Discussion The use of Flaps, Spoilers, and Crow for landing

[KurtMc]

I ran across this excellent tutorial on landing a full house plane (which I apparently need more practice at) written by Robert Bingham . Really good info for getting them home safely! Bob's answering a question about the proper use of flaps, spoilers, and crow for landing at Fermin:



Where to start. I guess you need to go back to the basics of 'landing'
a glider. As a backgrounder, I think you can understand pretty well
what's going on while flying on the front side of the slope, but as
soon as you want to land, things change pretty radically.

Your glider ability now transitions into a momentum management
ability. You only have so much momentum and if you use it up, you'll
pay a dearly price (i.e. pull flaps too early, stall to high and pitch
straight in with no control surely breaking something).

We fly at a number of different locations that provide some added
challenges and benefits. First, Vincent where you can usualy have a
headwind to help slow the glider down, and essentially have zero
flight speed while feathering the flaps. Second, Parker, where you
have to dive deep on the downwind side and use the up hill crab
technique to again, judge your momentum and time your descent
accordingly, using flaps as your brake. At Fermin, you have a
combination of all of the above, with the added benefit that is
changes drastically with the direction of the wind on the slope (north
being worst) and wind speed (more beeing worse turbulance) combined
together you have what we had on Sat. Each final approach I had was
different, and all of them were a challenge. There are easy landing
locations like Torrey Pines where you have a huge backside to make
aproaches, and if your too hot, you can go around again and again. We
also do some interesting landings at place slike Tehachapi and
Whitiker. Why do I bring all these locations up?

You need to get your head around the use of your flaps (we're talking
full house f3x ship here) as a momentum killer. If you know you want
to get to a certain place on the slope and you know it's going to be
laminar (smooth) all the way in, then you can take a more gentle glide
path and feather your use of flaps to nice affect. You can also
penetrate better if you know it's going to be bumpy, and take a
'hotter' trajectory, and use full flaps near the end to stop the added
speed of the steeper approach, again experience will tell you when to
pull, and how much. So slopes like vincent, you crab (pull into the
wind below the slope and sideslip up the slope, using flaps to make
your groundspeed zero (airspeed is still the wind hitting your face)
and fly the plane onto the ground and being ready for anything as you
get closer to the ground.

What does all this mean. Go and shoot approaches somewhere you fell
comfortable. Try high angle of approach, try low flare types if the
conditions warrant, try the slide on the grass at white point, and
try the hover into your hand as well. All of it will come in handy at
the loctions we fly. All of this stuff you can practice on the front
side of the slope too.

fly around in max drag mode, and make some turns, get used to how it
feels, and how much authority you have (which isn't much) but even
cracking it off a bit gives you much better stick authority.

plane setup isn't difficult, but I've seen some amazingly aweful
setups by some very top notch pilots. bottom line, you only need about
75-80% flaps (this 90% flap thing is overrated and risky as it puts
the flap usually below the fuse, and sure to strip servos if you don't
retract flaps before hitting the ground in time) You want a smidge of
up aileron in the 'crow/butterfly' setup. This helps keep the plane
from tip stalling as it get's slow, as well as adds a bit more drag to
the airframe when you want it. You'll need some elevator compensation
to keep the nose down. Most planes tend to balloon when you apply
crow, and you want a somewhat downward trim. This keeps the airspeed
up above stall without you having to worry about that.

All of this should be setup on the frontside. You should have no trim
changes when you pull crow, except for a slight nosedown. You should
just slow way down. The pitch stays the same, maybe a little bit of
down pitch change to keep your airspeed up, but that's it. Aileron
should be unchanged. If it isn't you need to make the changes (I do
this in the air, but your mileage may vary). Obviously, you want this
dialed in as close to perfect BEFORE your first flight, and I usually
open the menu of the radio to the screen for the elevator compensation
knowing I'll need to make those changes BEFORE my first landing
attempt. I fly around on the frontside with max crow, and adjust so it
flys along ever so slightly downward. Remember that once you enter the
landing cycle, you have NO LIFT, so you will be slowing to a stop, and
the risk of stalling is high. You need to 'drive the plane' down if
you are in full crow.

So at Fermin on sat, I like to walk across the street, avoid the
bikers, hikers, hot dog stand, gang bangers and climb the fence trudge
through the prickers (sorry Nathan) and setup my landing approach over
the hill (I personally think that the air is more laminar over the
hill then anywhere near that flat parking lot, but you allowed to do
it however you want.) As I dive over the hill, I dive pretty steep and
crack flaps to about 25% until I'm at the apex of my downwind approach
then pull them up to about 5%, knowing I'm going to have turbulance in
the LZ, I keep the speed up, even a little hot, and when I get about
15 yards away, I go max for a short burst (don't want to balloon at
this point!) and judge my momentum all along and keep the wings level
(oh yeah, no matter the pitch, keep the wings level, you'll minimize
any potential damage). At about 2 feet off the deck, up come the
flaps, wings level and set it down. Easy....

