ORIGINAL: CraigG
This topic surfaced on another thread and the OP requested it be taken elsewhere.
My understanding is that crow, (when both ailerons deflect up) cause the ailerons to act as spoilers. Spoilers decrease lift and increase drag. On full scale aircraft, they’re used to slow down and/or increase the rate of decent, but normally not on approach/landing (until after touchdown).
With r/c jets, they seem to help the approach/landing on jets that do not slow down well and/or tend to float on landing. The KingCat is a good example. It’s a tradeoff between a slightly higher stall speed and a more manageable approach and landing. Apparently most guys feel they can do a better with crow than without it on the KC.
Not so much agreement about using crow on various other jets, such as the UB. Some guys say yes, some no. Just wondering what others have to say.
BTW, where does the term ''crow'' come from anyway?
Craig
Craig, your understanding is perfect. Some jets or jet/engine combo's just dont want to land without an undesirably flat approach because there's too much residual thrust/and or the airframe is low drag (flaps alone not providing enough) and/or has a low wing loading....The Eurosport is one jet that achieves this thru the use of a speed brake rather than crow. Others have big honkin gear doors just for this purpose.
An added benefit of crow, as some have pointed out, is that the effective washout at the tips makes for retained controlability if the inner portion of the wing begins to stall. The wing doesn't "let go" all at once or even worse, as is common in some planforms, at the tips first.
Also, crow is also used in some cases to add drag even when the idle approach path
is reasonable, simply because the added drag then
requires power during the approach. This is because (especially older) jet engines are slow to recover from idle, creating a lag in response when power might be MOST needed on final or during a go-around. Added drag in these cases, requiring some power to maintain a comfortable approach path, ensures that the engine is in a responsive rpm range and that the power is available without delay.
In full scale this need for "spooled angines" is achieved with fuselage mounted speed brakes (vs spoilers) deployed during approach (common among fighters) or with lots of flap drag designed into the wing (common among other types).
Regarding the origin of the term, I'm certain that it's original reference within the glider or some other community was to crows manipulating thier own wings in order to achieve spot landings
and that the practice could just as well have been named after any number of other birds.