Moulded Version.

For those interested in the log of the moulded version of this plane, it starts at page 17.
Also, there is a lot of posts about my fumbling around with airbrushing. That can be skipped too as it has not eventuated. I still have secret plans to do one of my moulded ones with the bird look decor! But no promises!

Original thread started here:

I have responded to some gently prompting to post this build log. However, it will be only partial, as the project has progressed somewhat.
Anyway, I will do my best to explain what has happened so far.

The concept was for a low wing, light wing loading, "V" tailed aerobatic model. My design thoughts were much influenced by several other gliders, especially the Barracuda. I originally was going to build a medium/heavy loaded plane like the Barracuda. However, recent events have led me to realise my reactions and eyesight are not fast and good enough respectively, to fly the faster heavier models. And I do not have a composite model that will fly in light lift conditions. Also, I have yet to achieve a light composite model without going seriously over target weight. So we will see how I go with this one.

The vital statistics are:

Wing span - 1500mm wing area 25 sq.Dm.
Airfoil section -- Ritz 1-30-10
"V" tail
Target AUW 800 - 850 grams. for a wing loading of 32 - 34 g./sq.dm.

The fuselage will have slip on nose cone. I think this will suit the model best. But mainly because I am able to build one better than I can a canopy!
The fuselage plug was made out of second hand seasoned, clear grain Douglas Fir. This takes a bit of time to find: I go to the building recyclers regularly, so I'm able to look out till I find a suitable piece. This timber is not ideal due to the wide annualar growth rings, but that can be dealt with. Otherwise, it is fairly stable and easy to shape. And most of all, it is available (still).
I use a mix of polyester resin, "Q" cells and "wax in styrene" to surface up the timber and fill the large grain etc. Wet sand in the usual way. Multiple coats etc.

The plug is partly made, and the wing fillets have been recently shaped and glued onto the preshaped main fuselage section. I am designing this with the plan to use an inflation bladder to mould the fuse. I am already wondering how to get a bladder to go into the fillets. One possibility is to backfill the fillet cavities with shaped foam prior to placing the bladder in the layed up half.

The wing cores are cut and assembled with wood tips and LE. I used some Western Red Cedar for this, possibly not the most ideal. However, I did have weight in mind here - I have formerly used Aussie hardwood. Tasmanian Oak, which is very tough, but heavy.

For the spars, I experimented on a piece of foam scrap cutting the slots for them with my router. I used a 6mm plain bit and set it about 2mm deep. This made a very neat and accurate slot which when filled with two runs of 50k carbon tow wet out, filled to surface level very nicely. As can be seen in the picture, I doubled up the spar for the first 1/3 span.

This is just a start. I'll post more details soon.

The pictures are of the mock up of the plug and flying surfaces. The bird is our native "Wompoo", which provided the inspiration for the name, and also for the planned colour scheme. Just how much of likeness of this magnificent birds plummage I will be able achieve only time will tell!

Jim.

Nice Jim " Wompoo " never hard of one but digging up the facts now. Will we see the Wompoo at Borah 2011.

Dave

Dave,

Good to hear from you! This is a picture of the bird that inspired me. I even plan to use some of the superb colours of this creature, and dare I say, somelikeness of the feathers etc. For someone who has zero artistic ability, this will be really pushing my personal boundaries!

Jim.

I got into some difficulties with the wing. After some deliberation and consultation with others I decided to make pre made glass skins and glue them on with the customary PU glue.
I had put a lot of work in the preparation of the cores, with scarfed Western Red Cedar round tips and LE etc. Double tapered too.
I laid up some light skins on the glass in the usual way. 1 layer only of 76 gsm glass and 1 layer of veil (26 gsm.)
Apologies up front for the use of metric on this thread.
When I glued on the skins, I used a notched spreader which I cut specially for the job. The cores weighed 211 grams at prepared stage, and the skins around 100 grams. So all was looking good weight wise. However, they did not stick on the cores well. The result was a very wavery surface and some delamination. I did mist the cores lightly with water before assembling the skins onto the cores.
To make a long story short, I have now stripped the glass off the cores, which came off all too easily! I have used this method several times before with success, but formerly with thicker skins and maybe more glue.
I can only conclude that I did not use enough glue.
The only damage to the cores was some tearing of the TE which I am now attempting to repair with splooge, using the beds to form the shape.
I will find out if I have saved the wing tomorrow when I unpack it.

Watch this space........


Jim.

Great job on the log so far Jim. That Wompoo is one gorgeous bird, I never knew that pigeons could look like that.

Premade glass skin glued on with PU that sounds very creative, I'm learning already.

