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Final Trimming Setup by Flying? (How do I setup)

Old 05-12-2009, 03:39 PM
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LostMyPlane
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Default Final Trimming Setup by Flying? (How do I setup)

I have an EF Yak 54 74” that I think is nose heavy. I don’t have a good CG machine and though I tried to make one, it didn’t work to well and started leaving dents in my wing. I then balanced it as best as I could using the finger tip method. Anyone who has a big bird and tries this will tell you your fingertips get tired rather quickly!!!!

This got me in the ballpark, but after two flights I think the plane is very nose heavy. When flying a down line the plane wants to come out of the dive almost instantly back to level flight.

I read somewhere a while ago that you could trim your plane based on the way your plane reacts to flying up-lines, down-lines, inverted and maybe other ways that I can’t remember. So if anyone could tell me or point me towards any FAQs online that explains how to setup a plane by flying, your help would be very appreciative!!

I think I remember something like this by the way:

1) If you fly a down line and the plane pitches towards the canopy and comes out of the dive…Its nose heavy.
2) If you fly a down line and the plane fly’s straight down… The CG is perfect.
3) If you fly a down line and the plane pitches towards the landing gear (wants to go inverted) It’s tail heavy.

Again, I’m not sure about any of this; I might have it totally reversed. Can anyone elaborate?

Max
Old 05-12-2009, 03:55 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Max,

One of the best ways I know how to do it is to fly along into the wind (no wind is best as the wind can actually change what you are seeing) and pull a 45 degree upline, now roll the plane over, get it settled on the 45 degree line and inverted and let go of the sticks and watch the plane for around 7 to 10 seconds, less if it changes the nose position rapidly.

If the plane continues on the 45 degree line without raising or lowering the nose, the CG is neutral
If the plane raises the nose, it's tail heavy. (will raise the nose fast or slow depending on how tail heavy, fast means more tail heavy)
If the plane drops the nose it's nose heavy. (will lower the nose fast or slow depending on how nose heavy, fast means really nose heavy)

Do this more than once from left to right and then right to left to be sure you are getting the same result

I fly a lot of IMAC so I want a slightly nose heavy plane for snaps and spins. When I do what I describe it takes around 5 to 7 seconds for it to drop the nose and level off which for me is perfect. If you do a lot of 3D neutral or slightly tail heavy is the way to go. It's basically all about personal preference.

BTW, every plane will pull to the canopy on a downline if the speed is high enough, it's a law of physics and aerodynamics, as the plane gains speed coming down, the wing makes lift and if you are holding some or a lot of up elevator trim she will pull the nose level. In IMAC we use a throttle to elevator mix to make sure the plane stays pointing straight down. A nose heavy plane may want to land fast, depending on how nose heavy it is. A tail heavy plane will suddenly stall, sometimes suddenly and possibly violently (depending on the plane) during landing.
Old 05-12-2009, 04:59 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Bill hit it right on the money. Always get your cg set before trying to do any other trimming, ie thrust and mixes.
Old 05-12-2009, 08:41 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Follow Bills advice. Thats exactly how I do my initial CG tests. Make small changes and fly it 2 or 3 times after each change to get used to the feel. Repeat Bills tests after each change in CG.

I like a slightly tail heavy plane that flies with just a breath of pressure on the elevator stick when inverted. Most of my planes fly very neutral but will drop the tail very slowly on final approach when I am about 3 or 4 feet off the deck. A couple clicks of power to keep it from dropping a wing and just a touch of DOWN elevator makes them settle in for a 3 point landing 90% of the time. I don't even have to flair.

Most planes will pull to the canopy on a down line. Thats normal. You either fly it or run a mix. I don't fly IMAC so I just fly it. I DO run a rudder to elevator mix to deal with knife edge coupling. It helps if you run a 5 point curve. That way you can set the mix to work when the rudder is on low rates or high rates. Low rates is neutral and the first point left/right of the center. High rates are the outside points farthest from the center.

I also run a rudder to aileron mix to help with roll in knife edge flight. Depends on the airframe, some will roll in the direction of rudder input. Some will roll away from rudder input. You just have to fly it and creep up on the mix over 20 or 30 flights. Fly it left to right and also right to left. Fly it belly in and canopy in from left and right. Mix accordingly.

We've been working on the mixes for my friends' 2.6M Comp-Arf. We have it dialed in so smooth now he can just roll over and dump rudder........ the plane will track a straight knife edge the entire length of the field with nothing but rudder input and throttle. I want to put those mixes on a switch. Every mix you do introduces other undesirable flight characteristics. For example, let's say you have up elevator mixed in for knife edge. Every time you hit the rudder stick, you get a little bit of up elevator. Thats fine for flying, but not good for landing in a crosswind. If you need a bunch of rudder all of a sudden, you're getting some up elevator and a bit of aileron too. If you put all the mixes on a switch you can turn them on or off as needed. Take off with no mixing. Get into your box and then turn the mixes on. Fly. Turn the mixes off and then land.
Old 05-12-2009, 09:43 PM
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Jake Ruddy
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Default RE: Final Trimming Setup by Flying? (How do I setup)

I just wanted to comment on the switch comment. While some people do this I have not really found a need for it.

From my expierence most of the planes I have mixed for KE flight still require more elevator to do a rudder only flat turn. So in the case of a cross wind landing the rudder to elevator mix is helping you by keeping the nose up instead of going down with more rudder.

I like to fly both 3D and IMAC however since IMAC mixing is more important to me I generally will mix rudder to elevator and rudder to aileron for a flat turn so I can make rudder corrections easier without the judges noticing up and down movement. I then find in KE flight I almost always have to use a touch of down to prevent the KE pushing to the canopy.

