700 woes!

[t-rex pedro]

OK gang, I need your help. My 700 is giving me the run around. Specs are:

YS91SR / Hatori SB19
Spartan / BLS 251
JR 8915's
Radix 690 mains / Align tails
30% Optifuel

The problem is the tail (or manifesting on the tail). During normal hovering and flight the tail wanders (indicating low gain). Go into fast backwards or a pie dish then the tail wags to the point it can physically be seen and heard (indicating a high gain figure). The fuel tank foams and there is a mini storm going on in there. I have tried tuning the engine but it makes no difference. At idle the whole airframe vibrates turning the skids into a bit of a blur but this could be normal with a 90? Also, the tail assembly sounds and feels 'ratchety' and rough when controlled by the servo but nice and smooth by hand.

The list of changes I have made to try get the tail locked in are:

New boom (last one was a little bent, dont ask!)
New torque tube
New tail output shaft and TT gear
New engine bearings
Cleaned and regreased tail assembly
Fitted spare tail hub and grips as last resort
Tried a 9256 tail servo in place of BLS251 - no difference
Tuning engine for optimum power - no difference
Complete new plumbing

Its really wierd. The tail isnt locked in and wags in any kind of sideways/backwards flight (regardless of gain value).

Any ideas guys? Could it be the motor? Do I need to balance the fan/clutch? Could it be the tail blades? Could it be the Spartan?

A few clubmates had a look over it today. ChrisB kindly flew it for me to get an idea of the problem but even he said it was a headscratcher!!!!

Thanks for any ideas.

[jamiem]

have you tried a different set of main blades? its always worth trying a known good set off a mates machine if possible. me and sacko have been chasing tail problems on his beam this past week, swapping most of my beam in to his and still not working. in the end it turned out to be vibes caused by the cack main blades is the starter shaft straight and all bearings in this area good?

[Aidi]

We were going to put my SAB Red Devils on it, but the vibration is pretty bad even at idle, so didnt go ahead with swapping blades.

Pete, with the amount of vibration happening at idle, i would really be inclined to drop the engine, and give it a real good check over. Somm'at really aint right with that much vibration at idle.

Aidi

[sacko]

have you tried a different set of main blades? its always worth trying a known good set off a mates machine if possible. me and sacko have been chasing tail problems on his beam this past week, swapping most of my beam in to his and still not working. in the end it turned out to be vibes caused by the cack main blades

Yup.. The tail was getting to the point where it was uncontrollable. Borrowed Jamies Radix and the tail is sorted

[t-rex pedro]

have you tried a different set of main blades? its always worth trying a known good set off a mates machine if possible. me and sacko have been chasing tail problems on his beam this past week, swapping most of my beam in to his and still not working. in the end it turned out to be vibes caused by the cack main blades is the starter shaft straight and all bearings in this area good?

As Aidi said we almost tried his blades but it really seems motor related. I swapped my Radix around in the grips just incase but made no difference. I've got a set of Align 690's I can try which is something else ticked off at the very least. Thanks Jamie.

[t-rex pedro]

Pete, with the amount of vibration happening at idle, i would really be inclined to drop the engine, and give it a real good check over. Somm'at really aint right with that much vibration at idle.

Its been in and out twice already mate and put back together with surgical-like precision!

[jamiem]

check all the bearings in the clutch stack. apart from the engine itself, its the only bit that will be moving at idle.

[Craig33]

I have seen that behavior in my trex600 when doing funnels. I put it down to the grips locking up under high rpm because it only happened when i changed to the redline and ran headspeed above 2200. Changed to quick tail grips and problem disappeared. LIke you i rebuilt the stock grips a fair few times but yet still shakey tail in funnels. I changed nothing other than a straight swap of the grips.

Drift in the hover on a spartan for me has always been wiring. As a test pull your gyro/tail servo wires as far away from anything else as possible just to see if it cures it.

Foaming on ys should be partially ignored until at half tank because the pressure pulses from the return line froth the fuel a bit when the tank is full.

[barney]

A few likely ones are..

No 1/ Busted boom stay. The little pins at each end can snap internally or pull through the tube after very little airtime..very common I might add. You need to really pull the boom firmly side to side and watch for the slightest movement at the boom stays ends..The plastic ends also compress after a little time and the bolts usually require nipped up or the boom end wanders in its own bolt hole.

Did you dial Indicate the Clutch stack as it could be 10 thou out?

Boom clamp although the bolts are seemingly tight, can it be twisted at all?

Set motor to standard settings as the YS is normally close to that..

