Kevin_W

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About 6 years ago I sold my last ducted fan airplane. It was a PMP Gripen. I liked the way it flew, but it was confusing going back and forth between the hassles of a glow engine and my turbine. I finally sold it.
But when I built that one I also built another one just like it for a friend. It was completely assembled and glassed, just needed sanding bodywork, primer, and paint.
As it turned that airplane had never been finished. It had been sitting in his garage collecting dust and and filling in as a chew toy for his cat.
I got it back from him a few months ago and decided to convert it to take a P-60.

I had to removed the old inlet ducts, and design and build smaller ones that would allow room in the fuselage for larger fuel tanks.
I decided to build my own P-60 bypass too.
I had to build three conformal fuel tanks.
I didn't feel comfortable with the Spring air retracts on the main gear, so I modified the mounts to accept stronger Robart retracts.
I beefed up the main wing carry-through, and added another layer of glass both the top and bottom of the wings (4oz top, 6oz bottom)


Here is what I started with:

Kevin_W

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Oops,

Here is what I started with

Kevin_W

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These pics show a little bit of the process of building the intake molds

Kevin_W

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Intake cont. and some shots of the bypass

The last shot is the new intakes next to the old ones.

Kevin_W

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All told I ended up making about 11 molds for all the new parts that I needed for the conversion.

Kevin_W

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I didn't get any specific shots of the fuel tank molds, but here are the finished parts.

The molds were very temporary, there were made from styrofoam blocks covered with Econokote. This system works pretty well when you only need to make one or two parts and don't want to spend the time to make a proper fiberglass mold.

Kevin_W

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Various shots with parts installed.

The original kit did not have the splitter plates on the intakes, I made molds for those too. [&:]
I made the mold for the extension between the intake ducts and the bypass out of a pringles potato chip can covered in monokote.

Kevin_W

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And it got a paint job. High vis!!!

Kevin_W

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I am about 3/4 done with the stuffing, plumbing, and wiring right now. It should be ready to fly in a couple of days. Now if the weather would just cooperate. [:@]

B1Driver

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That is awesome Kevin!

Hell of a conversion

Luis

jetpilot

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Cool!!!
Talented man Kevin.
Scott

hmjets

Hello, look here the photos of this JMP turbine(j/c P80) conversion saab Gripen, nice plane.[sm=thumbs_up.gif]---http://www.rcmporto.com/

Ron S

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Wow, you did that all in one evening? You fast!
How many oz fuel are you carrying? I'm carrying 60 oz in my 106, plus 4 oz in a hopper, and I usually have to be on the ground at 5:30 from throttle up...
Color scheme looks like it will be very visible in the air. [8D]

Kevin_W

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I was just lucky to post all of that in one evening. LOL

I think I measured about 81 ounces total including the 4oz header tank. I should have at least 7 or 8 minutes worth with a little reserve.

My ducted fan Gripen was painted all black at first. I only put two flights on it before I repainted it yellow. This is not an easy airplane to see, I need all the help I can get.

GrayUK

Kevin

You have done a great job

I remember the 1000 hours or so working on the design of this model, carving the plug and laying up moulds.
It was always a great plane to fly with an OS 91 Ramtec combination, but I had often thought of building one for the Wren 44 Gold. It think it would be a great combination, as the fuel requirements are less.

I look forward to the flying video. [8D]

I have enclosed a picture of me with the final prototype; it was taken around about 1993 ish!
I had just won the UK Top Gun technical achievement award with it.

Well-done Kevin it is great to see one of the models still around and being cared for[sm=thumbs_up.gif]

Paul Gray

mr_matt

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Hi Kevin,

You_do_realize you are wasting valuable forum space normally devoted to discussing the latest way to hook up a clevis on a Chinese ARF.

Seriously, great thread. Thanks for taking the time.

2 questions:

1.) How do you make the parts from those molds? (in detail I mean). Do you wrap the glass in some way? I seem to remember someone used women's hose for that (Rich Fong maybe).

2.) How do you handle the "lips" of the bypass and the ducting ? I have seen Tad do it but I cannot remember how it is done.

Thanks again,

Kevin_W

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Oops, sorry my bad.

Not sure I understand the question.
Everything was made from a wet lay up. No vacuum bagging. There were a couple of sharp corners on some of the parts where the glass tried to lift and create a air bubble, I solved that by putting a peice of wax paper over the offending area and wrapping with masking tape.

[/quote]
2.) How do you handle the "lips" of the bypass and the ducting ? I have seen Tad do it but I cannot remember how it is done.

Thanks again,

[/quote]
The lips are all molded into the parts.
On the inlets,the long adaptor has a lip on the front and back so it fits over front inlets and over the bypass. As I said above, that mold was made from a Pringles potato chip can. Once the front inlets and the bypass were installed I just cut the ends of the pringles can to the correct angle(s) so it would fit perfectly between them (I actually had to wrap the can in several layers of craft paper to incread the diameter a little too), then I cut two circles (slightly larger than the OD of the inlet and bypass) out of 3/8" balsa and glued those onto the front and back of the can. Then I monokoted the whole thing (finally found a use for the pink monokote I had left over from the 80's). About 5 coats of mold release wax over the monokote, then sprayed on some PVA mold release, paint, then glass and resin. that part had to be cut off of the mold and re-joined with a strip of fiberglass tape.

Some of the other parts (like the fuel tanks) I had to form the lip with multiple layers of 1/8" tape.

Kevin_W

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Thanks Paul.
It's a great little airplane. I had a blast with my ducted fan powered one, and I'm sure it will be even more fun with a turbine pushing it around.

Did you happen to find the info on the control surface throws and the center of gravity yet?
I can't find any of the original instructions.

patf

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Kevin

I have the manual at the house and can provide this evening. Really love the way you did the molds for the inlets based off the center plate. makes sense in my ADD mind. Looks really good. Let me know if you go fly this week. Wednesday would work for me.

patf

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Well we are going to have to look to Paul. The throws are not in the manual (copyright 1995) but on sheet SGK 101. There is a reference to "small movements" on the throws work just fine and a big note to set the CG with the tanks empty. Were there any drawings rolled up in the fuse?

patf

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Kevin

If Paul cant get to the docs you may glean what you need from here... http://www.skymasterjet.com/arf39.htm

Kevin_W

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Thanks Pat, but I found the plans last night.

For some reason I had it in my mind that it was only one sheet, but it is actually about 6 or 7 sheets of plans. I probably missed them more than once in my searches over the last few weeks. [:@]

The Gripen is about 98% ready to go now. If the gyro comes in today I am going to take off work tomorrow and head up to Eagle field to test fly it.

GrayUK

Glad you found it!
The throws are very small, not like Skymaster.

They will look too small but trust me, they are correct

Paul

S_Ellzey

Hi Kevin,

I have a new JR 500A gyro setting around if you need it.

Steven

Kevin_W

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Yeah I remember on the ducted fan one it didn't need a lot of throw.
I have the controls surfaces split on this one with separate servos for each surface, but I have everything mixed so they all work as both elevators and ailerons. I like redundancy. I like redundancy.

Steven,
That is the same gyro I have on order. Hopefully it will show up today, if not I may just take you up on that!
Thanks.