Mixes, Perfect roll - Stratus

[Aviation addict]

Guys,

Do any of you employ mixing on your 3D machines for anything other than getting the swash plate to be perfectly level throughout its travel?

The reason I'm asking is that my heli does not seem to roll perfectly on its axis. It seems to drop the tail a little and basically flare off speed just a little. I've checked the C of G with half a tank of fuel (and the canopy on) and its neutral. Should it be neutral, or slightly nose heavy?

I'm slowly reducing my levels of Expo with the aim of getting them to Zero too as I understand Linear is best when it comes to 3D.

Thanks,

[Rada70]

if you have a 14MZ, go to:- http://www.helifreak.com/viewtopic.php?t=11836

[Aviation addict]

Nope - I use a JR 9X II, but I had a good look at the link anyway thanks.

I have done all of the points that relate to me like - setting the servo disc to exactly 90 degrees - then getting all the levers and bell cranks at 90 degrees also. I then used 2 off 7 point mixes to get the swash level throughout its whole range (using the MA swash leveling tool).

Don't get me wrong - the heli flys really well (I think), I'm just curious about the Rolling side of things and Centre of Gravity / Mixing as a possible solution....

[Zilly]

John,

When you are setting up your swash on the bench you can have it perfectly level and it will still not fly perfectly in the air. I used to use mixes to try and get the perfect movement however I no longer bother. Once I have set up the swash on the bench I go out on a fairly calm day and do some power climbouts both normal and inverted. I then use the ATVs to get the heli to climbout nice and straight. When back on the bench I was suprised at how much the swash was now out which goes to prove there is only so much you can do on the bench.

As for rolls I would forget the mixes as well and concentrate on how you fly them. There are not many helis that roll perfectly in both directions and when you see the top guys performing continuous perfect rolls its all in their flying ability.

z

[Aviation addict]

Cheers Z. You're probably right about the flying ability thing. I had another do today and did some much better ones. Ta.

[Dr.Ben]

Give me a day or two. I can write you a small novel on what it takes to get a model to roll on a clean, axial axis. I can't always make my model do them well, but it's not due to the model or the programming. Skill is a player, too.

It normally takes me several weeks and two pmixes (one of the a multipoint one) to get it really right.

There's a roll, and then there's an AXIAL roll. The latter can take a lifetime to truly perfect. You can't appreciate this until you've watched the likes of Curtis, Wayne, Cliff Hiatt, etc, to know what I'm talking about.

I'll write you up something to work with over my lunch break this week.

Ben Minor

[Knud Pedersen DENMARK]

Hi

My good old Fury Extreme did do some strange rool - it kind of "cork-screw" - the heli did lift the nose through the roll.
This was when doing right rool (as I prefer)
When doing left rool the problem was much smaller.....

I did remove the "linkage compensation" in the swash detail (Futaba T14 )
And set all swach mixing rate to zero.
I did some normal and inverted cliimpouts (no wind) and adjusted those mixers.

But still i did the strange roll.
When looking at the screw for "antirotation" on the swashplate - i could see that the screw did moved upward when applying right roll, and almost nothing when doing left rool (on bench)

Yesterday i did programmed a P-mix
Ail ->Ele: A linear curve for right roll = +6%
and zero when doing left roll

NOW the heli does the roll much better
:D :D

ChopperKnud

[Dr.Ben]

UH HUH!

That mix you used is the basis for a right roll. Less of one and in the opposite ele direction is typically required for left rolls, both assuming CW rotor direction.

More later.............

Ben

[Knud Pedersen DENMARK]

Hi
Dr.Ben – yes I am about to learn those damned helis grumpiness :-)
:wink: :D :D


But I was wondering:
If using those P-mixers (ex. Ail->Ele) to get a good Roll, could that then have bad influence/effect on other manoeuvre like: Ail-Tictac, stationer roll or other 3D manoeuvers ????


Quote Dr.Ben:
It normally takes me several weeks and two pmixes (one of the a multipoint one) to get it really right.
What others P-mix does you use to get good rolls?


ChopperKnud

[Aviation addict]

Thanks Ben - It would be good to know how to go about getting the perfect axial roll. I hear what you're saying about operator error being a factor too though.

