TOPIC: Profile F-15 Eagle for L-2

Looking good, I like the intake solution, it works very well visually as well as being a launch grip, good one.

It being a calm and sunny day, I took the F-15 down to the local (and small) recreation ground for some prelininary trimming launches to test the trim, CG etc.

Hand chucks revealed little; better were catapult launches after I had added a small hook to the nose.These were ''interesting", as they say: the model had a tendencey to climb, turn, go inverted and then, in a stable fashion, 'glide' to the ground at a steep angle. Hmmm ...

I added a couple of grams nose weight, which helped a bit: now it would consistently climb from a fast launch, but then dive with no stall recovery.This pointed to insufficient decalage, so I scored deeply along the bottom of the tailplanes and 'cracked' in about 1.5 mm 'up elevator', I removed the extra nose weight.

Now I was getting somewhere, even if the model was quite stally and could 'wallow' after an initial climbout. A bit more noseweight, perhaps? 1.5-1.6 grams seemed optimum, and I was now getting a consistent launch, which showed the need for right rudder to correct a left turn . After this it glided straight and, if one was lucky, it could glide quite a long way. if the field were larger, it would have been ready for time for a low-powered flight.

The trimming session was curtailed when the right rear fuselage broke off (these are quite vulnerable) and it was back to the workshop.

The tailpnane incidence can be 'tidied up',and broken rear fuselage are easily fixed, and it will be easy to hide 1.5g of lead in the nose. More worryingly, I feel the model could definitely do with more dihedral. But this can't, alas, be fixed.

Perhaps I should make a 'mk 2' with a stronger rear fuselage, more, 'built in' decalage and a sensible amount of dihedral?



Above: a somewhat battered F-15 after its initial flight tests. The extra 'White-Tac' nose weight looks a lot, but it's only 1.5-1.6 grams.





Above: two shots of the F-15's rear end. Note where the tailplane has broken off (does this need strengthening?), and the 'up elevator' achieved by partially cutting the tailplane and gluing in some reflex. I'm not called 'Roger the bodger' for nothing!

I'm now pretty sure the F-15 will fly OK under power, but perhaps I should have taken out the the model for some trimming tests before spending so much time finishing it? Will I never Learn?

Sounds good that you are getting straight glides, if the model will straighten up after of a banked catapult launch the dihedral is probably OK, if not it might help to either mount the motor lower or add some ballast near the motor position.

It certainly looks the part Roger. I was concerned about dihedral as well, but as of yet I have only glided it in my garden, so it's hard to tell. I watch and await your trimming progress with great interest. It is after all a prototype, so we are bound to run into these challenges. I think a Mk2 is on the cards!

Luke has just sent me this report. You will remember his F-15 is in a way simpler than mine and glided well from a hand chuck from the beginning, whereas mine, with sanded in airfoils and rounded edges, needed a bit of sorting out before it agreed to glide properly and the right way up.

Luke writes:

"We had dead calm conditions an hour before dusk and, having looked at the weather all weekend, thinking, "this is perfect flying weather, I was desperate to fly if I could! So I went out with the F-15 for its first flight testing. Initial glides [from a hand launch] were steady and straight so I popped a standard TSP L-2, lit up and launched ... it did a big loop...twice. So I stuck some Plasticine on the nose and tried again. This time the flight pattern much more impressive: a steady climb out with a bit of stall until it settled into some left hand circuits and glided down. The third flight, interestingly, spiraled in tighter circuits and wasn't so impressive. By then it was getting dark and cold so so I decided to call it a day.
I have some photos which aren't great but (I think you will agree) the F-15 Eagle it does look good in the air!".





Above: Luke's right, the F-15 does look great in the air. The third flight showed, perhaps, that if we fitted a thrust tab and took off the extra nose weight the glide would be a lot better and prevent the spiral to earth Something to try at Old Warden over the weekend.

rogersimmonds wrote:

This Guillows model is of course 'for display only' and non-flying, but could it be made, with a lot of modification and a bit of simplification, the basis for a flying model?

Just stumbled over this. This can absolutely be done. I flew the F-16 (same series of display model) ages ago as a slope PSS glider with tailerons. Worked like a charm.