I've been able to revisit my archives, and found some interesting thoughts about the Skyleada Super Sabre from expert modellers Mike Stuart (who built it) and Steve Bage. First, Mike wrote:
"Now I really like this model, which had been on my ‘to do’ list for quite some time. But, built as the plan (Perhaps Pete Smart was correct when he wondered if the later Skyleada models were ever test flown!) it is all but unflyable. I wondered if it suffered from the ‘inertia coupling’ of the full-size prototype, which was cured by increasing the fin area and extending the wing tips".
Steve believed the situation was even worse than this, and wrote:
"The motor is too far forward, leading to big trim change between the initial launch and ‘re-launch’: it needs to move back to straddle the CG and any nose-up pitch is then dealt with by downthrust.
Secondly, the way the model pitches up into a deep stall then sinks to earth, or flips over backward, is without doubt due to tip stalling. Swept wings tend to do most of their lifting at the tips and are especially prone to this phenomenon. Since the tips are aft of the CG, when they do stall, a nose-up pitch results. This was a serious problem on the full size F-86 and FY-100, so the behaviour of Mike’s model, the so-called ‘Sabre Dance’, is actually authentic!
The simplest fix would be to build in a stack of washout, maybe 4 - 5 degrees. I’m pretty confident that these modifications the model would fly in a much more predictable manner".
One thought I had was that Mike's model was very light, the implication being that the design needed the weight of a Jetex 50 under its belly to stabilise it, writing,
"Given the lightness of Mike's model, a little more weight will not go amiss: one school of thought has it that the faster your model flies, the more stable it is. Good news for us 'fettlers', who can't resist adding sheeting, extra stringers and wing spars"!
But the 'bottom line' is that some serious modifications to incidences and thrust lines will have to be made to this model.
There are quite a few designs and kits for the F-100 out there - it appears to have been quite a popular prototype to model. Here, for example is one from Comet:
and one from the French 'CB' brand:
Extracting the side views from these plans(and others) it is possible to compare them and see what changes the designers have made to make their model 'flyable':
Above: montage of some F-100 models. Top; Skyleada , next CB; next my own profile design; bottom: Bob Linn's profile catapult glider (published in the early 1950s)
One can even overlay the various designs, whereupon differences in the models becomes more obvious:
Above: overlay side views. green: Skyleada; blue: my profile F-100; red: Comet. The CB and Jetex 'Tailored' designs are also lurking in there somewhere!
OK, so this isn't s rigorous comparison, but I think the conclusions are pretty clear, viz: most designers have brought the wings forward, the tail plane back, and enlarged the fin and moved it back as well. I did all of this with my own profile design and trimming it went OK once I'd found the right motor as it is quite power fussy.
So: modify the Skyleada plan by bringing the wings forward (which will also bring the motor under the CG) and enlarge the fin and move it back.
Mike also noted that the original designers of the Super Sabre extended the wing tips to help prevent 'inertia (or roll) coupling. Perhaps the Skyleada design is a trifle 'under winged?
There was an easy way to test this by looking at the ratio of wing span to fuselage length for various designs:
The above table would seem to indicate that the Skyleada design is based on the original YF-100, whilst the later designs are more similar to the production Super Sabre.
I hope you have enjoyed this tour of my somewhat constipated thought process prior to tackling the Skyleada model. I really didn't want to end up with an unflyable model!
To conclude: I will extend the wings. Happily, this means they will match my templates better, I'll also incorporate 3-4 degrees of washout and bring them forward. I will also move the tail plane and an enlarged fin back. These mods, together with genuine Jetex power will, I hope, be sufficient to make the F-100 as splendid a flier as the Skyleada Mystere.
Other minor modifications, for example extra stringers, nose sheeting, diagonal ribs (to maintain the washout) will be added as I go along.
And so to the building board .....