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Big Tires and Expensive Lessons

Seaworthy

FOUNDER
Massachusetts
One year ago I purchased 26" Goodyears. My plane was in for annual March 2010 and the tires were installed (a few days ago) . Complete new weigh, recalculation of CG. The STC says the tires should move the datum one inch aft. The weigh and calculations seemed to indicate that the CG remained almost the same perhaps a whisker forward. So I took the PA-12 with the Kenmore STC for the O-320 around the patch.

Full fuel--one 185 lbs pilot---no other weight in the A/C. Took off with full nose up trim. After pattern altitude was reached, throttled back A/C to 2200. "Gee, that's odd, I have to hold stick back with full nose up trim." Abeam the numbers, carb heat, pull power back to 1200 RPM. Nose up to slow, stick gets heavy, stick gets heavier, let go of stick---nose plummets to earth. Add power---land with 16 kts on the nose 20 degrees to right---land at approx 68 MPH to keep control of A/C. Full stop----taxi back and consult with A&P/IA. Left access panel to tail spring retaining nut removed
and three ----three pound bags of lead shot placed in tail. Same take off---pattern altitude---throttle back to cruise, now I have to crank in two turns from full nose up trim to fly straight and level and 2200 RPM. Full stop, taxi back, tell A&P/ IA to remove 26" Goodyears and reinstall 8.5X 6 .

The 26" Goodyears carry a weight penalty of 52 pounds. The additional weight that would be required to allow the plane to fly straight and level with neutral trim and the cost to have same installed aft of the extended baggage would be prohibitive ( to me anyway) The risk/ benefit is not worth it. As it is---I am going to have to put some weight aft to offset the Kenmore STC which moved the engine out from the firewall 2" or more from manufacture.

Just another day in aviation. Perhaps someone local wants 26" Goodyears with two landings on them. The two landings were nice though.
 
Something sounds not right or I miss understood. Your C.G. sounds like it took quite a change for a tire swap. What else happened during the inspection, and how does the plane fly after the tires were removed?

Mike
 
that helper spring/cable broke/stretched/missing between stab yoke and top elevator cable?

or wrong length?

need shorter....
 
SW, I'm not buying it. As you recall I have Goodyears with the univair STC. So My -12 should be a little worse on cg than yours. Mine doesn't have any of the tendencies that you are noting. Something else has to be wrong. I love the Goodyears. I got a million touch and go's on ours and never a problem.

But if you really want to keep your 850's do that and I'll buy your old worn out goodyears. Even if I am not local.

Scott.....
 
The 8.50X6 got put back on this aft. Will fly the plane tomorrow morning and advise.

As far as I can gather from other folks that have the Kenmore STC on PA-12's they all have a tendency to have a heavy nose. Mine does--I have become used to the idiocyncratic flying charcteristics of the plane. I also fly a PA-18 with the manufactures tires on it---they look like donuts and I was flying the 18 the day before yesterday doing touch and go's. Two different airplanes. The 18 wants to glide forever, the 12 with the O-320 doesn't.

All I can say is that after the 26" tires were installed, the plane wanted to come down like a coke machine and that was with full nose up trim. As far as the centering spring, I have been through that drill---it is functioning as advertised.

Does anyone have a schematic of the jack screw assembly for a 12 and an 18? Are they identical ? I have 18 tailfeathers.
 
Tom

Put on the Thrustline mod....it will take away most, if not all, of the fwd cg issue. I had a similar issue with my 180hp Smith....UNTIL I put on Marks ThrustLine . Now I rarely trim after setting the stab for my load condition.

For what it's worth...I started with 8.50's then went to 26" GY's and finally 31" ABW's. At no time did I have a noticeable cg change. I did, however, have a fwd cg and need for full ANU trim on every approach until I did the ThrustLine mod.

Good luck in resolving the problem, whatever it is.

Lou
 
Louis

I had looked into that. I was told that the the thrustline Mod is for 18's only.

