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Thorpe F-20 build

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Old 09-19-2011, 09:36 PM
  #1
tlj125
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Default Thorpe F-20 build

I am scratch building an F-20 Tigershark from plans I purchased years ago from Thorp Brothers out of the UK. The plans are for a 45 size ducted fan. I plan to install a Wren 75 turbine in it. Does anyone have any experience with this jet with a tubine in it that can give me some tips and advise? I can post pictures of the build if there is interest.

Terry
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Old 09-19-2011, 11:20 PM
  #2
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Default RE: Thorpe F-20 build

I also purchased the plan pack -with control cables, canopy, instructions and litoplate sample- several years ago, when I was a teenager and still keep it in my plans colection.

I for sure will follow up your F-20 build thread and wish good luck with your project.

In the other hand I can´t help you much as lack experience both building and flying this model. What I have is the review of the fiberglass kit version Ducted Fan powered published in a pair of issues of RC Jet International many years ago. If you think it may be of help, pass me your mail via PM and I will scan and send you a copy of the articles.

Best Regards


Jesus Cardin
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Old 09-20-2011, 03:41 AM
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Default RE: Thorpe F-20 build

I have one that I had being flying with a .45DF, I have looked at it a few time in regard to converting to turbine, but a few things put me off, space for fuel tank (fuse is very narrow only 90mm forward of engine), fitting of retracts, as mine has the foam wing and they are just too thin to practically fit retracts, (used a dolly as a DF) and weight it would be heavy for size.
I think you could fit a wren44 but dont know about anything bigger.
Any of the guys that have converted the thorpe F20 to turbine, started with the fibreglass version as far as I know.

It flys great so no issue there.

What I would advise and what I have thought about doing a few times is to slightly scale up existing plans, you could get it done easy enough at a stationary store, slightly bigger would be much better in regard to wing loading and obvious space in installing equipment.
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Old 09-20-2011, 06:24 AM
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Default RE: Thorpe F-20 build

I will be using Spring Air retracts as they fit just fine. I started to build this several years ago for ducted fan with a Turbax I and OS 46. Now I think a small turbine would be well suited to this project. Space will be an issue. Would like to know what others did. I was thinking of making my own tank and putting it just behind the cockpit in the space between the inlets. Then maybe add two more tanks and put them inside the inlets just ahead of the turbine. Here are a few pics so far.

Xairflyer- can you give more detail about how the plane flies? Top speed, landing speed, pitch sensitivity, visability in the air, etc. Thanks.

Terry Jacobs
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Old 09-20-2011, 06:30 AM
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Default RE: Thorpe F-20 build

A few more pics...
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Old 09-20-2011, 06:33 AM
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Default RE: Thorpe F-20 build

and more...
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Old 09-20-2011, 08:22 AM
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Default RE: Thorpe F-20 build

I had one with a .46 ICDF. I thought it was fast, had a great glide (since my engine always quit) and was fairly hard to see.
I personally think Wren 75 is way too much power.

Having said that, I'd like to do another someday with a 90 mm edf.
Jim
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Old 09-20-2011, 09:39 AM
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Default RE: Thorpe F-20 build

It is fast in the air but can be slowed down once you master the nose high approach, I never noticed any problems with pitch, but the colour I had did make it tricky to see at times so I have a load of yellow arrows on the bottom.

The built up wing is probably better to mount retracts, I could'nt do it with the foam wing just too thin.
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Old 09-20-2011, 10:28 AM
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Default RE: Thorpe F-20 build

My friend had one and it was flown with a Wren 44 Gold which had ample power i think the 75 OTT plus being heavier! I am sure Gordon's F20 was fibre glass with foam core wings..

One thing I remember was we had to increase elevator as we ran out of movement on landing. I will try and find the pics... RIP Gordon

Alan
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Old 09-20-2011, 07:49 PM
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tlj125
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Default RE: Thorpe F-20 build

The reason for the Wren 75 is that I have one already that I can put in it. Why do you guys think it is too much power? It easily fits in the fuse and takes much less space than the Tubax I fan unit and OS 46. Thrust is only about 15 or so pounds. I estimate this model will end up weighing about 10-12 lbs dry with another pound or two for fuel. Doesn't seem overpowered to me. I flew a 17 lbs thrust P70 in a Yellow Starfire that weighed 14 1/2 lbs dry and it flew great. I should have never sold it.

How fast is this F-20 at top speed? 150 mph? 180 mph? 200 mph? I would like it to go at least 175 mph.

I am currently flying a 1/8 scale Tam F-16 with the Wren 75 and am use to landing slow and nose high. It is underpowered by the way. Does the F-20 land the same as the F-16? The F-16 will not snap. I don't care how slow you fly. What about the F-20? What speed does it land at? My F-16 lands at about 25-30 mph. Top speed is about 170 mph on a calm, cool day.

