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Crow Vs. Gyro to Stop UF Snaps

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Old 11-08-2017, 02:05 PM
  #1
Len Todd
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Default Crow Vs. Gyro to Stop UF Snaps

I have an Ultra Flash with a P-140. I have spent a ton of time ensuring the CG is in the right spot and have even played with it a bit. I set the CG with the Xicoy balance and the EZ Balancer. I also have the full flaps set at 3.6" and they are matched perfectly. But, the UF is prone to snapping lower speeds and bouncing on landing. I solve the bouncing by keeping the nose up until it comes down by itself. I have minimized the snaps by keeping the nose down on landing approach and when flying, keeping the plane at high speeds. I can land it just fine. But the landings are a bit unnerving, to say the least. There is a point at < half-throttle where I can't seem to avoid the snap when at lower speeds. Some folks have suggested using crow when on the flaps. Some folks suggest adding a gyro. So, ...

On a Spektrum Txer, how do you program in crow? I assume it is a mix based off the Flap Switch. I assume 5mm up would be a safe starting point.

Is a gyro really going to help a lower speeds? This plane has snapped to the inverted and I was instantly able to roll back to upright w/o changing speed. All I had in was a little rudder, when it snapped.

The plane has snapped on me several times. Flying it is unnerving to say the least.
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Old 11-08-2017, 02:16 PM
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Yup, mix crow to flaps. Make sure you match all the speeds. 5mm sounds very reasonable. And you might even like more.

Crow is about to change your life.

IMHO, you should have a gyro on the nose wheel. Anymore than that is icing on the cake.
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Old 11-08-2017, 02:19 PM
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Len, I have 1/8" of crow in mine at full flaps only . I can fly with full flaps and gear down with 5 clicks of throttle from idle , while doing steep figure eights and maintain altitude. It will not snap . If I get too slow it just drops like a stone but no rolloff. I slow on a close downwind leg with gear down and full flaps with 5 clicks of throttle. Then when I'm ready to descend I reduce the throttle 2 clicks and lower the nose a little, I maintain this attitude till about 5 feet above the ground then I go to idle and flare. If you have done it right the descent will be checked and you will touchdown at min speed and you wont bounce. If the plane starts to drop after you raise the nose to flare, ad a little power, a couple of clicks.

Bob Neal
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Old 11-08-2017, 03:03 PM
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Quote:
Is a gyro really going to help a lower speeds? This plane has snapped to the inverted and I was instantly able to roll back to upright w/o changing speed. All I had in was a little rudder, when it snapped
Geez that sounds scary.. if you were able to recover then you had a fair bit of speed on. Makes me think there is an inherent setup issue. I have never had a UF do anything other than what it was told. What CG are you running and what are your control throws? Are you running a heap of expo?

Paul.
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Old 11-08-2017, 04:02 PM
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Hi Len.
In my very humble opinion.. Gyro is not the answer to an aircraft that is prone to tip stalling.
The gyro can mask the poor aileron response that occurs as you get close to the stall speed. Slow speed sloppy control response is a good feedback indicator you are close to the stall.

An UF is a well proven model and should not behave as you describe. I had similar problems with my M140 powered Bandit, until I learned the correct approach method, and got the CG right. The correct set up and technique really tamed it. I'm sure you will get it sorted..
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Old 11-08-2017, 04:15 PM
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Likel I have said before...its a snappin' SOB! Crashed 3 of them and finally quit. Im not a rookie at this either. I love the way it flys but hate the way it lands. I really think the recommended cg is too far forward and leads to snapping. I now fly a FB Dolplhin and love it. They are releasing a Flash size really soon. For all you guys who disagree with me...glad you have had success.
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Old 11-08-2017, 05:34 PM
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Len:

The trick is the CG, what CG are you using? If I recall correctly, the max landing flaps to use is 3”
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Old 11-08-2017, 05:38 PM
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If it's snapping on you, your CG is wrong..just sayin

Or you have more than 3 3/4" of flap
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Old 11-08-2017, 05:43 PM
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Quote:
Originally Posted by tp777fo View Post
Likel I have said before...its a snappin' SOB! Crashed 3 of them and finally quit. Im not a rookie at this either. I love the way it flys but hate the way it lands. I really think the recommended cg is too far forward and leads to snapping. I now fly a FB Dolplhin and love it. They are releasing a Flash size really soon. For all you guys who disagree with me...glad you have had success.
Tom:

I hear you, while I’m no pro, I’m no rookie either, and I agree that with the wrong CG the UF will always drop a wing upon normal landing with reasonable speed, this was a very hot topic when the UF was released there was even a “Pro” who claimed the problem were the pilots even though there was plenty of video evidence of the wing drop at the original CG even in hot landings. Once the CG was corrected, the problem went away.
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Old 11-08-2017, 06:25 PM
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Quote:
Originally Posted by Len Todd View Post
... All I had in was a little rudder, when it snapped...
How much rudder and why. I don't use rudder when (jet) landing anywhere in the pattern more than a few inches off the ground.
The only other time for my rudder use is knife edge, slow or point rolls, snap rolls and rarely to correct a vertical line.
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Old 11-08-2017, 06:26 PM
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Yep, the problem went away with me...I wouldn't have one of the damn things again.
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Old 11-08-2017, 07:27 PM
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Len, I would suggest that the jet is a little nose heavy.. we flew mine with Crow and 45 deg flap, and it it would slow nicely way back in the day. I dont remember the CG, but it was behind the book
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Old 11-08-2017, 09:48 PM
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Crow with the correct c of g is the way to go. Gyro will never compensate for a tip stall, but it will mask the impending warning signs of a stall. Ultra flash definitely snaps more easily than the classic flash. I have both. My preference is the classic, every day of the week.
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Old 11-08-2017, 10:22 PM
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How heavy is your UF?
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Old 11-08-2017, 11:41 PM
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CG, CG , CG - if it snaps, if it floats on landing, if it bounces, etc etc etc

