I have a twin .25 sized A-10 ready for flight and have been mulling over its wingloading/overall weight. The wingloading is about 32oz. but I have large Fowler-type flaps and Horner tips to supplement lift and aid in stability. On the FS A-10, it also has LE slats between the fuselage and the wheel wells that obviously deploy at slow speeds. With that in mind, I'm wondering if I installed fixed position slats in the same area, how would it affect it's high speed flight? Would it even notice them or would it create too much turbulence? Would the slats even help in this case?

Comments appreciated!

Ted

tdwise,

The short answer is that fixed slats will increase drag for high speed, low angle of attack flight. Now for the longer answer. Slats give higher lift, usually for takeoff and landing, by allowing the wing to operate at higher angle of attack without stalling. If you imagine the airfoil section as the slat is deployed, you can see that it does two things. It increases camber near the leading edge, and it decreases the angle of attack of the wing, if you assume that flaps are not deployed at the same time. For high-speed flight, you don't need that added camber; it will only add drag. The bigger problem would be if the decrease in angle of attack actually pushed you below the zero-lift angle ( ie. the wing would generate downforce along the part of the span with the slat ). This would be pretty bad. I don't know what the fully deployed slat looks like on the FS A-10, but I would guess that it moves pretty far, and is visually obvious. If this is true, and you are after a scale look, you might want to make it a working slat, so you can retract it for normal flight. If you are happy with a smaller deflection, then it wouldn't be as big a deal. In any case, fixed position slats will have some drag penalty at high speed. It would probably be a fair amount of effort to build working slats that give a really smooth surface when they are retracted, but you are already doing fowler flaps, so you probably don't mind that.

I wouldn't break you back or compromise scale appearance for the Hoerner tips, I doubt you will notice much benefit from them. If it's handy, I'd love to see pictures of your wing details when you get that far.

Good luck,

banktoturn

That's a strange place to put them..... Obviously they are NOT for tips stall delay as used on most other aircraft. I'm thinking that they put them there to delay that the center section stalling and having a large turbulent wake bubble rob the engines of air....

Anyone?

BMatthews,

I think there are inboard, along with the flaps, because they are only deployed with full flaps, so the center section will actually stall before the tips, even though the slats alone would delay stall.

banktoturn

Those inboard slats never fully retract. They seem to be built for some motion, but it's obvious by looking at the FS one that they never actually retract flush

The reason that these are important to have near the fuse, is that the engines are directly behind the wings - which you all knew - and they draw alot of air. It is vital to maintain a smooth flow of air into the engines, especially when yanking a high-alpha maneuver. Same reason there is such a big root fillet on that wing. So, the slats are there more for the engines than the wing...... huh? Yeah, they keep the engines from eating a bunch of dirty air when the wing would have otherwise been causing alot of problems with airflow to the engines.

I will be building a big A-10 over the next few years, and I will put them on - fixed in place.

In case you're interested, here's a schematic I was able to pull off an A-10 website.
http://www.a-10.org/flightmanual/man...?PageID=1%2D60

I tend agree with John - the slats probably condition the air as it comes over the wing and enters the engines. Q: Could the airflow be at a higher rate from the engine suction at the wing roots whereby the slats take advantage of this for added lift benefit? Just a thought!

Ted

It seems to me that the main effect that slats would have on the intake air for the engines would be to prevent them from ingesting air from a stalled section of the wing. Until the wing is beginning to stall, I don't think that slats do anything to 'condition' the air, but I could be wrong about that. It is counterintuitive to me that the slats would need to be deployed under any flight conditions that are not close to stall ( such as high-alpha maneuvers ). Johng, can you give me a pointer to a write-up about this? I'd love to read more.

Thanks,

banktoturn

High Alpha....?
http://www.a-10.org/photos/p.asp?Fil...a10%2D08%2Ejpg

tdwise,

Sorry, alpha is the variable often used for the angle of attack.

banktoturn

You may be interested to know that Martin Heperle has resently expanded Java Foil to be able to analyse multiple element airfoils. See:
http://www.mh-aerotools.de/airfoils/javafoil.htm

Bank-to-turn....Just to help your good explanation of "Alpha" on most typical commercial aircraft the "Vanes" used to aerodynamically identify AOA used to be called AOA "sensors" or "vanes'...now just refered to as "Alpha" vanes or sensors.....they are strategically placed along the nose section of the fuse to reference WL or( center of Fuse)to the relative airflow....used for stall warning info and "auto" slat extension during "imminent" stall conditions....Also the slats on the A-10 could very well be needed in high "G" manuevers to keep Fuselage from "blanking" out airflow to the engines......Bill....

