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crow braking

Old 11-06-2006, 08:32 AM
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Heatseeker_Hill
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Default crow braking

i want to hook the ailerons into the flap on a current model and wondered if anyone had any experience of this ie if the flap lowers 45 degrees should the ailerons lift 45 or should i take into acound the surface areas of the ailerons in comparison to the flap and lower the movement accordingly.
Old 11-06-2006, 09:36 AM
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Mach1
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Default RE: crow braking

It all depends on the specific airplane, but in general with full flaps you should start with
the ailerons reflexed up about 3/16 to 1/4 inch and see if thats the effect you want.

Actually (again depending on the airplane) this amount is pretty effective to kill some lift.
Old 11-06-2006, 12:31 PM
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Default RE: crow braking

Mach-1 is right do your 45 degree on the flaps and start with 3/16 on the ailerons in the up position. I got about 1/8 on my jet, it works just fine for me, be ready to adjust the elevator to down position and don't let her get to slow on final, it will feel deferent during a head wind and no wind conditions, also keep a small amount of throttle all the way 'till you turn to final. [8D]

Happy flying and good luck.
Old 11-07-2006, 07:57 AM
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Heatseeker_Hill
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Default RE: crow braking

cheers guys,
Old 01-24-2011, 12:25 AM
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savasn
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Default RE: crow braking

Hi Guys, new to forum.
Have a Skymaster Hawk (first jet) and wanted to know, how does this crow braking set up work, as i am really battling to slow her down. at moment i have 2 stage flaps, 2nd for landing where the elev-up is mixed in.I initiate the first stage flaps on dwind, then nose pitches down then 2nd stage at base, but all this is not really effective.
What do you guys suggest, Crow on ail plus slight up-elev???
i am lost, on which will assist me the most.
thks in advance
Old 01-24-2011, 03:10 AM
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Default RE: crow braking


ORIGINAL: savasn

Hi Guys, new to forum.
Have a Skymaster Hawk (first jet) and wanted to know, how does this crow braking set up work, as i am really battling to slow her down. at moment i have 2 stage flaps, 2nd for landing where the elev-up is mixed in. I initiate the first stage flaps on dwind, then nose pitches down then 2nd stage at base, but all this is not really effective.
What do you guys suggest, Crow on ail plus slight up-elev???
i am lost, on which will assist me the most.
thks in advance
Savas you have got so many guys right here who would help you, Greg D, Greg C, Zane, myself and we just a phone call or flying field away.
Old 01-25-2011, 01:44 AM
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PHIL GREENO
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Default RE: crow braking



Yes a small amount of crow mixed in at full flap postion should help a lot.

As this puts the outer span of the wing at a negative angle of attack(washout) this should reduce any tip stalling tendancy as well as reducing float on landing.

I am surprised you have up elevator mixed in with full flap as on my models (Carf Hawk and Flash) I have the opposite.

CGposition can also have a big effect on landing speed.As you throttle back on the approach if your CG is too far forward the nose will tend to drop and speed pick up needing up trim.

It is a matter of balance between the the safest CGposition and the effect full flap has on the trim.

To check CG postition I always fly inverted to see how much down elevator I need to fly level.A small amount of down is desireable as for safety sake I always like a forward rather than rearward CG.Once you are happy with the CG you can mix in a small amount of elevator to correct any nose up tendancy on full flap if needed.

Phil.

Old 01-25-2011, 02:19 AM
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Default RE: crow braking

The trouble with checking C of G by flying inverted is that this will not take into account the longitudinal dihedral i.e. incidence difference between the wing and tail, a more accurate way IMO taking any incidence problems out of the equation is to see how the airframe enters a spin, from the stall does it snap into the spin, to nose heavy......well you get the picture.

Mike
Old 01-25-2011, 03:03 AM
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PHIL GREENO
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Default RE: crow braking

I would certainley NOT recommend any flyer of ourexpensive jet models to check your CG postion by entering a spin on the first few flights and most pilots would not be happy doing this.

As most of our jet models use either a semi or near semitrical aerofoil section longitudinal dihedral or "decalage" as is correctly named is very small 0-1-2 deg positive max. so only has a small effect on inverted trim. Flat bottom wing sections such as Clark Y require more decalage for neutral trim in normal flight.

Much safer to roll invered at a good height and check how much down elevator you need to fly level.

If the models CG is too far back (not a good idea) you will notice a pitch up in trim straight away.

Phil.
Old 01-25-2011, 03:37 AM
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Default RE: crow braking

Another thread going down the tubes under the weight of bad nomenclature

As this puts the outer span of the wing at a negative angle of attack(washout)........
The angle of attack does not change as a variable of crow , but the effective incidence is reduced as crow is added, creating the washout.


ORIGINAL: PHIL GREENO

I would certainley NOT recommend any flyer of our expensive jet models to check your CG postion by entering a spin on the first few flights and most pilots would not be happy doing this.

As most of our jet models use either a semi or near semitrical aerofoil section longitudinal dihedral or ''decalage'' as is correctly named is very small 0-1-2 deg positive max. so only has a small effect on inverted trim. Flat bottom wing sections such as Clark Y require more decalage for neutral trim in normal flight.

