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Sep 15, 2019, 06:35 PM
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Discussion

3 Channel Flying


I have a 3 channel old timer that I'd love to get flying smoother without so much wing rock. It's a Spook 96 which is a 96" gull wing that's very stable. It was originally designed for free flight. It takes a lot of input to get it to turn, then it takes a few wing rocks for it to stabilize out again. I don't think you can do a flat turn with three channels. But, I'm wondering if I should crank up the expo a bunch and learn to be more patient to try and smooth out my turns.

Any tips on smoothing out old timer 3 channel turns?
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Sep 16, 2019, 03:49 AM
I like real wooden aeroplanes!
Sundancer's Avatar
I have flown a couple of gull wing RET models and found the turn response to be a bit strange as compared to a straight dihedral or poly model. I think it depends upon how much of the dihedral is from the centre and how much from the gull break, so it is difficult to change an existing model. More fin area or thicker section fin of the same area sometimes helps, but mostly it is probably just a matter of fiddling with amount of rudder movement and expo until it feels right.
Sep 16, 2019, 10:24 AM
B for Bruce
BMatthews's Avatar
I think that this is something unique to the Spook. So not much you can do about it.

For other designs with either V or polyhedral they certainly don't have this issue. The ones I've flown all respond nicely even to small rudder inputs. Not rapidly mind you. They are big lumbering old timers after all. But smoothly and with a roll rate that is pretty consistent with good 3 channel sailplanes. But by what you're getting for behavior seems to point out the issue with gull dihedral that puts all the portions with the most dihedral angle in the wrong place.

Apparently it is responding but just not in a way that you're used to. I will suggest that a big old timer isn't going to respond like an aerobatic model. So you'll want to push the rudder input over a little and have some patience while it s-l-o-w-l-y rolls into the turn. And just feed in elevator to hold the nose up consistent with the bank angle as it s-l-o-w-l-y increases the angle of the bank for the turn.

I don't think expo is going to aid you in this. Instead it's a matter of patience while the model s-l-o-w-l-y bends into the turn and s-l-o-w-l-y rolls back out of them while you adjust the elevator smoothly in concert with the s-l-o-w paced transitions. If you're used to crisp responses to inputs this might take a bit of adjustment on your part.

If it helps perhaps think of it as guiding the model around from area to area and just enjoy the view... .
Sep 16, 2019, 12:26 PM
Registered User
As silly as it sounds try using the trims to turn. Thats why Im a fan of the old school mechanical trim.
or......

I always set up rudder servo on the aileron channel. (when flying rudder/ elev/thr)

Then set up your dual rates so that low rates are only 20% of full deflection. Easy way to desensitise the input.

Use High rates if you are in trouble
Sep 16, 2019, 01:23 PM
Registered User
Thread OP
Thanks for all the input. I do have several 3 channel gliders that fly just fine. But this gull winged old timer is something way different. I get lots of requests to see it fly, so I want to get smoother.

One thing I've been doing is going back to it's roots and try to mimic a huge free flight sortie. I'll take off, do a powered upward spiral then cut the throttle and do an even bigger downward spiral. I don't have the timing down good enough yet to do a dead stick touch and go, but I'll get it there.

I've learned not to do any cross wind take offs. That's a real challenge. You have to hold rudder to keep from wind veining, then when you rotate you need opposite rudder to keep the upwind wing down and sets up a rather drastic wing rock till it stabilizes. definitely makes it spectator sport. Basically, the stronger the crosswind the more dramatic the takeoff.

Final approaches sometimes get extended too much flying directly into the wind. So sometimes, I'll come in at a slight crosswind angle to help cut down on lift. Then at about the last foot or 2, I'll just keep the wings level and let it go wherever it wants into the wind.

The Spook 96 has been my favorite plane this summer.
Sep 16, 2019, 01:29 PM
AndyKunz's Avatar
Jeff - check your PMs.

Andy
Sep 16, 2019, 02:46 PM
Registered User
A lot of free flight models have small vertical stabs compared to what you see on RC models. If the wing rock is Dutch roll, a bigger fin and rudder would help with that and also improve control response. I'm assuming you're already using a lot of rudder throw, like 30 degrees or so.

Another idea, which would only help with the rocking, is to use a rate gyro set up to damp out yaw. Rudder response will still be sluggish, though. Rate gyros are cheap these days, though perhaps you'll have to get a regular one and turn off the heading hold.

Before you go too far, you might look up an article by Stan Hall called How Big the Tail. Compute the vertical stab volume for your model and for one whose handling you like. Keep in mind that increased effective dihedral will require a larger vertical stab.
Sep 18, 2019, 10:30 AM
B for Bruce
BMatthews's Avatar
It would be great to see a video of this oscillation. I think Lincoln has the answer if this is something which only happens after a big control input. But it's hard to say without seeing the effect.

When I've seen dutch roll occur it always tends to be stronger during the climb. Is that the case here?
Sep 18, 2019, 10:47 AM
I like real wooden aeroplanes!
Sundancer's Avatar
Dutch roll, IME, is usually worse on the climb and ALWAYS worse if the CG is a bit too far back. If it doesn't roll on the glide, then the probable cause is too much rudder movement which will be exacerbated by the slipstream, power on. Sets off a sort of PIO which can take a while to settle down.
Sep 18, 2019, 01:10 PM
Registered User
and also may be because the speed is higher on the engine stage.
Guy
Sep 18, 2019, 02:41 PM
Registered User
Thread OP
I had to look up what a Dutch Roll is. This description pretty much nails how my Spook turns.
Dutch ROLL and YAW Damper ✈ (4 min 45 sec)

I did try a stabilizer, all that would do with the stabilization turned down to 10% was just wiggle the tail more. At higher levels it made the Dutch Roll even worse.
Sep 19, 2019, 05:59 PM
Registered User
Are you sure you had the stabilizer set up right,and oriented correctly? Maybe something's in reverse.
Sep 19, 2019, 07:47 PM
Registered User
Thread OP
Quote:
Originally Posted by lincoln
Are you sure you had the stabilizer set up right,and oriented correctly? Maybe something's in reverse.
Yes, I even had a buddy second check it as I moved the plane.
Sep 29, 2019, 06:58 PM
Tripacer
I agree that a larger fin/rudder would help. Good luck!
Oct 01, 2019, 06:25 PM
Thermals, Tom
RyanNX211's Avatar
Quote:
Originally Posted by jwellsy
I had to look up what a Dutch Roll is. This description pretty much nails how my Spook turns.
https://www.youtube.com/watch?v=PtALTmdfD30
I did try a stabilizer, all that would do with the stabilization turned down to 10% was just wiggle the tail more. At higher levels it made the Dutch Roll even worse.
As a modeler and a 12 thousand hour jet pilot, I have to say that is one of the best explanations Ive seen.
The remedy is to reduce your rudder throws and let the plane fly as much as possible without your intervention. These are not back & forth models.

Back in the day, Sal Taibi used to design his prototypes with sheet balsa fins. Hed cut them down until they started to Dutch roll. Then hed add just a smidge more area.
Latest blog entry: Steak and Old Timers


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