Colt Relocate Battery Aft?

[T. Bix]

I already risked hijacking another thread but it was the opposite direction and there seemed to be some pretty decent discussion in the direction that the OP wanted to go. A buddy of mine tells me that the further aft I can get my CG the better she'll handle at low speed as in landing. I think this is a popular cub thing but wonder if relocating the battery box aft has been done on a Colt or Pacer. I realize the Pacer guys probably want it relocated forward but that's not necessarily the case with my Colt. Within normal operations at legal weights it is impossible to load my colt out of the CG envelope so it seems like there is plenty of room to go back if indeed it will improve handling. I know the best way to improve my landings is to practice and I don't yet have enough flight time to know if any improvement can be had with a CG shift but if there's any little thing that can improve handling, why not look into it?

[dgapilot]

I already risked hijacking another thread but it was the opposite direction and there seemed to be some pretty decent discussion in the direction that the OP wanted to go. A buddy of mine tells me that the further aft I can get my CG the better she'll handle at low speed as in landing. I think this is a popular cub thing but wonder if relocating the battery box aft has been done on a Colt or Pacer. I realize the Pacer guys probably want it relocated forward but that's not necessarily the case with my Colt. Within normal operations at legal weights it is impossible to load my colt out of the CG envelope so it seems like there is plenty of room to go back if indeed it will improve handling. I know the best way to improve my landings is to practice and I don't yet have enough flight time to know if any improvement can be had with a CG shift but if there's any little thing that can improve handling, why not look into it?

Have you run your W&B for your loading now? Each airplane will be slightly different. Is your current empty weight and CG really accurate now (When was the last actual weighing)? More often that not, weight and balance data is severely outdated or inaccurate. It makes no sense to even think about ballasting the airplane unless you really know where your CG is. Run a most forward configuration, and a most aft configuration and go from there. Figure how you fly the airplane and what possible loadings you will use before you change anything. Also don't forget to check all your rigging, I've seen a number of airplanes that the stabilizer movement was out of spec, making landings a little more difficult.

Of all the Pacers I've flown, I never had instances of wanting it loaded farther aft was necessarily desirable. The trim was always sufficient for all loading conditions within the CG range. Sometimes a farther aft CG could be problematic, exacerbating the tendency for tailwheel shimmy. I have flown other type airplanes where loading aft made landings easier, but I can't say that I've noticed that with the Pacer. Correct Flight Control rigging has been a greater influence on landing than loading.

[Gilbert Pierce]

On a tailwheel airplane moving the CG farther aft means more weight farther behind the the MLG. and a longer arm.That will make the taildragger more eager to swap ends. The weight wants to be in front of the MLG which is the reason the nose wheel was invented.

[Steve Pierce]

I have never had a CG issue with a Short Wing be it nose wheel or a tail wheel. The Colt has a lighter engine and a lighter prop and no oil cooler so you have already moved the CG aft over a Tri-Pacer. I run a very aft CG in my Super Cub when competing in STOL contests via weight at the tail spring because the airplane is more stable in the slow flight regime in that configuration. It takes away from usability if I were to do a permanent installation in that regard like moving the battery. I would suggest the SBS-J16 battery in the stock box and location to save the weight and would change the cg a little.

[deandayton]

The Colt is a great training airplane. I recommend leaving the CG alone and spend your effort practicing landings. When you get the experience level where you want to operate out of short sandbars or compete in STOL contests you'll probably want a different airplane anyway

Sent from my SM-G950U using Tapatalk

[T. Bix]

Have you run your W&B for your loading now? Each airplane will be slightly different. Is your current empty weight and CG really accurate now (When was the last actual weighing)? More often that not, weight and balance data is severely outdated or inaccurate. It makes no sense to even think about ballasting the airplane unless you really know where your CG is. Run a most forward configuration, and a most aft configuration and go from there. Figure how you fly the airplane and what possible loadings you will use before you change anything. Also don't forget to check all your rigging, I've seen a number of airplanes that the stabilizer movement was out of spec, making landings a little more difficult.

Of all the Pacers I've flown, I never had instances of wanting it loaded farther aft was necessarily desirable. The trim was always sufficient for all loading conditions within the CG range. Sometimes a farther aft CG could be problematic, exacerbating the tendency for tailwheel shimmy. I have flown other type airplanes where loading aft made landings easier, but I can't say that I've noticed that with the Pacer. Correct Flight Control rigging has been a greater influence on landing than loading.

Yes I have run my weight and Balance... Single pilot, two pilot, half fuel, full fuel, baggage loaded, any loading at all and it's near the front of the envelope.

The aircraft was physically weighed as part of the rebuild, I am reasonably confident that the W&B is accurate.

Again: "Within normal operations at legal weights it is impossible to load my colt out of the CG envelope so it seems like there is plenty of room to go back if indeed it will improve handling".

[dgapilot]

Moving the CG aft will have four effects (2 good, and 2 bad), the first is that it will be easier to get the tail low attitude when landing. Second, in cruise you will be more efficient (the tail doesn't need to push down as hard which creates drag). Third, the tail will be heavier resulting in more wear and tear on the tailwheel, and harder to move around on the ground. Fourth, having the CG farther aft will make ground loops more likely, so it will be less stable on the ground roll. Another potential issue will be unintended spin characteristics. While you may still be "in the envelope", consider that having a large mass farther aft will result in more momentum in the spin and greater resistance to recover (stop the rotation). Not saying this will happen, but it is possible. Moving the CG farther aft will also make the spin flatter (less nose down). While a different aircraft, on my Howard, when you installed ballast on the tail, you also needed to install a placard indicating that spins are prohibited. Recognize also that the farther aft your CG is, the less effective your trim will be, and the less stabile you will be in the longitudinal axis. So long as you are still within the envelope, you are OK, but if you go aft of the aft limit, you may find you go from positive stability to neutral or negative stability.