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Grumman American Cougar

Build Blog by Mark Elen

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Mark Elen25/04/2020 21:20:38
527 forum posts
1022 photos

As I am about at the end of my Peggy Sue 2 Build, I thought I would start a build blog for my next project.

I have had the plans for this for the last couple of years, and have been slowly accumulating the bits and pieces needed. I originally saw this model when it first came out in the 80s and I wanted to build it then.

The original design calls for Goldberg mechanical retracts, I have managed to get hold of a set of Robart air up, spring down 12 lb with firewall mounting noseleg. There will need to be some re-engineering of the wing to allow these to fit.

It also is based around a pair of OS Schnuerle ported 2 strokes, my plan is to put a pair of Saito 40 4 strokes in it. This will mean that the firewalls of each nacelle will need to be moved back and the tank bay will be shortened. More on this as I proceed.

The plan and build article are both here on outerzone: **LINK**

I'm looking forward to getting started.

Cheers

Mark

Nigel Dell25/04/2020 21:32:28
460 forum posts
46 photos

Hi Mark

That is a really nice design and flew well I seem to remember and typical of Dennis Tapsfield designs it is a straight forward pleasant build. You should enjoy that, Dennis was a super nice guy I have built a few designs of his and the Chilton DW1 was a favourite.

McG 696925/04/2020 21:35:45
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3298 forum posts
1252 photos

... it seems that you really are 'model-building' hungry, Mark.

yes surprise wink

Cheers

Chris

Piers Bowlan25/04/2020 21:43:40
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2166 forum posts
53 photos

Mark, I have mulled over this design on Outerzone on several occasions, as a GA twin is on 'my list' and this is such a nice design. It is a super project with two Saito 40 for power, good luck with the build and I will be following with interest.

Dale Bradly25/04/2020 22:45:58
17 forum posts
5 photos

Hangar One Kit if you are interested. I've built a couple of kits from this supplier and very happy with the quality

Mark Elen26/04/2020 23:00:04
527 forum posts
1022 photos

Hi Gents,

Many Thanks for your comments.

Nigel, That’s good to know, I had a look at the Chilton, that looks like a nice model, I’m surprised Mr Miller hasn’t had a go at that one, maybe its because it’s been done a few times before? It looks like it is right up his street.

Chris, there are benefits to being in lock down with no work... the downside will be no money coming in very soon.

Piers, I have always liked the look of the Cougar. This is the second set of plans I have had for it. I bought a set in the late 80s, but never got started on it.

Dale, Thanks for that. I have been buying balsa and ply for this build over the last year or so and I’m pretty much ready to go. Good to know though

I have been formulating a plan for the radio install, the plan shows a single servo for Ailerons, on snakes, a single servo for flaps, on torque rods and a single servo for both throttles, again on snakes. These will all be replaced with a Hitec HS85MG on each surface/throttle. That’s 6 servos in the wing.

The Elevators and the rudder will have 1 standard size servo each, then the noseleg steering and the retract valve will have a HS85MG each - fuselage 4 servos

The HS85MG is 3Kg/cm @ 4.8v and 3.5Kg/cm @ 6v, so should be sufficient.

I’m using Frsky Tanaris, so I had thought about using a couple of S-bus decoders in the wing, but have come up against the 9ms problem with analog servos, so have decided to use a RX8R redundancy bus receiver and a RX8 receiver to give the full 16 channels with redundant antennas, if I locate one of these in the wing, I will only need a 6 way connector for power and Sbus between the receiver in the fuselage and the one in the wing.

I will also use a pair of Life 2100 receiver packs and a power box switch/regulator.

The above is the outline plan. It may change

Cheers

Mark

Mark Elen04/05/2020 20:49:30
527 forum posts
1022 photos

Today, I made a start on this.

I have decided to start on the fuselage, as I prefer to build wings. One of the things that I haven't yet done is to build a laminated structure, so this was where I decided to start. The two fuselage laminated formers.

I bought a roll of proper tracing paper from e-bay just lately, and put it to use on the laminated formers. I found that the plan is not quite right, I traced out the formers, then flipped the tracing over and laid it back over the former. The curves were not symmetrical. F5 was 1/16 out at the worst point, F3A was closer, but I ended up rubbing out one side, then flipping over the tracing paper and tracing the same side so that I had a symmetrical former.

I then glued these onto a couple of sheets of 1/4 ply with upholsterers spray adhesive and set to work with the scroll saw and made a couple of jigs.

Cutting 16 strips of 1/4 wide 1/32 ply seemed to take a while.

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The other one is done as well, both now clamped up and sat drying overnight.

Cheers

Mark

Mark Elen05/05/2020 21:04:29
527 forum posts
1022 photos

Bit more done today. I got those formers out of the jigs and got the ends brought down to size and the angle sanded onto F3A.

The formers on the plan do not match the drawings... F3a needed 3mm off the bottom to match the side elevation, the box of F6 is shown 3mm too wide on the former drawing, as opposed to the plan. I have decided to measure each former off the plan and build to that. more on this later.

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Here is F6a traced and flipped over. Its miles out. I ended up doing the same with this, rubbing the wrong looking side out, flipping over the tracing and then tracing the same side twice, once on one side and once on the other.

