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Thread: Change in CG effecting stick pressure.

  1. #1
    Steve Pierce's Avatar
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    Change in CG effecting stick pressure.

    I recently finished up a lot of work on an L18C. Recovered both wings, installed headerless fuel system, and installed Dan's A/C underseat battery kit. Moved the CG forward as can be expected. Has Micro VGs same as before recover. My problem is the stick force in the flare is considerably more than was before the changes. The plane used to be real light on the elevator, now pulling back on the stick takes considerably more pressure. I am trimmed farther back. Can anybody explain to me what is happening?
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  2. #2
    Guest
    Didn't you say that you had moved the cg further forward? You've increased the nosedown pitching moment, and are having to generate more tail download to compensate.

  3. #3
    Steve Pierce's Avatar
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    Correct. I took the G35 battery out of the tail and put the light weight battery under the front seat. Seams to me if I am not trimmed exactly right or I want a little more back stick it takes more pressure to pull the stick back. It used to be real light on the elevator and now in the landing configureation it feels alot heavier.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  4. #4
    Wayne Mackey's Avatar
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    Nose heavey

    Steve,
    Do you have more wash out in the wings than you did before the rebiuld. This will
    give the feeling of being more nose heavey. Wayne

  5. #5

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    Most likely it is the forward shift in the CG., especially if it has more normal control pressures with wieght in the back. Better than being tail heavey.

    I have had the honor of flying several homebuilt airplanes on there first flight. I recall one having the CG so far to the rear that it required forward stick pressure in the turns, trim worked in reverse, and the stick pressures were everrrr so light. Believe me when I say I didn't stall it, and a wheel landing was the order of the day. Builder moved some heavey things around, added 20#weight to the flywheel and presto it flew (almost) normally.

    Don

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    delete

  7. #7
    Steve Pierce's Avatar
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    Didn't do anything to the elevator cables. The CG moved from 17.55" to 11.56". I actually weighed the A/C and calculated the CG. The previous W&B showed the A/C weighing 846.5. After I installed the light battery and removed the header tanks it weighed 945 lbs. I know the old W&B wasn't right. I never trust them unless I weigh them myself. The A/C was rebuilt in the 80s and the W&B says it weighed 780 lbs with a C90-8. It weighed more than that new. Now it has a C90-12 with 8.50 tires, saftey cables, Cleveland W&B, Scott 3200, Micro VGs, Micro-Air 760 Radio, B&C starter, heavy generator, back seat storage, front seat battery, oil filter adapter. I might try adjusting the elevator cables or just leave it alone. It just bugs me how much heavier the aft stick feels while slow.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  8. #8
    Guest

    change in stick pressure affecting stick pressure

    did you put your elevator helper spring back in for when trim is used?

  9. #9
    Steve Pierce's Avatar
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    I didn't change the trim system at all. The bungee is there. I did notice on the Northland CD they call for a different bungee cable. Does anyone still have the bottom bungee in place?
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  10. #10
    FlipFlop's Avatar
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    Speaking of weight and balance...

    With minor weight changes sometimes the mechanic will state on the 337 "weight change negligble"... I saw one yesterday that said "weight change negotiable"!...

  11. #11
    Guest
    Steve, if the control forces bug you, just move the CG back to the original location and the origiinal stick force will be restored. As I mentioned earlier, what you are describing is a normal consequence of the change you made and is to be expected.
    All the best,
    JimC

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