Some do like to have the mixes on a switch for 3D but once you learn your plane I dont think you have to worry about that either.


Just another opinion, only you can decide what works for you.
Old 05-12-2009, 10:15 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Here's a link to some good trimming information as written by Peter Goldsmith - http://www.nampamodelaviators.org/im...0Goldsmith.pdf.

Dan
Old 05-13-2009, 06:37 AM
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Default RE: Final Trimming Setup by Flying? (How do I setup)


ORIGINAL: aegis

Here's a link to some good trimming information as written by Peter Goldsmith - http://www.nampamodelaviators.org/im...0Goldsmith.pdf.

Dan
Dan,

The link is not working so I'll post another one. This takes you to the IMAC website. You may need to create an account to view this link as certain area's of the site require a login. It's well worth it though.
[link=http://www.mini-iac.com/InfoCentral/tabid/74/articleType/ArticleView/articleId/122/categoryId/37/Peter-Goldsmith-How-to-reduce-your-flying-workload.aspx]Peter Goldsmith's Trimming Guide[/link]
Old 05-13-2009, 07:04 AM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

I'm also going to comment on a few points discussed so far.

I've posted a link to the updated Peter Goldsmith trimming procedure. What you need to understand is trimming works for 3D as well as IMAC. You end up with a plane that is very predictable and that is worth a ton, at least to me. I like knowing exactly what my plane is going to do. To properly trim a plane cannot be done in one day and in most cases your going to need at least 40+ flights, most of them only 5 minutes long. I find it funny that someone comes to me and says "I got my plane flying perfectly with only KE mixing. I usually ask to fly it and tell them to grab a notepad, they will need it. I have yet to see any plane that did not need some thrust changes, CG changes, elevator halves setup changes, things like that. The only ones that even come close are QQ's planes and ONLY if you build them EXACTLY like he says.

First off is adding it to a switch. Purely personal preference in my opinion. I like to leave my mixes on all the time, especially the KE/Flat turn mixes. Unless you are tail heavy, leaving the rudder to elevator mix on is not going to matter, most likely you are already holding more elevator than the mix requires just to flair for landing. Also in a crosswind landing, without the mix, the nose is most likely going to drop, or even raise (depends on a lot of other factors) when adding rudder and having the mix on will certainly eliminate that UNLESS you have a lot of elevator mixed in and if you do you're either really nose heavy or you have some other problem.

If you are running a throttle to elevator mix for downlines, then that sometimes is a good one to have on a switch. I know of a 42% J'tec Extra that needs a ton of down elevator for the downline and if you leave that mix on, then landing is a real trick. On a downline mix you will use an offset so that the mix comes in at very low throttle. Fine for landing as you are flairing already, but if you have to give it enough throttle that goes past the offset then all of a sudden down elevator goes away and the elevator goes back to "normal" PLUS what you already have in for the flair, what you get is an instant climb. I also use a high idle mix that is on the same switch as my downline mix. I use a higher idle once I'm flying to help prevent deadsticks, pretty common thing to do on large gas engines. Mine increases the idle about 300rpm. That way anything violent I may do will not pull the fuel out of the engine.

If you do decide to use Peter's methods and I suggest you do, follow them EXACTLY, that's very important and wil save you loads of chasing your tail.

Now, I'll toot my own horn a bit, especially since Jake popped in here. Jake has flown one of my planes (Casper, 2.6M C-Arf Extra 260) and to me it looked like by the end of the second flight he had no problem running through his IMAC sequence. He also flies with another person that has flown the same plane multiple times and this same person has also fallen in love with this plane. Why, because I spent the time to get it trimmed properly. I have gotten so many people offering to buy this plane. That's what happenes when you take the time to setup a plane properly.

Casper:


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Old 05-14-2009, 08:40 AM
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Jake Ruddy
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Casper and I clicked quite well after we dialed down the rates a hair to my liking Flies extremely well.
Old 05-14-2009, 11:29 AM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

So far I’ve received some great advice. Thanks to everyone for your time and experience!!

So far I have about 6 trim flights and have nailed the CG to be almost perfectly neutral.

BubbaGates,

you mentioned something I didn’t think of. My elevator halves look like they are perfectly matched, but know that the littlest offset makes a ton of difference. What do I look for or how can I test it during a trim flight to check the elevators?

Max
Old 05-14-2009, 12:48 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Max,

While this is easily done, the best way I have found is not done while flying. It's done on the ground

Basically take two long sticks of balsa that are as close to perfectly straight as you can get and glue them to spring type clothespins (do not to tape the balsa sticks to the elevators). Now turn on the plane and the radio and clip the pins to the elevators. One on each side at the widest point and have the sticks meet behind the rudder. Now slowly move the elevators in both directions. The sticks should stay together the whole way through. If not, you have either a mechanical linkage problem, as slow servo, a weak extension, or you have too much subtrim in your setup or a whole host of other little things.
Old 05-14-2009, 01:18 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Makes a lot of sense! I used to do something similar to check wings for wing warps.

Thanks Bubbagates!
Old 05-14-2009, 02:30 PM
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Default RE: Final Trimming Setup by Flying? (How do I setup)

Dan,

The link is not working so I'll post another one. This takes you to the IMAC website. You may need to create an account to view this link as certain area's of the site require a login. It's well worth it though.
Thanks, Bill. I inadvertently included a period at the end of the link when I posted it. I agree that the document is well worth using. Should anyone want to access the document without going through the IMAC site, here's the link - http://www.nampamodelaviators.org/im...0Goldsmith.pdf

Dan

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