RCJetBazz

Why do you think the flap chord on any aircraft is much wider towards the root, for the good looks? lol

marquisvns

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highhorse

My Feedback: (2)

My comprehension of aerodynamics is actually very good, thanks. What's lacking is your perception that the above description was meant to be anything other than farcically partial.
Thanks for playing though.

InboundLZ

My Feedback: (10)

***POSITION UPDATE***

I have determined that the use of crow is only part of the reason I have solid, slow, high AOA approaches/landings. The main reason for this effect is I actually spend my time flying the aircraft rather than on line trying to convince everyone that I really should be a aeronautical engineer rather than the ***insert your current profession HERE*** I am. I have to wonder if Boeing is aware of this untapped talent pool?

Secret reviled!

GrayUK

Never said it did Harry.
Just works for me.
I use crow on all jets now and will continue to do so.

Paul

hofer

Hi guys,
As mentioned before here, a big advantage of raising the ailerons instead of droping them in landing configuration on model aircraft is the neutralizing effect it has concerning
pitch trim ! This is particularly evident on airframes with swept wings !
Of course, the real, full sized ships never raise the ailerons in landing configuration ! Rather, and as mentioned before as well, they drop it together with the flaps !
BUT, and that`s the vital point here - all the big ones (at least the ones I have flown) have a HORIZONTAL STABILIZER TRIM ! So they can counteract the resulting pitch down moment that normally occurs upon flaps ( and possible aileron down movement ) with the pitch trim ( adjustment of the whole horizontal stab ) and ergo, they still have the whole range of that ELEVATOR deflection at hand to control the approach angle and of course the landing flare !
Now, almost none of our model ships have such a horizontal stab pitch trim and therefore have to rely on the elevators alone !
Trimming out the plane in landing configuration ( especially with the ailerons dropped together with the flaps ) with the elevators alone might leave you with too little elevator up authority in difficult approach and landing conditions !
That is THE reason why I fly my jets with some crow in landing configuration !
And, believe me here, coming from the full size world, it took quite some time for me to accept that raising ailerons in landing configuration can be an advatage in the model world !!

see you
Hans

highhorse

My Feedback: (2)

It's odd that you would seek ridicule those of us who actually have some depth of knowledge in the field of aerodynamics and wish merely to assist a brother hobbyist (you). That's a shame but it happens sometimes.

No one will deny that you have solid, slow, high AOA approaches. No one will deny that you percieve your jet to have a slower stall speed. No one will deny that crow has many advantages for particular models in the toy jet world. The only point of debate is your wholly unsupported and persistent assertion, contrary to the laws of physics and the best efforts of your brothers to show you otherwise, that crow actually does lower the stall speed.

Crow does indeed provide some magical benefits. I and others have merely sought to clarify for you exactly how that magic happens and what the benefits are. If you chose to remain unconvinced, then I for one am completely okay with that and still value your comradeship as a fellow jet dude.

Perhaps we have assisted someone else though. Someone who might have otherwise glanced at your post and left here with the mistaken impression that crow somehow makes more lift and really does lower the stall speed.

I'm outta here and won't trouble you with any more factual information.

Don.

InboundLZ

My Feedback: (10)

Don,

I do value your input. My post was what appears to be a poor attempt at humor. I guess I am amazed how wrapped around the axle people get on certain subjects. My point is (was) that whatever magic is going on it works for me, real or perceived. I am sure many value your and others input and instruction on topics like this so by all means continue.

Regards,

highhorse

My Feedback: (2)

Oh. Ok then and peace be with you my jet brother !!

highhorse

My Feedback: (2)

oops. RCU got hung up (again) and I double posted.

VF84sluggo

My Feedback: (55)

Very true. Perfectly describes the A319/320. And also explains why in "Direct Law" it is critical to keep the horizontal stab in trim, so as not to run out of elevator in the flare.

Now, on the other hand, the L-1011-500 had an 'active control system (ACS) that flexed the ailerons up slighly to reduce the bending loads on the spar at higher weights.

rctech2k7

My Feedback: (1)

Another thing that confuses about the crow:

1. During considerable high alpha low air speed when ailerons are both up, the crow reduce early separation over the wings therefore delaying stall and increase lift as well...
2. during the above (#1) phase, the effective surface is lesser therefore lesser drag. Lesser drag means lesser engine power...

Negative effect of flaps at high angle of attack:

1. Increase air separation over the wings therefore promoting stall.
2. Drag is also increases therefore more power is required.


Differences:
Crow - decreases camber
Flaps – increases camber

Reducing camber increases stall AoA and increasing AoA increase lift up to approx 100%. Furthermore, increasing camber increases lift for approx 200% based on approx wings coefficient of lift.

rctech2k7

My Feedback: (1)

Btw, forgot to mention that decreasing camber also decrease lift. Therefore, using crow will shift the effective angle to the right meaning increase angle of zero lift up to max Cl. However lift is still greatly influence by the net camber.

rctech2k7

My Feedback: (1)

Although out of topic just for info, since TE flaps reduce stall angle, by introducing LE flaps or slats will increase stall angle and increase camber for more Cl as well.

