Square corner radius

Hi

Obviously a square manouver can't be flown as an instant 90 deg change in direction. Just wondering what contest pilots regard as an acceptable turn radius for these manouvers?

Please don't just guess off hand but closely observe your model and
try to estimate as best you can. Say line it up against something you can measure.

Calculations as well as measured data all seem to indicate about a 15 foot radius for the type of model flying today. This of course must be tempered by the need for energy management, especially in the square 8, as well as presentation. Wing loading and horsepower play a big part in this. Nobody does "the" 5 foot radius turn in the PAMPA stunt event.

For technical info on this, consult Frank Zaic's book, Circular Airflow and Model Aircraft, pp 140-145. There is also some good stuff in his 1951-52 Model Aeronautic Yearbook.

Most stunt airplanes can fly an "apparent" 5'radius corner. However, if you try to pop a corner and fly up some vertical line, such as the corner of a building or a light pole, you will see that the 15' figure is about right. Another informative experience is to position yourself close to the circle on the downwind side and observe what happens on the corners in the wingovers. The important thing is not how big the corner is, but how big it looks to the judges. The 5' corner you see every day is, in fact, an optical illusion.

>The
>5' corner you see every day is, in fact, an optical
>illusion.
>
>Jim

Hi Jim

Is that because the judges are centred on the manouver so the croner
is flown around the circle a bit from them where their view of it
forshortened somewhat?

Also I should have asked what line length these 15 foot corners are flown on?

I only have a .15 engine these days I guess I need to scale the
corner down some. I don't do comp but the reason I ask is that
I get as much if not more from design as I do from flying.
So I'm trying to get an idea of the capability to design the plane
around and to gauge my flying ability and plane against.

Also I really want to thank you blokes for these answers.
You obviously have put quite a bit of effort into determining it
realistically at some time ant that is very helpful.

Good strobe photo too!

No wonder I can not do a square loop. A square loop is really a 30 foot diameter circle with 4 tiny flat spots.

3.5 meter

loo to:

[photo not recovered: radius.jpg]

the fuselage is 1.1m long

There is a way to see--in real time--how wide our models turn as opposed to what appears to be the case, especially when watching the models of others fly.

As model approaches point where you are intending to do a square corner--entry to reverse wingover is good, as model is at that point in pattern heavy in the nose--look ahead to a fixed point about 5 feet high. Fly model through your field of vision while remaining focused on fixed point.

It will appear to turn like a pig.

The technique works for me, even if results are depressing.

15-17 feet is what I observed on videos of what looked like the very best flights. I'd definitely accept Igor's 3.5 m reading.

In spite of that, the smooth snapped rotation looks wonderful on a great stunt ship (flown by a master), it stirs the soul. (Well, maybe not, if you're not hooked on Stunt..)

I know that Bob Baron and Wild Bill developed a 1/2A model actually capable of doing the 5' corner, but I can't imagine it being as impressive as a modern full sized stunt ship.

Speaking of fabulous modern stunt ships, Ted Fancher's latest is certainly awesome. I can imagine what it looks like flying. I need to steal some of his belly pan styling ideas for my FX. I'm not really satisfied with the slotted deal I made.

Ted, I wish you would do a comprehensive article on carving cowls. You and Randy Powell..

[photo not recovered: 3e69bb3870f12ad5.jpg]

"God may be subtle, but He isn't mean." -Albert Einstein

>
>{Ted, I wish you would do a comprehensive article on carving
>cowls. You and Randy Powell..}
>
>A Men!

Nuff said!!!

Ken, and particularly Igor...

Fantastic sequence shot! I think the end of the trace shows what happens. Here in the USA we'd call it dirt-tracking, I guess. For those in other continents (Igor, HI!), it is more like a race car drifting a corner with much oversteer rather than neutral slip.

What I mean is that in the last 'stops' as the model turns vertical it looks like it is slipping 'toward the wheels'/ away from the "center" of the "corner," rather than tracking as it does earlier.

I noticed this slip after moving from around sea level to ~5000' (~1,5 KM) altitude. Turning to level from vertical dive looked like a two-step action -- model turns horizontal, then sinks in that horizontal a few inches. Not much, but that close to the ground, a bit stimulating.

By the way, Wild Bill Netzeband, ageless guru for CLPA in USA, holds that the max g loading we might ever see is around 35 g. That would be a 10'(~3m) radius... It is very important to manage energy. Too much energy can disspiate if we try for consistent, too-small corners. We are not flying Carrier or RC 3D prop-hanging. I guess it is another plus for long lines: There IS more room to show a flat side between "corners."

Everything depends where the judge looks. If he really looks to CG path, or pitching, or its combination. The example can be Beringer’s Suchoy which is almost flapless model. It has very high pitching rate what gives illusion of tight corner, but CG path is very open. On opposite side light flapped model with 18%-20% can do really tight corner, but looks like rotating around tail.

So it is everything about AoA in turn. If we have model making 90 deg corner at 10 deg AoA, then the perfect turn will end up at situation, that after 90 degrees arc model has +10 deg AoA. If you can instantly change pitching, it will clearly do that “wave” at conversion from circular to straight flight. That is not acceptable for judges and thus it is much better to do only 80 deg turn (the fuselage has already proper angle for next straight flight – its axle is paralel, but there is still some distance) and last 10 degrees slowly (well it is quickly in real time) opening the radius so the fuselage angle is still constant and that mean AoA is lower and lower. If it is too much (means too high AoA in turn, means too heavy model for that lift available) then it gives that strange look that after corner it still moves in original direction perpendicular to wing area.

It means if you have too light model you will end up in problems at end of corners, because lower AoA in turn means less time for conversion from circular to straight flight. If you have heavy model (or small flaps for example), you will have advantage of more time, but experienced judge see your round sides in corners (well … not everyone ).

Here is again that picture from my home page showing AoA in middle of the turn.