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Geoff's Jet Provost - Build Log


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I have the Vac form bits for the Gnat, Hunter and Provost. I also have three FMS fans. So after much deliberation I have decided to start with the Provost.

I have cut out the parts using my Laser/CNC cutter.

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Glued the wing sections together.

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Started on the fuselage. For some reason they cut 10mm too short on the X axis, I may need to check calibration of my stepper motors.

I chose to splice a 10mm strip into each side rather than re-cut them both.

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I cut former 6/7 as a single piece then cut out part 7 and tack glued it back on. I am not sure how useful this will be if I need to replace the fan at any point because the hatches are all in front of the fan - so you are still going to need to hack away a portion of the fuselage, at which point you could probably loosen the hot glue securing the motor and pop it out the front of the former.

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More later...

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Hi Barry.

I am working with the free plan that came in the magazine.

The programs that I use are all available to download for free (I use mac versions):

Inkscape - for tracing out parts (I use the bezier curve tool)

J Tech Photonics laser tool - an extension that you load into Inkscape which produces the gcode.

CNCjs - for sending the gcode file to the laser cutter.

If you have a look at my Oodalally build log here, I have gone into a bit more detail.

The only difference here is that I did not have a PDF of the plan to start with so it was a case of scanning each part from the plan. One thing to note is that Inkscape works in a resolution of 72dpi. So you must scan at that resolution otherwise the scale will change (ask me how I know angry).

Hope that helps.

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Hi Geoff,

looks like a nice neat build coming along there.

I love the CNC cutting equipment, just a bit beyond me I think. I have built the Provost too but had to use my trusty bandsaw and scalpels for cutting out. Started on the Gnat now as well. The equipment you have would be a great help for some of the parts of these jets as they are a bit fiddly and delicate to cut by hand, just have to take it slow.

I'm thinking of getting one of the SLEC building board kits like you have. Are they any good?

I use a magnetic building board at the moment with modified lego blocks that are very versatile as they are infinitely adaptable.

Steve

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Geoff; I see our tastes are the same. As soon as I saw the parts were available on tony’s web site I ordered them for the provost gnat and hunter. My provost is at about the same stage as yours. I too spent time generating Goode to CNC cut parts and I am pleased with the way they came out. I will be doing the same for the gnat and hunter when I have the provost a bit further along. I am looking forward to first flight once the snow disappears- I am in Canada.

best of luck with the remaining construction.

Mark.

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I have cut out the side cheeks.

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And the canopy is waiting for the glue to cure.

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On a painted model I usually fix the canopy after painting, but as I am not painting this model I thought I would try it the other way around.

I have also had to lengthen the ESC to motor wires slightly so that I could get the ESC as far forward as possible.

More later...

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  • 3 weeks later...

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...

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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

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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

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