Holes in Spoiler or Not

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Bille Floyd

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You can always push the stick forward as you retract the flaps, no?
I , "Need" to do , exactly that , when i retract the flaps on my
rigid-wing Hg ; flaps down , i need to speed up a bit before
i retract them.

This story is why i'm so interested in this Thread ; My Exxtacy
turns with spoilers, and i can hit Both for glide control.

For you Victor Bravo :
This happened just North of your story ; Slide Mt , located
between Carson and Reno .
Had just quit the Tut team (Heir to coca cola, Tut Woodruff)
who was paying me to film HG movies.
Had launched off Slide Mt with an early rigid type wing
the Fledge II B. That glider had tip rudders for turning; and
you could deploy both to reduce glide.

So cloud base was near 13K , with a rather high laps rate,
when i caught a good thermal about 1500 ft/min up. That turned
into 2000 up and just kept getting stronger. Had 2k before i
hit cloud base and had to do something fast. Deployed both
rudders and pulled in ; that don't do Squat, and was still
going up Fast . let go of the rudders and pulled in Hard
to try and reach the edge of the thermal.
OOPS !
I hit HAIL ; and it was Big ; was worried about it taking
out my Dacron sail, so i went into an inverted spin, (the
fledge does that ), and centrifugal force holds the suspension
lines to the harness taught. To help match the decent rate
of the hail, i held inside rudder, and slowly pulled in to speed her up
a bit. That makes the glider exit the spin, and enter a spiral.
It's also the most dangerous thing you can do in a Hang glider
because the exit usually makes the frame explode !
I held it , till i was 200' off the deck ; then pushed out to re-enter
the spin, and exited that with ease with just enough altitude
to turn into the wind and land.
It was still hailing, when i landed ; and Yea , i ($h!t my pants)
but lived !!!

Bille
 
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lr27

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But did the spoilers have holes in them when you landed?
 

Bille Floyd

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The Dacron sail, had to be replaced .

Our reserves are not built to withstand a terminal free-fall; so
leaving the glider, is not an option.

My Exxtacy gets a lot more lift than the old fledge ; a
spin is not an option on that composite rigid-wing, because
they placed the control bar too far forward so it wouldn't spin. If
i encounter cloud suck, i'd like to have a better option , than just
pulling both spoilers, and speeding up. Playing with strong
thermals is what glider pilots dream of ; screwing up like i did
can be brutal !!


Bille
 
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Pops

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Working lift with the little SSSC one day and hit a good one and almost got sucked into the bottom of a huge very dark cloud. Hot summer day and I just had shorts and a tee shirt on and got so cold I was shivering. Never thought to look at the altimeter, I was very high and took about 30 minutes to get down to my grass field to land. Had to be 10+K. Got in it at about 2500'. Fun going in circles and watching the ground drop away.
 

proppastie

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So I did a simple rough calculation of the amount of lift generated on the area of the top cap of my spoilers.....assuming that is what we are talking about.

I used .569 sq ft for the top caps of one wing....and CL coefficient of lift of 2 ( about the highest possible) speeds of 30 and 70 mph.....65 mph is the never excede speed for the original Carbon Dragon.

I came up with at 30 mph a lift of 2.6 lb and at 70 mph 14.3 lb. Does this look reasonable? Are my assumptions wrong/right?

Logic tells me I have to know how strong to make the actuator mechanism to keep the spoilers from sucking up like what happened to VB. To do that I need to know the loading.
 

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lr27

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Wouldn't it be better to go by the pressure, at max Cl, at the point on the airfoil corresponding to the spoilers? Or between that and the vent or hole that would have the highest pressure? Since they're likely to be at tne high point of the wing, I suspect it will be somewhat more force than you've calculated. At least when the spoilers are closed.

If you're maxing out at 70 mph, I'm sure the force will be far less than it would be on a ballasted, hi tech sailplane diving for the gate and then pulling up.
 

proppastie

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Wouldn't it be better to go by the pressure, at max Cl, at the point on the airfoil corresponding to the spoilers
Are you saying the CL could be higher than 2 ?

.I picked CL of 2 as a worst case as I do not think any airfoils have a higher CL.....thing about these rough calculations exact or perfect is not always necessary for the purpose of the calculation.....More than likely yes it will be less if my assumptions are correct, but I am not sure I understand the mechanism/physics of this lifting spoiler problem and rather than try to use words like I did in post 29 I have posted a calculation.
 
