big lama not self hovering (and a sim question that relates)

prof_fate

OK, new to helis. Got a big lama last week and it will not self-hover - lots of minute inputs are needed (even indoors) to get it to hover.

It's not a trim issue (on the tx anyway). I've managed to to hover it but it's a constant workout.

From all I can tell this is not normal on a coax bird. The FMS sim is even harder than the real chopper. So learning anything there is near impossible.

I DLd the clearview sim and the honey bee is a tad touchier than my lama (faster reacting but the same otherwise). The coax bird they have is way way way way more stable than mine...

Whats' teh deal? It was this way new...I've since broken a few blades (haven't we all?) and now have 3dpro blades on it - same thing, hard as heck to hover.

Any suggestions on what I should check?

TIA

tombo242 · Posted: Wed Sep 01, 2010 9:37 pm Post subject:

Hi Prof_fate,

You do not give us much information here other than hard to hover. Constant minor inputs are not unusual if they are always in different directions or caused by air reflections jogging the heli off course.

In still air well any from walls, air cons, fans, open doors or windows, does it tend to always go in one direction or is it totally random?

How high are you? How big is the area that you are flying in?

All this and more is needed before anyone can give you a considered opinion of what - if anything - is wrong here.

Tom.

prof_fate · Posted: Wed Sep 01, 2010 10:24 pm Post subject:

did some googling and took the info and did a major trim - adjusted servo arms to be 90 deg to the levers, levels the swashplate by eye (did good on that too), then adjusted the proportoin so both motors start at the same time (the lower one was starting first).

It is much more stabile now and will hold a hover hands off, in doors anyway.

It's behaving more like the sim - as I fly foward/back the nose rotates left then right (or vice versa, but consistently now). The rudder is much more sensitive now.

Only one minor issue...one of the black rubber covers on the flybar came off and of course the brass weight came off too - that I found. A bit of elec tape and then a bit more and it's as good as new...well, OK,not really. Since the flybar was straightened by me (and it's good, but no perfect) i ordered from china - one to mod and one to use.

tombo242 · Posted: Thu Sep 02, 2010 4:55 am Post subject:

Hi Prof,

It is essential that the flybar is balanced if you want a stable flight. the vibration caused by any imbalance between rotating surfaces will throw the heli into drifts or worse. If you want "hands-off Hovering" then all 4 blade must be balanced in their pairs and the flybar also. If it were single rotor CCPM then there is a lot more to correct as well.

You have done well in getting the servo arms at 90º to the links, that's a good start, now comes the fine tuning in static and dynamic balancing of all parts. also get the CG under the mainshafts. Then you will get something like a "Hands-off" hover.

Do not try to get a VW to run like a Porche, you do not have a Herbie there.

Tom.

prof_fate · Posted: Thu Sep 02, 2010 9:13 pm Post subject:

I"m learning as I go - thanks for your help.
I have new bits on their weigh and when I get a bit better and stop smacking it around I'll be sure to balance everything - yeah, I know it would be easier now to do it as it would make it easier to fly but I"m beating the hell out of it IMO- i'd have to stop and rebalanace every 2 minutes LOL I'm learing 'faster' how to fly because it is wandering about like a drunken sailor on a ship in a storm.
My goal is to get a 1-2 minute hover and a full batt of flight without touching down (been touching down to avoid running into things like walls).

I do seem some vibration - even when new - so when all the new bits arrive I'll pair up the blades, etc.

I have a postal scale but I suspect the blade balancing will require a finer scale or something - any suggestions on what to use?

pjdog · Posted: Fri Sep 03, 2010 12:26 am Post subject:

Update your proflie 'location' so we know where you are.

Jack

tombo242 · Posted: Fri Sep 03, 2010 12:52 am Post subject:

I use a bolt and a few nuts to hold the blades together, balanced between 2 shot glasses to find the heavier. Mark that one with a tracking felt tip line and take them apart.

Now use round pencil to roll the heavy blade on at 90º and find its CG mark and transfer the mark to the lighter blade.

Now using clear tape bring the CG on the lighter blade to the same position as the heavy blade. Use to tape either at the root or tip of the blade as required. Make sure that the tape starts at the trailing edge goes over the leading edge and finishes at the trailing edge.

Now bolt them back together and match the weights by adding tape (over the leading edge) only at the CG of the now lighter blade.

You should now have a pair of well balanced blades.

Tom.

prof_fate · Posted: Fri Sep 03, 2010 5:09 am Post subject:

I'll give everything a good balance and see that that does. thanks!

prof_fate · Posted: Fri Sep 03, 2010 7:04 am Post subject: getting there...

the air finally calmed down some so I got some outside flying time.

The blades were balanced, CG off on the lower ones by 1/4" but I left that alone since they were otherwise in balance.

And the flybar was way off balance but is now very good (electrical tape - not aerodynamic, but functional).

OK, much smoother, much more stable.

I'm getting a lot of rudder back and forth - seems related to rotor speed maybe.... At a low hover (6 inches) things are fine, move up to about 2 feet and it wants to nose-left. Move up to 12 feet and it wants to nose right, and as you move up and down it wags one way up and the other down. I can handle it but is it normal?

One other thing I've noticed, not sure if its normal or not - I can hover about chest high and at times - can't pinpoint the cause(and it happens inside so it's not wind related) the heli will sink to near the deck. Also from a chest hover I can do 1 notch of throttle and it will rise to 12 feet or so and sit there happily..i have to drop about 2 or 3 notches of throttle to bring it back down. Normal or not?

tombo242 · Posted: Sat Sep 04, 2010 6:05 am Post subject:

All sounds like a typical co-axial to me. The Left/Right thing with height is as the blades move in and out of ground effect, the lower ones obviously have the greater effect and this differential causes problems especially with a heli the size of the big Lama.

Rising and falling seems to happen with all helis that are sightly out of trim.

Sight along the upper blades hold the flybar to take up any slack (push gently against the direction of rotation) and ensure that the flybar is parallel to the blade holders. You may have to screw the link in and out a little (sometimes up to 6 turns).

Tom.

platinum · Posted: Wed Jun 01, 2011 12:34 pm Post subject:

I have fun to fly two big lama out door in clam day. Thanks for all interesting posts.

platinum