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I fly a PA12 on Amphibs, as such I am constantly triming the aircraft. It has the flying horiz

S

Shuswaper

Registered User
Is there a mod out there that can double or triple the mechanical advantage of the crank by increasing the size of the pully, or something along those lines.
Hate trimming


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More than likely you are right at the forward CG limit. An aircraft will require more trimming and more a constant trim adjustment at the forward CG. As a generalization, it has been my experience, that the PA-12 requires more trim adjustment than the PA-18 as well.

Bill
 
Bill Rusk said:
More than likely you are right at the forward CG limit. An aircraft will require more trimming and more a constant trim adjustment at the forward CG. As a generalization, it has been my experience, that the PA-12 requires more trim adjustment than the PA-18 as well.

Bill
Click to expand...
This is also my first thought. Amphib floats always pull the CG forward on any airplane. This has an adverse effect on stability in all axis. A suggestion for you to test this would be to place some weight in the aft end of your baggage area. Enough to place your CG for the flight at or close to the aft CG limit. Do this and report back here after the flight.
 
Is the trim 'creeping'? - mine does a little in my PA18 - watch the trim crank for movement.

Frank
 
Thanks for the advice, I dont think the trim cable is slipping. I will definately try a flight with some extra weight in the back to see how much trim adjustment I need to do. I might also look into the jackscrew with a greater M/A. Idealy it would be nice to only have to crank one or two turns to go from some flaps down to no flaps, now I probably crank that little sucker 6 or 7 times, maybe more.


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Do you ever fly with a passenger? How does the trim differ with and without?

6-7 turns would have me checking to rule out slippage in the pulley.
 
I usually fly with my wife, but she's only 118 lbs so her weight doesnt really change things, unless she's flying in which case I dont bother trimming. No just kidding, that wasnt very nice. Just did my first flight of the season yesterday so dont really recall how much trim I had to use with a big guy in the back, will have to do that as soon as it stops raining out here in western Canada, if it ever does.


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i make NO trim adjustments with flap deployment in my -12. I use flaps to modify the zero-stick-force airspeed.
 
PA 14 trim

Gordon Misch said:
i make NO trim adjustments with flap deployment in my -12. I use flaps to modify the zero-stick-force airspeed.
Click to expand...

I agree with Gordon. I rarely need to touch the trim. Four position flap settings take all the stick pressure away. FYI PA-14 with Whip 2100A's.
 
Well I just got the airplane late last year so perhaps I need to learn to fly it like a pro. I will try that technique and see if it works for me.

Thanks for the tips. Cheers


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Gordon Misch said:
i make NO trim adjustments with flap deployment in my -12. I use flaps to modify the zero-stick-force airspeed.
Click to expand...

I don't trim much at all either. Once it's set in cruise I don't touch it all the way to landing. If I didn't estimate it right for takeoff CG I adjust once in cruise but usually I am pretty close.
 
Last edited:
Shuswaper said:
I usually fly with my wife, but she's only 118 lbs so her weight doesnt really change things


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Click to expand...

Knowing it is a 12, just invite your girlfriend- Her and the wife should make at least 200 lbs:lol:

On a serious note: Trying to compare amphibs to wheels in handling is really not reasonable.
 
aktango58 said:
On a serious note: Trying to compare amphibs to wheels in handling is really not reasonable.
Click to expand...
True but if he gets his CG under control there will be a marked improvement. Every Wip amphib that I've been involved with has had an out of forward CG issue. One big airplane required 120 lbs of lead at the tail wheel location.
 
Pour / pump a gallon of water into each rear float compartment. When you are loaded up in the back pump it back out. Simplest CofG corrector I've ever used on floats.
 
Great idea for ballast control. I too rarely touch the trim in my PA12 amphib. I has about 7.7 pounds of ballast, hydraulic pump, in the very rear though. Switching to an 18 trim system also helped the slippage system.
 