Brian

[t-rex pedro]

I have seen that behavior in my trex600 when doing funnels. I put it down to the grips locking up under high rpm because it only happened when i changed to the redline and ran headspeed above 2200. Changed to quick tail grips and problem disappeared. LIke you i rebuilt the stock grips a fair few times but yet still shakey tail in funnels. I changed nothing other than a straight swap of the grips.

Drift in the hover on a spartan for me has always been wiring. As a test pull your gyro/tail servo wires as far away from anything else as possible just to see if it cures it.

Foaming on ys should be partially ignored until at half tank because the pressure pulses from the return line froth the fuel a bit when the tank is full.

Thanks Craig. A few things for me to try there. The gyro/servo wiring is seperate from the rest and there is a good amount of cable free at the gyro itself. It seems the wandering is the result of low gain but an increased gain increases the wag.

The tail grips could be the cause but then again I tried another set without success and clubmates run the plastics without issue.

Thanks for the suggestions.

[t-rex pedro]

A few likely ones are..

No 1/ Busted boom stay. The little pins at each end can snap internally or pull through the tube after very little airtime..very common I might add. You need to really pull the boom firmly side to side and watch for the slightest movement at the boom stays ends..The plastic ends also compress after a little time and the bolts usually require nipped up or the boom end wanders in its own bolt hole.

Did you dial Indicate the Clutch stack as it could be 10 thou out?

Boom clamp although the bolts are seemingly tight, can it be twisted at all?

Set motor to standard settings as the YS is normally close to that..

Brian

Thanks Brian. I'll check the boom stays.

I didnt dial indicate the clutch stack as I dont own one!!!!!!!! This could be the issue.

I have the motor set at std run-in settings with a few clicks to the lean to get it running with a cool backplate and good power.

[moonmanflyer]

I have seen that behavior in my trex600 when doing funnels. I put it down to the grips locking up under high rpm because it only happened when i changed to the redline and ran headspeed above 2200. Changed to quick tail grips and problem disappeared. LIke you i rebuilt the stock grips a fair few times but yet still shakey tail in funnels. I changed nothing other than a straight swap of the grips.

Drift in the hover on a spartan for me has always been wiring. As a test pull your gyro/tail servo wires as far away from anything else as possible just to see if it cures it.

Foaming on ys should be partially ignored until at half tank because the pressure pulses from the return line froth the fuel a bit when the tank is full.

My 600 was buzzing a bit in funnels today, mind you it was a bit blowy.
Also my spartan doesn't like strong winds at all, perfect in low winds but horrible today, was struggling quite a bit, yet the align gyro on my 600 was handling it fine bar the buzzing funnels

[ChrisB]

This certainly had me stumped today,i flew Aidis quickly and it was as smooth as silk in comparison.

To add to this my 700N also has a bit of a vibration very similar to Petes in fact but not so pronounced in flight but its certainly nothing like as smooth as Aidis was so a bit of an eye opener for me.

My gut feeling is that the fan/main hub etc is out of balance somehow as when its idling and you rev it you can hear/see/feel resonation in the airframe and at higher revs inflight it must be playing havoc.

I will also appreciate all input in this thread as i feel mine to a lesser degree has the same problem and always has.Mine has not been stripped in any way since new and all parts are original.

I also run the ys91 sr and get the severe storm in the tank.

[Craig33]

Thanks Craig. A few things for me to try there. The gyro/servo wiring is seperate from the rest and there is a good amount of cable free at the gyro itself. It seems the wandering is the result of low gain but an increased gain increases the wag.

The tail grips could be the cause but then again I tried another set without success and clubmates run the plastics without issue.

Thanks for the suggestions.

Like you i tried all the same things but still nothing fixed it except when i lowered the headspeed or changed out the grips. I always wondered why no-one else reported the same problem/fix but i couldnt think of anything else.

Just out of curisosity how many push rod guides do you have on the boom and are they equally spaced? I just wonder if the long push rod is picking up some natural harmonic when under the load seen in funnels.

Forgot to ask as well, when you say wandering you mean wagging back and forth or a constant one way drift?

[t-rex pedro]

Like you i tried all the same things but still nothing fixed it except when i lowered the headspeed or changed out the grips. I always wondered why no-one else reported the same problem/fix but i couldnt think of anything else.

Just out of curisosity how many push rod guides do you have on the boom and are they equally spaced? I just wonder if the long push rod is picking up some natural harmonic when under the load seen in funnels.

Forgot to ask as well, when you say wandering you mean wagging back and forth or a constant one way drift?

3 pushrod guides evenly spaced Craig. Maybe I'll add another.

The drift is a slow back and forth oscillation as if the gain is too low (as it probably is) and it also kicks out on punch outs etc. If I increase the gain, the wag gets worse in other tail first manouvers.