Use crow, fall out of sky, SOMETIMES

It's what you eat when you're wrong!

Chad! You kill me!

Um, who said it was magical magic that just lets you have magic landings?

Well, I like that explanation, so I'll go with that. I like crow.

Steven,

Fully agree with your explanation as this is exactly what i have experienced with myBoomerang XL. However one thing is still puzzling me, i have tried to use crow on my Boomerang Intro on a couple of occasions and i was lucky enough to avoid disaster when the BI started tip stalling on finals (although i was not that slow actually was even faster than in usual landings with full flaps only) and i was able to recover from this situation. Never used crow on the BI since then but only full flaps to reduce speed and i have to ajust rate of descent by pitching down till touchdown. With this configuration i hardly miss a landing on our very short paved runway!!!

Rgds,

Anyone flying a Reaction longnose recomend crow I did not use the speed brake?

I'm with Rav on this one. I use crow on every plane I own....it adds benefit in my head, and therefore adds benefit to my plane. I don't care what anyone (including science) says, crow reduces the stalling speed of the tips of the wings and allows me to land slower....I don't care about the AOA crap.

Take it or leave it, use it or don't. I like it, I use it.

Chad

how much up deflection of ailerons would you say you have? and was it with take off or landing flaps?

1/4 - 1/2 depending on plane. Landing flaps only.

I'd like to put conclusion to this topic from a different point of view since the analysis has come to a clear explanation. Given with full flaps, for high cambered low wing loading aircraft a reduction of camber is required, hence by using crow increase effectiveness of the wings at low speed flight. It reduces load from the tail while balancing stability to maintain control during low speed flight. However, this topic is related to many aspect of an airfoil which is critical in determining landing performance. Our goal is to get the slowest stable speed as possible above the safety margin to minimized energy dissipations on landing or the amount of energy can handle per unit time without failure. Jets are highly energy performing aircraft in which to carry power on landing is an advantage. With smaller wing surface and drag coefficient, higher wing loadings are the factors of higher speed requirements. Therefore using surface extension, camber and other high lift and drag devices are necessary to get the objective. I believe some jets with lower wing loading can land at idle and a reduction of lift and drag is necessary to increase airflow. On otherhand, adding small fins on the wings as vortex generators or micro VGs can reenergize airflow, delaying air separation on the wings even without reduction of lift camber.

Much is said by a lot of smart people here

I just missing some parts. When ailerons are lifted in a crow configuration the trow of it will deside if it will funktion as brake ore increased washout. Just like the flapsetting "takeoff/landing" one increase lift and the other kills lift and will funktion as brake.
The wingcorde and wingtype has a lot to say, if not all to say regards what realy happens with the airflow over the wing when the ailerons are moving

I allways use 2-5mm up aileron when flaps are deflected, if it's crow ore not I'm not shure. On a MB 339 ore A-10 that have this type of wing I would have used much more.

I like crow too, I use it too, I also recognize real benefit, agree 100% to a point.

But crow "reducing stall speed" of the wing or any portion of the wing is not what's happening here...not by a long shot. However, rather than a rhetorical argument which risks offending your "faith" (as opposed to science) I propose an experiment.

If crow "reduces the stalling speed of the tips, allowing you to land more slowly", why not reflex the flaps in addition to the ailerons? I mean, why not "reduce the stalling speed" of the ENTIRE wing rather than just the tips? If reflexing lowers stall speed of an airfoil then why not take full advantage of that phenomenon? (You could still reflex the ailerons more than the flaps if you're worried about protecting the washout/controlability concept). Why not just bolt the wings on upside down from the beginning? Why don't STOL aircraft have the camber of their fat wings facing the dirt rather than the sky?

The reason, obviously, is that the science does matter. A negative camber (reflex) reduces the amount of lift a wing can make at a given speed (c/l) and reducing the amount of lift that any wing, or even a portion of that wing (reflexed ailerons in crow), is able to produce increases the minimum speed at which that wing must fly thru the air (stall speed) to develop enough lift to stay in the air.

Not comprehending the science, not caring about the science, denigrating the science...none of those things makes the science of the AOA and c/l "crap" any more than spending one's entire life wandering on the Great Plains of this country means that he can accurately state that Earth really is flat, no matter how long he has been "knowing what he knows" and interpreting that as fact.

No one need take offense for my having defended the science. I'm sure I will take a hit for trying to help though, for trying to keep the discussions of basic aerodynamics based upon...reality.

