there,

An update on my Provost...

It has always flown ok, once the tricky launch is mastered.. needs the biggest shove off of all the models (Gnat, Hunter & Hawk) but I have always been a little disappointed at the performance. It seems to need more power than the others.

So looking through your posts I decided to enlarge the underside cheat hole to 65mm by 45mm.

I added a little more nose weight to move the cog a little... WHAT a transformation !!

Now the take off is still tricky but once in the circuit the cruise power is much less and the flying much much smoother. Gone is the tip stall in the turns tendency.. RESULT !!

So now she joints the fleet as a great flyer .. well pleased

Steve

Cheat Hole

Front

Rear

Edited By Steve Jones 2 on 13/07/2020 22:29:50

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  • 2 months later...
  • 8 months later...
On 01/03/2020 at 12:45, adrian garnham said:

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 /CuteEditor_files/images/emsad.gif

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 /CuteEditor_files/images/emsmile.gif

Following my previous post ....

I decided to redesign the provost (based loosely on Tony's balsa design) to accommodate a constant 50mm dia thrust tube and to ensure it would be light I made the fuselage and wings from hot wire cut foam.

The resulting model doesn't look pretty as it is very experimental but it flies extremely well considering I have never designed a model aircraft before.

All up weight including a 4s 2200 maH battery is 710g.

Static thrust measured by placing the nose on a set of scales is 735g.

I am using the same esc and powerfun EDF as before .... go figure.

20210604_180819.jpg

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  • 3 weeks later...

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