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Sep 16, 2020, 08:18 AM
Retired US Navy
Evan D's Avatar
My post was in response to MoMo's question.
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Sep 16, 2020, 08:24 AM
Registered User
Tank is here from Aliexpress already, looks to be the exact one used in the k45 video earlier in the thread.

Amusingly it may never see the inside of this Mig-29 as that will depend on how I feel about the elevator setup when I get the plane but being 1000cc it won't go to waste.
Last edited by raydar; Sep 16, 2020 at 08:33 AM.
Sep 16, 2020, 08:36 AM
Lee Liddle
Knife Liddle's Avatar

Reversed Yaw Affect?


Has anyone else noticed a strong reverse control effect when using rudder in aprox 45 degree banked flight?

I was attempting a banked fly by (photo opp style pass). Over controlling opposite rudder to help maintain the banked flight caused a quick reverse response. It would roll back to neutral and even past.
I repeated the action 3 or 4 times ,(at a higher altitude) and got the same result.

A little yaw input was ok. Past some point (to be determined) the reverse action came in quickly and without any warning.

Is this normal for the Fulcrum, or is it an indication of the verticals twisting under load? That can be seen in the roll axis on weak wings that can cause a reverse roll because the whole wing twists opposite of the aileron deflection.

Please let me know. Thanks
Sep 16, 2020, 08:48 AM
Serving the Motherland
Moskva's Avatar
The skymaster F-15 will do the same, they dont like to knife edge for to long and will return to level flight pretty quick on their own. the faster you go the longer you can hold knife edge

Quote:
Originally Posted by Knife Liddle
Has anyone else noticed a strong reverse control effect when using rudder in aprox 45 degree banked flight?

I was attempting a banked fly by (photo opp style pass). Over controlling opposite rudder to help maintain the banked flight caused a quick reverse response. It would roll back to neutral and even past.
I repeated the action 3 or 4 times ,(at a higher altitude) and got the same result.

A little yaw input was ok. Past some point (to be determined) the reverse action came in quickly and without any warning.

Is this normal for the Fulcrum, or is it an indication of the verticals twisting under load? That can be seen in the roll axis on weak wings that can cause a reverse roll because the whole wing twists opposite of the aileron deflection.

Please let me know. Thanks
Sep 16, 2020, 10:28 AM
Lee Liddle
Knife Liddle's Avatar
Thanks that's great news. I was afraid that the vertical stabs might be under strength, but if it's the same on some of the bigger turbine versions then that indicates it's just the nature of the beast.
Sep 16, 2020, 10:37 AM
Lee Liddle
Knife Liddle's Avatar

Speaking of going Faster


I've been busy getting the battery bay cleaned up by only using the blue box for gear, gear doors and lights. Still plenty easy to remove the wings (3 color coded servo leads and a light lead.

Also installed the 8s 120a esc's. Just did installed amp measurements using the same battery to (7s 6000 Turnigy Graphenes).

7s Amp/Watts Results

Right side....110a approx 2750w
Left side.......102a approx 2550w

Disclaimer.....There's no guarantee that the motors can handle that power level for more than 10 second bursts or so. That's my plan.....to use full power for speed passes and extended vertical maneuvers only.

Will report back when I get some video and several flights in the log book.


I have a programming card on the way to check the esc settings and try to optimize them and match the sides that way. If I can't get them closer, I may separate the two on different channels and fine tune that way. One side benefit of using separate channels is that the power can be mixed with yaw and/or roll to smooth out turns and rolls if desired.
Last edited by Knife Liddle; Sep 16, 2020 at 10:57 AM.
Sep 16, 2020, 11:36 AM
Retired US Navy
Evan D's Avatar
I cleans up nice doing this plus the receiver under the battery tray. I posted pics earlier.


Quote:
Originally Posted by Knife Liddle
I've been busy getting the battery bay cleaned up by only using the blue box for gear, gear doors and lights. Still plenty easy to remove the wings (3 color coded servo leads and a light lead.
Sep 16, 2020, 11:52 AM
Lee Liddle
Knife Liddle's Avatar

Wiring Mods


I needed more room for the 2 x 7s 6000 Graphenes. I bypassed the blue box except for the gear/gear doors and lights. Then moved to blue box and rx to the right side of the factory rear lipo location. The two auxiliary packs will go on the left of the rear main pack. The rear main pack will hold the two auxiliary packs in place with no need to secure them further. Then the front main pack and airborne radio packs can be shifted around to adjust the cg.
Last edited by Knife Liddle; Sep 16, 2020 at 12:28 PM.
Sep 16, 2020, 12:04 PM
Retired US Navy
Evan D's Avatar
In that first picture you can see your retract Y is not seated very well....
Sep 16, 2020, 12:13 PM
Flying Hazard
SU-4ever's Avatar
Quote:
Originally Posted by Knife Liddle
Has anyone else noticed a strong reverse control effect when using rudder in aprox 45 degree banked flight?
That's absolutely normal on fighter jets of similar layout. Su-35 does that too, among others. These jets are not DESIGNED to do knife edge.