Yes it does have the PA 18 trim system. And 0360, so could be pretty heavy in the front. I am going to put some water in the back of the floats and see how it flys that way. Wife says if girl friend comes along she'll be throwing me out. Hmm


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Shuswaper,
Do yourself a favor. Determine the cg of the compartment which you are going to use. Determine the exact weight of your water ballast. Get reasonably accurate W&B information when you do your test so that you can properly understand what you have done. Just pumping some water in a compartment without knowing the numbers can be counterproductive. Do equal amounts in each float for balance.

I set up a very simple weight and balance spread sheet on my computer for these exercises. You can add & subtract items in various locations in an instant. Watch the CG move around. Item Weight X Arm = Moment. Simple.

An O-360 on the front of a PA-12 on amphibs is almost certainly out of the forward limit when loaded, especially without a passenger or baggage.

I'm not even addressing the loaded weight vs legal gross. Just the CG.
 
A sandbag is way easier to experiment with. Two or three are even better. Every floatplane driver should play with trim and step speeds with different CGs. This situation isn't much different.
 
Thanks guys, I am learning a lot and really appreciate your advice. I think its time to get serious about weight and balance. And timely too. My son who just got his license a week ago asked me about the weight and balance of my plane because I just had the seats recovered in leather and high quality foam. I figured We added about 6 or 8 lbs to the aircraft. My response to him was, no I didnt do a new weight and balance calculation because it is a lot of work etc. ( I've been flying too long and sort of sluff stuff like this off). Warning Bell. He will be happy that I am going to address my weight and balance and my trim issues. Cheers


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I'm curious, what is your official empty weight and cg? What is your approved maximum gross weight? Do you have an extended baggage area? If so what is the arm of the aft end?
 
Gordon Misch said:
i make NO trim adjustments with flap deployment in my -12. I use flaps to modify the zero-stick-force airspeed.
Click to expand...

I add flaps when I'm slow enough they relieve stick pressure, in both 18 and 12. No trimming required after trim for level flight. Works great for me. But maybe something's wrong with his airplane or loading.



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Skywagon8a: my empty weight is 1610, and max weight is 1935 lbs. Empty weight CG 12.15 inch's. No extended baggage.


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So the plane might be within W&B limits if you fly it solo from the back seat, and even that's questionable. There's no way to fly with a passenger and stay within the envelope. Your son was smart to question the numbers.
 
Shuswaper said:
Skywagon8a: my empty weight is 1610, and max weight is 1935 lbs. Empty weight CG 12.15 inch's. No extended baggage.
Click to expand...
Since I don't have access to the Wipline limits or the 0-360 limits, I'm using the original Piper limits with an 0-235 on EDO 2000 for this discussion. If your limits differ we can make an adjustment.

Piper's forward limit is a sloping number from +9.2" - +15.2", moving aft as the weight increases. Since your gross is higher than Piper's I'm going to use 16" as your forward limit at 1935 lbs.

Your most forward weight/CG with a 170 lb pilot and minimum fuel of 6 gallons is 1816 lbs @ +11.79". That is 3.21" forward of the forward limit. You will need 42.7 lbs of ballast at the tail post to bring the CG aft to the forward limit with a loaded weight of 1858.7 lbs.

Your most rearward weight/CG with a 170 lb pilot, 130 lb passenger, 38 gallons of fuel and max baggage of 41 lbs is 2179 lbs @ +14.93". That is still 1.07" forward of your forward limit as well as 244 lbs over gross. You will need 13 lbs of ballast at the tail post to bring the CG aft to the forward limit and will be 257 lbs over gross.

If you leave the 42.7 lbs at the tail post your most rearward will be 2221.7 lbs @ +18.39" with the above loading. If you reduce your fuel load to 23 gallons you will be on the rear limit.

Frankly in my opinion someone has screwed the pooch. There is no way that airplane should be approved as airworthy under these circumstances. Yet someone did. AND these numbers prove that what Bill and I have said above show why you have difficulty trimming. You have no idea of how many times I've come across this type of scenario.

Should you, ....well I'll go no further.

You do the numbers, hopefully you can prove me wrong.
 
Forward CG is easily managed when light. This trim issue is a combination of forward CG and over gross weight. Many of us have experienced overloading to over gross with an aft CG but over gross with forward CG is unusual.
 
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