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Does crow aileron reduce landing airspeed?

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Does crow aileron reduce landing airspeed?

Old 02-20-2018, 09:59 AM
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mr_matt
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Default Does crow aileron reduce landing airspeed?

Someone please explain?
Old 02-20-2018, 10:07 AM
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Si_B
 
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I always thought it reduced lift and changed the approach angle of the model slightly allowing a more nose up attitude. The crow also adds wash out to the tips so less likely to stall.

By coming in at a higher angle of attack, you get more drag which I guess will slow you down. Like everything, there is a sweet spot. I always use now.

Simon
Old 02-20-2018, 10:10 AM
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DelGatoGrande
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It also kills lift and adds one more switch to use on your radio=one more thing to go wrong.
Why you need such a mix?
If you must reduce landing speed you can use flaps or airbrakes?
Old 02-20-2018, 10:18 AM
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Dave Wilshere
 
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It changes the AOA on the wing, so yes the nose generally raises, this is where the drag comes from (and presenting the flap more to the airflow) It also reduces lift, (Why it does not work well on heavier loaded jets)
Generally it comes in with landing flap, so no more switches!

What aeroplane you have in mind?
Old 02-20-2018, 11:01 AM
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ravill
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Originally Posted by DelGatoGrande View Post
It also kills lift and adds one more switch to use on your radio=one more thing to go wrong.
Why you need such a mix?
If you must reduce landing speed you can use flaps or airbrakes?
Many different jets can get significantly increased good landing behavior with crow. One of the most glaring examples is BV's venerable kingcat. Try landing that thing without crow.

And no extra switches needed either!

At first I immediately thought that crow would necessarily increase landing speed as the airframe trades lift for drag/control, hence to be able to keep flying, you need more thrust to make the same amount of non-crow lift.

But you aren't asking about flying, you're asking about landing, ie when you want to STOP flying.

I would venture to say, that you don't necessarily decrease landing speed, you just get down to that speed faster! Q.E.D. (LOL!)
Old 02-20-2018, 11:24 AM
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mr_matt
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The question is more theoretical. I have it on a bobcat already.

But I don't know if it actually lowers the landing airspeed. I know what_I_believe the answer is, I am curious about other's observations.

Last edited by mr_matt; 02-20-2018 at 11:59 AM.
Old 02-20-2018, 11:45 AM
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LA jetguy
 
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In my opinion it reduces lift, and prevents speed built up on descend... Also helps AOA for a nice main to nose touch down...

All my sports jets have approx 5mm, except for the Ultra Flash which has slightly less.

David
Old 02-20-2018, 01:29 PM
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David Gladwin
 
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Crow does NOT decrease landing speed, it actually increases it because of the lower C of lift. ( Cl) It does, however, increase drag so can provide a more speed stable approach.

If if you wish to decrease landing speed , one needs to DROOP the ailerons to increase the camber of the wing.

I do that on my heavy BVM F 4 which has no tip stalling tendencies being almost a delta.

Next time you you guys fly on an AIRBUS watch what happens to the ailerons when flap is lowered! ,

I believe some other airliners are similar.
Old 02-20-2018, 02:25 PM
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Kevin_W
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Matt,
I'm sure you probably remember the Interceptor(s) I flew back in the late 90's. I did a little kit bashing when I built those and redesigned the wing planform (I don't remember exactly why). The result was that the damned thing flew like a bat outta hell, but it even with full flaps it took three laps around the field at idle to get it to slow down enough for a landing approach. I solved the problem by adding crow.
With flaps only the nose would drop (actually looked like it was flying downhill in level flight) and it would not slow down. When I added the crow the nose stayed level, it took less up elevator to maintain level flight, and the plane slowed down quite nicely for landing, and I actually had to carry a little power throughout the approach.
I don't know if it allowed the plane to fly any slower, but it certainly achieved the goal of slowing it down in a more timely fashion, i.e. more positive control over the planes airspeed.

