Nose down PA-12

[Barton]

I need some input from the PA-12 experts and some comparative input from the PA-18 crowd.
I just bought a modified PA-12 and am getting back into tailwheel flying after a long absence. I have about a 1000 hours of tailwheel time with several hundred in J-3, Stinson 108, Pacer and PA-18 so I'm not a newbie at this but my new airplane is making me scratch my head.
This is a 47 -12 with a stack of STC'd mods including 150hp Lycoming 0320-A2B, PA-18 flaps, Atlee Dodge -18 landing gear with 3" extension and Alpha Omega Suspension, 850x6 tires, -18 tail with Dakota Cub trim system which includes an up spring on the elevator control and a bunch of others that probably don't relate to the issue I'm having.

Basically this airplane seems to take an inordinate amount of back pressure on the stick in slow flight, meaning anything less than about 80 mph. Starting at takeoff with trim just slightly nose up the back pressure required to lift off at around 50 mph indicated is substantial, it gets progressively lighter as the speed increases to the point that at around 90 mph it's "normal". The airplane will cruise about 100 mph at 2350 rpm with the trim indicator set one mark up and stick forces are nominal. Pull power back and the stick forces increase as the speed decreases. Pull in a notch of flaps at bout 80 and the forces are reduced, pull in another notch and it seems to be about right. Pull the third notch at about 65 indicated and it might even take a bit of forward stick but as the speed bleeds off in a three point landing attitude it will continue to increase all the way to touch down at around 40-45 indicated. Keep the power up to about 1500 rpm with 2 notches of flaps on a three point landing and the stick still gets heavy but not uncomfortable . When I first flew the airplane with the seller/builder in the back seat (185 lbs) it took two hands on the stick to get it to fly down to the stall somewhere less than 40 mph indicated. Oddly enough it doesn't seem to make much difference if my 100 lb wife is back there or even solo so it doesn't really seem to be a CG issue.

I'm perplexed by the fact that this airplane seems to need flaps to do a three point landing otherwise the stick forces are so high that it requires full nose up trim. At that point if you add flaps or power the nose pitches up and you're rolling nose down trim into it. Is this normal? Apparently the seller/ builder just did wheel landings and rolled it on between 65 and 70 so he didn't see a problem but to me it seems if you're going to put a bunch of stuff on an airplane to make it capable of landing on a back country strip or a sand bar you shouldn't have to land it a 70 to keep the stick forces nominal. I mean that with this airplane even with 2 notches of flaps the back pressure required to three point it is significant to me and my wife is pulling real hard on it. Makes it hard to move smoothly and consistently, she tends to jerk the stick because each movement requires a conscious effort.

Any input our advice would be appreciated .

 

[cubdriver2]

Are you using the full range of the trim?

Glenn

 

[Barton]

Are you using the full range of the trim?

Glenn

Glenn,

The problem with trying to use all the trim is that it's so responsive to speed and flaps. If I put in a bunch of nose up trim then add power or flaps I find myself pushing pretty hard to get the nose back down. Then end up rolling all the trim I just put in out.

 

[PIPER J5.5]

I suspect you have the long engine mount. What engine stc do you have? This has been talked about a lot here. The short swing mount like the super cub has is probably what you want. There is a reason the super cub has the shorter mount.

Everyone who who has the short mount wouldn't trade it for anything but there are hundreds flying with the long mount.

There is a bungee that helps with back pressure but I don't have it. I have the short mount.

 

[bigrock]

Welcome back to tail wheels, Barton. I will let the experts answer your questions but I just wanted to introduce myself and let you know that we are neighbors. I have an -18 and I am hangared at Rusk County in Henderson. Drop in sometime and ask for Rocky.

 

[aviationinfo]

My plane has the long mount with the bungee, and although you can't completely trim out the stick forces during a full stall landing (with full flaps) it is totally manageable.

Have you tried different techniques as you configure the flaps? For instance---don't change the trim at first for the initial flap increments, and only trim or delay trimming until after each flap application takes effect. Sort of like using the flaps as a substitute for elevator trim as the airplane decelerates. Just a thought.

 

[Barton]

My plane has the long mount with the bungee, and although you can't completely trim out the stick forces during a full stall landing (with full flaps) it is totally manageable.

Have you tried different techniques as you configure the flaps? For instance---don't change the trim at first for the initial flap increments, and only trim or delay trimming until after each flap application takes effect. Sort of like using the flaps as a substitute for elevator trim as the airplane decelerates. Just a thought.

Basically that's what we're doing now, just leave the trim alone and let adding flaps adjust the back pressure. On short final with 2 notches of flaps I just hold the nose slightly up with 1500 rpm on it and it works ok. Will fly on in a three point attitude at about 45 indicated and pretty fair controlability in the 5 to 10knot X wind we've had the past few days.

Not sure about the engine mount but there is about 3" from the aft side of the muffler to the fire wall. Would the short mount have it closer than that? Hard to believe a couple of inches on the mount would make that much difference.

