Torque Tube Bearing Spacing

[J-S-Q]

Just replacing the torque tube in my 700 and I'm wondering about the bearing spacing. According to the manual, the two bearings should be evenly spaced along the tube (which is the way I did it when I built the heli) but I thought that there would be less resonance buildup if the bearings were unevenly spaced. So why does the manual recommend even spacing and should I just build it as per the manual?

[wayne123]

Just go by the instructions they are there for a reason.

[adieuk]

if you do it any difference you will get vibes in the t/t

[trillian]

I was just reading about bearing spacing for the 500 and it only uses one bearing and they recommend that it is placed slightly fore
or aft of the middle so that it is not evenly spaced. Presumably to avoid a resonance.

I would think whatever general practise is advisable with TTs using two bearings would apply to the 700 (but maybe not ?).

On the Avro for example there are two bearings and the placement is supposed to be 219mm from one end and
194mm from the other end.

The Robbe Futuras have a bunch of bearings and once again they recommend uneven spacings, like 140mm
then 160mm then 150mm etc.

I suppose this principle may apply less if the TT is a really large diameter or something, the presumption
being that it wouldn't be able to flex as easily, but that's just a guess.

[Ross Northcott]

I added a second bearing to my 600 and got a vibrations when they were evenly spaced, after i changed it to make them not equall the vibration stoped straight away.

[xygax]

It is typical when fitting tourque tube bearings to ensure the spaceing distances are all different.

The reason is to stop any vibrations at spot frequencys adding and making the vibration worse. therefore for a twin bearing tourque tube with asymetrical distances the three resonant frequences are all different and hence if one section just happens to beat with the engine for some reason it cant amplify as its only a part of the tube that will vibrate at that frequency.

As Ross said his stoped vibrating when we moved a bearing.


Steve

[J-S-Q]

It is typical when fitting tourque tube bearings to ensure the spaceing distances are all different.

The reason is to stop any vibrations at spot frequencys adding and making the vibration worse. therefore for a twin bearing tourque tube with asymetrical distances the three resonant frequences are all different and hence if one section just happens to beat with the engine for some reason it cant amplify as its only a part of the tube that will vibrate at that frequency.

As Ross said his stoped vibrating when we moved a bearing.


Steve

Yes, that's exactly what I thought so I wondered why they would have them evenly spaced in the manual.

[xygax]

Maybe there is some delibrate design flaw that makes the body and tail resonate at the same frequency that is tuned out bu having the tourqe tube fatuige itself by becoming a counterbalance and opposing the resonance......

I doubt it the manual is most likly just wrong

Steve

[millerman]

i run all mine on an offset and have no tail probs at all

[J-S-Q]

i run all mine on an offset and have no tail probs at all

Ok, I reckon I'll offset them. I suppose it's not important how I offset them? I'm just aiming for the 3 gaps to all be different, right?

[millerman]

as it goes i run 3 on the outrage 90 as i had vibrations along the boom that sorted it

Ok, I reckon I'll offset them. I suppose it's not important how I offset them? I'm just aiming for the 3 gaps to all be different, right?

pretty much what i did

[Eckchaz]

For some reason I always chuck an extra bearing in compared to the manual.. I dont have them exactly equally spaced but random thereabouts and never had any problems

[millerman]

For some reason I always chuck an extra bearing in compared to the manual.. I dont have them exactly equally spaced but random thereabouts and never had any problems

great minds eddie LOL

[GravityKills]

BTW, completely off-topic but maybe not: What apparently makes quite a difference in tail performance is an additional push rod guidance ring.
I use four of them on the 700. Maybe it's just superstition, though.

[millerman]

BTW, completely off-topic but maybe not: What apparently makes quite a difference in tail performance is an additional push rod guidance ring.
I use four of them on the 700. Maybe it's just superstition, though.

Oh might have to test that then


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