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As the 'words and music' call for pre-bending the sides and the doublers before putting them together, and, because I have been meaning to make one for a long time, I have finally got around to making a 'vice bending tool'. The plan is that each half will screw into a couple of new vice jaws, that I need to make, and will turn the vice into a bending tool. Lets see how this pans out....

Here is the start:

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The cougar sides bend by 7 degrees, I have set this up at 5 degrees per side, to make 10 degrees included. Hopefully this will allow for any spring back once the wood is released. Its a bit of a shot in the dark...

Cheers

Mark.

Mark Elen06/05/2020 20:17:19
527 forum posts
1022 photos

Not had a lot of time today, as I have been at work...hurrah.

I finished off the female part of the balsa bender last night, and this afternoon when I got home, I got the male part made. I have made the male part .5mm shorter than the female. This is for a cross piece that will align the bend to 90 degrees. Its coming together slowly...

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Cheers

Mark

McG 696906/05/2020 20:38:05
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3298 forum posts
1252 photos

Hi Mark,

To be honest, I don"t understand a iota of what you are doing...

But, no probs, as I will be waiting as usual when it all clears up.

Mega tidy as usual, anyhow..

Cheers & stay clear

Chris

Mark Elen06/05/2020 21:30:32
527 forum posts
1022 photos

It’s ok Chris. I’m not sure I know what I’m doing either....

I can see some testing going on soon, before I try to bend the fuselage sides.
Cheers

Mark

Mark Elen07/05/2020 20:41:53
527 forum posts
1022 photos

I got the fuselage side bender completed today. I had to make a new set of vice jaws first to screw the bender to:

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Now I just need a pair of fuselage sides to go in and try it.

Cheers

Mark

Danny Fenton07/05/2020 22:13:50
avatar
9649 forum posts
4458 photos

Will enjoy following along, the Grumman American range are a favorite of mine. No compound curves except the cowls and canopy. Been doing an AA1b "Yankee" for indoor. 800mm span 50 grams so far.

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John Minchell is also building a Cougar, not sure if it is from the same plans?

If I can understand what you are doing you have made a tool to bend the balsa fuselage sides?

Will enjoy following along.

Cheers

Danny

Gary Clark 107/05/2020 22:43:31
avatar
242 forum posts
131 photos

Following along Mark. No doubt I'll learn something new so looking forward to it

Gary

Mark Elen08/05/2020 10:50:41
527 forum posts
1022 photos

Many thanks gents for your kind comments.

That looks superb Danny. Yes, the bending tool is to pre-bend the fuselage sides just behind the wing seat. Dennis Tapsfield suggests this in the build article.

Thanks Garyyes

This morning, I have got the fuselage sides traced out:

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and re-designed the wing hold down plate, so that it is at 90 degrees to the wing bolts:

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I bought 48" x 4" 1/8 sheet for the fuselage sides, it is about 4" too short and 1" too narrow:

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so, I'm going to have to join it. The current thinking is to splice 2 pieces together over 6 inches or so, with the join falling on the flat part of the front fuselage where there is a 1/32 ply doubler. There will also be a 1" strip along the bottom. Is this the best way?

Cheers

Mark

Mark Elen09/05/2020 18:11:06
527 forum posts
1022 photos

I got a bit more done today. Starting with making a big enough piece for each fuselage side:

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I then used my tried and tested way of making 2 doublers that are exactly the same. Take 2 blanks, stick them together with upholsterers spray adhesive, then using the same adhesive, glue on a tracing of the doubler. This can then be cut and shaped to the correct dimensions. Once done, the sides can be easily pulled apart and the glue can be removed with thinners:

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In amongst todays work, I made up a test piece to try out the bender. I was concerned that the bend will be on a part that has a tiny sliver glued on and that the wetting of the balsa would weaken the aliphatic and release it. I didn't need to worry:

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I glued the test doubler piece onto this (using evo-stick the same as the sides will be using) and wetted the outside, then using a scrap piece of 1/32 ply to protect the balsa, it went in the bender and was left for an hour or two:

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If anything, it has worked a little too well, as the expected spring back hasn't happened. This is it pinned into place where the fuselage side will end up:

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Cheers

Mark

Danny Fenton09/05/2020 22:26:32
avatar
9649 forum posts
4458 photos

Impressive, that has worked very well

Cheers

Danny

Mark Elen10/05/2020 20:13:27
527 forum posts
1022 photos

Thanks Dannyyes

I got a fair bit done today. Starting with getting the doublers evo-stuck onto the fuselage sides:

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Then I actually remembered to draw on the locations of the formers. I always seem to forget this step:

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Then into the bender:

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Excuse the mess!

They came out not too far off:

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I then got on with the 3/32 square on the top and bottom and the wing seat 1/4" treblers:

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The next job is to draw out the plan view onto my building board. The plan view and the side elevation on the plan do not match up. The former drawings are also wrong. F10 and F11 are a long way out.

Cheers

Mark

Mark Elen11/05/2020 19:02:49
527 forum posts
1022 photos

I got a load done today:

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Cheers

Mark

AndyD11/05/2020 19:35:01
avatar
771 forum posts
553 photos

shouldn't even be thinking about this plane as ive got so many projects on the go at the moment but ive got suitable motor.s and retracts so down loaded the plan just in case lock down persists longer than thought.

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