BR

 

[cubdriver2]

Glenn,

The problem with trying to use all the trim is that it's so responsive to speed and flaps. If I put in a bunch of nose up trim then add power or flaps I find myself pushing pretty hard to get the nose back down. Then end up rolling all the trim I just put in out.

I don't have flaps, I trim 12 turns from cruise to landing with the stab all the way down.

Glenn

 

[Barton]

I suspect you have the long engine mount. What engine stc do you have? This has been talked about a lot here. The short swing mount like the super cub has is probably what you want. There is a reason the super cub has the shorter mount.

Everyone who who has the short mount wouldn't trade it for anything but there are hundreds flying with the long mount.

There is a bungee that helps with back pressure but I don't have it. I have the short mount.

This one has a spring on the elevator control back in the tail that pulls the elevators into a neutral position. On the ground you can push the stick and feel the spring but when you pull I don't feel it. Is that what you're referring to?

 

[aviationinfo]

Barton it sounds to me like you're on the right track but with 1500 rpm at touchdown the true stick forces are being masked by the extra thrust and airflow over the tail. What happens if you try to land at idle?

 

[Barton]

Glenn,

So on a go around are you having to roll out a bunch of trim as it accelerates? On take off do you start with a bunch of nose up trim?

 

[Barton]

Barton it sounds to me like you're on the right track but with 1500 rpm at touchdown the true stick forces are being masked by the extra thrust and airflow over the tail. What happens if you try to land at idle?

It can be done but requires a significant amount of back pressure. My little 100 lb wife can't do it, that's why I came up with the idea of adding some power. Oddly it acts like it's nose heavy but putting weight in the back seat doensn' seem to affect it much.

 

[cubdriver2]

If I had to go around I trim about 6 turns down. Use your stab to hold the weight, that's why its adjustable. On take off its in the middle somewhere, I like to hold a little back pressure when climbing so I can feel it start to unload if I climb to steep.

Glenn

 

[Barton]

Glenn,

So what about take off, do you have nose up trim in it then?

 

[cubdriver2]

I added to post 13

Glenn

 

[180Marty]

Barton, yours sounds about like mine but I don't have flaps. Definitely have to trim nose up and I've just been doing wheel landings because it's been windy. Should try some stalls sometime I guess. Not sure if I'm excited about AOSS after getting used to the 180 Cessna on Bushwheels. Seems like no suspension at all with the 26 Goodyears.

 

[DENNY]

My cub is also sensitive to both trim and flap input. I use it to my advantage because it allows me to adjust for a wide weight range. I change my trim on every take off, during my flight and at landing. Depending on how heavy and how short I have to land each landing is different and I trim accordingly. One thing I would recommend is to figure out how many turns it is from full up to full down trim. Than figure out how many turns from full up or full down you need for take off and landing heavy and light. With flaps and power and without. This will help a lot the day that little indicator wire snaps. If I have to stop short I will normally land with full nose up trim to help keep from going over with hard braking. Doing this means I have to hold forward stick pressure until I am ready to flare. The good thing is once I release forward stick pressure I know I am at the edge of stall and do not have to look at airspeed, it will be slow.
DENNY

 

[Scooter7779h]

There are a lot of threads on PA-12's and trim issues. I have a lot of time in -12s and usually, abnormal trim issues are not about the trim system, but an artifact of something else going on with the plane like CG or bent frame or incorrect rigging, etc.

Here is a post I made from a thread in November about PA-12 pitch forces. Only updated my time in current -12:

I had a -12 79H with long mount for 30 years, 3400 hours in it. Empty CG was right at 12", forward limit. Only when loaded at minimum weight with forward CG would I run full nose up trim. Most loading configurations the trim was not full nose up if you trimmed off pressures, and I usually would for landing and takeoff. For three years and now about 420 hours I have been flying the -12 MCS Mike built for Sierra Bravo which has Charlie's short mount. Empty CG is around 14". Mike had rebuilt 79H too for me and for the most part had the same mods on 53M. Within a few hours I knew the short mount was a world of difference better. With this plane I never trim at all from cruise setting all the way to landing. Transitioning from deploying flaps and slowing down I have some stick pressures but not bad, and once slowed to 40mph pretty much neutral pressure. I do have elevator/rudder gap seals on 53M which I got field approved but only made elevator more responsive didn't change stick pressure any. Both had mirco VGs, but 79H did not have them on the tail as I got them field approved before the STC and tail VG part. With the short mount the sight visibility over the nose is more similar to a widebody -18 than a -12 with the long mount. I do not find there is any load I cannot put in the belly pod or extended baggage's (both -12s had them) that is limited by the different CGs, just load it a little differently.

I was always a naysayer about a short mount till I got one, now a believer that this is one of the really good -12 mods. I only trim a half a crank or so in cruise to make sure its hands off level and don't touch it for landing. This trim setting pretty centered on the jackscrew. YMMV but I think having a good flying -12 is all about knowing the planes and building everything right and rigging it right. Anomaly about trim and pressures tells me there probably other things going on with the plane than just elevator trim that manifest in the way the plane flys.

