RV-9 tailwheel weight

I'm about to finish up the transition to TW configuration and wondering what kind of TW weights the 9 drivers out there have. Main reason is to consider whether I should move my battery to get a reasonable CG. I would like to do this (if necessary) before the "official" weigh-in rather than have to weigh it twice (I know, I could do it by calculation afterward).

thanks,
greg

Hello Greg,
I reeally dont think you need to ballast your -9. Your engine should put you a good CG situation. When i can i will forward you my W&B.

Where would you move your battery?

Ah...you must be thinking you might have a fwd CG? I still doubt you will have an issue. My -9 is a bit aft CG for my liking. You should be in good shape. I will still fwd my w&b later.

Mine is also aft cg with mains at 512 and 514 and the tail at 62. That's with io-360 and cargo 3 blade.

Here's my W&B

Right Wheel 484
Left Wheel 485
Tail Wheel 54
Total 1023

The reason that Van's lists an RV9 baggage weight at 75# rather than 100 is, according to Bruce Reynolds, purely for weight and balance reasons. The c.g.s are generally aft in RV-9s. The more weight you can get forward the more baggage you can carry. (I'm already planning to start with a 20# crush plate b/c I need the full baggage weight. Will lighten it later if it becomes possible to do so.)

Greg,

I have the PC680 on my firewall and the CG worked out just perfect with the O-360. With the old O-290, I was tail heavy, like the rest.

I suggest you just leave the battery right where it is, on the firewall.

Here are my numbers:
Right wheel__512
Left wheel___507
Tail wheel____49
Total______1068

Thanks guys for the info. I currently have about 113 pounds on the tail (that's with a bathroom scale and sitting at 3-point attitude). My battery is just aft of the baggage compartment, and was put there to lighten the weight on the nose in a "former life." So, I'm thinking I will move it back to the firewall now that the little wheel is in the back.

Just what I needed to know.

cheers,
greg

We just weighed ours and it came out somewhere in the 60's on the tail (don't have the numbers in front of me). Also a 360 & catto but full classic aero interior....battery up font. W&B works out fine except at almost empty fuel and lots of bags. Waiting on paperwork and then it should be a blast to fly!

Cheers,
Stein

Finally got around to an "official" weighing with certified scales. I ended up with:

L 540
R 521
T 61

total 1122

Seems a bit heavy but I do have a FP Sensenich prop. I'm wondering if anyone has any suggestions why my L wing is heavier than the R by 20 pounds. I do have the AP servo out there, but I also have my camera stuff in the R wing which should help counterbalance things. Nothing else out there that I can think of that would result in such a difference. Too bad, as it would work out better if the R wing was the heavy one.

My CG came out only slightly different from the 9A version - moved aft by 0.15 inches, but still very nicely centered.

greg

It's not unusual for one wing to be a little heavier than the other, but 20 lbs. is quite a bit. I think I would investigate. Are you sure the left tank is empty? Nothing laying on the left wing? Aircraft laterally level? Only left half of a heavy interior installed?

Mel,

I agree and have been scratching my head on this one. The only differences in the wings that I can think of are that the L wing has the AP servo, pitot/AOA assembly, and an Archer antenna in the wingtip. R wing has the camera setup (about the same location as the AP servo on the L wing) and an APRS unit in the wingtip. And yes, both tanks were drained. Interior is spartan and symmetrical. I can't think of anything in the engine compartment that would cause this. My battery is on the R side of the firewall. There must be something that I'm missing..... When it had nose gear, the weights were L 435 and R 437.... Maybe I should swap the scales (L & R) and see if that gives me the same numbers - could be something to do with the scales, but they were just calibrated a couple days before I used them.

greg

Greg, are you sure one of your rockyology students didn't sneak into your hangar and put a piece of fubarite in your wing tip?

Ok, the only thing I could come up with that makes sense is that the tailwheel maybe wasn't perfectly straight. If it were cocked to the right, that would shift more of the overall weight to the L main. Would that be sufficient to cause the 20 pounds difference?

A quick calculation on the center of gravity indicates that the lateral CG is about an inch left of center. If I assume that the TW was off-center by 4 inches (probably at or beyond the limit of reasonability), the calculations show that to end up with the same CG, the weights can only change by a couple of pounds. Therefore, I conclude that having the TW cocked cannot reasonably account for the difference in weights that I measured.

So, after an hour of figuring on this, I still don't know why the difference in weights, other than 1) some sort of unknown weight on the L wing (fuel? but I'm pretty sure I drained the tanks completely - nothing was drooling on the hangar floor when I got done); or 2) a scale error. It would require about two gallons of fuel in the L tank to cause the problem I'm observing.

And I'm pretty sure there is no fubarite in the wingtip.....

greg

Greg Arehart said:

Ok, the only thing I could come up with that makes sense is that the tailwheel maybe wasn't perfectly straight. If it were cocked to the right, that would shift more of the overall weight to the L main. Would that be sufficient to cause the 20 pounds difference?

A quick calculation on the center of gravity indicates that the lateral CG is about an inch left of center. If I assume that the TW was off-center by 4 inches (probably at or beyond the limit of reasonability), the calculations show that to end up with the same CG, the weights can only change by a couple of pounds. Therefore, I conclude that having the TW cocked cannot reasonably account for the difference in weights that I measured.

So, after an hour of figuring on this, I still don't know why the difference in weights, other than 1) some sort of unknown weight on the L wing (fuel? but I'm pretty sure I drained the tanks completely - nothing was drooling on the hangar floor when I got done); or 2) a scale error. It would require about two gallons of fuel in the L tank to cause the problem I'm observing.

And I'm pretty sure there is no fubarite in the wingtip.....

greg

Click to expand...

Slight geometry problem with the new main gear?

How much did it weigh as a nose dragger? Can you account for all the difference?

Chip,

I don't think there is a geometry problem (flies and ground tracks nicely). In addition, I can't see how a slight shift in gear position would drastically affect the CG. If my calculations are correct, the wheel position would have to shift by about two inches to cause the apparent difference in weight. As I write this, however, I am thinking of how the airplane was weighed and may have an explanation. I did not roll the airplane up on the scales, rather, I picked it up with a hoist and set it back down. When one does that, the gear springs downward. Then upon lowering the airplane, the lateral friction from the tires keeps the gear from spreading fully. The total weight is probably ok, but it may be that one leg or the other (or both) is geometrically off and could account for as much as a couple inches. Hmmmm. Guess it would be good to try the reweigh and see what happens. Thanks for the prod to think about this in a different way (weigh).

I have not tried to account for all the differences due to the changeover. I don't know the weight difference between all the different gear legs, tailwheel parts vs. nosewheel parts, different engine mounts, removal of the "A" gear towers, etc. I did lose 25 pounds overall.

Cheers,
greg

Did you check the scales before you weighed your -9?

I typically stand on each scale before we roll the plane on them, just to make sure they are all within a pound or two of each other.

Just because a scale is "certified" doesn't mean it is accurate.

Bill,

Good thought, though these were literally just back from calibration so one would assume that they are correct within a couple pounds. I did not, however, check them. I'll add that to my list of checks for the reweigh.

greg

Greg,

Mel may have touched on something earlier that is a factor, that being weighing the airplane level. IIRC from my time as the tenant in your hangar, its not quite level. If the scales check out and the method (roll on or lower on) doesn't make any difference, try finding a more level spot (come on over), or weigh it tail in, then nose in. Just trying to help ya think it through.

Cheers,
Bob

PS: Cool new avatar, by the way!