It happens every time, I'm used to it now, so flame away.


Don.

Don....I doubt anyone can reasonably argue against your point. However as a famous baseball player once said "the game is 90% mental and 50% physical"...point being that flying model jets is a head game as much as anything. If you "believe" you have a engine that will never flame out you will fly more daring manuvers, if you believe your radio link is as solid as it can possibly be the thought of loss of control never enters your mind, and if you believe that crow let's you land slower without a worry of dropping a wing then you WILL land slower without the stress of thinking she is gonna depart any second. I think we all agree that most of us land at speeds much higher than we need to anyway.

As I tell my guys at work all the time. Perception IS reaility, and that is a fact.

Agreed.

My biggest concern is not to convince those who "know what they know", as they may be intransigent anyway. I learned that lesson in the downwind turn thread and another concerning a viper crash. It's a "You can lead a horse to water but you can't make him drink" sort of thing.

Rather, I'm more concerned about the casual reader who is curious about crow, comes here looking for informed advice, and might then leave here thinking that a temporarily inverted camber somehow actually does create more lift and a lower stall speed. [X(]

If I can help just one guy there then it's worth it. Usually.

Peace y'all

Don.

I think the experts agree that Crow increases drag and reduces lift, so the aircraft will stall at a slightly higher speed. However, in my opinion it is all about which side of the drag curve the aircraft is on. In simple terms, if the aircraft is flying on the 'right' side of the drag curve with fixed power, a small increase in speed (caused by a transient effect) causes a small increase in drag, which effectively slows the jet down a little - the aircraft is speed stable. This is typically the regime in cruise/high speed flight. If the aircraft is on the wrong size of the drag curve, a reduction in speed sees an increase in drag, which slows the aircraft further, etc - speed unstable. Many full size military jet aircraft make approaches on the 'wrong' side of the drag curve, with the configuration as 'dirty' as possible. This means that the engine is at a higher power setting, so is more responsive to throttle movement, and spools up to full thrust quicker in the event of a go around. This leads to the high alpha approaches, 'dragging' the aircraft in to the landing.

What does this mean for modellers? For really slippery model jets, the thrust at idle with flap may not allow the jet to slow down enough to ever get on the 'wrong' side of the drag curve. Crow will allow higher drag, so the model will land slower than without. (it will still stall at a higher speed, but the approach and landing is slower, which is good) The downside is, that if you do actually get the aircraft onto the 'wrong' side, it will slow down very quickly without a bunch of power to catch the speed decay - hence the stories of nearly losing models on finals turn. Properly setup Crow is a very effective way of getting a jet onto the wrong side of the drag curve, which is where you want it for the final approach and landing. Many guys here have shown that they like the setup, because it works - these guys are probably keeping the power and speed high enough around the finals turn to avoid stalling issues, which is ideal. For those of you who have nearly lost a jet around finals, here's my two cents worth: As you apply crow, be ready to apply power to counter the extra drag caused. If you do actually have the crow setup so that the drag is high enough to put the aircraft on the wrong side of the drag curve, the speed will decrease very quickly, and lowering the nose will not be enough to catch it - you will need to add power even in a descending turn.

Bottom line: Crow can reduce landing speeds on slippery jets by increasing drag - stalling speed will be higher though. If your crow setup increases drag enough to put the jet on the wrong side of the drag curve (IMO, where you want it, for final approach and landing), you will need a much higher power setting, and will need to be working the throttle down the approach to keep the speed constant and safely above the stall speed. Properly set up, crow works.

So what happens if each aileron goes up and down at the same time? That's the case with the full scale A-10 which uses split ailerons as speedbrakes. Obviously it creates the intended drag but is total lift (and stall speed) changed? Does the increased lift effect of the lower half counteract the decreased lift on the upper half?

Having flown the full scale A-10, I can tell you that any change in lift/pitch is not noticeable when using the speedbrakes. We mostly only used the them during formation rejoins or on landing.

Now here's an aerodynamic brain teaser: with the A-10 speedbrakes deployed, the roll rate was dramatically increased...maybe twice as fast, even if the speedbrakes were only cracked a few degrees. Never really could explain that effect from an aerodynamic standpoint. Anybody want to try?

