I want to try using spoilers on a prop jet I'm building. I've read all the theory ie good low speed roll control and positive yaw etc, but I don't know if it works in practice. I would appreciate any words of wisdom.
Dave

Me too. I was thinking of using them on a big cargo twin that has full span flaps in addition to roll control spoilers.

Frankly I doubt if anyone has done this. I think I'll need to build a test wing for some old hack model to try it out.

Dipsy...I know the glider flyers use them quite a bit....probably a good topic for "Ollie" seeing he likes those gliders......I know the Ziroli P-61 Black Widow..has spoilers as the scale version has them...they work fine on the P-61........the full scale (Northrop) plane was originally built with spoilers only, then small ailerons were added to give "feedback" to the flt crews so they would have a "feel" of resistance as roll inputs increased.....The model flys very well and does nice rolls as well....should work out fine ...give them a try....Bill.....

I think it will require some experimentation to get spoilers to behave the way you want them to for roll control. One of the German manufacturers made spoilers that consisted of a series of pie shaped elements that rotated up out of the wing in progressive sequence. In effect the spoiler got longer spanwise as it was deployed. I think this would give much more linear roll control than a conventional single blade or trap door type spoiler. Spoilers stall part of the wing and tend to be an all or nothing sort lift distrubition control unless they progress spanwise during deployment. The aspect of spoilers that is more linear is the drag produced. This means that the more the spoiler is deployed, the more proverse yaw. Trying to get the right combination of roll and proverse yaw could be a real problem with single blade or trap door type spoilers.

Ollie, I'm not so sure I'm with you on this one. Full size airliners use basic barn door types to good effect for minor corrections with the ailerons only coming into play for the more meaningful requirements.

But I do agree that some experimentation is in order to determine the size and placement on the wing. I'm thinking that there is a reason why the roll control spoilers on the airliners I've flown on and the MU2 are placed far to the rear on the airfoil.

I have built a few high-wing trainer types with spoilers, based on numbers in Andy Lennon's book, and had good results, using the general guidlines (for a "plank" wing) of:

Spoiler location: at 70% or more from the leading edge of the wing
Spoiler chord : 10 to 15% of the chord
Spoiler span : 50% of the semi-span
Deflection : Depending on useage for roll or as brakes/lift dumping


There's more info on ailerons in NACA report 605, at http://naca.larc.nasa.gov/reports/1937/naca-report-605/

Andy also points out that, with slotted flaps depoloyed, the spoiler is much more effective, as it opens the slot lip further, and dumps a lot of the flap's lift.... functioning as a "slot-lip aileron". It works great on a model too.

I've got Andy Lennon's book in front of me 'The Basics of Model Aircraft Design' and he suggests that spoilers are hinged at 20% chord with the spoiler being 10% chord. He suggests about 50% span.
All the RAF fighters I've worked on or have seen have for want of a better word 'barn door' type spoilers. In particular the Tornado.
I wonder how much the wing loading affects the type of spoiler you use. and would a higher loading reduce the amount of proverse yaw.
Dave

I think the position of the spoilers may have a lot to do with what you're trying to achieve. If you just need to dump some lift then the 20 to 35% back from the leading edge probably does the best job of spoiling the lift. But for directional control Mike's numbers may be better for leverage with less yaw inducing drag.

Here again the full size aircraft roll spoilers all seem to be farther back.

As for the proverse yawing. I would think that would be desireable as long as the drag induce yaw was in harmony with the rolling action.

I wasn't too clear on my last note. I should have said that the hinge position was 20% from the trailing edge. Wonder what effect the spoiler will have on the airflow over the flap. If you have spoilers you will almost certainly have full trailing edge flaps?
Sorry for confusing folks.
Dave

Bruce....The biggest thing that differentiates models with full scale is airspeed.......The spoiler panels on lets say a B-757 consist of six panels on each side.....4 on each side are capable of flt/grnd spoilers and 2 on each side are grnd only......grnd spoilers are to reduce the lift of the wing to enable much more effective braking, especially on wet runways.....now the flight spoilers at higher airspeeds might come up 2 or 3 inches(10deg) from faired( during a turn).....above 250k indicated.airspeed.. with a maximum travel of 35-40 deg which you wouldn't see under "normal flying".....for higher sinkrates out of altitude you might see 25 deg or so for all 8 panels.....which still function in turns(one side panels less deflection with opp side more deflection)....like it has been mentioned the spoiler panels are above and slightly fwd of T/E flaps...which is roughly @ 70% of wing chord....the proverse/adverse yaw is negligable........I think you could make a nice combo of aileron/spoilers very effective with some experimentation ..... keeping in mind the slower flying speeds models have....Bill...

Welp, I guess there's only one way to find out. I'm just finishing up a drawing for a antique'ish 3 channel model. I think along with the tip dihedral 3 channel wing I'm gonna make me a second set of feathers with spoilers for roll control but keep enough dihedral in there that I can at least get the kite back on the ground if they don't work. And I think I'll make them multi paneled so I can try the size and position.

More in a couple of months. Dipsy, I'll keep you in mind and PM ya when I have some real world results.

In the meantime here's a sketch of the cargo twin I want to use the spoilers on;

If I can I'll scan the page on spoilers and send it to you. It may help a bit. If it helps here's the ISBN : 0-911295-40-2 'R/C MODEL AIRCRAFT DESIGN by Andy Lennon.
Dave

I'm still considering the Graupner spoilers sold by Hobby Lobby for my 13.5' span turbine U-2 still under construction. I'm concerned about having sufficient roll control.

The early U-2s, 80' span, didn't have them but the latter, TR-1/U2S 103' span, did require them after flight test findings.

