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Pulling brakes while on speed bar


JP Tulo
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Can anyone elaborate on the physics as to why it’s a bad idea to use even a small amount of brakes while on the bar? Someone told me it’s safer to pull the entire rear riser instead and I’m struggling to understand why. Any help would be much appreciated, TIA!

-JP

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As best as I can gather:
A "reflex" aerodynamically shrinks the wing chord so only a proportion of the leading section is lifting and the trailing edge is neutral or even producing negative lift (like a tail does on a typical three axis)
Ergo: the wing loading goes up causing more speed.

When you pull down on the trailing edge, you are "abruptly" pulling out the reflex and returning the wing to a slow high lift profile beginning with the trailing edge which momentarily place the leading edge (highly loaded portion of the wing) into a negative angle of attack....
The Trailing edge is basically "flaring" and pulling the leading edge into a negative angle of attack.
(I THINK)

A reflex profile, in general, is not divergent (no tendency to "nose down")  and a more standard profile is. (Edit: might be the other way around.....?)

Some reflex wings allow the use of breaks while trimmed out and (or) on full bar and I am "guessing" they do this by maintaining an amount of reflex that is NOT fully neutral and the breaks pull more than just the extreme trailing edge (very heavy break pressure in reflex mode)  so the transition is not enough to have the trailing edge pull the leading edge into a negative angle of attack.

I think its a bitch to get a perspective on because a lot of what is occurring is "aerodynamic".... the angle of attack switch is not obvious.

Edited by Blackburn Mark
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I was beginning to think that I wasn’t going to get any replies because I don’t have a lot of posts, thanks so much for your reply Mark! That’s exactly the type of answer I was looking for, too. Now I have an actual reason why not to do that, for risk of frontal collapse I gather. Versus not knowing what the danger of doing so would entail.

Now I suppose it makes sense why I was told to pull the entire rear risers to steer while on bar, to prevent going into that negative angle of attack you described. Wish I had the option for tip steering!

Btw, I hang from Gin Pegasus 2 28m with motor risers and am strapped to a ParaJet Maverick w/ Moster 185.

Thanks again for the reply! I’m not really new to the forum btw. I spend a lot of time reading and just don’t post often! Cheers from the US 👍

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4 hours ago, JP Tulo said:

Gin Pegasus 2 28m

I couldn't find the manual for the "2" but the Gin Pegasus seems to be a sensible safe wing where breaks can be used in all configurations.
I'm sure most of the more recent wings are the same.
Coming from thousands of hours of free-flight, it would be unwise of me to fly a wing that forbids the use of breaks as I find it very, very difficult not to instinctively revert to active flying when things get hairy.
 

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10 hours ago, Blackburn Mark said:

I couldn't find the manual for the "2" but the Gin Pegasus seems to be a sensible safe wing where breaks can be used in all configurations.
I'm sure most of the more recent wings are the same.
Coming from thousands of hours of free-flight, it would be unwise of me to fly a wing that forbids the use of breaks as I find it very, very difficult not to instinctively revert to active flying when things get hairy.
 

https://www.gingliders.com/pdf/ppg-pegasus-2-manual-en.pdf

That’s kinda what I thought... I posted a vid a little while ago and in said vid I was using brakes to make small corrections while on the bar and a few of my peers were very quick to tell me how dangerous it was and that it should never be done. I’m still relatively new, I’ve been flying for around 70 hours with around 15 of those with a speed bar and never had an issue though so I was surprised to hear that.

Like you were saying if things got hairy, I feel like instinctively I would ease off the bar before any major inputs were made.

This wing has been good to me. I feel safe on it and I’ve flown it in the 30 as well as the 28 as I’m right in between sizes, but it’s all I know as I haven’t flown any other wing.

 

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It seems there is an issue with applying "symmetrical" breaks with open trimmers on your wing (I tried to copy and paste from the manual but it doesn't work from a PDF)

So I would advise to fly with speed bar off and trimmer in when its hairy (as we both already do)
Best efficiency is in that configuration anyway and is how I fly 99% of the time including 100+ mile xc flights.... more interested in a leisurely meander than blowing my eyebrows off :) 

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