I was reading an article this morning that struck a chord with me. You know how many tip stall crashes we've seen at the downwind leg turn to crosswind at Rogo? What the author indicated was that the stall can be induced by up elevator movement. He described it like this.
On the downwind with a strong wind it's easy to have good ground speed but marginal airspeed. We don't know how much g-force we induce with the elevator. 1g doubles the weight of the model and also doubles the wing loading. We are already marginal and it's easy to exceed the limits of the wing to support the weight of the model. Because we are so low and slow we cannot recover and have this cartwheeling crash.
The answer seems to be to keep up your speed so you remain flying at all times and only seriously slow down on final.
Any comments?
Jack.
I think that's very true, and it's compounded by the fact that we have to turn tight because of the road. It doesn't happen at the south end of the field where we have lots of room for a large, and therefore, faster, turn to final.
The downwind turn stall is a huge combination of things most of witch we are at a disadvantage. We have no instrument airspeed indication, as you fly further to the left or right of your position the aircraft seems to be dropping because of our perception causing some to feed in more elevator and the ground speed can give us less time to nail the turn point again because of perception. Another thought is that when the plane approaches 90°to the wind some of the lift is "blown off" the tip encouraging the tip stall.
These are things I've collected over the years and some may disagree. Just my thoughts and I agree that adding elevator near stall increases the wing loading.
The solution is simple. We just need to move Stouffville road a bit further north.... say 500 ft.
Can we do that during our spring clean-up?
It's all your fault anyway Rob.
You should have cleared the field 500' further south!
Jack.
I have had a few such crashes/mishaps preparing to land from the south.
The fault is in our flying; not in with the field.
Slow, curved and banked (ailerons) approaches, with up elevator and reduced power, are a recipe for crashing.
Keeping the plane as level as possible in the turn, keeping speed up, keeping the nose down, flying low, and flaring just before landing, is the best 'approach'.
The downwind problem is exacerbated with a a quartering tailwind from outside of the traffic pattern, i.e from the southeast in a left-hand (counterclockwise) circuit or from the northeast in a right-hand (clockwise) circuit. For example, on the downwind with a SE wind, as you start your turn onto the left base, the wing experiences a 40% increase in the tailwind component until the plane catches up with the tailwind. Not a good place to be when low and slow.
Andy
Sure! Sounds easy enough, Michael ;D
Hey Jack. I suggested that when we first saw the site, but Michael didn't want to :P
Further south meant a lower level, which meant wetter.
It was a reasonable compromise at the time.
OH! so now you're both to blame. Anyone else you want to throw under a bus? LOL.
Jack.
I expect my name will pop up somehow.
Quote from: Michael on February 28, 2014, 02:59:38 PM
Further south meant a lower level, which meant wetter.
Yes. I know. We would have had our own float flying site. You're making things worse for yourself ;)
That's O.K. We know it was really Simon's fault.
I agree.
It's Simon's fault.
With all that's been said. I think the safest approach to avoid a tip stall is to fly against the pattern on your final circuit and perform a split s over the north edge of the field. This will set you up perfectly for a nice landing. No turns involved.
I've seen numerous 3/4 split S's performed.
That's what I did with my Nooner!
Why do I get the profound feeling that I am surrounded by mental giants?!! ;D
You could take that in multiple ways, Andy!
Quote from: Andy Hoffer on March 01, 2014, 12:07:12 AM
Why do I get the profound feeling that I am surrounded by mental giants?!! ;D
Mental yes I will give you that one but giants? That might be a stretch. (get it stretch and giants...)
You guys are all talking about downwind turns, but the turn to final is upwind ;)
In all the downwind turn discussion you usually see this is the point so often missed. It is the turn back to upwind that is the problem.
Turning downwind is rarely a problem for most pilots.
There is of course no upwind/downwind from the model's perspective, the problem is one of a ground based pilots perception of the airspeed.
Keep the ground speed up on the downwind pass, and start your turn earlier than you think you need to.
Pat MacKenzie
i have been reading this thread with great interest. It has brought back memories of full scale flying. I will let Andy confirm this but this what i remember (also one of my scarier experiences as well).
What I have learned last year is that model aircraft follow the same physics and rules as full scale.
Pat is dead on, the advantage is the instruments and that "feeling" of the plane on your butt which you do not have on the ground
The most dangerous turns are turning into base and onto final. abrupt control changes can cause the wing tip to stall causing your plane to spin without any room to recover
I remember turning final, 20 degree flaps, and the plane drop, i think that 172 was just hanging there. Got on the ground ok, but the instructor was as white as a ghost.
Lessons learned, always keep ahead of the plane, nice turns when low and slow.