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Geoff's Jet Provost - Build Log


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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 !!

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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???

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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.

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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.

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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.

img_4718.jpg

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.

img_4719.jpg

img_4720.jpg

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?

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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.

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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.

img_4689.jpg

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.

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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.

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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.

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Mark, those decals look really good. I've not had much success printing on vinyl, the colours always seem dull when I print them. What vinyl did you use? My roundels I made by cutting red, white and blue discs on CriCut cutter and putting them together. The lettering was also cut on the cutter using the RAF font.

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Posted by Geoff Gardiner on 09/03/2020 17:08:48:

Hi Steve.

It was me whom produced the decals.

I printed them on some A4 sheets of vinyl that I got from eBay here.

Printed at photo quality, I was pleasantly surprised with the print quality.

I also purchased some transparent vinyl but I haven't tried that yet.

Geoff...

I also used the same vinyl and printed on my inkjet at high quality and was very pleased with the result.

I used white vinyl where the roundels needed to be white over the red wing, but the black numbers I printed on clear vinyl and stuck them as a block over whatever the base was - works OK.

One thing I did was to spray the printed sheets with a clear lacquer before cutting out the shape, just to give some protection to the ink in case of bad weather!

Dick

topside.jpg

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Hi Martin,

If you're using Silhouette Studio, I can send you a file set up for that.

You just send it to your printer first, it will print with registration marks.

You then send it to your cutter and it first scans the registration marks and then starts cutting.

The fin flashes I cut out manually.

I'll PM you.

Geoff...

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This is how I produced the cutting file in Silhouette Studio:

1. Set the page size to A4 and the cutting mat - in my case I use a portrait cutter

1.jpg

2. Import the decal file into your library.

2.jpg

3. Select it and it will open up.

3.jpg

4.jpg

4. Click on it and resize to the correct scale.

5.jpg

5. In the page setup box, click on registration marks and configure as shown in the picture below.

6.jpg

6. Now select trace from the right hand menu. Click 'select trace area' and draw a box around the first roundel. Click on 'solid fill' and 'trace outer edge'.

7.jpg

7. You can adjust the threshold if needed and you should have a cutting line around the first roundel. I have deleted the decal layer in the picture below so that you can see the cutting line underneath.

8.jpg

8. Repeat with all the other graphics on the page and you should have something like this. Note it is easier to cut the fin flashes and union jack by hand.

9.jpg

9. Send the page to your printer using the best possible print quality and print onto the vinyl.

10. Stick the page onto your cutting mat and load the page into your cutter. On the portrait cutter, it has two load paper buttons - one for normal prints and one if your are using registration marks. Make sure you use the correct one.

It should then feed the page in, scan the registration marks and start cutting (works best with the lid closed).

If it can't automatically find the registration marks, you can do it manually. There are four arrows in the print window that allow you to move the cutting knife. You just move it until it is over the black square registration mark and then click send.

10.jpg

That's it.

Hope that makes sense.

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  • 4 weeks later...

Now that mine is complete I hope that you do not mind me putting it on here.

It is covered in tissue then painted. I did a test piece to ensure that the water based Ferrari red was compatible with the Humbrol matt white enamel base coat and it dried just fine. Not so after a couple of coats had been sprayed on because to start with it attacked the masking tape and bled through everywhere. Quite a job to patch up later, but fine after spraying with Tufkote substitute.

Despite tissue and dope generally coming out at no heavier than Oracover I cringed when I put it on the scales. Even a 3300 Lipo would not bring the cg forward enough but an additional 1 1/2oz of the dreaded did so.

Loads of power though and not far short of lighter than air using a pack on storage charge only.

Pics.

provost 001.jpg

provost 002.jpg

provost 003.jpg

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