SRX- 2X build thread

[MaxQ]

Well, someone suggested a build thread on this SRX and I agreed to do so, if I got around to it.

I've several other projects in various stages which I'm working on but I was getting very curious looking at this thing - trying to decide how to translate the unique body shape with the complex curves to something bigger.

If I had a full workshop..I would do this proper - and laminate some pine boards together and begin the tedious process of carving a buck or male master with which to eventually pull a female fiberglass mold, and then mold a body shell in two halves with a parting board where the wing would be.
(Or maybe a vacumform sheet of each half, but that would be a pretty big vacumform).

I don't have a full workshop or the patience to do that.

So I'm going to try something quick and dirty.

I got a contour gauge and took bulkhead impressions along station points along the longitudinal axis.

Then I drew up bulkheads for each station point, enough bulkheads to capture the contours and curves, and enlarged them on a copier.

 

[MaxQ]

So, I checked each of the bulkhead drawings for symmetry...basically half a cross section drawing folded over and made into a left and right side, to even out contour gauge discrepancies.

Pasted the bulkheads...all twenty or so, on a foam core board and started cutting.

 

[MaxQ]

Once I got the bulkheads cut, with an appropriately sized hole centered in each one, assembly of the bulkheads began.

 

[MaxQ]

I think you see where this is going...what is needed now is to fill the voids between the bulkheads..

 

[MaxQ]

Pink foam board...got lots of it...

So began the tedious process of filling voids.

Boring, but easier (for me) than trying to be a sculptor and whacking aways at a hard piece of pine and constantly measuring the cuts ..

 

[MaxQ]

Many hours later, I had a pink lego looking blocky thing...anxious to start whittling away and sanding....the edge of the foam core bulkheads would give me a guide to cut and sand down to...

 

[MaxQ]

Once the rough cuts took place to get rid of excess pink foam block, shaping and void filling began.
In pretty short order I had an approximation of the small scale SRX...only twice as large.

The edges are uneven, but they will be cut away and a wood strip set along each side.
It is the curved body form that I'm interested in...the two halves molded off of this will joined on a central triangular wing...

Now the down side is, this thing is a real pig.....and the foam core bulkheads are fragile and the edges won't take a lot of abuse...plus the pink foam will need a good bit of final shaping and filling ...and some recontouring of the fuselage/airframe to get it right - before it can be used for anything.
(This is not unlike you guys turning a foam block nose cone on a lathe only to fiberglass it later...except this thing is completely unsymmetrical so a lathe couldn't be used).

The upside is - in a couple of evenings I have something I think I can use to approximate a male mold...something I can try and fill over with wood filler, bondo or dryvit (I saw a sculptor do an entire bass relief backdrop for the Pope's visit to Washington DC in the eighties - using a dremel tool on foam board with a coat of dryvit over it for stiffness...)

 

[AstronMike]

Max,

That is looking cool, especially in that you are trying to recreate all of the molded details on the original. I am still batting around doing an 'Astronized' 3x version, by that meaning mainly folded/splined Readiboard to approximate the curvy stuff. Would look pretty blocky without those curves but if I cant do something quick I usually dont do it at all. Besides, I want to keep the end up weight down to G capable, which is rather difficult on something on this order....

So, are you making this foamy one you started to fly, or is it going to be the mold for a glass based version? Be neato either way.

BTW, since I dont have any dimensions handy, what is the overall length and width of the original? I thought it was like 18" long and 11" span but maybe not. Need to know this to assure that a 3x isnt unwieldly.

 

[MaxQ]

Max,

That is looking cool, especially in that you are trying to recreate all of the molded details on the original. I am still batting around doing an 'Astronized' 3x version, by that meaning mainly folded/splined Readiboard to approximate the curvy stuff. Would look pretty blocky without those curves but if I cant do something quick I usually dont do it at all. Besides, I want to keep the end up weight down to G capable, which is rather difficult on something on this order....

So, are you making this foamy one you started to fly, or is it going to be the mold for a glass based version? Be neato either way.

BTW, since I dont have any dimensions handy, what is the overall length and width of the original? I thought it was like 18" long and 11" span but maybe not. Need to know this to assure that a 3x isnt unwieldly.