I'll be watching your build with much interest

Alex

Alex,

There is a thread on the pre-made skins technique. I'll find the link later.
I hasten to add that I have had success with it using a moderate to heavy lay up. It has advantages which are discussed in the thread.
In future, for light lay ups, I will stick to conventional vacuum bagging.
The mylars can be painted, or at least primed, which saves much sanding and painting/filling etc., which in turn saves weight.

Jim.

Originally Posted by tashmish

Will we see the Wompoo at Borah 2011.

Dave

Dave,

I certainly plan for that to happen!

Jim.

These are some pictures of the plug which is coming along nicely. However, I am a bit concerned about the lack of draft angle on the wing saddle. It will be 0 deg. (or 90 deg. depending on which way its expressed).
Will it release from the mould lay up I am wondering? Can anyone advise please?

Should I follow a sequence that might go something like this?:

Start with the two mould halves laid up on the plug about half thickness for flexibility, drill clamping bolts holes etc. then split and remove the plug. Once release is assured, it all could be reasembled and subsequent layers built up to provide necessary thickness and stiffness? To be sure, to be sure? Or is the recipe for inaccuracies?

I got into a slight amount of bother with the filling and grading of the wing saddle. I am surfacing the plug up with polyester/"Q"cells/wax in styrene mix.
I applied a liberal amount to the wing saddle and then used the wing cores as a mould to shape it. I covered the wing with drop sheet plastic. However, the solvent(s) of the polyester mix leaked through the plastic and started to melt the foam!!!
Fortunately, I was able to rescue it in time and allow it to offgass before filling with spackle/"Q" cells. All's well again.

Jim.

I think that you be will fine. Here is a mold that I recently made that has 6 flat surfaces (3 in the canopy area, wing saddle, and two on tail plane mount) that are perpendicular to the parting plane. The plug did get a few paint chips when extracted. All the parts have come out of the mold with no damage. This is a bladder processed part so there no openings in the flat surfaces. I have to drill holes in the saddle and canopy of the part, insert some carbon rods into the holds and pry against the mold flange (wood blocks on the flange) to get the part to come straight out of the mold. The mold is far from flexible.

Adam

Originally Posted by wyowindworks

I think that you be will fine. Here is a mold that I recently made that has 6 flat surfaces (3 in the canopy area, wing saddle, and two on tail plane mount) that are perpendicular to the parting plane. .................. The mold is far from flexible.

Adam

Excellent Adam! That is just what I wanted you to confirm for me.
Mine will also be a bladder sealed job, so I can use the same, or similar removal technique if necessary.

Jim.

Originally Posted by Jimbello

Excellent Adam! That is just what I wanted you to confirm for me.
Mine will also be a bladder sealed job, so I can use the same, or similar removal technique if necessary.

Jim.

Jim I will mention that the release is done with Frekote 770-NC and the mold is painted with a primer. This makes for a pretty easy release. Wax only would be an issue. Using PVA and wax should work just fine. In the worst case scenario your could spritz some some water around the edge to soften the PVA and give you a little more relief.

Adam

Hey Jim, on my jart mold with the fillets I use brass tubing in the bladder opening to help "pry" the fuse from the mold. It works like a charm and if I pry too hard I usually end up bending the tubing and not breaking the fuse, well Usually.

I had to figure this technique out after having problems getting my first few fuses out. Especially since I overbuild the fuses with fabric and there is no possibility of flexing the fuse to help removal.

Thanks Adam and Alex. I take note of the release methods required: I plan to use wax and PVA at least. My local advisor/supplier has a fancy release system decribed as similar to freekote, which I will find out about when I go to him to have the polyester gel coat sprayed on the plug.
As an alternative, I plan to approach the local auto spray painters to see if they would like to spray it with 2 pack paint for me. They are much closer to where I live.

And the two leverage methods of plug removal might be of assistance when the time comes.

Otherwise, everything is on track!

Jim.

Originally Posted by wyowindworks

I think that you be will fine. Here is a mold that I recently made that has 6 flat surfaces (3 in the canopy area, wing saddle, and two on tail plane mount) that are perpendicular to the parting plane. The plug did get a few paint chips when extracted. All the parts have come out of the mold with no damage. This is a bladder processed part so there no openings in the flat surfaces. I have to drill holes in the saddle and canopy of the part, insert some carbon rods into the holds and pry against the mold flange (wood blocks on the flange) to get the part to come straight out of the mold. The mold is far from flexible.

Adam

I'm getting towards my first bladder mold, so I ask simple questions.

Where's your bolt throughs on your pics above Adam? As the guru of bladdering your departures from the dogma are noted. Am I missing something? Maybe you just clamp?

thanks

And good luck Jim on your thread so far, I'll be starting my own shortly, just doing some trials now so I dont make too much of a fool of myself.


Ben