Rocket 305 Weight and CG

[SpamPilot]

I've been enjoying my Rocket 305 for three years now.  I've made a few upgrades along the way, always dutifully tracking the changes in the Weight and Balance log.  I have also corrected a couple major mistakes in the math made long ago.

Starting from the original factory Basic Empty Weight of 1923 lbs @ 43.4", 290 pounds of new equipment have been added to the aircraft (mainly the Rocket 305 conversion, built-in O2, and Charlie weights, plus a new COM radio and two G5s).   90 pounds of old equipment originally delivered with the aircraft have been removed (KFC 200, KCS 55A system, BX2000 system, and associated wiring).

Q: How much *should* the aircraft weigh now? (Basic Empty Weight, including 10 gallons unusable fuel for the Rocket 305)

A: 2123 lbs (@ 43.5")

Q: How much does the aircraft actually weigh?

A: 2273 lbs (!!!!!!!!) (@ 36.5") (!!!!!!!!!!!!!!!)

Obviously, I'm freaking out.  That's a 150 lb increase and a 7 inch forward CG shift that are unaccounted for.

I've been all through the airplane with my A&P.  There's nothing we can find that comes anywhere near explaining even a 15 pound difference, much less a 150 pound difference.  The panel looks like a ghost town with all of the ancient avionics gone.  I've got 20 lbs of wiring alone that was just removed.  There are no errors remaining in the historical W&B entries.

I read with great interest Rspencer612's topic Mooney Missile CG.  I read about the possibly incorrect arm for the main and nose axles.  Even if I can justify ignoring the actual measurements we made, adjusting to the referenced numbers still leaves the CG off by at least 3" from where I expect it to be, and where other Rocket 305s are.  I also read that Rspencer612 appears to have resolved his problem by installing the Charlie weights that had never been installed when the Missile conversion was performed.  In my case, though, the Charlie weights are definitely installed.  I also have a heavy O2 bottle that should be biasing the CG well rearward.

We tried this with two different scale sets, and they agreed to within 0.2%.  Yes, we followed the correct leveling procedure, twice.  We weighed with full tanks and subtracted the weight of 70 gallons usable fuel, per the POH weighing instructions.

Has anyone seen a ~150 lb weight increase *and* been able to explain it?  I read some comments on this forum and elsewhere about significant weight gains in aircraft as they age, but I haven't found anyone that was actually able to confirm the source of the gain (as opposed to just guessing that it might be dirt and oil, etc.).

 

[philip_g]

The increase is odd but the forward cg is just normal for rockets. I couldn't put enough lead in baggage to shift the cg aft enough with two big guys up front 

[PJClark]

Well, it gets odder...

My 86 252 Rocket was weighed around 2014 (before I bought it) and it was balanced right on station 48, the fuel station. Has 19 lb of Charlie weights in back. Nowhere near as "forward" as one I looked at earlier-- an 84 231 conversion if I recall--I saw the W&B for that one and I'd never have been able to put my wife in the front with me without about 120 lb of baggage or ballast in the baggage area.

I've seen Rockets advertised on Controller (Spring of 2020 there were two of them, both 231s) that had 1025 and over 1100 lb useful loads. Mine had about 850 before my avioncs all got ripped out, now I'm around 920. Same time I bought mine there was another at Jimmy Garrison's, also an 86 252 conversion, and it had a 960 lb UL with all the same legacy 86 stuff that mine had--they were the same airplane separated by maybe 50 serial numbers and more than 100 lb different on empty weight. How does that happen?

BL--I've about concluded that the W&B of all these airplanes is so scattered that it may be nearly meaningless.  I still never load over my own GW limit, but the numbers are so wild I think there must be some fiction in nearly all of them if they haven't been weighed recently.

if you figure it out let me know--I want my 86 252 Rocket to have the 1100 lb UL "feature".  

[SpamPilot]

So it turns out that we *did* use an incorrect procedure to set up the weight and balance.  You need to read the Service Manual very carefully, not just the POH.  The A&P had not done that, and I had to do my own research and ask a few questions to uncover this.  But the biggest problem was the scales turned out to be uncalibrated.  You can't trust any numbers from uncalibrated scales, and you can't use uncalibrated scales for an official W&B.  Having no calibrated scales, the A&P went with the "by calculation" method, after visually confirming the absence of any unaccounted equipment and having performed an excruciatingly detailed review of all the W&B changes going back to when the aircraft was new.  The weight and CG now appear to be in family with the other 231 Rockets that have modern avionics and end up with a UL of 1050+- and CG > 43".

We had removed about the same weight of avionics and wiring from behind the panel as was removed from the tailcone, but because the arm is so long to the tailcone, this means the CG shifted forward about half an inch in the process.  That's not great news for a Rocket, but it's manageable.  Flying with two modern-sized people in the front and full fuel requires at least 50 lbs of baggage to stay within the W&B envelope.  I already fly with ~25 lbs of tools, oil, random gear I will probably never need, and tiedown ropes.  On any trip I'm likely to take with one other person, we'll easily add another 25+ lbs of bags.  When I fly locally with a CFI for training, I have some lead weights I put in the back.

Charlie weights are a must-have for the Rocket.  Interestingly, I can see in my logs that the Charlie weights were not installed back when the Rocket STC was performed, but were added just a couple months later.

I do want to say that, while I am often near the front edge of the W&B envelope on takeoff (because I'm operating in the narrow "doghouse" area at the top of the Rocket W&B envelope), the aircraft is *not* nose-heavy.  With correct trim, it flies itself off the runway with no back pressure on the yoke.  It never slams its nose on landing, even those rare times when I (oops) drop it.  I've seen lots of comments saying "it's nose-heavy", but that's not my experience.  The big TSIO-520-NB up front is statically balanced by the two batteries way back in the tail, plus the Charlie weights.  Odd that everyone focuses on the big engine and concludes "nose heavy" without considering all the added weight and moment arm at the rear which, by the same line of thinking, should give it a "tail heavy" reputation.  With my O2 bottle in the tailcone, my CG is within 0.1" of the CG when the aircraft was born as a 231.  Anyone who is experiencing a heavy nose flying a Rocket is, I'm guessing, probably not actually inside the W&B envelope, or is landing overweight, or both.  If you are flying two modern males, full fuel, and no baggage, and especially if you don't have Charlie weights, you are probably forward of the CG envelope, at least with a 231-based Rocket.  You also need to burn off fuel before you land to get below the landing weight limit.  Load and fly it according to the CG envelope and it flies and lands just fine.

Edited December 20, 2021 by SpamPilot

[carusoam]

There are a few WnB error posts around here…

If there is a way to mess up the calculation… it’s been covered.

Rockets have the added stress of being heavy up front…

And have their WnB changed significantly mid life…

Sorry, TLDR… unable to read the font using my iPad…

-a-

[aviatoreb]

I'll mention what I have remarked on the forum earlier.  For a price the weight and balance of the Rocket can be improved significantly.  I have the MT 4 blade prop which amongst many other nice aspects of it - the main thing that sent me shopping for it 6 or 7 years ago was that it is 35lb lighter than the big McCauley that comes with the rocket, and taking 35lb off the nose really moves the balance back quite a bit leaving a much more harmonized balance.  It feels much lighter in pitch.