B400 maiden...death wobble in idle up!!!!

[SeanOC]

Hey guys this is my second heli after I tought myself to hover on a CP about a year ago. I need some help diagnosing a problem:

So I got my blade today...

Unpacked and checked all controls, everything looked OK however the tail servo does NOT center. Not bad if you only put small inputs in but full deflection and it wont even come close to centering. Oh well, I bought a DSP75 to install and planned on using the stock tail servo as a cyclic spare.

I wanted to get at least one flight with the heli just as it came from the factory, so....

Charged up the pack, changed the plugs over to Deans and out I went. Its cold here so I gave the heli 10 mins sit time outside before I flew.

Immediately noticed a slight wobble in the head on spool up and I needed about 6-8 clicks of right rudder. Nevertheless I did some hovering and noticed a tendency to bob up and down and its especially bad when doing piros.... the heli drops bad during piros!

I figured I would idle up and try them with more HS. This is where my problem really stood out. MAJOR Vibrations! So much so it shook the tail boom supports out immediately. The heli was just shaking really bad.

Landed, took it inside to look for issues. The flybars are equally spaced and level. The main blades are balanced. The swash is pretty darn level. Belt tension is what the manual calls for.
The blades needed a half turn adjustment for tracking.

The only thing I can think is that the main shaft is bent? Do you guys have any other ideas?

At this point I installed the dsp75 on the tail and changed the ball link to the third hole. I switched the gryo to digital mode and reversed the rudder on the dx6i. I increased the gain to 68% in normal mode and added +25 expo on the cyclic controls.

So after all that I took her out for a few more flights. No change in flight characteristics aside from the expo. Still needed a bunch of right rudder trim. Death wobble in idle up still there.

Any ideas on what I should do next??

[vicrc]

Balance the main wood rotor blades before changing anything. The B400 is really smooth at least mine is. make sure they track well.

[sokal]

i had the same issue with my tail
i centered the trimm found center on servo arm and center on shaft
used subtrim to get true center on servo
look in to the vids form fineless about tail build up good general info helped me

befor i changed my servo and gyro it held ok and its normal for the servo not to center in HH mode my original servo moved more that the slider allowed and is the cause for mine to fail (i think) if u hear a buzz in the servo when full inputs ar applied u may be hurting the servo.
as for the head a friend of mine had a slightly bent main shaft and it wobbled also he noticed the head block screw was stripped.
both of our spindals were bent from factory which caused vibs

[SeanOC]

At least I dont think so,. Just had it out, seemed to roll true on a glass table. If there is a bend it is minute.

[SeanOC]

both of our spindals were bent from factory which caused vibs

OK Im embarrased to ask, but what is the spindal?

Edit...figured it out. Spindal is the same as feathering shaft. Doh!

[SeanOC]

Balance the main wood rotor blades before changing anything. The B400 is really smooth at least mine is. make sure they track well.

I have a small scale thats accurate to the 10th of a gram and they were even.

[sokal]

its the shaft that ties your blade grips together
just spin the screw to check for bends while its installed
(looking for no grip ossilation) if thier is then its bent

[vicrc]

Placing them on the scale is not enough, they are wood so it makes it even harder to get right than carbon ones. Here is a good link for balancing http://www.helihobby.com/html/balancing_blades.html

The spindle on the B400 is like the one on the Blade CP? I am thinking its same thickness and why they did that I have no clue and I don't remember how many spindles I went through with the CP. :arggg:

[vicrc]

I forget to mention, removing the rotor blades and seeing if the vibrations was induced by the blades. Don't go 100 percent throttle maybe bad for the motor. If its smooth, then its probably the blades.

[SeanOC]

Thanks everyone for the ideas, I will try them all out tonight. One thing nobody commented on was the altitude loss during piros. Any ideas?

[SeanOC]

I just got off the phone with HH tech support. They told me to add shims to the head in order to solve the wobble. Does this make any sense to you guys?

If so where do I get the and how do I install them? Thanks!

[sokal]

if u yaw in the opposit that of the rotor blades spin u will climb if you go with the blades u decend. its like that even in full scale helis

shimms will make the heli more responsive doesnt seen as though it will help the wobble
im sure some thing is bent or pitch is un equal
but shimms may increase the wobble.

check that at half stick blades or 0 deg
and +10 up and -10 down to do so un plug motor and swith to stunt
or set you pitch curve in throt hold like stunt 0 25 50 75 100
then u wont have to unplug motor.

[SeanOC]

if u yaw in the opposit that of the rotor blades spin u will climb if you go with the blades u decend. its like that even in full scale helis

shimms will make the heli more responsive doesnt seen as though it will help the wobble
im sure some thing is bent or pitch is un equal
but shimms may increase the wobble.

check that at half stick blades or 0 deg
and +10 up and -10 down to do so un plug motor and swith to stunt
or set you pitch curve in throt hold like stunt 0 25 50 75 100
then u wont have to unplug motor.


I dont know about that.... this thing DROPS during a piro, almost out of control. Its nothing like any heli on a simulator I have flown.

[carlo_the_wonder_frog]

It all sounds like low headspeed to me, can you increase the throttle curves?

[sokal]

its helicopter physics when you taw with the rotation of the blades the head spead over the body is now lower so you will desend and agains the blades the head speed increases so u climb.
i crew UH-1 and CH-47 and its true in both not as much in the 47 but still thier
i guess its all apart of the fact helicopter arent physicaly capable of flying
"Braking the Law" so if increasing speed will help with the decend be slower and the climb to be faster.

[sokal]

i know it all sound off but its true this is a link to a rotocraft handbook and it explaines everything about how and why a helicopter flies explains the yaw effect and why tail rotor aircraft hover one side low
most is explainded in chapter 3 but othe usefull info about flight cracteristics

http://www.esnips.com/doc/9b97e4c9-5d1b-44e5-a786-41770defbb78/Helicopter-Rotorcraft-Handbook

[SeanOC]

Dude I'm not disagreeing with you at all, Im just saying I have seen numerous videos and flown a bunch of simulators... hell even my blade cp would piro all day long without a noticeable drop in altitude like this does. Something is wrong...

HS sounds like the issue but my settings are bone stock using brand new packs, I dont get it.

[Wolfpackin]

I thought the the stock, normal, throttle curve was a little low and slow.
I changed it from 0-25-50-75-100 to 0-50-80-90-100.

But if you are flying in Idle-up only, you should be alright on head speed with the throttle curve over 85% in all positions.

[SeanOC]

...and Im embarrassed to admit that it was simply a matter of the main blades being tight enough.

Thanks for the help guys! The positive was after watching Finless' video and the link provided here on blade balancing I really got the thing flying smooth.

...until I plowed it into concrete from about 30 feet in idle up and didnt hit throttle lock.:o:o:o:o But thats another story.