I have started a new project. It is a 1:5 scale SAAB T-17 model. I chose this plane because it is a simple construction, has no retractable landing gear and is a high-wing plane. It should be easy to design and build, and should fly like a trainer.  It is also the first time I use fibre-glass and vacuum-forming, so it is also my ‘practice airplane’.

I’ll be using my standard construction methods, which is CAD based. When using CAD (and CAM), it’s extremely easy to make parts with notches and groves, which literally makes alignment of parts a snap. No more “this part must be places 5 cm from the leading edge”, kind of things.

Specifications:

Crew: 2
Wing-span: 8.70 m
Length: 7.0 m
Height: 2.60 m
Max Speed: 260 km/h
Range: 900 km
Weight – empty: 600 kg
Weight – loaded: 1200 kg
Armament (Trainer): None
Armament (Military): Rocket launcher

My 3-view comes from Arne in Sweden. One of the fabricators at SAAB that used to work on the Supporter. I have also had an extraordinarily huge amount of help from Thomas and Kjell Aa in Norway, who has flown the real thing.

The wings of the SAAB/MFI T-17 Supporter are swept forward, for better visibility from the huge glass cockpit. Apart from that, they are basically straight, with the exception of a slat near the fuselage.

Just a few pictures of the tail assembly. They have been designed to be light, yet strong. The elevators are located at the top of the rudder, making strength a must.

The fuselage former shapes came from Thomas in Norway. Thank you Thomas! Thomas has documented his build of a 45″ Supporter here.

After consulting with some friends, I decided on the O.S.91 engine with a pump. It is a 4-stroke engine with lots of power for a model of this size, and just fits, if I make a fibreglass cowl. I drew a rough model of the O.S.91 in Alibre CAD to get a feel for its size.

I had to work on the engine cowl, to make sure everything fits. After 2 days of struggle, here is what I came up with – front view and seen from the back with the OS91 engine. I probably went a bit overboard here, as all that is required to make a plug for a fibreglass mold is the outline. All the details and bumps are not necessary.

Next I made the engine mounting box. For an R/C scale aircraft, this must be made from pretty solid pieces of wood, to prevent the engine from ripping the aircraft apart. I had an “AHA” moment, when I realized the engine can be angled and turned up-side down to get the propeller axle at the top of the aircraft. The aircraft mounting box is slanted back to offset the angle of the engine mounts. I have placed a servo behind the firewall. This should be connected to the engine carburettor to adjust the engine speed.

After about one month, I have got the following CAD drawing. I would have shown the design phase here, but due to a harddisk crash at the web-server, I have lost most of the documentation. I do, however, still have the design files and drawings.

This is one of the aircraft I need to complete this winter. I have done a design review today, and I need to do the following:

1. Add more longerons
2. Re-enforce front of plane.
3. Find wing mount that looks like original and at the same time can hide the servo wires.
4. Add servo trays in wings, and for elevator and rudder.
5. Make front landing gear so it has suspension and is steerable.

That’s about it for this plane. I will update this build-thread after I have fixed these.

IT IS SOON TIME TO CUT SOME WOOD.

To make the fibreglass cowl, I first made a plug with the exact shape of the actual cowl.I did this by slicing the CAD model and printing out each slice.

I then cut them out from wood and made a wood/PU-foam sandwich. PU foam is poly-urethane foam. It is similar to the green foam you can get from the florist, except it is much firmer. It can be cut and sanded without worrying about poking a finger through it.

The wood/PU-foam sandwich was then sanded to shape. Any holes and bumps were then filled out and the plug was sanded again. This filling/sanding work continued until it was the right shape and completely smooth. The picture shows the plug after its first sanding/filling cycle.

The plug was then spray painted with an automotive primer. This made the plug real smooth, making any tiny imperfections visible. Filling and sanding was necessary once again.

I went to an airshow in early June where they had some SAAB/MFI T-17 Supporters on display. These will surely help me complete this model.