W&B for retracts

Matthew

Matthew

Touchdown! Greaser!
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Matthew
I'm getting my feet wet with an Arrow now, my first experience with a retract.

Going through the W/B calculations, the tables have a moment arm for the gear retracting.

The CG moves aft when the nose gear retracts. The table includes that arm in the math, so it is accounted for when you calculate the CG. But, if you load the airplane so that the calculated CG is right on the FRONT of the envelope, then when the gear is extended you'll be out on the front side. It's only by less than 1/2", but it's still out.

OK - common sense will tell you not to let your load get that close to the edges of the envelope.

On other aircraft, how much of an affect does swinging the gear have on the CG? Is it usually negligible?
 
On Cessna retracts, all three wheels move backward when retracting, not just the nosegear. The difference on a 177RG is about 2800 in-lb. That corresponds to a whole inch at max gross, somewhat more at lighter loading.

You sure can feel the change in CG (and aerodynamic moment) when the gear goes up. Never do this right off the pavement or you won't like the result....

But, I thought the CG limits were generated with the gear out. Certainly, aircraft weighing must be done that way
 
MAKG1 said:
On Cessna retracts, all three wheels move backward when retracting, not just the nosegear. The difference on a 177RG is about 2800 in-lb. That corresponds to a whole inch at max gross, somewhat more at lighter loading.
Click to expand...

Depends on the Cessna. The nosewheel on the 182RG and 210 retracts forward while the main wheels go back. I don't recall the CG change during retraction, if they even list one, but i've never been loaded close enough to the limits that I thought it would matter.
 
Yes, and inflight bugs hit the leading edges and windscreen. Someone should plot that CG change too. Critical stuff we're talking about.
 
I would think that CG in landing and take-off configuration is more significant that in cruise configuration. At low speeds control surfaces have less authority. At higher speeds, the issue is inherent stability. The further aft the CG is, the lower the stability.
 
My plane doesn't give you any info on the gear for W&B. The mains are incredibly heavy but they retract straight up (well, they swing towards the centerline). The nose gear retracts aft, but since the plane tends to be on the forward CG limit anyhow, I'm not concerned about it moving aft.
 
Consider what could happen. If the CG is too far forward with the gear down, its possible the stabilator could lack sufficient downforce to raise the nose and rotate the aircraft into climb attitude. If it were critically so, you'd never get off the runway (though you could conceivably have a nasty overrun).

The more dangerous condition is GC aft of the envelope, because this dampens the nose-down response to a stall.
 
MAKG1 said:
You sure can feel the change in CG (and aerodynamic moment) when the gear goes up. Never do this right off the pavement or you won't like the result....
Click to expand...

I was taught to leave them out if there was usable runway.

But I never found the aft CG move nor the mild resulting pitch up objectionable. I was usually still getting the trim set for the climb anyway, so it just was one more little pitch change in getting it juuuuust right.

Plus you usually gained a few knots once they tucked away and that more than made up for the CG change.

Bigger problem was Cessna gear creates a hell of a lot of drag while in-transit. That changed pitch and speed far more than the CG shift.
 
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