Craig

Easy one...(Sorry, it is if you're an Aero E nerd wannabe, anyway. Found this in an Aero E text book some years back)

I'm sure there will a tweak or two added by a real Aero E soon enough, but essentially it's this: Split flaps create more lift than a simple hinged flap (aileron) for the same surface area. When using "aileron" in that config you essentially have a split flap acting in opposite directions on each wingtip rather than an aileron as we know them.

Do I get a cookie, or perhaps a star on my test to show mom when I come home?



Don.

Never thought of it that way but I get the idea. Guess I still don't understand why a split flap creates more lift than a "simple" flap. I need a layman's explanation before you get the cookie.

Craig

Hi Craig - here's my thoughts on it: By splitting the ailerons even a little, you are widening the trailing edge of the aileron. The turbulent flow behind this wide trailing edge effectively increases the area of the aileron, as the 'smooth' airflow across it only comes back together a bit further back. They use this effect on many aircraft by putting a T section on the trailing edge of a control surface to improve effectiveness. Same effect with your split ailerons, just magnified a lot! And with the full split, the increase in drag must have been phenomenal. What sort of power increase did you need to maintain speed when you used the split aileron airbrake?

Cheers - Pat

Easy Craig, if you reduce lift at the outboard section of the wing, (which is what I guess happens if you split the ailerons) you reduce roll damping and therefore you get an INCREASE in roll rate !

But may I ask with all the A10s in the USAF didn't any pilots, particularly instructors and standards pilots on the type , find out from Fairchild EXACTLY why this happened, so as to give squadron pilots a fuller understanding of how the aeroplane worked ? Just curious !

.........and Don, does a split flap REALLY create more lift than a plain flap, thought it was to create a drag as well as lift increase, it was on the Canberra, which didn't use flaps for T/O.

and Pat, are you sure that many aircraft approach on the 'wrong side " of the drag curve, (the slower you go the slower you go !) none of the types I have flown do that. Concorde was on the " wrong" side of the drag curve on approach BUT used auto throttles even with hand flown approaches to cope with the speed instability.

Some types, Vulcan, Victor , Lightning, approached with the airbrakes out to get them on the "right" side of the drag curve and create speed stability and the B47 even streamed a chute, in flight, to get it on the "right" side of the curve. As a cadet in the RAF I used to watch them, with fascination, landing at Fairford, makes me really old !

Good debate tho !

David

Thanks Don, Pat and David for your comments. Right now, Pat is in first place for the cookie for his explanation!

Pat...I don't know how much power it would take to compensate for the speedbrakes being fully opened because I never tried it. Normally we were at idle and just trying to slow down, closing the speedbrakes as soon as we killed the speed. The speedbrakes opened variably, so most of the time we would just "fan" them open a little anyhow.

David...the roll rate thing was something we discovered during the early days of the A-10. It was just viewed as a peculiarity since we rarely used the speedbrakes and it didn't affect any of our tactics or procedures. I'm sure in the 30 years since I flew it, somebody has figured out why it happens. One of the reasons I asked here.

Craig

Howdy Craig, I suppose I'm gonna have to buy my own cookie then cus I don't have the explanation. I just have a texbook reference stating that the flap styles in order of effectiveness for increasing the c/l are, in ascending order, "plain", split, and fowler.

Good question Craig,

Ailerons that goes down produce lift and drag, while ailerons that goes up produce drag and counter lift. Yes, you got total drag from both surfaces while net on the lift.

Congrats to the winner! So far I don’t have much idea about the increase in roll rate due to speedbrake of an A-10. But I can say that the increase in trailing edge thickness caused by the kind of speedbrake has greatly influence the boundary layer on both sides of the wings. It produces high pressure solid airflow (laminary) on both sides until it goes to a high turbulence separation at the trailing edge.

Yes David, it does. And yes it's very draggy. The best example I can think of is your beloved Spitfire, the second best fighter to serve in the ETO. The Royal Navy in particular used them for t/o by lowering the two position only flaps (Up and landing) and stuffing a wedge of wood into them and retracting them, thus clamping the wood into place and giving the normally landing -only flaps a makeshift t/o position. After the Spit left the deck the flaps were lowered so as to drop the wooden wedges into the sea and then they were placed into the up position !

I believe highhorse has the cookie! An aileron is essentially a plain flap that can go in either direction. The A-10 with aileron brakes open is essentially a split flap that can go in either direction. Since for any change in angle a split flap creates a greater change in Cl than a plain flap, the split flap/open ailerons will create a greater roll rate than the plain flap/closed ailerons.
H