InboundLZ

My Feedback: (10)

Errrr...huh?

rctech2k7

My Feedback: (1)

To answer the question about the topic, just like many who have mentioned compensating flaps effect for lesser elevator trim. Another use of crow is for descend to produce downward push as well as drag on leveled flight down to negative AoA. I tried using crow for few times on landing to see how's the difference. After finding that it causes to increase my landing speed, I plan to use it for high speed landing proficiency but due to the danger of using it on landing I just reduce the flaps instead to get the same benefits. The last function of the crow on my planes is like a ground spoiler use to add drag, eliminating lift while on full flaps and increase landing gear traction.

David Gladwin

Not sure crow would have helped here !



‪Korean 777 - Terrible landing#x202c;rlm; - YouTube

mick15

He he, what was wrong with that, it's in one piece isn't it?

m

sskianpour

My Feedback: (2)

This stuff's too technical for me. All I know is on my large 45 lb MB339 with a 600 foot runway at 5500 feet altitude, if I don't use crow, she goes off the runway at landing because she refuses to slow down, and goes into ground effect no matter how much flap is dialed in...with crow, she lands in 300 feet. I think the "dragginess" mentioned in this thread is what I like about crow, it makes planes that glide forever much more predictable. Same thing applies to my boomerang XL.

And my Kingcat NEVER bounces with crow. Just nice glide path to runway, flare and settle. Will be trying crow on my ultra bandit maiden this weekend. Will get back to you all on how that works out.

Cheers all,


Shaz

extra 300

My Feedback: (3)

Have used Crow on my Boomerang XL and never missed a landing on our 400 ft. runway. This jet becomes so predictable that you can easily do spot landings with very little practice!!!

Rgds.

CraigG

My Feedback: (40)

So Shaz, since you started this whole discussion with your question on the other thread, I expect a full report (with technical explanation) on how crows works with your UB. I was actually considering trying it on my UB but I'll let you be the test pilot instead.

Craig

rctech2k7

My Feedback: (1)

Technically, you have lesser air density causing lesser air mass flow on your wings and propulsions. Air density is a factor of lift and drag meaning, your plane require more airspeed and power. Engines up there has also lesser efficiency. I guess you have the same effect for same setting except without crow if you raise AoA by increasing elevator trim on landing and of course slight increase in power to compensate.

rctech2k7

My Feedback: (1)

How about if you try not to use crow but instead increase nose up on landing and add slight power to maintain rate of descend. However my suggestion to increase AoA instead of crow will probably effective for less cambered and high loading wings. Otherwise, a reduction of camber is required to reduce lift and drag in order to maintain sink rate, airspeed and control authority for high cambered and lesser wing loading aircraft.

rctech2k7

My Feedback: (1)

This is my point why not to use crow on landing:

1. Require higher AoA and lesser engine thrust to maintain rate of descent
2. It increases rate of descent at lesser AoA
3. Reduces lift and drag of the wings
4. It increase stall speed therefore higher time of recovery
5. Higher chance of error for aborted landings

For me these are the major function of crow

1. To increase rate of descent without gaining too much airspeed (not for final and not recommended)
2. On the ground after touchdown - to eliminate lift while adding drag.

I'm also open for a final report of this subject including technical explanations...

S_Ellzey

Opinion of an Aerospace Engineer and long time KingCat owner/pilot.

For a given angle of attack, raising the ailerons will decrease the wings lift and increase its drag. Any time you turn the air it takes energy and that is drag. So if you fly the same angle of attack with crow as with out you have a higher sink rate and more drag that you can compensate with either more power or a steeper descent. For most of us this makes it a bit easier to pick your landing spot.

Raising the ailerons also increases the effective washout on the wing with makes the model more tip stall resilient, which decreases the possibility of a departure.

Raising the ailerons reduces the maximum lift the wing can generate, that is just the effect of negative camber. Since the wing is making less lift the stall speed is increased and the approach speed should be higher also. This allows the control surfaces (all of them) to generate more control authority to deal with upsets due to gusts or pilot mistakes. The KingCat can land so slow that it can get into trouble in gusty conditions, crow helps this a lot; many other models are the same. However crow really only helps out on lightly loaded models, which is why it is of no use on full-scale aircraft. The manufactures of airliners are trying to improve the L/D in landing configuration so they can use less power and make less noise on approach. On a clean, lightly loaded model we would like a lower L/D so it does not float as much.

You can decrease the flaps and get some of the benefits, but that also decreases the drag, so you shallow out the approach and find it harder to pick your spot, and you decrease the effective washout which increases the chance of a tip stall.

Steven