500 T/R question

[fling-wing_1]

We have a 4 bladed T/R on a 500D. I just had to install an overhauled 4 bladed T/R fork, two serviceable T/R hubs, and one new HTC T/R blade on the inboard hub. For what it's worth the three older blades are the old style with swept abrasion strips.

So today we installed the inner hub, attached the MicroVib just back from calibration and ran up the aircraft. The initial reading was 1.5 ips just at flight idle, after a couple moves per the computer the ips were up to almost 3.8 ips. A few more moves showed the computer just couldn't figure out the moves. I pulled the horizontal just in case it might be causing a problem. We didn't dare run up to 70% due to excessive ips.

I moved shims from one side of the hub to the other and ignored the computer making moves off the chart. I was able to get ips down to .45 at 70% but the moves are still irratic, one small move can make the ips jump from .4 up to .8 with a small weight change.

I need some ideas as I'm running out and putting way too many starts on the engine.

[RVDT]

Is the IPS "doubling" and the plot going through the centre at each change. That normally indicates that you have no centre axis i.e. something is loose.

TRGB bearings, trunnion bush (straps will move), elastomerics etc etc

To prove a point do you have an arbor shaft with a counterweight you can put in the hub and put it on some knife edges. Going back to steam days but it does work and saves a lot of starts. Normally gets you to about .3 or less.

You are obviously aware of the vagaries of the D/E and the horizontal "damper".

[Hughes500]

Never had a 4 blades tr as they are not as effective as 2 blades but had a similar problem on a 2 bladed one. The answer was the elastomeric fork. The bearings where bonded into the fork are not symetrical. We ended up with feeler gagues and common sense( dont beileve the manual) to put the hub into the middle of the fork not the middle between the bearings. Having spent 2 days with engineers ( I am the operator) I pointed out the hub didnt look like it was in the middle, put hub in middle, 5 runs job done. Also take off the whole T tail when you do it

[skidbiter2]

I flew a 4 blade E for a while, while I never had to do this (and my memory could be failing me), I am sure I was told, if you did a lot of work at the tail end of things, you would leave off 1 set of blades and balance up the other set first, then put the other blades on and start again.
Apparently it made it a lot easier.
Now as I said, I could be WAY off track, but thought I would mention it.

[500e]

Got to be balanced first in pairs , then as a set of 4, rear /nearest to boom first pair, at 1700rpm 80% I think, then when both OK at this setting at 2000 rpm at 103%. the rpm and maybe the rpm is not accurate to a 100 or so only what I remember reading in the book some time ago (not much interest to me as we only have 2 blades I understand Europeans go for 4 blades due to a noise tax) but rpm critical. blades have to be centreral but don't forget the delta hinge offset
Also check the weight static of the HTC blade against the other 3 you may as well start with them within a gram or 2 of each other, would bet that's why you could not get to 60% to start with.

[22painter]

Hi have just fitted and balanced 2 new blades into a 4 bladed system
using the Aces pro balancer system After removing balance washers from the pitch change links that had been prevoisly fitted and only using tip weights it came good in 3 runs, Without the need to balance in pairs

[fling-wing_1]

Finished up the T/R balance this afternoon. Thanks to everyone for the suggestions! :ok:

Turns out it was the vertical stab going into resonance with the T/R. I made two runs this morning with some success then on the third run the ips went from .7 up to almost 4.0 in a few seconds. I looked back at the stab and saw it start shaking and go to almost a blur as the ips went up. Pulled the stab off and had no problems from then on. I had originally thought the stab was just shaking in response to the T/R vibe, I never considered it might be contributing to it. Funny things these beasties :cool:

Should have started out with all four blades installed as I was able to pull all the P/C weight off the inner set after I installed the outer set. Ended up with no P/C weight and minimal tip weights. Don't know what it is about that vertical stab but it must match up with the frequency of the four bladed system. After all was said and done it's less than .1 and no vertical or horizontal shake from flight idle all the way to 103%.

[mfriskel]

Check your part numbers and see how they stack up against HMI-2

(38) The 369D21640−501, −503, −505, −507 tail rotor blades are two−way interchangeable with the 369D21613 tail rotor blades in sets of two only.
The 369D21641−501, −503, −505, −507 tail rotor blades are two−way interchangeable with the 369D21615 tail rotor blades in sets of two only (installed on the same inboard or outboard hub).
The 369D21642−501, −503, −505, −507 tail rotor blades are two−way interchangeable with the 369D21606 tail rotor blades in sets of two only.