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proppastie

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Two of the most experienced glider pilots here have highly recommended an over center device to keep the spoilers from lifting, I have not finalized the actuation design, I wanted a simple spring return but a spring pre-loaded to say 20 lb will be a much higher load at extension and probably weigh more than a cable down/latch or over-center handle with cable and pulleys....As was mentioned lots of potential gotchas.
 

Hot Wings

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For an example here is the over-center mechanism from my AV-361 project. Adding a spring to snap the over center in place, and not effect the control force significantly should be doable.

As for the lifting forces I'm using the max pressure at limit "G" load - which for the AV is around 40#/ft^2 on top @ 48% chord. Multiply that by 2 for upper and lower to be conservative.

spoiler overcenter.jpg
 
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Hot Wings

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The pulley is for the aileron cables but the mount does serve as the stop for the over-center arm - which is shown in the neutral position.

Edit: Add AV-45
AV45 brake.jpg
 
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proppastie

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my .569 sq ft is 82 in sq, which using only 1/2 you number because I am only on top gives me 1640 lb which seem like a lot of up force on that little cap of a spoiler. My whole limit load test will be about 800 lb on my LH wing.

Edit.... forget it, I have to run my limit load ....can not use your limit load.
 

Aesquire

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Billie, the Tut team? We're you at the Region 9 championship at Stamford NY back in uh, darn, I forgot the year.?? '78?

If so, I probably was your wire man, or landing zone judge.

Cloud suck can hit anyone. I nearly got sucked into a thunderhead at Honeoye Lake when it came over the back side, not visible from launch. Near zero wind launch and I was just sustaining in weird, surging air, when I suddenly started to climb, then heard the rumble of thunder. I rolled to look up and was under the leading edge of the dark cloud. No spoilers on my Flexi Floater, so I did steep diving turns, not good enough, and visibility went to feet. I Then did a whip stall, and came out of cloud about 200 feet above the trees, nose down and rolled about 130 degrees from level. Barely made it over the ridge to the valley & landed as the rain hit.

Luck saved me, I can't claim it was skill. ( If yelling "oh #$%&!" over & over counts as prayer, that too. )

Spoilers are nice to have.
 

Victor Bravo

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I should mention that the glider I was flying in the above incident HAD an over-center on the spoiler control. The main spoiler blades themselves were not moving, it was the thick white "contoured" spring loaded caps that were bouncing up and down on their mounting springs. Those springs were to keep the caps flush with the wing surface, and had little or nothing to do with the over center mechanism.
 

lr27

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Are you saying the CL could be higher than 2 ?

.I picked CL of 2 as a worst case as I do not think any airfoils have a higher CL.....thing about these rough calculations exact or perfect is not always necessary for the purpose of the calculation.....More than likely yes it will be less if my assumptions are correct, but I am not sure I understand the mechanism/physics of this lifting spoiler problem and rather than try to use words like I did in post 29 I have posted a calculation.
When the spoiler is closed, it's merely part of an airfoil. Low pressure is not evenly distributed over the airfoil, so if you place it in an area where the pressure is lower than average, there may be more force than your Cl estimate of 2 accounts for.
 

proppastie

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Great to have knowledgeable and helpful friends. I never designed an over center device.....I was once told a good designer is a pirate.

Edit and of course the first layout is wrong....but I get the idea now. Better to be wrong on paper than after cutting metal.

1586177649810.png
 
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BJC

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Great to have knowledgeable and helpful friends. I never designed an over center device.....I was once told a good designer is a pirate.
A good designer (or physician, or artist, or bomb disposal technician, or ...) learns from others’ successes and failures.


BJC
 

proppastie

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Experienced designers have a phrase "everybody thinks he is a designer" or "everybody's a designer" .....too many insist on doing something different rather than what worked in the past....sort of like designing the Carbon Dragon out of aluminum.
 

Hot Wings

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learns from others’ successes and failures.
And the associated concept:
"If my student doesn't eventually surpass my abilities, then I failed as an instructor."

There are several here on HBA, I fear, that I may prove to be failures - as teachers. 😞
 
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