Quote:
Originally Posted by Knife Liddle
I was attempting a banked fly by (photo opp style pass). Over controlling opposite rudder to help maintain the banked flight caused a quick reverse response. It would roll back to neutral and even past.
I repeated the action 3 or 4 times ,(at a higher altitude) and got the same result.
That's not a reverse response anyway, what you are describing is outright yaw-roll coupling. Jet rolls to the same side you are yawing in. As in, flyby, right to left, banked to the left, applying right rudder to hold nose up and the jet snaps back to level, rolling to the right.

So you yaw to the right and the plane rolls to the right. That's not a reversal. A reversal would be if the jet snaped (rolling left) into inverted flight with the same inputs in those conditions.

Quote:
Originally Posted by Knife Liddle
A little yaw input was ok. Past some point (to be determined) the reverse action came in quickly and without any warning.
Absolutely normal, and as mentioned, the 'cure' is to fly faster and use less rudder. Preferably with some gyro help too.

There are a few things going on here but consider:

#1- Static condition; Wing sweep and sideslip: When you deliberately put the plane in a sideslip condition when performing knife edge or similar maneuvers, one wing aligns with airflow while the other becomes almost straight-angled to it. This causes a difference in lift from one wing to the other which produces a rolling moment. (Roll due to sideslip)

#2- Dynamic condition; Roll+yaw coupling: Regardless of wing sweep, When you apply yaw, the jet advances one wing while the other falls behind. Thus you are essentially making one wing flying faster than the other. Advancing wing sees airspeed + rotation speed while the other sees airspeed - rotation speed. Lift is proportional to speed squared, so this also produces a rolling moment. Hence why many aircraft can be controlled only with yaw and no aileron input whatsoever, even if being a bit cumbersome. (Roll-yaw coupling)

Quote:
Originally Posted by Knife Liddle
Is this normal for the Fulcrum, or is it an indication of the verticals twisting under load? That can be seen in the roll axis on weak wings that can cause a reverse roll because the whole wing twists opposite of the aileron deflection.
This does not have anything to do with vertical stabs twisting or bending.
Sep 16, 2020, 12:21 PM
Lee Liddle
Knife Liddle's Avatar
thanks for the detailed explanation

Good to know that it's me, not the jet
Sep 16, 2020, 12:22 PM
Lee Liddle
Knife Liddle's Avatar
Quote:
Originally Posted by Evan D
In that first picture you can see your retract Y is not seated very well....
thanks, I'll fix that
Sep 16, 2020, 12:23 PM
Registered User
janmb's Avatar
Quote:
Originally Posted by Knife Liddle
Has anyone else noticed a strong reverse control effect when using rudder in aprox 45 degree banked flight?

I was attempting a banked fly by (photo opp style pass). Over controlling opposite rudder to help maintain the banked flight caused a quick reverse response. It would roll back to neutral and even past.
I repeated the action 3 or 4 times ,(at a higher altitude) and got the same result.

A little yaw input was ok. Past some point (to be determined) the reverse action came in quickly and without any warning.

Is this normal for the Fulcrum, or is it an indication of the verticals twisting under load? That can be seen in the roll axis on weak wings that can cause a reverse roll because the whole wing twists opposite of the aileron deflection.

Please let me know. Thanks

Sounds fairly normal to me. With a few exceptions, every aircraft in existence has some degree of positive (same way) rudder to roll coupling. A lot of three channel trainers are basically constructed on that principle. When applying yaw, one wing flies slightly faster than the other, causing a difference in lift.

When it comes to jets snapping out of (or even snapping inverted) if forced to knife edge is also completely normal, but I suspect there are slightly different aerodynamic explanations to that vs the normal rudder to roll coupling. (or easier: What Jandro said lol)
Sep 16, 2020, 12:25 PM
Registered User
janmb's Avatar
Quote:
Originally Posted by Knife Liddle
thanks for the detailed explanation

Good to know that it's me, not the jet
Well, it kinda is the jet, but it is normal :P
Sep 16, 2020, 12:30 PM
Lee Liddle
Knife Liddle's Avatar
I like to do presentation passes but obviously need to adjust my technique for jets like this

thanks to everyone for the coaching


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