Unless the 1 in 100 landings you get something nasty, like happened to
me sat. I've landed at Fermin at least a 100 times over the years, and
that was first damage from landing. My mistake was assuming I was
close enough to the ground to apply a bit more crow to make it look
pretty before a gust caught it and it ballooned up to about 10ft with
no speed. kaplunk into the path. Oh well, I know what I did and will
drive it down with more authority next time.

After years of experience, I know that I can always crab it up most
slopes apply flaps and setup a handcatch, find a soft looking bush. As
long as I'm not pressed for time and can have a couple of wacks at it,
it'll most likely work. Confidence comes with time, and the knowledge
that these planes are darn durable if you think about it! Of course,
it's a good idea to ask the locals the approach, and if possible,
watch a few of their landings!

Landing is the time to be of highest alertness on the controls. Don't
get lazy, or it will bite you in the ass. Most damage happens when you
think your safe or on final or have done it the same way at the same
place so many times that you take for granted everything, then the
wind shifts or you fly through a sink pocket and you simply don't have
enough time to react. Think the sky is falling at any moment the
entire time during your approach. Don't even blink ;-)

I'll tell you, after thinking and writing a bit about this, I think
socal has some of the toughest landing LZ's in the civilized F3F
world. So this was a good topic to think through.

[target]

...

[Tuomo]

Originally Posted by target

Crow is more for added roll authority than slowing down, IMO.
It does help to stabilize the wing though.

You mean rising ailerons with flaps going down?

Raising ailerons actually decreases aileron control authority. You have to do it with differential reduction, and it is still not good... And contemporary planes are not tip stally either.

So most F3J flyers keep ailerons near neutral in landing configuration. Better control power, slower approaches... Everything better If you come in to landing with float settings on, you can even keep the slight camber in tip panels. I do this on Aspire and it works perfectly, although I like to use normal flight phase for landing approaches.

If you want to get fancy, make a curve mix for ailerons. Ailerons first going slightly down with flaps, then turning back to neutral (or few mm up) with full flaps.

--

Regarding the opening post of KurtMc, I find it makes simple thing complicated. What I like to do is to keep steady glide slope for the last 20 seconds. Difficult to say how steep, but it is steep enough to keep plane moving even with full flaps at middle position. In windy weather I keep more airspeed, steeper aproach or less flap.

After stabilizing a good approach the rest is simple. When flaps are adjusted to position where speed looks good, just fly the plane to spot at that speed, pushing down at 1 meter. If you are early, go to full flaps - if late, just dive the plane to ground with flaps in. It is good practise to pull flaps up before impact, but I do not allways do that.

All in all, I try keep it calm and steady. Many flyers play the flaps much more agressively, but it is their style. For that style, the plane has to be perfectly trimmed, though.

[target]

...

[FLY F3B]

T,

Tuomo is right, Crow, or upward deflecting aileron does not increase roll authority, it reduces it. If max. role authority is desired, then one should not use any Crow, or upward deflecting aileron.

M

[djklein21]

Yep, in my experience with slope flight, slope racing, and the people that frequently get bit by landing there, Crow (or butterfly) is a big culprit. Often, pilots mix generous amounts of up aileron with their down going flaps in order to increase the braking affect that the flaps have. The biggest problem is that in doing so, they didn't increase the overall drag of the plane very much, but they lost a lot of aileron authority. So in the end, they get the plane too slow, they hit some turbulence, and they have no control to correct the plane before it hits something hard and unforgiving.

I usually recommend to not using any up-traveling aileron to inexperienced pilots. With the up-traveling aileron, comes even more complicated mixes of reverse differential...in order to control adverse yaw and such. Most pilots are not ready for that level of setup and mixing. Furthermore, getting it wrong is dangerous. When landing a heavy plane, with a small tail (slope racing F3F or F3B style) in a turbulent environment, adverse yaw can be very, very dangerous. So I say, keep it simple, don't use crow.

[target]

Posts retracted.

[KurtMc]

The tip that sunk in for me reading this stuff is that setup for landing starts on the bench (dialed in in the air), and setting your glide path with flaps deployed using flap/elevator compensation so that the plane is flying slightly nose down, to keep her on 'autopilot' and always conserving energy and avoiding flare/stall when full flaps are deployed.