How much of effect does the (fore/aft) Centre of Gravity of the model have on rolling in your opinion? I've found through my initial efforts that it's quite important.

[Dr.Ben]

As far as static set up is concerned, a DEAD level swashplate at all collective positions and a CG that is either neutral or slightly nose heavy are quite important. A tail heavy model has lovely tendency to stand on its tail during the inverted portion of a roll, especially a right roll. Any aft trim in the swash when upright causes the model to pitch down when inverted in the roll. Fore trim creates a pitch up when inverted. Hence the need to have a level swash as a static set up before using mixes to tweak the roll.

Ben

[Zilly]

"As far as static set up is concerned, a DEAD level swashplate at all collective positions"

Ben what if you set up your swash level on the bench and then in flight you find the model tends to pull off to the left or right when doing power climouts I have trimmed mine out using ATVs to get nice straight power climbouts and it is not nearly as straight after I have done this? So which way should you do it?

z

[DavidH]

I trim the model to fly straight and level. This requires a level swashplate. You have to decide if you want to do straight power climbouts or you want the model to fly straight and level. At the events I attend I do not see many just doing power climb outs.

David

[Zilly]

David, perhaps power climbouts is the wrong description. What I mean is when I pull into fast forward flight I found the heli started to roll of slightly. I dont have any problems correcting this but am just interested as to why if your swash is dead level the heli still rolls off to one side or other. Is this more to do with Gyroscopic forces?

z

[Dr.Ben]

Needed point of clarification:

Dead level swash must always be maintained in the fore/aft axis. Models hover with a bit of right trim and need a slightly different roll trim for FFF. I still set stuff up mechanically and initially dead level, and from there only alter the roll trim as needed. I NEVER touch the elevator trim. EVER.

As for the query about using ATV's for correcting FLYING trim shifts at extremes of collective, my personal opinion is to use ATV's to level the swash statically at extremes of travel, then use a multipoint pmix to add a point or points of mix at the collective position(s) where the trim errors occur.

Using the ATV's to correct trim problems in one attitude, such as straight up or down will invariably introduce other trim issues in other flight attitudes such as FF as David suggested.

ALSO, I've had the question of trim shifts directed to many many times over the years. Though not always the case, I've seen a tremendous number of cases where VERY small errors in paddle alignment have cause major trim shifts at extremes of collective travel. It seems to be even more an issue with 3D models which often or set up with less inherent stability in the head, IE lightweight paddles and lower bell/hiller ratios. I know on my FAI models, they'll pretty much go straight up and down or hold FFF inverted and right side up pretty much hands off. FFF takes a touch of roll cyclic trim, which is normal. The swash sits level fore and aft, however. You'll not see a model which is in perfect trim in hover and in FFF in the roll axis with the same swashplate angle. Rotor dynamics prevent that.

Ben Minor

[GM1]

To add to what Ben and David are saying, FFF trim is also speed dependent so getting the motor in the model to perform consistently is an absolute necessity to get the model into as close to perfect trim as you can get. I lost a motor right before the NATS last year and the motor I used as a replacement was not quite as potent so my top speed was reduced and as a result all my FFF trims and mixes were off just a fuzz and made flying the model MUCH more difficult.
Gordie

[allen]

here is the setup!!!!

take off head, use the ma swash plate tool, put on mian shaft, turn on transmiter and set stick to middel for 0 pitch, use a square and sub trim all servo perfict 90 degree to frame, adjust bell cranks 90 degree to frame with links from servo to bell crank, then adjust the links from bell crank to swash to make swash level, then you should be able to go full + colective and swash should be level and full - collective and swash will be level, WITHOUT MIX!!!!. then put head back on and set up head, sub trim will move the ball on the servo .001 of a inch it is very percision.
keep radio on the whole time!!! :)

[DavidH]

then you should be able to go full + colective and swash should be level and full - collective and swash will be level, WITHOUT MIX!!

That is true. Provided your lucky enough to get three servos that travel the same distance exactly and at the same speed. I have not been lucky enough to get three servos that would move exactly the same in my 5 years of setting up eCCPM helis. I don't use subtrims. If the holes on the servo wheels will not be in the exact spot needed. I drill a hole in the wheel where needed.

David