Straight and Level

[danoliver]

This is my first year as a Pietenpol pilot. I finished up my project last October. I'm getting close to 70 hours on her now and am learning all the ups and downs of Pietenpol flying. One peculiarity I've notice is that when it's cold out, say 35 or less, I can fly hands free straight and level. As a mater of fact, one day this winter I flew from Red Stewart Airfield to Sportys (about a 40 minute flight) and literally never touched the stick while cruising. I was able to tweek my pitch with just very small changes in throttle. The warmer it gets, though, the more back pressure I got to put on the stick to keep a level attitude. Now that it's full on summer I'm keeping lots of back pressure just to keep the nose up. So much so that I'm thinking about adding some kind of trim set up.
Can anyone help me out with the physics behind this behavior?
At first I thought maybe it's a weight and balance thing, seeing as how you wear more layers in the winter, but I've ruled that out by loading her up in various ways. Then I figured maybe it's a density altitude thing but I'm not completely convinced because I'm not even trying to maintain altitude, just to maintain attitude. If that makes any sense?
While were at it, if anybody's got any trim methods that work good I'd like to get some ideas.

Thanks,
Dan Oliver
NX3469B

[Clay Hammond]

My bet is on DA. Only other thing I would think of is heat and moisture in warmer season moving things around in your airframe. How are all your wires?

[danoliver]

Good point Mr. Hammond. The control cables do seem get more slack the hotter it gets. I especially notice it in the ailerons. Probably because that's the longest loop. Something to think on a spell for sure. Thanks.
If it really is density altitude though, I can't figure out how that'd make you tend to nose down?
I reckon the real question is then, is this a normal flight characteristic or is this just something peculiar to my particular Air Camper?

[taildrags]

Dan; I think what Clay is referring to is that with increasing density altitude, the wing has less air molecules available to generate lift to keep the plane aloft with the same power setting. The only way to generate more lift without adding power is to increase the angle of attack of the wing, which in your case means holding back stick since you don't have elevator trim. That's my guess.

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

[danoliver]

Well, I went and added a little trim set up with some string, a bungee and a little crank under the seat. I'm enjoying hands free cruising even when it's hot out. It's seems to have also improved my landings. I guess there really is something to that whole stabilized approach thing they talk about.

[taildrags]

I've tried a couple of different setups for elevator trim but none of them have worked out in all situations. The most trouble-free has been a bungee setup behind the seat, with the bungee attached to the top horn of the walking beam, which effectively adds nose-up trim and also keeps the elevators from drooping quite so heavily when the plane is sitting on the ground. The problem has been that the bungee slowly loses its bungee-ness since it's in continuous stretch. Every time annual condition inspection rolls around, I have to put in a new bungee. Got any pictures of your setup? I'm all for improving my landings!

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

[Richard Roller]

34KP has (had) a vernier throttle cable that attaches to the top of the walking beam with a hardware store extension spring. It only supplies up elevator trim. Ken put it in for the benefit of lighter pilots. As I've expanded over the years I've no longer needed it!

[taildrags]

Richard, I think I'm going to have to start following you around. You drop great little tidbits everywhere you go! This is a really simple and straightforward way to apply a cockpit-controllable pitch bias to the walking beam and I'm going to see if I can rig mine up this way and dispense with my bungee arrangement. I tension the bungee from under the pilot's seat in a very simple way, using a cord with knots in it, and running the cord through a sort of keyhole-shaped opening in the pilot's seat support plywood so I can just pull the cord and drop the next knot into the slot part of the keyhole opening, or vice-versa. The vernier control is a lot less dorky and more controllable. Now to see if I can find a good used one on eBay...

Oscar Zuniga
Medford, OR
Air Camper NX41CC, A75 power

[danoliver]

Here's some pictures of the way I did mine. Pretty much the same but instead of a vernier, or a keyhole, it's a crank and a spool.
The whole contraption weighs seven and a quarter ounces. Two and a quarter of which is the 3/8" bungee, and para-cord.
One key to this here set up, which you can't see in any of the photos, is to use a wave washer. That way you can set how much holding pressure you got.

And now that I'm looking at these photos, I guess I need to vacuum from under the seat!

[taildrags]

Clever setup, Dan! My only gripe is that it still employs the one thing I've had trouble with... bungees that lose their stretch over time. Or maybe it's the Harbor Freight bungees that I'm using?

-Oscar