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Grumman American Cougar


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Hi Gents,

Thanks for your comments. I used to be indecisive, now I'm just not suresmiley

I have now swung back around to the built up idea. I have had a re-jig of the design, and have decided to keep the rear spar, but it is now spaced 1/4" forward of the rear 3/8 block that will hold the hinges. I have decided to laminate 2 x 1/8 bass joiners and they will fit between those two.

The front spar will have a 1/8 bass joiner each side. It will be interesting to get this on the scales, along side the sheet tail that is nearly complete.

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96cae009-69b8-45c9-afd0-3153a6c6dd8e.jpeg

I have used aliphatic for all of this.

Cheers

Mark

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I have got on with that today, a couple of hours work and its nearly done:

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6b8d3d0c-b34c-434d-80d0-26d4b73a7196.jpeg

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The 2 solid block stabilizers on the scales are 75 grams - without any joiners, that 1st half with the joiners, but no top sheeting came in at 28 grams, so it looks like I'm going to save a little, I only hope my nagging 'nose heavy' intuition isn't correct.

I'm now reconsidering having a go at the fibreglass nacelles. If only I could make a decision.....laugh

Cheers

Mark

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Hi John,

Thanks for your comments.
I haven’t got a lot more done in the last few days, I have put this to one side, to see if I can ‘build a wing in a week’ for the Peggy Sue 2, to replace the one that got damaged on its maiden day.

One thing I have definitely decided though, is that I’m not going down the fibreglass route for the nacelles. At 76 inch span, 815 square inches and with a target weight of 9 and a half pounds, by my reckoning, that gives a wing loading of 26.85 oz per square foot.

Reading some other twin blogs, and seeing a couple with a shorter span but coming in well over this figure, has given me a bit of reassurance. Although, I have just ordered some ‘contest grade’ 3/8” and 1/2” to make the nacelles with. Talk about ‘Equador Gold’... it needs to be, the price of it.

Cheers

Mark

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To be honest Mark you could make the nacelles in 1/8" sheet top and bottom with a wide 1/2" or 3/8" sheet profiled piece to give gluing area to the wing skin and some triangular 1/2" in the corners to hold the sides to the top and bottom. With a proper birch ply engine bulkhead, tied into the corner triangular reinforcements, that's about all it needs. That would save a couple of hundred grams.

John M

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Thanks John,

All of the comments regarding the weight of this thing have been playing on my mind the whole way through this build. Not any more.
Last night, I picked up the 2015 summer special edition of RCM&E - the one with Tony Nijhuis’ electric de Havilland Mosquito. It’s span is 72 in (shorter than this) wing area is 5.2 sq foot (less than this) and it weighs in at 14 lbs! (Dennis Tapsfield got his Cougar built to 9.25 lbs)

Tony gives the wing loading as 40 oz/ sq foot (although, by my reckoning of the above figures it is more like 43)

If I can get somewhere close to 9.5 lbs, I will be happy.

Cheers

Mark

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Cubic wing loading on this design, at 9.5lbs, comes in at 11oz/cuft - it'll fly just like a normal sport model, and the rectangular wing will have good manners at take off and landing. I don't think you have much to worry about.

That Mossie, cubic wing loading is near 18oz/cuft which is more like a fast EDF/jet/pylon racer. No idea how that manages to end up at 14lbs!

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  • 2 weeks later...

Hi Mark,

Hope you're getting on with the cougar when you can, looking forward to an update when you are able.

Don't be put off by the weight, an extra pound here or there just means you have to fly a bit faster! As long as you know the model, you just fly it how it needs. Being light isn't everything in my experience.

Gary

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  • 1 year later...

Many thanks for all your kind comments gents. It is appreciated.

I have a colour scheme in mind, but it’s an all solid colours civil one, it may be a bit beyond my comfort zone, but there is lots to do before I get to that stage. I’ve got plenty of thinking time yet.

I seem to have done loads in the last couple of days, but got nothing much to show for it. That tail has been on and off a load of times messing about with the linkages.

I did get the elevator ‘prong’ and the rudder torque rod both made up and silver soldered.

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I then set about F11 to give some clearance to allow that torque rod to swing. No room to get in, and a chunk of 1/8 ply to remove. Result is a bit of a mess, but no one is going to see it.

Cheers

Mark

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I got home early from work today, so got a bit more done. Made up a bracket for the retract valve and did a bit more work on the servo bracket for the fuselage

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There is a bit of tidying up work left on that, but it’s nearly there. 
I’m thinking I’m going to run one of those receivers in the fuselage and the other in the wing, that way, the 4 fuselage servos can run off one, the 5 servos in the wing can run off the other and I will need to run 2  cables to the wing (power and S-bus)

I’m going to run 2 Life receiver batteries along with a Powerbox switch

 

Cheers

Mark

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I wasn’t happy with that servo plate, the retract valve servo was not pushing and pulling the valve properly, due to the rubber feet allowing too much movement side to side, so I tried it at 90 degrees and it was much better, so, made up another plate and it’s now done and glued in:

large.B7ABAD86-88B9-48AA-BE88-AC0C6C59D6C3.jpeg.03e6ddaeef88d18cc20925c3e3c76a29.jpeglarge.403CA0E4-0692-40CC-9E3F-454D3E07F018.jpeg.2b310158a60ffd61a6f83eb9109a7f9c.jpeglarge.7DB4A9A1-ED20-47DB-9D84-F39A67F72C04.jpeg.8663e0e590b5dad2daa019864194abe8.jpeglarge.FB23DFDC-DB81-4780-B46F-D310AA6419DE.jpeg.18272330d569dc69be381fc1666e9502.jpeg


Here is the bodge from yesterday:

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There is still some work to do at that back end, but it’s coming together

 

Cheers

Mark

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