Much safer to roll invered at a good height and check how much down elevator you need to fly level.

If the models CG is too far back (not a good idea) you will notice a pitch up in trim straight away.

Phil.
Again, U meant "incidence". Ur jet won't have "decalage" unless it's a biplane.

I do at least agree that spinning the jet isn't the most cost effective way to check the CG, especially if it happens to be in error to the rear.
Old 01-25-2011, 04:29 AM
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PHIL GREENO
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Default RE: crow braking

The word "decalage" means the difference in angles of incidence between two planes.Yes this term is used to measure the difference in incidence between thetwo wings of a biplane but I have always used the term to measure to difference in incidence(or longitudinal dihedral as some call it)between the main and tailpane of a monoplane.

When you activate crow the angle of attackof the wingfor the area of the aileron in this case takes on a negative incidence in relation to the remaining wing attack angle.

I think we are talking about the same thing.

Phil.
Old 01-25-2011, 05:44 AM
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Default RE: crow braking

All perfectly true when you are talking about a composite airframe, the difference in incidence between the tail and wing would be built in, but with a built up structure especially with a pod and twin boom type this difference in AOA can be out by quite a bit according to how bad a day the person assembling has had. LOL

I did say enters a spin, on any first flight the stall characteristics should be explored with flaps, without flaps or with crow or without the point being to see how it behaves when landing, if it is going to drop a wing I would prefer to know witch one and how fast it was going to rotate by trying the stall with a little rudder on, if the C of G is to far forward the nose will drop at slow speed and the speed will increase witch can make landing difficult.

I have always understood the reference's as below:

Longitudinal dihedral is the reference to the difference between the incidence's of the wing when compared to the tail.

Incidence is the AOA of the wing or tail with reference to a datum line drawn through the fuselage.

Decalage is as Phil says any reference between two planes irrespective of their position or reference to the Datum line.

Mike
Old 01-25-2011, 04:31 PM
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Default RE: crow braking

ORIGINAL: PHIL GREENO

The word ''decalage'' means the difference in angles of incidence between two planes.Yes this term is used to measure the difference in incidence between the two wings of a biplane but I have always used the term to measure to difference in incidence(or longitudinal dihedral as some call it) between the main and tailpane of a monoplane.

When you activate crow the angle of attack of the wing for the area of the aileron in this case takes on a negative incidence in relation to the remaining wing attack angle.

I think we are talking about the same thing.

Phil.
OK, u can mix and match the terminology to the point of inventing your own nomenclature and describing apples as oranges if u desire, but I think it will just confuse people.

The rest of us will continue to use the long ago established industry standards, describing incidence as incidence rather than decalage ( Please note that I wouldn't have gotten into pedantic details with you except that you took it upon yourself to "correct" Mike's terminology, which was not erroneous).

I hope that u won't mind if we don't further confuse incidence with AOA. The AOA of the entire wing remains the same, even as a portion of that wing changes shape at the trailing edge. The AOA and the incidence are seperate issues.

To be sure, you have the basic principles of crow correct. But as I said, ur nomenclature needs tweaking and Mike's is correct, even though I don't subscribe to his spin-vs-CG analysis.

Thx, Don.


Old 01-25-2011, 05:31 PM
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DAN AVILLA
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Default RE: crow braking


ORIGINAL: Heatseeker_Hill

i want to hook the ailerons into the flap on a current model and wondered if anyone had any experience of this ie if the flap lowers 45 degrees should the ailerons lift 45 or should i take into acound the surface areas of the ailerons in comparison to the flap and lower the movement accordingly.
On my bandit I use 1/2" of crow and on the king cat I use 1" both work well. Depending on the plane you might need to mix up or down elevator. Good luck Dan Avilla
Old 01-26-2011, 10:56 AM
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savasn
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Default RE: crow braking

thks guys, i am understanding exactly what is required of me to do on my Hawk, as damn, every landing was a challenge. Yes the full flap/up elev did help, but im sure with crow ,things will be a lot manageable.
as said this is my very first Jet, that i bought RTF here in south africa, and a good friend set it up for me well enough,bt now i need to get to grips with it and set-up, set-up, which i am very accustomed to from my pattern days.
Old 01-26-2011, 04:23 PM
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Default RE: crow braking

Savasn,

One of the key benefits to crow is to create enough drag so that you are not only able to get the airplane to slow down, but you must also then APPLY power to make the runway. This non-idle approach means that the engine will be "spooled up" and respond much more quickly in the event of a go-around.



On my set-ups (an many others' as well, I'm sure):

1) the flaps themselves are slowed, and take at least 5 seconds to fully extend or retract. This greatly reduces pitching.

2) the ailerons are slaved to the flaps so that they reflex proportionally upward as the flaps extend from half to full, while remaining "normal" from zero to half (for take-offs).

3) the aileron reflex condition immediately cancels out (and at full servo speed, snapping back into a normal aileron mode) if the throttle is advanced past approx 3/4 so that all of the wing's lift is available during a go-around.


I hope that this helps? Wishing lots of fun and good luck with your new toy,

Don.

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