The slats are there mainly becuase of the engine location. The engines are subject to losing airflow when the wing is stalled at high alpha. The slats fixed this problem and also helped the engine from flaming out when the 30 mm was fired.
The slats automatically deploy based on air pressure, but do have a tendency to stick from gun exhaust debris.
As far as the small .25 size goes, I would try and keep the wing as simple as possible. That size model is too small to see any improvement in performance. Now the larger A-10 out of Germany would benefit from working slats. Models in the .25 size range need to be built as light and simple as possible.
Simply put, light wing loading on these little guys makes them fly great!
Chris
http://www.rcuniverse.com/gallery/sh...papass=&sort=1

Rather than look up quotes from my books, I sent Chris a note about this thread, knowing he works with the Hog as part of his job. I also found a bit a verbage upon further examination of the a-10.org site:

http://www.a-10.org/flightmanual/man...?PageID=1%2D59

I doubt they would make much difference on a small hog, but they also wouldn't weigh much, if you just made a couple out of 1/16 balsa mounted on 1/16 stick spacers. It'll make the guys at the field think you know what you are doing

I read through the flight manual that tdwise posted, and it was very informative. As a couple of you mentioned, it confirms that the slats are deployed automatically to protect the engine from ingesting 'dirty' air as a result of stall on the inboard section. It also says that the system is programmed to deploy the slats in a 'fail safe' mode if the automatic system is damaged, so that the engine is still protected. It points out that if this happens, drag will go up.

czonio, whether the complexity is justified or not, I disagree that the slats would have no effect on a .25 sized model. There is nothing I know of about scale effects that would necessarily make slats ineffective.

banktoturn

banktoturn,
I did not say "the slats would have no effect on a .25 sized model", I said it would be a very small improvement.
You have to realize that the Reynold’s numbers are completely different from full scale to small models.
What kit model are we talking about? Is it Combat models or a scratch?
Chris

The "kit" is a little bit of everything rolled into one! Actually, I bought it a year ago through an internet connection. It's an "Imagination Aviation" kit which I've never heard of. The design is from John Kidd which his plans for this same plane are also available through Model Airplane News. Like I said, this A-10 is a little bit of everything - John Kidd, Keith Sparks and "Me"! The original design called for 2 .09's, 2 Channel (Elev/Ail) and hand launched. But since it already had a 56" WS, I felt it was within reason to "bulk it up" to carry twin .25's, retracts as well as flaps. The wing area was increased by 15% in both span and chord. I also gleaned alot of information from Keith Sparks' design that was featured in an issue of MAN about 2 years ago. In fact, I obtained a set of his nacelles and used them on mine. So, to answer your question - it came from a kit but it's been bashed!

Ted

Got pics?

Yes, I do but I need your email address so I can send them (I don't have a website...sorry). A friend took them and sent them to me but they're a little on the big side and haven't been able to figure out how to re-save them in a reduced size. But they're typical jpg's so there shouldn't be a problem. You'll have to excuse the fact that when the pics were taken, I didn't have the nacelles in place yet. I was breaking the engines in that day and left the nacelles at home so they wouldn't be in the way.

My email is [email protected]

Ted

Unless you have a perfectly square wing, your tip will always stall first.

That's a great post with the actual manual for the aircraft. Turbofan engines are hungry monsters and stall very easily if their inlet airflow is interrupted. We can't even run engines with thrust reversers deployed below 60 kts on the real thing or the engine can stall on its own, turbulent reverse thrust.

An engine stall is, after all, defined as 'An interruption of the smooth flow of air through the engine'

Not quite. There are lots of things that affect tip stall.

banktoturn

I'm speaking very generically. With the wing design of the A-10, the tips have a much smaller chord and will definately stall first. Of course, this is much more pronounced in swept back wings.

Square as in aspect ratio one or square as in rectangular?

Both aerodynamic washout and geometric washout can prevent tip stall in a tapered wing if the right amount of washout is used. Even a tapered and highly sweptback wing can avoid tip stall if enough washout is used. Sight down the wing of any modern jet transport for an eyefull of washout. The designer didn't put it there because HE was twisted.

The picture I had in my mind was a perfectly flat/rectangular shaped wing, but in hindsight, that was way too general a reference to this situation.

The A-10 wing is a fairly rectangular wing, with the tip chord being shorter than the root, this was the basis of my example. I know of know military or widebody aircraft that stalls the innerwing before the tip, that is a very dangerous situation.

Any stall can be dangerous but, usually tip stalls are much more dangerous than root stalls. Tip stalls result in a violent snaproll. Root stalls without tip stalls result in a mush and rapid loss of altitude but, without the violent snaproll.