Trim Assist Kit Option

[jrevens]

It's been a few years since the last post about this subject... how are you guys who have the spring assist on the 7SS (or other models) liking it? Pros and cons?

[airlina]

Hi John, I have a Series 5, with an IO-240 up front.(read heavy) During my build many years ago I did everything possible to keep weight aft and my CG came out fine ,however when at my over the fence speed there was always just a hint of a tug on the stick required. I never liked this trait so when the trim assist kit was introduced I went for it and never looked back. A simple concept that has worked well for me. With the trim assist, I can trim to hands off on final which is what I was after. Later I also added gap seals on the stabilizer which aided with slow speed elevator effectiveness. I have enjoyed following your build and your excellent craftmanship. Sounds like you are getting close . Bruce N199CL

[DesertFox4]

John, they work great and are simple to install. After flying several 7's with trim assist springs installed I ordered one for my 7SS build.

Started typing all the reasons I like them but all those reasons were covered below in previous posts.

BTW, i would think they should work as well on model 4, 5, and 6's. Same mixers.

[jiott]

I have had my trim assist on since day 1, now 520 hours, and am pleased with it although I have no before and after comparison. Everything about it seems positive to me except possibly one thing- if you have to do a go-around at the last minute and don't have time to take out the nose up landing trim, the forward stick pressure is quite heavy, partly due to the trim spring back pressure. This happens so rarely and can be dealt with that I don't really consider it a negative. The nice thing about the spring is that it can very easily be disconnected if you don't like it ($85 wasted). I vote to install it.

[n85ae]

I still think the trim assist kit, can lead to a situation where you don't run the
tail incidence to the proper angle (because the spring is alleviating pressure)
and under the right conditions it can lead to a tailplane stall. Which I
encountered at altitude when screwing around. I did a nose over tail tumble
at 8000 feet, and removed the spring after, and have mechanically blocked
the 22 degree notch ... Never want to do that again.

I don't think I've ever heard of anybody else having it happen, but it happened
to me and it's not gonna happen a second time to me.

I pushed nose over, pulled in 22 degrees of flaperon, and about 2 seconds
later it felt like somebody kicked the tail straight up. I smacked my legs
up into the instrument panel, and everything from the baggage compartment
ended up plastered into the windshield. Scared the **** out of me.

Jeff

[jrevens]

What you describe is similar to an aerobatic "bunt" maneuver, Jeff. There can be a lot of necessary downward force created by the horizontal control surfaces , especially when holding the nose high to perform something like a power on stall, for instance. If that tail gets into some disturbed air, like from the flaps, at a particular angle of attack, it can result in a tail stall, instantly loosing all of that down force. A forward CG can be one of the contributing factors to something like this as well. The result can be spectacular... I experienced it once also, in another aircraft type, and it was a wild ride for a guy who didn't know exactly what was going on. Even though the nose went beyond vertical, and I was hanging from the shoulder harness, the tail remained in disturbed air and stalled until I retracted the flaps, and had lost about 7,000 ft., pulling out less than 500 ft. AGL. My first thoughts were that something had broken in the elevator control system. If I hadn't had mechanical flaps, with the flap lever sticking up to remind me that they were deployed, I would have ridden it into the ground. It was a fast, slick little airplane, on it's second test flight, and even if I had figured out what was happening a few seconds sooner, electric flaps may not have retracted soon enough. Anyway, I think it's important to share your experience like you did. I'm glad you got out of it in time. I don't think it will keep me from trying the spring assist. My belief is that the test flights of a new airplane, performed at altitude, are very important for discovering any adverse traits and the conditions under which they can occur. I'll make sure that I'm looking for that when I'm testing mine. Thank you for letting others know.

[n85ae]

Very similar experience, I grabbed the flaperon handle and shoved it to zero
past vertical, after which the tail started flying again and I got it under
control. In addition to the mods to remove the 22 degree's I also added a
baggage net with tiedowns. I never fly with much more than a map loose
after that anymore.

I have an IO-240B and was solo, so it was a forward CG as well.

One of the very few moments where I was sure I had just killed myself ...
Words can't convey the fear, since it was not even in the realm of things that
I expected at that moment.

[colospace]

I'm not flying yet, but I bought the spring kit (ages ago it seems) and I recall John McBean suggesting that it not be installed until after the initial sorting out flights. FWIW

[southwind32]

I asked Debra about it a few weeks ago, and she suggested the same thing, wait till I do the initial flying. So I will wait.

[jiott]

Jeff brought up a point that got me thinking; when you trim the horizontal stab for hands off straight and level cruise flight with the spring assist what you are really doing is trimming for a constant back pressure equal to the spring force. Seems like this would add some drag to your cruise efficiency. I realize that the spring pressure is small with flaps up (the mixer system adds more spring back pressure as you add flaps, which is when you need it) but with flaps up there is still some spring pressure.

I decided to do a little test today and went up and settled into hands off trimmed cruise flight and carefully noted my cruise airspeed at a stabilized 98 mph. Without touching engine throttle, I then pushed the stick slightly forward with about the same estimated force as the spring backpressure to effectively neutralize the spring assist effect. Of course the nose went down so I retrimmed to return to straight and level flight, but now holding a constant forward stick pressure. After things stabilized in this condition I then noted my cruise airspeed at 99 mph. This effect was so small as to be difficult to measure, but it does seem to indicate that the spring assist does add a small amount of drag in trimmed cruise flight, robbing you of about 1 mph. Personally I believe this very small negative effect does not cancel out the greater positive effects that the spring assist gives during landing approaches. I plan to stick with my spring. What do you guys think? Was this a valid test?