I appreciate the input guys.

Terry
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Old 12-15-2011, 08:14 AM
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Default RE: Thorpe F-20 build

Getting back to the F-20. Started planking the fuse. Also glued second base in place under the nose and started shaping it into place. Here are a few pics of my way to plank. No one ever showed me how to plank, so this is just what I came up with. If someone knows a better way, please tell me.

I use paper to make a pattern to make sure I get the geometry right. Then I cut the balsa sheet to the pattern with #11 exacto knife. Then spray windex on the side that will not be glued and work it till it softens and bends easily and make sure it fits. Sand here and there for a good fit. Then mix up some 30 minute epoxy and put it in the stringers, bulkheads, and edges where the plank will set against. Try only to put glue on half the plank where another plank will have to be glued later. I don't put any glue on the plank. Then I pin the plank in place and scrap up any excess glue. I use little spring clamps sometimes also. After the glue sets (30 min) I pull the pins and clamps. Any loose spots are glued with quick CA.

I have ordered a Wren 44 for this plane. Decided against using the Wren 75.

Terry
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Old 12-16-2011, 12:41 PM
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Default RE: Thorpe F-20 build

Did the nose. Made the middle piece from plywood to have something to shape to. Also will be better to support the model when placed on its nose. Made a paper pattern first from the shape of the nose on the plans. Then cut the plywood out on a scroll saw. Glued 1/2" and 3/4" balsa sheets on with 30 min expoy and sanded the whole thing into rough shape before gluing onto the nose of the model.
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Old 12-16-2011, 12:51 PM
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Default RE: Thorpe F-20 build

Then plane and sand...
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Old 12-16-2011, 12:55 PM
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Default RE: Thorpe F-20 build

Looks like the nose on the plans to me. Close enough anyway.
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Old 12-16-2011, 01:03 PM
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Default RE: Thorpe F-20 build

Nice work!
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Old 12-16-2011, 09:38 PM
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Default RE: Thorpe F-20 build

Thanks Andrew. And now for the inlet ducts. This was tedious. Cut several pieces until I got a good fit. Wanted to use 1/64 ply for these but the hobby store had 1/32 so that is what I used. Cut the inlets with the scroll at first but then found it easier to cut them out with siccors. Sprayed them with windex and rolled them up to get them into place. Once a good fit was achieved, I glued them in with medium CA. Then sanded them flush with the bulkheads. Turned out pretty well.
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Old 12-16-2011, 09:43 PM
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Default RE: Thorpe F-20 build

More pics of the inlet ducts being put into place and sanded.
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Old 12-17-2011, 05:42 AM
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Default RE: Thorpe F-20 build

Terry,
It looks great. I love the building thread.
Glenn
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Old 12-18-2011, 08:01 PM
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Default RE: Thorpe F-20 build

Thanks Glenn. I threaded the control cable tubes. Used 36" Sullivan Gold-N-Cable #508. But the ones for the rudder and elevator appear about an inch short. Need to see if I can get a longer set for these. For now I am not going to glue them in place.
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Old 12-20-2011, 06:24 PM
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Default RE: Thorpe F-20 build

Vertical stab and rudder were next. Glued together 3/8"x4" balsa sheet with a 1/8"x3/8" spruce piece in the middle. Traced the outline from the plan and cut on a scroll saw. Then capped the leading edge with 1/32 ply and sanded to an airfoil shape per plan.
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Old 12-20-2011, 06:28 PM
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Default RE: Thorpe F-20 build

Checked airfoil thickness and compared to plan. Kept sanding till it was right. Took a while but it turned out pretty good.
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Old 12-20-2011, 06:34 PM
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Default RE: Thorpe F-20 build

Then cut out and hinged the rudder. I chose the non-scale rudder which is longer. I used Robart hinges and drill guide. Still have to square up the holes so the hinge will recess into the wood. Used a #11 exatco knife and a small file to fine tune the fit. Did not glue the hinges as yet.
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Old 12-20-2011, 06:39 PM
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Default RE: Thorpe F-20 build

Also put a spruce cap on top and sanded it to shape as shown on the plan. Then glued the vertical stab onto the airframe with 30 minute expoxy making sure to get it as vertical as possible and a good fit with the exhaust tube and spruce stringers.
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Old 12-20-2011, 09:50 PM
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Default RE: Thorpe F-20 build

Shaped and hinged the elevators the same way.
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Old 12-20-2011, 10:06 PM
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Default RE: Thorpe F-20 build

I will follow this thread closely. I purchased this plan and the F104 at a swap meet. I got to find the canopies though. Keep up the good work,
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