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Thread: How do you trim for short field?

  1. #41

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    Spinner2
    yes it is a PA 18 160 hp. How hard do you break once you get on the ground? That is the reason for the nose up trim. As far as takeoff trim I don’t do full nose up. Depending on load and surface high may use a lot of nose down trim. However, If I am on smooth ground and have a clear runway ahead of me then it is nine turns back from full forward. I do not attempt to pick up the tail. I simply let the tail come up on its own, it will lift a few inches above the ground initially and then at around 35 mph it will start to lift again at that point if I hold the stick and pull flaps it flies off the ground smoothly. By using this technique it takes the pilot out of the equation and adjust for any headwind it will most always be the shortest takeoff. This works empty or with an average load. Some may ask why not lift the tail for a better view? This is a really good idea if you have rough terrain or need to maneuver around obstacles. However when you lift the tail you now squat the front tires this slows you a bit when you first start to roll and gives you more tire drag versus wind drag, It is noticeable if you are down to three psi. The second point is now it is up to the pilot to determine when to rotate, if you rotate too early and hit your tail wheel you are going to lose distance on takeoff. If you rotate too late you won’t strike your tail wheel but you will have given away ground. I’m an old guy so taking my decision out of the rotation and leaving it to the Aircraft to tell me when the wing it’s ready makes it more dependable. Hope that all makes sense to everyone. Every cub is going to vary some from the trim settings I mentioned. And once again for the lower time pilots neutral trim is fine on landing and throw some nose down for takeoff.
    DENNY
    Last edited by DENNY; 01-12-2020 at 12:47 PM.
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  2. #42

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    Speaking of tire pressures Denny.....Do you change your psi between everyday use and STOL comps? More pressure gives less rolling resistance but more bounce if you land firmly and less contact patch while braking. Too little pressure lengthens t/o roll but helps on the backside. Am I over thinking?

  3. #43

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    You’re thinking is spot on. The gear also becomes a factor with tire pressure. I change tire pressure a LOT! And takeoff the difference between 3 pounds and 5 pounds can be 20 to 30 foot. I used to run around 3 1/2 - 4 with bungees now that I have a AOSS I can run a little harder on takeoff because I don’t have the bungee bounce factor on landing. I normally run around 4 1/2 for competition now. I always carry a 1 pound electric compressor with me. If I am going to a new spot or soft spot I will air down to 3 - 3 1/2 pounds for landing once I can inspect the runway if it’s firm enough I will bring it back up to six for takeoff with the pump. For a normal flying known firm spots I run 6 to 8 psi.
    DENNY

    edit: If you’re not going to be flying for a while pump your bush wheels up to the max pressure listed on the side wall it is a lot easier on the tires and easier to push around.
    Last edited by DENNY; 01-12-2020 at 03:19 PM.
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  4. #44
    spinner2's Avatar
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    Quote Originally Posted by DENNY View Post
    Spinner2
    yes it is a PA 18 160 hp. How hard do you break once you get on the ground? That is the reason for the nose up trim. As far as takeoff trim I don’t do full nose up. Depending on load and surface high may use a lot of nose down trim. However, If I am on smooth ground and have a clear runway ahead of me then it is nine turns back from full forward. I do not attempt to pick up the tail. I simply let the tail come up on its own, it will lift a few inches above the ground initially and then at around 35 mph it will start to lift again at that point if I hold the stick and pull flaps it flies off the ground smoothly. By using this technique it takes the pilot out of the equation and adjust for any headwind it will most always be the shortest takeoff. This works empty or with an average load. Some may ask why not lift the tail for a better view?

    DENNY
    I like these type of discussions.

    I brake with the tail up on almost every landing. I hold the tail down with elevator and sometimes power. The brakes are Grove 1.75” double puck, so plenty of braking power. Even when there is plenty of room to roll out I still pick a spot and stop with brakes. It keeps me sharp.

    On skis, when I three-point land, I have plenty of nose down trim dialed in. Yesterday I pulled the 31s and put on straight skis since we finally got some valley snow.

    Click image for larger version. 

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    You can see where my trim was after sliding up to the hangar.

    On takeoff the tail pops up almost immediately trimmed like this and as the airspeed flashes though 25, with 2 notches of flaps pulled, I tug on the stick and up we go. I’m then taking the flaps out followed by trimming for neutral.

    If I have full up trim dialed in it just seems to take forever to get airborne.

    With up trim dialed in for landing, for me, it is harder to hit the spot and the AOA seems high with reduced visibility.

    It is easy to fall into routines and established patterns. So a couple of years ago I re-tried it all, after wondering if my nose down trim was really helping me. Neutral trim, some up trim, full up trim, changes in flaps and flap timing. I’d pace off my distances after landings. Same with takeoffs. I did the same on skis on a big reservoir where I could make dozens of landings and takeoffs in virgin snow and see without a doubt where there were ski tracks and where they ended.

    With me in my Cub there was no doubt what worked the best.

    When I had my 160 hp PA18 I made similar tests and got started on using some nose-down trim. With this Cub I worked on refining my technique.

    This is my experience with thousands of landings FWIW.
    "Fast is fine, but accuracy is everything." Wyatt Earp
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  5. #45
    CamTom12's Avatar
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    I have significantly less experience, but I use nose down trim for my landings and take offs too.
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  6. #46
    Steve Pierce's Avatar
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    Quote Originally Posted by KevinJ View Post
    Speaking of tire pressures Denny.....Do you change your psi between everyday use and STOL comps? More pressure gives less rolling resistance but more bounce if you land firmly and less contact patch while braking. Too little pressure lengthens t/o roll but helps on the backside. Am I over thinking?
    Making fun of my first landing at the last Hondo even I see. I tried a little extra air and it bounced big time.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  7. #47

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    Quote Originally Posted by Steve Pierce View Post
    Making fun of my first landing at the last Hondo even I see. I tried a little extra air and it bounced big time.
    I figured your auto inflation/deflation malfunctioned when you were in the pattern. Between your nitrous shot on takeoff and your flap dump switch, you’ve got a lot of buttons to push.

  8. #48

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    Spinner2
    I have experimented with trying to blow the tail down as I was braking hard right at the end of the rollout, it worked but lengthen my landing a bit. Something good to have in the back pocket if you felt it going over! bit of thread drift, what cowling do you have? It looks great! Is the engine/ motor lowered?
    DENNY

  9. #49
    spinner2's Avatar
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    Denny I sent you a PM.
    "Fast is fine, but accuracy is everything." Wyatt Earp

  10. #50

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    Empty, what should my 1200# Cubs tail weigh?

  11. #51

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    Depends on a lot of factors. Are you talking 3 point or in level flight/What type of gear (stock, 3x3, ect)/ Tire size/how much weight on the nose (180HP, club prop or cato, ect). All the factors combine to affect the weight of the tail at a given position. Basic cub with 31 inch tires, 160hp, Borer, stock gear in level flight should be around 80 lbs give or take 10 lbs when the cub is static. Once you add airflow, you add another long list of factors.
    DENNY

  12. #52

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    Thanks, Denny

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