As you well know--every plane has it's own characteristics and no two are alike. My 12 certainly flys fifferently than any 18 I have ever flow. problem is, I have never flown another 12 with the Kenmore STC moving the engine out several inches and making the nose heavier that a "stock"
12 so I have nothing to compare with other than the 18.

What's odd is that the mathematical calculations indicated that the change should be negligable, however the flying characteristics indicated otherwise. I am not going to fly an airplane that reuires full nose up trim to make it fly straight and level at cruise or slightly less than cruise.

As soon as I have a passenger or camping gear etc aft--the problem ceases to be a problem.

Maybe I'm just getting too cautious in my dotage----or I'm just becoming a pussy. My comfort level was just way out of synch. Whatever the case. Flying tomorrow will provide more subjective data.

Best

TC
 
Seaworthy said:
....

Does anyone have a schematic of the jack screw assembly for a 12 and an 18? Are they identical ? I have 18 tailfeathers.


he didn't have the jack screw-yoke off, and put it back on upside down maybe???
 
mike mcs repair said:
He didn't have the jack screw-yoke off, and put it back on upside down maybe???

That could be, I have heard of guys used to Pacer maintenance doing this in the past..

Scott...
 
Best of luck

Tom,
Bill Here, Hope you get it worked out as so many are running the 26" Sneakers I would guess it will work out, IF you don't get it working for you Please keep me in mind, this might be the excuse we need to move up to those 26" sneakers we so badly want!
Maybe I'll catch you at Hampton, it will be good to see you again.
 
You keep mentioning Kenmore STC for the 150HP. My good buddy Dave installed that STC and I don't remember him moving the engine forward 2inches. Beefing up the tubes yes. He's fly's like it did before only better. Dave did you move your engine 2 inches forward? I'd be inclined to look at all the rigging. Also don't forget you added a heavier prop up front as well. It is metal isn't it? His is a Sensenich wood. Hmmm. Maybe we're on to something.
 
fatcub said:
mike mcs repair said:
He didn't have the jack screw-yoke off, and put it back on upside down maybe???

That could be, I have heard of guys used to Pacer maintenance doing this in the past..

Scott...

actually now that i think about it... that would have the opposite effect he has.... lack of front stab up.....
 
12 Geezer said:
lack of front stab up.....

Mike, isn't that backwards? He's having a hard time getting the nose up? Or am I misunderstanding something here??? Hmmm, bet I am, but not sure what!!!

ummmm.. nope, thats what I mean.... with the yoke right or wrong the stab always can go all the way down and hit the upper longeron... but will not be able to go up as far when upside down....
 
My "12" has the Kenmore STC. The original mount is beefed up but not extended 2 inches. I have a Sensenich 74" prop. Straight and level requires some nose up trim (about half way between normal neutral on the trim indicater and full nose up) I've been thinking of FAT tires but perhaps the old stock stuff is fine. Really like the way it flys and really don't want to add any weight ---1084 empty. When I asked my AI about the nose up trim, his reply was "Think about it, dummy, anything you put in the plane will be behind you." Of coarse he is accustomed to hauling large loads of moose meat in his plane. :D Just my 2 cents---Happy with my 12 in Wisconsin. 8)
 
I was kind of wondering about the Kenmore STC too.....Why would you move the engine forward 2 inches.....

Was the STC a gross weight increase??

I'm not following.

Thanks

cafi
 
I agree with everyone else here, something is wrong.

Although I have a PA-18 not a PA-12, I went from tiny stock tires to 26" Goodyears to 31" Bushwheels, with negligable change in CG.
 
cafi19 said:
I was kind of wondering about the Kenmore STC too.....Why would you move the engine forward 2 inches.....

Was the STC a gross weight increase??

I'm not following.

Thanks

cafi

I had the Kenmore STC. It uses the stock PA-12 mount with a doubler on the lower legs, but it isn't lengthened. The plane was quite nose-heavy, and I'm using the Crosswinds short mount STC in this rebuild.
 
ummmm.. nope, thats what I mean.... with the yoke right or wrong the stab always can go all the way down and hit the upper longeron... but will not be able to go up as far when upside down....


