I am thinking the holes in my spoiler are a better design....not ever designing a spoiler before would put it out there for the list to comment on.
Holes in Spoiler or Not
- Thread starter proppastie
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They'll be lighter, but create less drag. Probably not a significant-enough reduction in drag to actually matter for their intended use, but still.
I was thinking , the spoil of the lift was primary, plus less stress on the structure. Would the spoil of the lift still be the same?
Victor Bravo
Well-Known Member
Depends on whether you are trying to spoil lift or create drag. Any large protrusion above and in front of the thickest point of the wing will spoil a lot of lift. Drag is proportional to the amount of flat plate area facing into the airflow.
This is why there are various different devices "spoilers", "air brakes", "drag brakes", "speed brakes", and "dive brakes". We tend to use theseterms interchangably, but there are technical differences.
I am guessing that the holes will put less stresss on the structure, and thus be able to be opened at a higher speed without ripping out of the wing. But less stress on the structure ALSO means less effect on the aircraft in flight.
To address this in the design phase, you will need to first decide what type of effect you want these devices to have on the aircraft, and with what limitations in speed. Do you want them to simply give you a little help here and there when picking your landing touchdown location, or did you want to pull the lever at 10,000 feet sucked up into in a cloud and have them guarantee you will not exceed Vne coming out the bottom of the cloud vertically?
This is why there are various different devices "spoilers", "air brakes", "drag brakes", "speed brakes", and "dive brakes". We tend to use theseterms interchangably, but there are technical differences.
I am guessing that the holes will put less stresss on the structure, and thus be able to be opened at a higher speed without ripping out of the wing. But less stress on the structure ALSO means less effect on the aircraft in flight.
To address this in the design phase, you will need to first decide what type of effect you want these devices to have on the aircraft, and with what limitations in speed. Do you want them to simply give you a little help here and there when picking your landing touchdown location, or did you want to pull the lever at 10,000 feet sucked up into in a cloud and have them guarantee you will not exceed Vne coming out the bottom of the cloud vertically?
Airbrakes like these have so many quirks and subtleties and gotchas that I would stick with what's in the plans until a need to deviate is demonstrated. Once they work, they work great, but making them deploy, stow, and seal properly under a wide variety of operating conditions is a bear.
The use of the name "spoiler" by the soaring community is a misnomer. They're drag brakes, and their primary function is to increase drag, and be able to modulate that increase by the amount of deployment. The most-common usage is during pattern work and final approach, with the same function (but inverse actuation) as a power pilot would use throttle. Sailplane pilots tend to set up an approach that's a little high, and then modulate the glideslope with the "spoilers", by adding and removing drag instead of thrust.
What would you recommend?...
I copied the size of the Woodstock another of Jim's design, but decided my type was cleaner, with less chance of lifting in flight. The Woodstock was the forward hinged flat plate style. Woodstock is simpler less prone to binding but was worried about lifting in flight, I worry about binding of my design hence the thought about holes.
Victor Bravo
Well-Known Member
What do you want to achieve?
This type of discussion is so very very useful .....Thinking it is not a contest machine, but a floater, and getting sucked into a cloud probably is not an issue,....However it appears the opinions of the knowledgeable soaring crowd so far is for more drag rather than less.......I would assume that I could execute this design so that binding and lock up of the spoilers will not occur. A design without holes looks like the answer.
“Luke, I am your X!”
“X, I am your father.”
”Luke, I X your father.”
Holes in a spoiler, hehe.
“X, I am your father.”
”Luke, I X your father.”
Holes in a spoiler, hehe.
So the as-designed Carbon Dragon doesn't have airbrakes? Hmmm...
The hard part of making Schempp-Hirth airbrakes work properly is keeping the caps from fluttering or pulling upwards while extended, but having them still seal the airbrake opening under 2g or 3g bending of a long, shallow, and limber wing. Typical practice is to suspend the cap on eight or so posts, each with a compression spring. When stowed, each airbrake paddle pulls away from its cap by about 3/16" so that the springs snug the cap down into the recess in the wing. There are two or three distinct families of solutions to the various problems that ensue, each with its own set of tradeoffs.
Conventional practice is to use an adjustable overcenter mechanism that secures the airbrakes in the stowed position against the accumulated compression of the airbrake cap springs. The first generation or two of composite sailplanes tended to locate the overcenter at the wing root or even in the fuselage. Later generations tended to locate the overcenter inside the airbrake box near the inboard arm. This refinement reduces the loads on the long push-pull tubes to the airbrakes, making their adjustments more robust and reliable.
For a shorter, deeper, and stiffer wing, and for modest performance expectations, you can probably dispense with the separate airbrake cap altogether, and just size the top of the paddle so that it fills up the slot in the wing. That will eliminate a whole host of problems. But I would still have an overcenter mechanism to keep the airbrakes from sucking out.
--Bob K.
After an early pilot was not able to land until after dark and the wind died, they added a large paddle over the aft fuselage,....It has been reported that it worked but was difficult to actuate. Another builder added the Woodstock type and reported large pitch changes on actuation. Phil in Ireland has the Schempp-Hirth style and destroyed a plastic wheel the first time he actuated it. He needs to refine his actuation system before more reports may arise.
Victor Bravo
Well-Known Member
I had the spoiler caps suck out and flutter up and down on those springs one beautiful day, in a near-vertical dive through the start gate at a national level contest. Please accept my sincerest assurance that you don't want this to happen to you if you can avoid it. Anything less than a brand new LBA certified German-engineered racing sailplane would likely not have gotten through that episode with just a few cracks in the gel-coat.
Yes it was 1000% my fault, a stupid and indestructible young jackass pilot doing something he ought not have done, trying to postpone the laws of physics (and risk) while determined to win at all cost. Hopefully you're a lot smarter and more careful than I was 33 years ago... but... whatever you do please absolutely make 200% certain you have a good over-center mechanism or some other POSITIVE locking force on that type of (vertical) Schempp-Hirth spoiler.
By the way a "floater" like the CD or the Alum-D is more prone to cloud suck than a heavier ship, and it cannot dive out of the cloud nearly as fast or as safely as a heavier ship.
John.Roo
Well-Known Member
Hello!
We tried air brakes with and without holes and my subjective feeling is that with holes was efficiency of air brakes better.
It means - higher drag.
Best regards!
Martin
We tried air brakes with and without holes and my subjective feeling is that with holes was efficiency of air brakes better.
It means - higher drag.
Best regards!
Martin
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pictsidhe
Well-Known Member
I've read at least one paper on experiments with holes and without. Possibly on dive brakes. Either NACA or British ARC.
The only thing I can add with regard to holes or not:
The ones without holes stung more.
School policy at one time was to wear a belt. I was a bit of a nonconformist. :gig:
The ones without holes stung more.
School policy at one time was to wear a belt. I was a bit of a nonconformist. :gig:
that type is what was added to the Carbon Dragon when they decided to add one as an after thought. My thoughts here are that is purely drag and does not spoil the lift..... All of my glider experience has been with aircraft with "spoilers" on the wing.
pictsidhe
Well-Known Member
Here's a 42 summary to peruse.View attachment 2614.pdf