 

[stewartb]

You don't mention trimming to relieve stick pressure. I assume you're cranking it. Maybe your trim is slipping on the pulleys? I'd disregard any trim indicators and just use trim as necessary. I'd also verify the yoke is installed correctly and isn't upside down.

 

[Anzack]

Does it have a PA12 tail or an 18 tail?

 

[Gordon Misch]

Just to chime in here, with another point of reference - - My 12 is O-320 with short mount, -18 flaps, -18 tail feathers, -18 standard gear, 26' tires, empty CG 12.6". I almost never touch the trim, except for changes in loading. As I slow down I add half-flaps, then full flaps when slower. That keeps the stick forces light.

I do not worry about having to hold some stick force; to me it seems like less effort and distraction than messing with the trim.

I will say it is much easier to flare than when it had the standard PA-12 (long) engine mount, even though my neutral trim setting is lower at the front of the stabilizer than your picture shows. I can't help but wonder if covering the gear would help that.

 

[Gary Ward]

I purchased a 12/0320/160HP last fall and it is equipped very similar to yours. I think I'm fighting the same problems as you with heavy pitch forces. Here is a link to a thread I started a few months ago

PA-12 Pitch Forces

What is your EW and CG? Mine is 1135# at 11.11"

I sure wish there was someway to lighten the pitch forces. It would sure be much more pleasant to fly. When I am maneuvering around, changing speeds, power settings, flaps etc. I am constantly fighting the pitch forces and trimming like crazy. It would take a lot of muscle power to fly a full pattern without touching trim!

Gary

 

[skywagon8a]

.....I sure wish there was someway to lighten the pitch forces. It would sure be much more pleasant to fly.

Elevators ( PA-18 ) with the aerodynamic balance will lighten the pitch forces.

 

[n40ff]

What is the bungee spring on the elevator horn/horns configuration on the 12's?

Reason I ask. I started flying a friend's J5A-75 back in 2007. Having never flown any Cub before I found it odd that landing with full nose-up trim I had to hold a bunch of back pressure. Power off with full nose up trim it would glide at 90 IAS....... Several local pilots had owned/flown it for years and all simply said it was normal.

I found it could/should NOT be normal because regs. require an ability to trim within a certain % of approach speed. Looking at the drawings I found that the bungee "helper" spring/cable could be added from the trim yoke to upper elevator horn. We ordered the kit from Univair , installed it and the thing became a different airplane.

Anyway, just a data point. I assume the heavier -12's with big engines, increased weight, multiple STC's have both upper and lower bungee springs on the elevator?

If not they could easily become rather "heavy" and/or require using the full range of trim or even run out of trim.......?

If everything is correct, I'd think that considering the relative larger CG range and relative large useful load plus pitch change cause by flaps, that the need to use the full range of trim would be NORMAL.....

Maybe?

Jack

PS. I should add that the bungee added to the above J5A may have been a band aid? It had been wrecked and was a marriage of two airframes and who knows how straight it was? I think you should be able to trim a stock J5A-75 on approach speed w/o the bungee. Replies to my questions both here and on the J3 forum suggested that some J5's could be trimmed and other's couldn't?

 

[Gary Ward]

Elevators ( PA-18 ) with the aerodynamic balance will lighten the pitch forces.

I do have the 18 horizontal stab and balanced elevator. Barton mentioned in his initial post that he has it also. I think it may be required as part of the STC to upgrade to the 0-320.

If these were experimental, I believe I could build a horizontal and elevator that would lighten the forces. If the area of the "horn" forward of the hinge point was greater, I would lighten the forces. Also, adding weight to the forward most part of the horn could help as well. Some control systems incorporate a bob weight in the system to artificially increase the stick force per G. The weights on the horn would actually do the opposite and decrease the stick force per G.

Gary

 

[Barton]

Does it have a PA12 tail or an 18 tail?

It does have -18 tail and Dakota Cub trim system.

 

[Barton]

I've read about the yoke being installed upside down and backward but so far I still don't know what it looks like when installed correctly. I can take a picture of mine since the builder put a nice big access panel on the bottom of the fuselage at the tail if that would allow someone to tell me if it's installed right.

 

[kevin]

If I remember correctly, the "v" needs to go down.

 

[12Geezer2]

Just an observation : Been around 12s for about 40 years, have seen some with fuselage differences at the tail. Hard landings ???? bad repairs ??? who knows. Sighting down the lower longerons I often see there is some differences from the lift handle to the tail post. ( Usually pushed up) Any changes here can affect the horizontal stabilizer angle which will affect trim---am I right ????? I think my 0-320 long mount flys very nice --with flaps and VGs --have not noticed much heaviness in the controls--but do trim nose up a couple turns for landing---do have double groove trim---18 tail--- OR perhaps my right arm is stronger than I realize----HA !:???: geezer Dan

 

[180Marty]

Sighting down the lower longerons I often see there is some differences from the lift handle to the tail post.

According to the blue print, they are supposed to angle up---I think I remember 1 inch. I used to weld for a guy that made 12 fuselages.