Yes - - but stab front up = nose down, right? So more nose down is the opposite of what he's needing - - Or am I still thinking wrong about what you're saying?
 
Curiosity is fine for the internet, but your mechanic should be answering your questions and resolving the issue. Limiting your plane to little tires isn't fixing it. With all the Kenmore -12s in the fleet that use big tires I'd say that's evidence that something's peculiar about yours.

SB
 
OA-12 nose heavy

I have had several PA-12's with 150/160 and 180. The original mount length is for 100HP /O-235 which. along with the prop, weighs a lot less. All of mine were nose heavy and the big tail didn't change things much for me. Charlie Centers 180 on our PA-12 works great, but the mount is a LOT shorter. We always had to weight the tails to fly well. Or carry lotsa gas and baggage, but when you land low on fuel, watch it!

Also the trim yoke can be installed two ways, right side up or down,. I always put them on so the stab would crank all the way to the longeron. What kind of battery do you have, and where is it? Also check the wing rigging, angle of incidence, avionics etc in the panel? Do you believe the W&B or is it "calculated" as opposed to actual from recent weighing?

Every one of them flew differently. About like people and personalities. It ain't "store bought" like a Cub Crafters or a Husky.

:P
 
12 Geezer said:
ummmm.. nope, thats what I mean.... with the yoke right or wrong the stab always can go all the way down and hit the upper longeron... but will not be able to go up as far when upside down....


Yes - - but stab front up = nose down, right? So more nose down is the opposite of what he's needing - - Or am I still thinking wrong about what you're saying?

Ding, Ding!
just thought of another third way it might be... Which would cause this...

Yoke upside down AND the stabilizer torque tube that attaces to it on TOP of yoke...

This would create his type of problem....

Need him to pull cover and take a picture...
 
cafi19 said:
I was kind of wondering about the Kenmore STC too.....Why would you move the engine forward 2 inches.....

Was the STC a gross weight increase??

I'm not following.

Thanks

cafi

Cafi, Most of us refer to the long mount as the stock length, as opposed to the univair style mount that is actually shorter. The short mount seems to solve alot of handling issues that some of pickier pilots don't like. You can tell what mount a -12 has if you pay attention next time. I think the short one also makes a more aesthetically pleasing nose, but take it from me work on the ass end of the motor can suck at times..

Scott...
 
Well,
Flew up to Hampton, NH today and had lunch with Jeff Russell, FMD ( John Meade), Crazy Ivan, Tool Time Tim, Bill (aerial images) And another gent from northern NY ( my apologies --I'm forgetting names.) Beautiful 70 degree day--terrible turbulence.

The 8.5 X 6's were on and she flew like she always flew. Trim was mid between centered and full nose up---from reading past postings from geezer and others---this is the norm for a 12 with the O-320.

I am a parrot--when I asked six years ago---" Why my nose is so damn heavy?" I was told that the Kenmore STC moved the engine out from the firewall an additional 2"--- What do I know? I have asked if people have schematic diagrams of origiginal 12's------------------silence. I guess they no longer exist. How do people build or rebuild 12's? Guesswork or do they repeat someone else's mistakes? I's still like to see a photo or a Piper schematic of this "yoke". The rationale why it should be installed one way as opposed to another and the consequence or aerodynamic changes if it is installed innapropriately. Stearman 600---I now know that the "yoke can be mechanically installed where the V is superior and the flat or longitudunal side is inferior or vice versa. Why not install the component as advertised by Piper. This is maddening. You get the appropriate installation guidelines and no that I find that it is "optional." What else is "optional"?