Another note on the subject, if you are going to use crow be vary careful not to throw it all in at too high an airspeed. On my first Interceptor (the ducted fan one) I threw the flaps and crow in while it was still doing about 140mph and the plane went all weird, I had to hold a lot of aileron and rudder correction to bring it in for landing. After finally getting it on the ground I found that he top wing skin (foam wing, balsa sheeting, and glassed) on the right wing had cracked from the center of the leading edge diagonally back to about the middle of the flap. It took a lot of twisting force to make that happen!
I added carbon fiber strips to the sheeting of the next two (turbine) versions of that plane that I built!
Old 02-20-2018, 03:23 PM
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roger.alli
 
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My understanding, is that Crow will (slightly)increase the STALL speed.

For example, a wing, during a stable approach, with 45 deg flap and neutral ailerons, will have a lower stalling speed than the same wing, when set up with 45 deg flap and 5 deg negative ailerons.

In theory, a wing at neutral ailerons (no crow) will stall the slower, and have the lowest possible landing speed.

HOWEVER. We never make approaches at Vs , and rarely land at stall speed. Crow obviously has many advantages in the circuit, and the slight increase in stall speed is made up for by these advantages.

I am however, just an amateur in these things..

Good topic Matt. Keen to hear your view.

Last edited by roger.alli; 02-20-2018 at 03:28 PM.
Old 02-20-2018, 03:34 PM
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Originally Posted by David Gladwin View Post
Crow does NOT decrease landing speed, it actually increases it because of the lower C of lift. ( Cl) It does, however, increase drag so can provide a more speed stable approach.

If if you wish to decrease landing speed , one needs to DROOP the ailerons to increase the camber of the wing.

I do that on my heavy BVM F 4 which has no tip stalling tendencies being almost a delta.

Next time you you guys fly on an AIRBUS watch what happens to the ailerons when flap is lowered! ,

I believe some other airliners are similar.
I believe 777 may have crow with full flaps.
Old 02-20-2018, 03:43 PM
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Kelly Rohrbach
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Well I'm no rocket scientists but what I noticed it allows me to get my bobcat into a nice aoa without it floating down the runway and allows to carry more throttle without increased speed.
Old 02-20-2018, 04:46 PM
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jws_aces
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I believe the biggest thing crow does it keep the wing tips from stalling as quickly as the center closer to the fuse. That keeps the wings more stable along with aileron control up to stall and even after the wing begins to stall. It reminds me of a Full scale trainer wing like the Piper Warrior and Cessna 172. The wing had built in wash out to keep the air across the ailerons during a stall moment. Lazy rudder control was the biggest reason for this design in my opinion. Crow is a way to have that feature on a wing with no wash out. It's a must have on high wing loaded, high landing speed jets. The small hawks benefited from crow.
Old 02-20-2018, 05:10 PM
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CARS II
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Agreed with some of the comments here.

I use Crow on my Boomerang XL because it floats on final and I like to do short approaches, I don't like the long flat ones ( eyes are not as young as they used to be ) it adds drag and makes the approaches to land more predictable.

That's all
Old 02-21-2018, 04:47 AM
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Dr Honda
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As above... it adds drag, but more importantly... it adds stability. If you have a model that has tip stall issues if the speed gets low... crow will make it feel more locked in, and stable.

I'm half and half on it. My Firebird, and Falcon120 don't need it. (both are stable and slow at landings) My Shockjet and old Starjet doesn't need it, but without it, the landings are long. My little t45 ABSOLUTLY needs it. (T45 have a nasty tip stall habit)
Old 02-21-2018, 05:03 AM
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Henke Torphammar
 
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Originally Posted by Dr Honda View Post
As above... it adds drag, but more importantly... it adds stability. If you have a model that has tip stall issues if the speed gets low... crow will make it feel more locked in, and stable.

I'm half and half on it. My Firebird, and Falcon120 don't need it. (both are stable and slow at landings) My Shockjet and old Starjet doesn't need it, but without it, the landings are long. My little t45 ABSOLUTLY needs it. (T45 have a nasty tip stall habit)
For sure! But the main question is tricky. Can it fly slower with crow? Even though crow removes lift I think it can fly slower as you make it stable. You make it stall instead of dropping one wing first, which makes is possible to fly it slower. Plus all the other making it more comfortable, predictable etc...

With the Jeti telemetri I should be able to test this IRL too... (no promising)
Old 02-21-2018, 07:00 AM
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I used to show people what the kingcat would do with and without Crow.. the stall speed at altitude was roughly the same, indistinguishable to me, but what It did do, is with crow, it would simply mush, without it would snap out. So i was demonstrating the wing tip stall vs washout. Airliners mostly dont use it, as they are extremely high wing loads and different R numbers..

