TOPIC: Converting catapult kits to Rapier or TSP power

Following on from the Concorde catapult model that I posted about in the 'Models for 2022' section elsewhere, here is the 9 inch wingspan DPR catapult profile model kit representing the Folland Gnat trainer that I received recently as a present.

What am I doing with this? Well I hope to try it out as a Rapier/TSP powered model, but it needs a few alterations, I also have some quibbles with the outlines as it doesn’t immediately convince as a Gnat but it is good enough for a youngster wanting to fly a scalish catapult model. Me being me I would now like do a better model at some point, we shall see.

The laser cutting and wood selection are excellent and quickly makes up into a neat little model. One of the wing pieces needed a little fettling to get a good joint and you might see that I have started filling in the catapult notch on the underside and made a separate thinner fin instead of the 3mm fin that came as part of the fuselage. If I need to catapult the model I can add a pin under the nose, as is my normal practice. I have also deleted the undercambered slot for the wing with a balsa infill and re-cutting a straight slot as undercamber is not needed for our purposes as it would cause the looping tendency to be stronger.

The pic of the loosely assembled model still needs the nose side cheeks fitting, which will not only strengthen the nose but add the balance weight needed. Getting the model to balance without extra weight is presumably the reason why the wings have been swept back more than the actual aircraft. The stickers look fairly good although the undersides of the wings and tailplane are left bare so the model will need some protection there if it ever to fly over wet grass. Unfortunately the stickers are thicker than expected and so are a little on the heavy side in my opinion.

I don’t know if the Gnat ever sported a smoke generator pod underneath as the Hawks of the Red Arrows do, but it has now!

This looks to be a nice basic model, with some strange features: the over-thick fin and increased sweepback for example, which reminds me of the proposed Gnat mk 2, which would have had a supersonic performance:




I would certainly be very tempted to reduce the sweepback to that of original Gnat. The coloured stickers are a good basis for your own model and could be scanned, modified (for the underside flying surfaces) and printed on tissue.

At 9" it should be just right for a TSP L-1. Will you be 'fleshing out' the fuselage?

After doing some test chucks over the bed last evening the model needed 2g of tail weight! The original wing was a bit bendy and I thought the wings might warp too easily. so I have already made a more scale shaped wing out of quarter grain balsa, to move the CG forward. I have also thinned the tail end of the fuselage somewhat and it looks like the nose can be slimmed down in places too. Currently the balsa assembly weighs 9g, so probably around 18g all up when finished.
I might do the undersides of the flying surfaces in Solite film if tests show I can keep the balsa flat enough.
Thanks for the MK2 pic, I had not seen that before.
I am trying to keep this one nice and simple so I will probably keep it flat as per the kit. If I ever get on to doing all of what I would like with the design it will be larger and much more 3D, but definitely not red again. I well remember being inspired by Mike Smart’s neat little L1 sized Gnat but never saw it fly.

The new wing with all shaping and sanding finished, it now weights 8.23g bare.

The centre of gravity is a long way back on this model at 57% of the overall length of the fuselage so the motor position will not that far ahead of the low tailplane. Adding a thrust tab without weakening the tail area is tricky so this time I will try setting the motor with some downthrust. If that doesn't work I will have to glue on a downthrust tab under the tailplane with a fillet type backet, yuck.

A couple of pics to show the process of getting stickers on this model. I have only applied one nose sticker and the fin stickers at this point, more will come later at my usual snail’s pace.
As you can see I have roughly painted all the edges with a (nearly!) matched acrylic paint which is easier to do at this stage rather than later and you don’t have to worry about being neat. Then I painted all the balsa with well watered down R/C modeller’s glue as the adhesive on the stickers is not that great. Once dry I sanded everywhere and then applied a coat of neat UHU por to the edges by wiping it on smoothly with a finger. This last stage needs doing to ensure the stickers can be fully boned done and to make sure the edges won’t lift up again (fingers crossed). As soon as the por has dried a little I carefully aligned and applied the nose sticker, gentle pressure was used working out from the centre. Rather than putting slits around the edge of the sticker I slowly and gently boned down the edges. It is tricky to get the paper stickers to go round the double curvature and a few creased will show on close inspection. To ‘bone’ the edges I used a suitable implement - my finger nail.
Although the model is pretty well flat everywhere the tiny bit of shaping on the three thicknesses of 3mm balsa on the nose really pays off.

This is looking really nice. I want one! Who says you can't turn a sow's ear into a silk purse?

Added 06/10/2022:
This model is still avaiable from the Balsa cabin, if you are willing to wait for dlivery (Wanda couldn't say exactly when this would be).
Howard notes there is also a Tornado.

I aim to scan the sticky-back plastic bits and, after some manipulation/corrections, print them on tissue or 40 gsm paper. They can then be glued (or doped) to the shaped balsa parts.

This is what I did with a a catapult Alpha Jet some years ago:



Above: original Alpa Jet (Catapult-powered) kit. Nice livery, but, being plastic, unsuitable for Rapier power:S

I doubt I shall be able to resist the temptation to 'flesh out' the fuselage (like the old Veron 'Quickies'). The Gnat, though, should still be suitable, like my very similar Alpha Jet, for my aged, and low power, Rapier L-2 LT motors.

My scans of the original parts were printed on paper, and the templates attached to balsa parts.



Above: Alpha Jet for L-2 LT.

We shall see.