Now to the interesting portion of my return trip. Upon arrival in Plymouth after a 1.2 and a terribly bumpy trip with incredible thermals I open the right hand door and discover the entire right hand side of the aircraft is covered in oil. Hmmmmmmmmmmm, this is troubling. I get out and make the observation that oil is dripping off the entire right side and bottom of the aircraft. I hop up on the wheel and check the oil. It hasn't drained down yet---but I have between 1 1/2 -2 quarts remaining. I open the right cowl and see the the oil return from the most foreward piston's retaining nut backed off and the oil return was spraying oil over the exhaust manifold. That is distressing! Never smelled anything, never saw any smoke. Everything was fine when I departed hampton. Oddly enough
on the way north I had originally talked to Boston apprrch and asked for penetration of Boston class B at 3500 out over the ocean for a direct from Plymouth to hanson. I was cleared through, then just before I went feet wet, Boston said, " Turn left 240 for vector west of Boston." The Atlantic ocean is now 40 degrees F. If you go in---life ceases to exist after 8-15 minutes depending on body mass/fat index. Hypothermia is within 8 minutes. No matter what--you will not survive. Seems like someone was watching out for me today. Even odder--I never--ever fly out over the ocean unti July when a ditching becomes survivable. Never had so much as a burp before---the one day I decide to chance the Atlantic---I come close to having a catastrophic loss of the engine. Go figure?
 
Well,
Flew up to Hampton, NH today and had lunch with Jeff Russell, FMD ( John Meade), Crazy Ivan, Tool Time Tim, Bill (aerial images) And another gent from northern NY ( my apologies --I'm forgetting names.) Beautiful 70 degree day--terrible turbulence.

The 8.5 X 6's were on and she flew like she always flew. Trim was mid between centered and full nose up---from reading past postings from geezer and others---this is the norm for a 12 with the O-320.

I am a parrot--when I asked six years ago---" Why is my nose so damn heavy?" I was told that the Kenmore STC moved the engine out from the firewall an additional 2"--- What do I know? I have asked if people have schematic diagrams of original 12's------------------silence. I guess they no longer exist. How do people build or rebuild 12's? Guesswork or do they repeat someone else's mistakes? I'd still like to see a photo or a Piper schematic of the proper installation of this "yoke"and the rationale why it should be installed one way as opposed to another and the consequence or aerodynamic changes if it is installed innapropriately. Stearman 600---I now know that the "yoke can be mechanically installed where the V is superior and the flat or longitudunal side is inferior or vice versa. Why not install the component as advertised by Piper? This is maddening. You get the appropriate installation guidelines and now that I find that it is "optional." What else is "optional"?

Now to the interesting portion of my return trip. Upon arrival in Plymouth after a 1.2 and a terribly bumpy trip with incredible thermals I open the right hand door and discover the entire right hand side of the aircraft is covered in oil. Hmmmmmmmmmmm, this is troubling. I get out and make the observation that oil is dripping off the entire right side and bottom of the aircraft. I hop up on the wheel and check the oil. It hasn't drained down yet---but I have between 1 1/2 -2 quarts remaining. I open the right cowl and see the the oil return from the most foreward piston's retaining nut backed off and the oil return was spraying oil over the exhaust manifold. That is distressing! Never smelled anything, never saw any smoke. Everything was fine when I departed Hampton. Oddly enough
on the way north I had originally talked to Boston approach and asked for penetration of Boston class B at 3500 out over the ocean for a direct from Plymouth to Hampton. I was cleared through, then just before I went feet wet, Boston said, " Turn left 240 for vector west of Boston." The Atlantic ocean is now 40 degrees F. If you go in---life ceases to exist after 8-15 minutes depending on body mass/fat index. Hypothermia is within 8 minutes. No matter what--you will not survive. Seems like someone was watching out for me today. Even odder--I never--ever fly out over the ocean until July when a ditching becomes survivable. Never had so much as a burp before---the one day I decide to chance the Atlantic---I come close to having a catastrophic loss of the engine. Go figure?
 
My PA-12 used the McKensie STC to install an O-320, and it always cruises with neutral trim. I'm no expert on engine mounts, but I believe it uses a stock mount that has been reinforced.

I realize he's a long way away, but Mark Drath may be a good one to review your plane from stem to stern to find out what's wrong.
 
Glad your Safe and Home

Wow,
Thats no way to end a great day with great people but I'm very glad you made it safe. Hope it's an easy and fast fix and back in the sky quick! Let me know if I can be of any help in any way.
You've got my Number and E mail address.
 
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