What I find is with models, they tend to pick up speed when the fuse is flat or nose down, and with the lighter wing loaded planes, the tendency is to be too fast not too slow, because we are worried about tip stalling.. I recently put crow in a gryphon evo.. I didn't see anyone using it online, and it was not recommended.. Well, I finally got it slow and stalled it accidentally.. what happened is it tip stalled a tiny bit, but it was recoverable, and I landed.. when I stall it clean or without crow, it will snap out like a P-80 with the less swept wing..

If you want to play with Crow or washout and see its affect for yourself, program aileron up into your foamy trojan or something like that and mess around with it and see how much stability it adds.. with a prop job, I can add power, which increases the prop wash across the flight controls and gives a locked in feeling.. with the jets, It forces me to carry power, which is a good thing actually..

FWIW..goose
Old 02-21-2018, 07:29 AM
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Steve Collins
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I use Crow on my Boomerang XL because it floats on final and I like to do short approaches, I don't like the long flat ones ( eyes are not as young as they used to be ) it adds drag and makes the approaches to land more predictable.
The Boomerang XL will seemingly glide forever without crow. I consistently had trouble getting mine landed and stopped on 600 feet of runway because it would just float and float and....... After crow was added, that floating tendency was greatly reduced and I could reliably land the bird and get stopped often on only the first half of the 600 ft runway.
Old 02-22-2018, 07:07 PM
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It was kind of a trick question, it implies that "all else is equal" but the crow/no crow.....and I don't think crow works that way.

I think they are basically behaving as spoilers. That provide a steeper decent angle (without excessive speed buildup) by reducing the lift to drag ratio. With a steeper decent, any error lining up with the touchdown point will not result in a long error down the runway (like you would have with a flat approach).

I am not sure how they improve stability, I am sure they do I just dont understand it. They amount of crow would be close to the amount the TE would move if you twisted a couple of degrees washout into the wing tip, so maybe >1/8 inch? Most crow is going way way more than that.

As to the original question, I think the crow actually increases airspeed (all else being equal) because you have less lift available therefore need more airspeed to have the same lift force. But in a steeper decent, your groundspeed may actually be less. Who knows
Old 02-22-2018, 07:21 PM
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From a purely aerodynamics perspective.

No, it does not make you land slower. It just slows you faster to the natural landing speed....which is directly proportional to the weight of the model and the amount of lift the wing produces.

As stated earlier, only changing the camber of the wing actually lowers the stall speed, hence lowers your landing speed. In addition.....lowering the weight does it too....but it's a hard thing to do on models.

​​​David
Old 02-22-2018, 07:39 PM
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On my old f22 since the Ailerons where so far back from the cg they acted more like a slight up elevator and extra drag. This was ideal since the flaps would drop the nose. Crow would eliminate that and even bring the nose up for a hands off approach to landing. Just wiggle the throttle stick to touch down.

my sport jets. Crow makes landing more predictable. It does not help it fly slower but helps hit the right point on the runway and when it touches down it stays down.
Old 02-23-2018, 01:29 AM
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erbroens
 
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Originally Posted by ravill View Post
Many different jets can get significantly increased good landing behavior with crow. One of the most glaring examples is BV's venerable kingcat. Try landing that thing without crow.

And no extra switches needed either!
Q.E.D. (LOL!)

Raf, you are my brother from a different mother. :-)
Old 02-23-2018, 02:45 AM
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So is it right to say crow on ALL jets can do no harm and only help with landings ?
Old 02-23-2018, 03:36 AM
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gunradd
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Originally Posted by Rich Few View Post
So is it right to say crow on ALL jets can do no harm and only help with landings ?

for most but not all. Pretty sure crow on a euro fighter would not work well.
Old 02-23-2018, 06:46 AM
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Originally Posted by gunradd View Post
for most but not all. Pretty sure crow on a euro fighter would not work well.
I would think that crow on a delta wing could be set up to work well, BUT it would be tricky to do so. You would have to have separate elevators and ailerons, not just one piece elevons, and you would have balance the aerodynamic forces of the ailerons and elevator or else you will have a dramatic and exciting and spectacular pitch change.

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