Forums: Skydiving Disciplines: Swooping and Canopy Control:
Adverse roll

 


Premier billvon  (D 16479)
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Jul 11, 2006, 11:48 AM
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Adverse roll Can't Post

Have noticed something interesting on my Nitro.

When I fly back, I often find myself holding one brake to make the thing go straight. Didn't think much of it; I then loaded that side with my legs, the problem went away, and I could continue back in with very little "body input" and it would fly straight.

Over the past few weeks I've been experimenting to see what's really going on. And I've noticed the following:

When I add a very small amount of right toggle, the canopy turns left. This is interesting because it's how aircraft turn - drop the right aileron to turn left. Aircraft have a rudder partly to counteract "adverse yaw" - when you drop the aileron on the right, drag increases on that side, so you need the rudder to counteract the tail's desire to slide to one side.

Canopies, of course, depend on that adverse yaw to turn - that's why pulling the right toggle makes you turn right (usually.)

So initially, I'd pull just slightly on the right toggle, the canopy would turn left, I'd add a little more toggle, and it would stop. There's a point at which a moderate deflection of the tail produces straight-ahead flight, I assume at the point that roll balances yaw. It makes sense, but I am suprised I haven't seen this before on other canopies. Maybe I haven't been paying enough attention, or the Nitro is unusually sensitive to this.


dharma1976  (D 28634)

Jul 11, 2006, 12:02 PM
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Re: [billvon] Adverse roll [In reply to] Can't Post

or maybe your brakes are set wrong causeing your rudders to fly above the canopy more than expected in design...

so that when you pull down on the right toggle you are actually returning that brake to the neutral setting and the other side is set in a negative setting causeing the turn.

Dave


(This post was edited by dharma1976 on Jul 11, 2006, 12:03 PM)


marks  (D 22296)

Jul 11, 2006, 12:25 PM
Post #3 of 10 (914 views)
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Re: [billvon] Adverse roll [In reply to] Can't Post

Quote:
So initially, I'd pull just slightly on the right toggle, the canopy would turn left, I'd add a little more toggle, and it would stop. There's a point at which a moderate deflection of the tail produces straight-ahead flight, I assume at the point that roll balances yaw. It makes sense, but I am suprised I haven't seen this before on other canopies. Maybe I haven't been paying enough attention, or the Nitro is unusually sensitive to this.

that is odd, I have never noticed that either.

I think I will see beezy this weekend, I will ask him if he has seen this. but im sure he will see this post also.

is it obvious it is a turn? or does it seem more like a slip?


(This post was edited by marks on Jul 11, 2006, 12:27 PM)


Premier billvon  (D 16479)
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Jul 11, 2006, 12:27 PM
Post #4 of 10 (909 views)
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Re: [dharma1976] Adverse roll [In reply to] Can't Post

>or maybe your brakes are set wrong causeing your rudders to fly
>above the canopy more than expected in design...

Perhaps, but I doubt it. I have about 6" of slack in the lines and the canopy flies normally other than that.


dharma1976  (D 28634)

Jul 11, 2006, 12:53 PM
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Re: [billvon] Adverse roll [In reply to] Can't Post

did you add the six inches from stock? or is it just six in ches of slack before you notice tail deflection?

Dave


The111  (D 29246)

Jul 11, 2006, 1:08 PM
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Re: [billvon] Adverse roll [In reply to] Can't Post

In reply to:
It makes sense, but I am suprised I haven't seen this before on other canopies. Maybe I haven't been paying enough attention, or the Nitro is unusually sensitive to this.

Think it has something to do with the little winglets which are unique to the Nitro, AFAIK?


yardhippie  (D License)

Jul 11, 2006, 1:26 PM
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Re: [billvon] Adverse roll [In reply to] Can't Post

Ive got around 650 jumps on a Nitro 120 and havent noticed anthing like that.
My first line set I did have to extend the brake lines about 6" to get the tail flutter out of it when I did my front riser turns.

I'll have to try it on my next jump though. Im interested to see if I can repeat the a similar reaction on a different size wing. What are you loading yours at?

But truthfully, I dont use the toggles much for anything other than holding in brakes and flairing. the rest is mostly harness and front risers.


Pendragon  (D 104102)

Jul 12, 2006, 1:36 AM
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Re: [billvon] Adverse roll [In reply to] Can't Post

All canopies will do this; it's just that pilots don't generally notice as the effect is often subtle. Don't CReW jumpers use this as a technique though?

The reason is simple: trim and brake lines are adjusted such that "toggles up" on a parachute is way faster than maximum glide (which actually requires brake/riser input to achieve). This is to have the right characteristics for a good opening. When you use a small amount of toggle, it converts some of that excess speed and actually generates lift on that side, inducing bank and causing the canopy to turn in the opposite direction. More brake input will degrade wing performance on that side, losing lift - but also slow it down - so the canopy both banks and yaws in the direction of the toggle input.

The question as to why it is quite pronounced in your Nitro (as compared to other canopies you've flown) isn't obvious. Might it have something to do with the way it is trimmed?


Premier billvon  (D 16479)
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Jul 12, 2006, 9:06 AM
Post #9 of 10 (680 views)
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Re: [dharma1976] Adverse roll [In reply to] Can't Post

>did you add the six inches from stock?

I replaced the lower brake lines with Dacron a while back. I trimmed them so it took about 6" to get tail deflection.

>What are you loading yours at?

1.9 to 1.


mgattini  (D 40947)

Jul 12, 2006, 1:28 PM
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Re: [billvon] Adverse roll [In reply to] Can't Post

Had the same thing happen to me Vx 69 at 2.7 and Vx 55 at +3.0.



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