This is a plug for a mold...maybe a couple of body shells...

Original SRX:
The ws is 11.25"
length is 17.5"

 

[kjohnson]

Interesting project. I like that you are using a technique that folks without a big workshop can use. Keep us updated on the progress!

kj

 

[MaxQ]

Max,

That is looking cool, especially in that you are trying to recreate all of the molded details on the original. I am still batting around doing an 'Astronized' 3x version, by that meaning mainly folded/splined Readiboard to approximate the curvy stuff. Would look pretty blocky without those curves but if I cant do something quick I usually dont do it at all. Besides, I want to keep the end up weight down to G capable, which is rather difficult on something on this order....

So, are you making this foamy one you started to fly, or is it going to be the mold for a glass based version? Be neato either way.

BTW, since I dont have any dimensions handy, what is the overall length and width of the original? I thought it was like 18" long and 11" span but maybe not. Need to know this to assure that a 3x isnt unwieldly.

So, I was looking around on Ebay and found this modified SRX for sale...
He was going to make it electric ducted fan or perhaps pusher prop....Note the enhanced wingspan..what do you think?

 

[AstronMike]

Even though the additional fins added to the rear of that modded SRx bring the overall CP aft a bit, they look too wierd though....reminds me of a flattened X24 or something. Completely un-SR like.

They probably did this to add more wing area and reduce the wing loading since electric propulsion was added. Neat idea, but this looks like flex wings on a Saturn V.

 

[MaxQ]

Wasn't sure if they would do much good in my case...don't like 'em much myself.

But I now own that little glider with the wing extensions and I'll probably test fly it...

 

[MaxQ]

I took a break from the other projects and put a layer of wood filler on this foam block assembly.


Once I get it smoothed out and sanded, I'll probably want to lay up some fiberglass over this, (maybe several)...then primer it and sand it until I get a really smooth finish.

Then I need to consider what to do to make a plug out of this thing and cast a two part mold....

I think a "parting board" could be set up between each half of the mold, where the wing is - making a top and bottom mold, from which I could lay up a fiberglass shell for each half....like in the "how to" pictures herein:

https://www.cstsales.com/tutorials/fiberglass_mold.pdf
Any suggestions on what grade of cloth and the resin to use?
I've done sailplane wings and fuselages using West Systems and a few other brands..but want to know what you guys with recent experience are doing..

 

[U812]

It's nice to see someone truly scratch build. Your doing great there Max.

I wrote this book: https://www.sneillfx.com/page21 on making hulls and one of the ways is using the foam as you have but I use the templates for wire cutting and then butt the foam end to end.

https://www.sneillfx.com/page13 This page shows some of the process. The templates get removed from the foam and then I use 377 to tack them together. I just used a few layers of 4 oz. on this one. It was plated in styrene but if I hadn't I would have gone to 2 oz. next. Sand fill, yada, yada.

Can't wait to see more of this. Great project!

Steve

 

[MaxQ]

It's nice to see someone truly scratch build. Your doing great there Max.

I wrote this book: https://www.sneillfx.com/page21 on making hulls and one of the ways is using the foam as you have but I use the templates for wire cutting and then butt the foam end to end.

https://www.sneillfx.com/page13 This page shows some of the process. The templates get removed from the foam and then I use 377 to tack them together. I just used a few layers of 4 oz. on this one. It was plated in styrene but if I hadn't I would have gone to 2 oz. next. Sand fill, yada, yada.

Can't wait to see more of this. Great project!

Steve

Glad you are here...
I'm sure I'll learn tons of info given your past experience.

 

[U812]

If I can be of any help just ask.

Steve

 

[MaxQ]

Here is the previously rough shaped pink foam block airframe...shaped with some additional wood filler and sanded.
Much improved.

 

[MaxQ]

The edges are rough but they'll come off when it is set up to make a mold.
There are some rough spots here and there that need some leveling...other than that, I'm anxious to get some heavy fiberglass on this and begin doing final prep work...

Given what it looked like when I started , this has actually taken much less time than trying to carve and sculpt it out of blocks of laminated wood...