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Century Helicopter . MTA Hobbies . Model Rectifier Corp

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Henseleit 3DNT - Rocket - 3DMP > Vibrations at high revs
 
 
Pascal
Senior Heliman
Location: Paris, France

As I start flying my Three Dee NT with now confidence, I am gradually increasing the speed of the engine.
At 1650 rpm, the 3D is fine.
At 1700 or above it vibrates.
I am using an OS91 turning rightwards, and I checked the balancing of the blades, the paddles... everything looks OK.
With a 7.7 ratio, I should be able to go up to 1900rpm but I should cure this vibration first.

Did anyone encountered the same problem ?

Pascal
05-18-2003 Over year old.
 
 
helifever
Senior Heliman
Location: BE-8750

what you can check:

slight difference in degrees in paddles perhaps, balace of the head is almost impossible

i would also change the heck shaft

though it is perfectly normal with the os91 engine that at some speed, the engine is running rich and causes vibrations, many pilots (almost all) have this

it should get better and better when the engine has run in (30 to 60 liters!)

and yes, i have it to but it doesn't matter because my engine (and pitch) change constantly when flying



helifever
05-18-2003 Over year old.
HOMEPAGE  
 
 
DangerousDick
Veteran
Location: Cheshire, England

I run the GV-1 on mine at 1,700 revs and the canopy shakes a whole lot. The horizontal fin has even fallen off a number of times now.

I have a 1,300 rpm setup also but at that speed all is OK. At 1,700 I don't usually stay in one place too long and it flies OK - I'll try to reduce it a little next time I'm out.

Cheers
Richard.
05-18-2003 Over year old.
 
 
Pascal
Senior Heliman
Location: Paris, France

I checked paddles 'position. Shaft are new, as the helicopter has never had any accident, yet...
I am using SAB carbon 710mm blades and checked their balance which was perfect.
AC blades are the plastic ones recommended by Jan and are OK.

I am also using a GV1, which is why I am concerned about vibrations, the rpm stays very constant that way. And it really vibrates between 1700 and 1800, I did not dare to go higher.
I was thinking that the horizontal fin could fall, so the fact that Richard mentions it does not surprise me.
However the engine had only 12 liters of fuel, so may need more fuel to get better.

Pascal
05-19-2003 Over year old.
 
 
1hander
Senior Heliman
Location: San Antonio, TX

hi im preparing to get one, im using the webra 91 left rotation, with 7.7 ratio, please repost if you figure out the problem, i would def like to know..
regards rick
05-19-2003 Over year old.
HOMEPAGE  
 
 
helifever
Senior Heliman
Location: BE-8750

i also started flying with the gv1 but i wasn't satisfied with it, now i fly without and it is much much better (and cheaper)

why : the engine has so much power that the gv1 in order to keep rotor rpm constant only needs very little changes of the gas, so once the engine is running rich the gv1 gives a little more gas to keep rpm constant, and i think it is in that part the heli starts vibrating

when you fly without you won't have this problem as there are more changes in the throttle during flight

you should try it

it only takes a while to get a good throttle curve but it's worth it!

helifever
once i had vibrations due to bad allignment of the engine, i losed the 4 screws and then refit it and it was perfect again
05-19-2003 Over year old.
HOMEPAGE  
 
 
DangerousDick
Veteran
Location: Cheshire, England

I only fitted the GV-1 recently - flew without for over a year. I like the way it doesn't overspeed coming down with the neg pitch in idle up 2. Now I just switch the gov on and just fly in Normal mode - same pitch curves in all modes on my Tx.

I recently replaced the blades (NHP710's) and feathering shaft and it seemed to get better, the feathering shaft can bend very easily not just through crashing! I've even managed to bend it through transporting the heli in the back of the car before

Cheers
Richard.
05-19-2003 Over year old.
 
 
1hander
Senior Heliman
Location: San Antonio, TX

vibration

has anyone using a webra and gv-1 experienced this vibration..
rick
05-20-2003 Over year old.
HOMEPAGE  
 
 
3DPP
Senior Heliman
Location: Vienna/Austria

It look like that the mainrotorblades do not run in a line at the same pitch range.This you have to adjust with a pitch gauge exact on the end of the blades,it is not possible to do this like by an other heli during flight by looking because the heli is so lightweight.
The blades are running in line most of the time if the failure is little but the heli begin to shake.
If you use not the FX you have to use a 8,3 gear ratio, because SX or SX-C and also the Webra have to much power and the rpm is going to high and the heli do not like this.
I found out that the flybar must be exactly straight and it is not allowed to be a little bend.
Also the padles must be perfect paralell togehther and paralell to the main blades,little difference here cause that the blades do not run in line,here you have to work perfect.Always check it with rotate the mainrotor 180° and look .
I put on 10g weights on the flybar this helps also a little.
A 53cm flybar works also well if vibrations do not want to go away.
My 3D father Bernd Pöting use only 45cm and the purple K&S and he is happy with the cyclic response.
If you have the vibration only on the vertical or horizotal fin this is normal for the older one over 1700 and the new one over 1850 this come from the tail drive belt.You can make it a little betterthat the vibrations a little less if you make the belt tension stronger.Temperature make a big difference here,hot outside belt tension more loose-cold outside belt tension more strong.
hope this helps a little
br peter
05-20-2003 Over year old.
HOMEPAGE  
 
 
Pascal
Senior Heliman
Location: Paris, France

Hello,

Many thanks for these advises.
I saw no tracking on the 3DNT but will check the pich on both blades.
I use 20g SAB paddles which have been aligned using gauges.
Cyclic answer is OK, not too hard, but smooth. As mentionned by Thierry I can do a roll in 1.7 seconds , while his 3DNT takes about 3 seconds with 30g SAB paddles.

the engine is an FX with 7.7 ratio, (both the 3D and the engine were ordered directly from Jan Henseleit)

I will also check the tension of the belt, it is a very recent 3DNT with the carbon wheels. Temperature went up since I adjusted it.

Pascal
05-20-2003 Over year old.
 
 
Pascal
Senior Heliman
Location: Paris, France

The vibration problem is over.

It was created by the AC belt. I increased its tension and it went away.
Thank you for the advise. I did not realise that the belt tension would decrease when temperature went up.
Now at 1800rpm it is not vibrating any longer, but the power is awesome, and with 11° of pitch the engine is still adding some rpms while climbing.
Visualisation is still an issue now it goes even faster.
I will add some more fluo tapes.

Pascal
05-25-2003 Over year old.
 
 
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Henseleit 3DNT - Rocket - 3DMP > Vibrations at high revs
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