I'd probably mix them in after a pre-determined aileron deflection, much like some airliners do.

The ones by Graupner are 10.7" long, 1.1" wide and 3.5mm thick. not sure exactly how they are actuated. Probably pull cables.

I had a smaller version U-2, 80" span, by Knights Of the Air and I experienced insufficient roll control with just the ailerons

Jack

BM, not entirely correct on spoilers. Spoilers are an integral part of the flight control system on real aircraft. They are propotionally mixed in with aileron inputs, which allows much less flight control input. Spoilers used in roll control are mixed with aileron input and only deploy on the down-going wing, and will always start deploying from the most inboard position, gradually increasing displacement outwards. This is why airliners use multiple spoilers. In speedbrake use, they are deployed symmetrically in varying degrees. As ground spoilers, they are used after touchdown to spoil lift and increase braking effectiveness. You will almost always find the spoilers located directly in front of the flaps on a real aircraft. This adds stability on rollout, as lift is being dumped from the very areas of the wing where it is being created by the flaps.

A couple things to remember if using spoilers.

Use VERY LITTLE deflection!

Do not use spoilers and flaps at the same time, they will negate the purpose of having flaps deployed and greatly increase drag.

Hmmmm, I could have sworn I remembered the outer spoiler coming up in conjunction with the airleron for larger control inputs....

You're right about one thing though. The ailerons are the first thing to move followed by the spoiler to assist the roll. I was remembering it back**swards. But I'm still pretty sure it was the outer spoiler that is used for roll input assistance. The inner to outer progression was for speed brakes I believe. And then on touchdown they must have some sort of "Big Red Switch" that snaps the whole lot up on landing....

I'm flying again in March I'll have to watch more carefully.

Now, I can not speak for all aircraft, as I've only worked on about 10 different types of airliners, but in general, you use your innermost control surfaces first, especially at high speeds. You are correct, at the control input increases, you will see large deflections of the spoilers going outboard. Watch the wing between takeoff, cruise, and landing. You will see very little deflections until the landing phase where you will see decent amount of spoiler deflection.

As for the 'big red switch', every airliner type that I've worked on uses some sort of an auto ground spoiler system. This is usually tied to the main landing gear wheel speed transducers. The crew will arm the auto spoilers on approach and as the plane touches down and the wheels spin up, the spoilers will automatically deploy to full ground spoiler. This system is also interlocked to the throttles, so if the pilot must do a go around, pushing the throttles forward will automatically retract the spoilers again.

I know you say don't use spoilers and flaps at the same time, but on fighters spoilers are quite often the only form of roll control. The prop jet I'm building is a Sepecat Jaguar. I know this doesn't have ailerons. Tornado is the same, it differs in that it uses differential taileron when the wing are swept.

Well that would be a different story now wouldn't it! I guess I should clarify and say don't use spoilers as speedbrakes or to spoil lift while also using flaps.

A few trs back a Tornado pilot decided to do a roller after landing, he was very worried about the high speed coz he hadn't taken off again. You guessed it, he'd selected lift dump on landing and forgotten about it.......oops!!!

'

You want to dump the lift just AFTER landing!

Most aircraft have a warning system to tell you that you are selecting a lift dumping device at the same time that you are selecting a lift-augmenting device!

We're talking military pilots here, cream of the cream and all that crap. I think the tornado's throttles rock outboard to select dump. Don't know what warning devices the 'Tonka' has, haven't worked on them yet, the RAF in it's infinate wisdom has stuck me on helo's. Helicopters are the devils work !!!!!
Dave

pssst! I think you meant 'cream of the crop'

Sounds like you've been working with these guy's a while to. Do airline pilots get upset if you don't worship the ground they walk on? We have one in particular, he's a big bloke, so if I know he's flying the helo, I put his seat all the way forward and rudder pedals all the way back. It's good for a laugh, and makes for good banter on the intercom on startup.

The father rearward the spoilers are mounted, the more they act like an inverted split flap, and the more proportional control you get from them.

If you think about a spoiler mounted at the thick point, it doesn't take much deflection to completely separate the airflow from the rest of the wing. by the time it's up 10 deg. the wing is fully spoiled. There is no more lift to be killed. Functionally, you only add some drag by deploying the spoiler further.

The spoiler mounted further back is more proportional, as it takes more deflection to kill an equivalent amount of lift and creates proverse-yawing drag in proportion as well. It actually will start to show some of the properties of inverted split flaps, as it will actually start to deflect air up and create a relative high pressure area on the wing skin in front of it, to create the rolling force.

THe MU-2 uses spoilers for roll control in part because then the whole trailing edge can be used for flaps. That allows this tiny-wing airplane to slow to halfway sane landing speeds. Having the spoilers in front of the flaps serves to magnify their effect on roll control, even at slow approach speeds.

I had slot-lip spoilers on an Oly2 glider that I had built with slotted flaps. That was great for glide path control. With flaps 60 deg out, it would descend at a pretty steep angle, maybe 25 degrees with the nose pretty level. Pop up the spoilers on top of this, and it would decend steeply, but slowly at maybe a 45 deg angle, with the nose level. You could easily see thru the wide gap beteween main wing and flap when approaching like this. Cool gadget for sure.

How about a real simple answer to the location of spoilers on an aircraft...

What is in the wing??? FUEL. The main load bearing area of the wing in 99.9% of aircraft is a big fuel tank... why would you bother building anything in that area when you can put them at the back where there is easy access. Placing the spoilers over the tank would require plumbing hydraulics, wiring, and control cables through the fuel tank, around it, or etc... not very practical now, is it?