Forum: Scale Models - F-16, F-35, F/A-22, F-2

It's known that the F-16 can't fly well without its' FBW system. So my question is, how F-16 R/C scale models can do so?

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Their CG is different - farther forward of the CP in the RC models.

Many of you may know that getting your CG too far aft in an airplane can cause it to "swap ends". That's how the F-16 is intentionally designed, with the CG just barely in front of the CP. That way when you want to turn you can do it very quickly becuase the plane is on the verge of doing it anyway. I can't think of the aero term but the mechanical analogy is that of rotational moment of inertia. It's kind of like having a mid-engine car with a very short wheelbase, or a figure skater spinning with her/his arms tucked in. Conversely it is very hard to maintain straight flight in this configuration. That's where FBW comes in, it allows the computer to constantly command the control surfaces to maintain the pilot's intended velocity vector.

In another thread I think someone commented about shifting fuel around to move the CG and the results it had on turn performance. The point is that by moving your fuel (and your CG) around you can change the stability or maneuverability of your aircraft.

In an RC model you move the CG forward (or the CP aft) such that the RC model is stable enough to allow "manual" flight.

Hope that made sense.

Also, even scale RC models are not fully to scale.

Polar moment is the word you're looking for, G.

Thanks guys, that's make sense.

Yeah, rotational, polar - the two are used interchangeably but usually refer to mass distribution. I guess the point I was trying to make is the distance between the CG and CP being viewed as a kind of a moment arm. Does anyone know the aeronautical term for the distance between the CG and CP? or is this the definition of the term (relaxed) static stability?

Dunno if there's an exact term for it, but the reason I mention polar, was because you mentioned a car, and the term used there is polar moment of inertia.

What was the post-WWII prop job that was "mid-engined? Bell P-39? The mid-engine design was done for the same reason on that airplane - the lower polar moments were intended to increase maneuverability.

Hello, I have a F-16 RC model myself. The CG is indeed moved forward: this makes a naturally stable flyer, no need of any computers. In fact, if you would build a full size F-16 without FBW, the CG would be more or less in the same position like on the model.

The RC model (powered by a miniature turbine) can fly like a real F-16: slow, high alpha manoeuvring with high power setting, spin turns, etc. On the other hand, it can be a real pussycat, landings are quite easy and flights are very stable.

Greetz, Michel

Back in the late 80s I saw an RC model of a B-2 fly - with a pusher prop setup. It was a homebuilt design, no kit. The palnform was accurate, wingspan about one meter. No fancy computers there, just a smart RC builder.

With some imagination and knowledge you can build anything in RC, I have even seen RC beercrates and lawnmowers (hope I spelled this right).

Michel wrote:

With some imagination and knowledge you can build anything in RC, I have even seen RC beercrates and lawnmowers (hope I spelled this right).

I definitely agree Michel.....you can even make a stop sign fly! Very Happy

Anyone ever seen pics of those fly-powered planes? (yes, the insect)

Oh yeah, very original. Surprised some fly insect rights group hasn't been up in arms.

lol, those fly-planes are definitely crazy! Although I prefer something I can control myself instead of seeing it fly away and never turn back. Laughing

Michel, just leave some food out. They'll be back..... Wink

Forum: Scale Models - F-16, F-35, F/A-22, F-2

Are RC F-16 models also inherently unstable?