Mine is an absolute p#$$$ cat, with ZERO vises, my go-to-jet every day of the week .... sort out your CG.

Jan
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Old 11-09-2017, 12:13 AM
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Wow.. Lots of misunderstanding here.. CG has almost zero effect upon an airplanes stall tendencies. Airplanes stall because of 2 things.. Critical angle of attack or insufficient airspeed (generally leading to critical angle of attack). Now if your CG is too far back, your pitch rate can become uncontrollable (due to static instability). Too far forward, and you begin to lack elevator/tail power to effect pitch changes, the most common situation being running out of elevator to land properly.. which often causes a bounce. Granted this is somewhat an oversimplification of things, but CG really only affects stability.

Tip stall is simply one wing stalling before the other. If it's always the same wing, the wing is probably not straight, or the tip has a higher angle of attack than the root (wash-in), or you're skidding around with yaw input. Crow helps fix this because it reduces the angle of attack at the wingtip vs the root, causing the root to stall first, which has less rolling force because of the moment arm relative to the wingtip.

Last edited by Doug Cronkhite; 11-09-2017 at 12:18 AM.
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Old 11-09-2017, 03:42 AM
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That's what I was thinking Doug, with all the claims going from one spectum to the other (horrible plane/best plane ever), makes me think there might be a quality control issue going on. Maybe some wings are straight and some are not causing either a great plane or a terrible one.

just a thought.
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Old 11-09-2017, 03:58 AM
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I added crow & it never tipped again. That was the result in my case.
Jay
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Old 11-09-2017, 04:08 AM
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I like the QC/different wing theory, but I think it is more likely to be a weight or Cg problem. Doesn't a too far forward Cg cause you to use more elevator to try to produce a greater moment to counteract the nose-heavy Cg? Resulting in exceeding the critical AOA? I'm pretty sure Cg will affect the stall speed.
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Old 11-09-2017, 06:12 AM
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I know it's factory built to a high standard, but have you done a lateral balance check on it? Or did you just assumed everything just weighed out evenly?
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Old 11-09-2017, 06:19 AM
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The two are just barely linked. Now.. to be completely accurate, there is a change in stall speed with CG change, but it's so small that I doubt you could detect it outside of a wind tunnel. What happens is.. As the CG changes forward the pitching moment of the wing increases, and more downforce is required to hold a given angle of attack. That change in downforce from the tail requires the wing to counteract the reduction in lift from the tail for level flight(yes, the tail does provide some lift), so yes, an increase in angle of attack is required. BUT, we're talking miniscule amounts here. For reference, a Cessna 172, at the most forward CG at 2400 pounds, compared to the most rearward CG allowed, changes the stall speed by 1 knot. One.
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Old 11-09-2017, 06:25 AM
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Quote:
Originally Posted by Sparhawk View Post
I know it's factory built to a high standard, but have you done a lateral balance check on it? Or did you just assumed everything just weighed out evenly?
Good question.. Are you carrying any aileron trim? If you have trim in it, the wing with the aileron moving down has a higher angle of attack than the other side, and that can definitely cause problems. A lateral balance check is a good idea!
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Old 11-09-2017, 07:16 AM
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One thing to think about. A small amount of crow adds a bit of washout to the wingtip which helps with tip stalling and snaps.
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Old 11-09-2017, 07:32 AM
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Quote:
Originally Posted by BarracudaHockey View Post
One thing to think about. A small amount of crow adds a bit of washout to the wingtip which helps with tip stalling and snaps.
More often than not, the crow setup really just puts a bandaid on things.. It doesn't fix the underlying problem.
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Old 11-09-2017, 08:50 AM
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Quote:
Originally Posted by Doug Cronkhite View Post
The two are just barely linked. Now.. to be completely accurate, there is a change in stall speed with CG change, but it's so small that I doubt you could detect it outside of a wind tunnel. What happens is.. As the CG changes forward the pitching moment of the wing increases, and more downforce is required to hold a given angle of attack. That change in downforce from the tail requires the wing to counteract the reduction in lift from the tail for level flight(yes, the tail does provide some lift), so yes, an increase in angle of attack is required. BUT, we're talking miniscule amounts here. For reference, a Cessna 172, at the most forward CG at 2400 pounds, compared to the most rearward CG allowed, changes the stall speed by 1 knot. One.
but pick an extreme nose heavy Cg & it won't even be able to rotate. Move it back inch by inch & eventually it will fly. That's all Cg induced.
Jay
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