Holes in Spoiler or Not

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proppastie

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Airbrakes like these have so many quirks and subtleties and gotchas ....... making them deploy, stow, and seal properly under a wide variety of operating conditions is a bear.
As I am finding out.....These should be "air tight" as spilling air up around the spoiler from inside the wing coming from openings at the root will spoil the lift of the wing even when the spoilers are stowed......Is trying to make the wing airtight at the root ever done? .....To do that I see the cable actuator as a problem but I could use a grommet, or maybe a 1/8 hole is not an issue?
I have been thinking of V-seal around the edges of the top plate,.... I see felt used, but with .032 built up at the LE I do not have much thickness to play with.

Any thoughts?
 

thjakits

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Hi all,

....excuse the ignorance - I got a ride in a motor-glider some 40 years ago and try to make a living in the opposite of gliding/soaring in aviation (unless I ever lose and engine and autorotate...)

I understand "spoiler" would do that - spoil something - in this case lift...
I understand "drag brake" would do that - brake by creating drag...

IF you want drag, why not put the brakes on the underside of the wing - in theory you will never have a problem local air pressure trying to pull th brake/spoiler out...?
IF you want drag - why not on the belly of the fuselage? Or clamshells on the tail (...or in your case at the end of the fuselage)

IF you want spoiled/destroyed lift - how about a few well placed holes on both sides (upper and lower) connected with a valved duct - open and high pressure from below should create some impressive lift destruction plus some drag?
Not sure about the effect the holes would have when the vslve is closed - possibly the top hole could be made into somewhat elongated channel - reducing a negative effect when the valves are closed...

As I am not in the box (soaring) - I thought I think a little..... maybe it was worth it..

thjakits
 

proppastie

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IF you want......, why not put......:
most of those ideas are used in one form or another......not sure about the valved air from bottom to top, but that might be worth a research project. I had flown gliders with spoilers on the top of the wing and also one with high angle flaps for drag but no spoilers. I liked the former and did not like the latter.......My project is mostly an exercise in aircraft stress and mechanical design, the platform is a copy as is location and size of the spoilers. Having also drag brakes on the bottom would have been twice the weight, complexity, and fabrication time, and I think spoilers are all that I need, as this is not a contest machine but rather a floater.
 

Victor Bravo

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'Pastie, looking at your drawing I'd say yes reduce the holes to 1.25 to leave more metal around the holes. Again, there are people here who may know a lot more than I do, but as long as your spoiler blades are able to be un-bolted and new ones bolted on (with larger or smaller holes) then I feel confident in letting you go ahead and build a prototype using my guess-timate.

ALSO, you might be wise to build two or three sets of spoilers, mount them on top of your car with some sort of force measuring load cell,a nd see what the differences in drag are at the speeds you will be flying. I'd say you need to test 25-60 MPH.
 

proppastie

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see what the differences in drag are at the speeds you will be flying. I'd say you need to test 25-60 MPH.
Is drag the primary issue with a spoiler or is ruination of the lift over a large portion of the wing more the reason we have spoilers.(probably both).....I would think a flat plate drag calculation is fairly straight forward, with the holes added it is now somewhat less......but the spoilers effectively removes a large portion of the wing out 45 deg, from each end (I have been told).....They are also located at the larger span so the amount of wing area is a fair amount less. The induced drag should go up from the turbulence over the wing too. , Anyway I can measure the drag, from my car but I am not sure what that will tell me as to the effectiveness given the other factors. However seeing how the spoiler holds up at 70 mph is a worthwhile exercise given the out of plane forces and generally ugly (not elegant ) mechanical design. I do not plan on getting sucked into a cloud, and if I do I certainly will wish I had more drag though.
 

Victor Bravo

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I believe the spoilers do both of the things you mention, and then they also put a big break into the spanwise lift distribution, which has an effect of reducing the efficiency of the aircraft further.

But since the actual stall speed only goes up a little bit with this type of spoilers, I would say that reducing the raw amount of lift is not the largest single part of what they do.
 

proppastie

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If sucked into a cloud is it better to point the nose down with full spoiler or stall spin with full spoiler?
 

proppastie

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At Cd=2 ... I get total drag of the spoilers (both wings) of almost 32# flat plate and limit load calculations. (Cd was calculated from limit load as per Glider Criteria)
 

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Bille Floyd

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If sucked into a cloud is it better to point the nose down with full spoiler or stall spin with full spoiler?
I can say this with full knowledge gained from 45 years experience , in
sailplanes , hang gliders and paragliders :

Look at the vertical height of the cloud , (Before you play with it) ;
after your , "in" it , (it's kinda too late).