Also, keeping crow settings from interfering with overall aileron authority by not overdoing the upwards ailerons in crow setup.

Good stuff.... I had an aborted landing go bad on me a few months back with my Acacia, as I'd dialed my aileron throws too far down, and mixed out flap-ail coupling (to smooth out the F3F course). Didn't switch back to high rates before setting up for landing and when I tried to go around after a too hot approach, I hit a patch of rotor, she got knocked around pretty good, and I just didn't have the enough aileron left to correct it. Point well taken for having sufficient roll rate during landing

Peace

[Rich Speroni]

Originally Posted by KurtMc

The tip that sunk in for me reading this stuff is that setup for landing starts on the bench (dialed in in the air), and setting your glide path with flaps deployed using flap/elevator compensation so that the plane is flying slightly nose down, to keep her on 'autopilot' and always conserving energy and avoiding flare/stall when full flaps are deployed.

Also, keeping crow settings from interfering with overall aileron authority by not overdoing the upwards ailerons in crow setup.

Good stuff.... I had an aborted landing go bad on me a few months back with my Acacia, as I'd dialed my aileron throws too far down, and mixed out flap-ail coupling (to smooth out the F3F course). Didn't switch back to high rates before setting up for landing and when I tried to go around after a too hot approach, I hit a patch of rotor, she got knocked around pretty good, and I just didn't have the enough aileron left to correct it. Point well taken for having sufficient roll rate during landing

Peace

Hey Kurt, you don't need all this new learned stuff. Just use that opposite rudder pylon turn skill you've acquired. Now granted lots of opposite rudder with v-tail is not as effective as a cross tail. But if done just right you can SLIP into a tight spot. What nice about lots of top rudder is that it produces all kinds drag and in conjunction with flaps, CROW won't be needed.

Rich

[KurtMc]

That's a great suggestion Rich -- I'll have to try slipping/crabbing her in next weekend at the Slot race I promise not to beg for doubles if you show up dude! Hope to see ya. Peace

[Zimodile]

Crow is the best thing going for landing with! I can't believe that we have a thread which has ended up talking about how bad crow is for landing 3m ships! We can't judge crow based on people having it set up wrong - get the set up correct and it is a pleasure to use in any conditions.

Z

[wizardcompact]

I have to agree with z, crow set up right is best,just try land a fully ballasted f3f ship in lift without it ,your asking for trouble,its needed,best regards scott

[satinet]

Originally Posted by djklein21

Yep, in my experience with slope flight, slope racing, and the people that frequently get bit by landing there, Crow (or butterfly) is a big culprit. Often, pilots mix generous amounts of up aileron with their down going flaps in order to increase the braking affect that the flaps have. The biggest problem is that in doing so, they didn't increase the overall drag of the plane very much, but they lost a lot of aileron authority. So in the end, they get the plane too slow, they hit some turbulence, and they have no control to correct the plane before it hits something hard and unforgiving.

I usually recommend to not using any up-traveling aileron to inexperienced pilots. With the up-traveling aileron, comes even more complicated mixes of reverse differential...in order to control adverse yaw and such. Most pilots are not ready for that level of setup and mixing. Furthermore, getting it wrong is dangerous. When landing a heavy plane, with a small tail (slope racing F3F or F3B style) in a turbulent environment, adverse yaw can be very, very dangerous. So I say, keep it simple, don't use crow.

complicated mixes of reserve differential. You must be a futaba user then........

Crow is the best. vive la crow. Yes bad 'crow' landings are the cause of a lot of crashes. but landing must be 99% of all crashes that happen. imagine how many more crashes and broken models there would be with no crow. I've seen plenty of crashes in light or no wind situations and very windy conditions on the slope - reason: crow brakes don't work much in little or no air and they work too much in big air (if used badly) so you get crashes caused at the other end end of the scale by models being stopped too short or hung out to dry over a turbulent LZ (etc etc). Landing is a judgment. we all get it wrong sometimes.....

I've never had a problem with aileron authority. I never understand why people mention that. I never found it to be an issue even without "complicated" differential settings. What are people trying to do? roll it with the brakes out.

[Jurgen]

Jack Womack once stated using ailerons down instead of up, and liked it.
Maybe he can confirm still doing so?
I did not like that, this whole crow issue seems once more a personal habits & style thing.
J.

[target]

It seems that there's some confusion; the discussion involves landing in "rotors" for F3F slope sites, not flat field F3J/TD ladings.
One has little to do with the other, IMO.

R,
Target