G Load Limits

[Caveman]

Scott,

Are you just wanting to take a passenger for a ride without aerobatics or for an aerobatic ride? You may already know of all this...

https://www.atsb.gov.au/media/24397/...701033_001.pdf

Here's a good thread on 4's and aerobatics with passengers:

http://www.vansairforce.com/communit...d.php?t=112843

[rvbuilder2002]

Originally Posted by ChiefPilot

If the weight addition is in fact linear, then you've done the math correctly by starting with the aerobatic G loading and extrapolating from there. But the weight addition won't be linear - it will be concentrated in the fuselage...in the passenger seat, to be exact.

What effect would this have on the bending moment at the wing root? The extra mass is no longer linearly distributed along the span of the wing (or along the length of the fuselage), which would imply that the bending moment at the wing root, if linear, has some coeffcient on it which probably results in a G-loading less than achieved by linear extrapolation.

Ding, Ding, Ding...... we have a winner.

This is why if you extrapolate the max gross weight of any of the aerobatic RV's, against it's approved aerobatic gross weight at 6 G's, it doesn't work out in round #'s

[Scott Hersha]

Thanks for all the responses everyone. My main interest was in determining if the G load limits were a linear calculation. It sounds like they are/or not - depends on whose explanation is correct. There are other discussions here that says the aerobatic gross weight limit doesn't include wing fuel, which would also indicate that 'spreading out' the 100 pound increase over the airframe isn't necessary. Not sure I believe either one of those ideas. My only interest here was to be able to take an adult for a ride in my RV4. Not planning on ever doing aerobatics at that weight, or with someone in the back seat. I've done W&B calculations with a normal sized adult in the back and as long as I have about 10 gallons of fuel or more, I'm still within the CG limit - but over the 1500 pound max limit. If the calculation was linear, then the max G limit at 1600 pounds would be 5.156. I thought that limiting my G load to no more than utility category (+4.4/-1.75) any time I'm over the aerobatic gross weight would be safe. I have done testing at an increased gross weight and find the airplane to be controllable and stable in all normal maneuvering right down to a stall. Stick forces in pitch are, of course much lighter, but not that much different than at 1500 pounds. Power isn't a problem with an O-320 that produces approximately 175 hp, and takeoff and climb performance are still very good off our hard surface runway at 630 feet above sea level. Not sure I'm going to change anything in my POH, or W&B paperwork, because it's still unclear what is safe and acceptable.

[ChiefPilot]

Originally Posted by Scott Hersha

There are other discussions here that says the aerobatic gross weight limit doesn't include wing fuel, which would also indicate that 'spreading out' the 100 pound increase over the airframe isn't necessary.

That's been a thing that just won't die. The factory weighed in on it a couple years ago: https://www.vansaircraft.com/pdf/let...2015-11-20.pdf

[luddite42]

Originally Posted by Scott Hersha

because it's still unclear what is safe and acceptable.

There is no such thing, in absolute terms. I'm unclear on your concern given your statement about not doing acro with a passenger when operating above aerobatic gross. Why are you trying to nail down the theoretical "exact" G-limit when over aerobatic gross when no acro is involved? Is this a true concern of yours, or do you just like theorizing the numbers? Even when aerobatics is involved, it's not as if there's some sort of magic protection at the 6G threshold, and that you enter "unsafe" territory with any amount under that number.

[Scott Hersha]

I'm just trying to stay within my written limitations in case I get ramp checked with a passenger. I know what safe is. Just trying to cover my buns, and I'm selling it, so I want to make it right.