To get an idea for that day's weather , and what it could do to
you ; Google search this :
soaring , best reference for days lapse-rate

Bille
 

Victor Bravo

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Before you are sucked into a cloud, you also need to know what is the maximum safe descent rate that your aircraft can achieve without losing any parts, flutter, etc. That may be at "dive speed" with spoilers out, or it may be in a stable spin with spoilers out.

However, thinking that you can just do a Vne dive may not be realistic:

1) Vne with spoilers out may be lower than Vne with spoilers in, because the spoilers could possibly get ripped off the wing at "regular" Vne. That's an engineering question of course. This is why the European sailplanes have what are called "Terminal Velocity Dive Brakes", which are strong enough to keep the airplane under Vne even in a vertical dive.

2) Vne is almost always calculated as smooth air Vne, and then there are other V speeds for turbulent air, control deflection, etc. If you are sucked up into a cloud against your intentions, then there is a 99.99% chance that you are already in turbulent air, and it can easily get worse inside the cloud. So your only safe option is diving at "Turbulent Air Penetration Speed", which will almost always be significantly less than Vne.

3) Many sailplanes will not stay in a spin for long, they will transition themselves into a spiral dive. The reason for this is that the mass of a sailplane is more in the wings than the fuselage, and when you start to spin the forces will pull the nose down. This is the opposite (and for the opposite reason) as some short winged airplanes will go into a flat spin, where the nose comes up,and cannot be recovered from the spin. Those are usually heavier fuselages with light, short wings. So if your sailplane tries to "spiral dive out" of the spin, you would be in a pretty bad situation with increasing speed and load on the airplane. Pretty much without a paddle.

So all I'm saying is before you go off soaring in an experimental sailplane, you need to figure all this out ahead of time. Have a clear understanding of what the fastest SAFE rate of descent is for your aircraft in turbulent air. Then practice it outside of a cloud so you know what you need to do by instinct.

Then pay close attention to what Billy is saying about sizing up a cloud first, because his experience in really lightly loaded soaring aircraft (HG's, PG's) is even more relevant to an Aluminum Dragon than anything I learned in the glass ships.

The bottom line is that with a really lightly loaded aircraft, there are going to be some fantastic soaring days where you have to stop climbing and scoot out from under the cloud at a much lower altitude than in a heavier or faster glider.
 
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Bille Floyd

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Another consideration for if when things go really bad :
Can your reserve take a terminal velocity deployment ?

If you ever do get sucked up into a cloud, and your motor glider
breaks ; you are gonna need to wait till your have a low AGL , before
tossing laundry , or the reserve will just suck you back up into the cloud.

I came across a Really good deal, on a BRS Model 500 ; but declined
for that exact reason.

Bille
 

proppastie

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Mounted the slightly bigger panel and ran up to 70 mph, here is a screen-shot at 70mph...One thing I noticed was there was lots less deflection on this test than on the load test.....So I screwed up the loading on the load test or the Glider Criteria is very conservative as regards loads.
Nothing bent or broke so looks like this assembly will survive NE speed.
 

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Bille Floyd

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Mounted the slightly bigger panel and ran up to 70 mph, ...
...
I gave ya the thumbs-Up , because all that work your doing
is gonna apply to my rigid-wing, when i put the engine on it !!

My VNE in turbulent air is 59-mph ; so your work is near
perfect , for my application.

Bille
 

proppastie

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I seriously thought about waiting till after the load test to install because if the load test fails then I would have saved a lot of work. However I wanted to get an accurate weight of the wing and if the load test passes then I can just wrap in plastic and put it into the barn, which is easier than clearing a space back in the basement.
 

proppastie

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so your work is near
perfect , for my application.
Let me know if you want drawings....If you could take my Autocad drawing file it would be the easiest. They are not dimensioned, but rather drawn full scale and I print and paste and cut on the lines......
 

Bille Floyd

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...If you could take my Autocad drawing file it would be the easiest. ...
Autocad wold work ; got plenty of friends that can translate
it for me , (and my ineptitude) LOL !

NO Hurry though ; i have several months of work to do
designing my pod and landing gears. I'll let you know
when i'm ready.

And Thanks : Bille
 

proppastie

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NO Hurry though
K and I am not done yet with the over center, stop, and spring.....then it might still bind (stay up) under load when I add the skin around it on the wing. Working on adjustable control rods for it today.
 
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