Logo 400 SE spec analysis

[egaus]

Hi,

I've a attached a spec analysis screenshot showing my spikes well under the yellow line, maxing between 336 and 350.

This is where I'm at after rebuilding the tail with a carbon tail box and new gears (discovered a few chipped/worn teeth).

How does this look? I'm hoping it is good to go.

e

[MrMel]

Yes, that is so low it's no issue on those spikes.

[egaus]

Thanks, that's great.

Now I do it again this time with the tail hub/grip/blades on. Everything looks good until the spoolup just ends and I'm at max headspeed. I think this is too high headspeed because the tail blades make a noise and the spikes are labeled at like 16,000 RPM. Absent the main blades is it possible I am doing this test with unrealistic (too high) headspeed?

I spent time correctly balancing the blades/cg.

Thanks!

e

[egaus]

Did more tests, narrowed it down to the tail blades, wildly out of balance. Edge 72mm. Guess I need to get a better method/device for properly balancing tail blades.

e

[clayboy]

had a set of edge 72mm that balanced perfect but was drilled wonky so the blades did not track

[egaus]

Yeah, I'm wondering if mine are like that too! I'm just going to use another set of new blades, see how it goes. Either way, these blades as delivered were unacceptable and contributed to my crash. Ultimately I was at fault for not checking.

e

[egaus]

I bought some new Radix 72mm tail blades, balanced them. Put them on a new rotor hub with new blade grips. Balanced the whole assembly. I double checked mesh of main gear to front tail gear and moved it out just a little as it was likely a little tight, checked alignment.

Same result. Tail blades off, no vibes. Tail blades on, extreme (4000 @ ~200hz).

This after installing all new tail parts - shaft, bearings. New front tail gear/bearings.

I've read all the Logo 400 tail vibe threads (there's many) and tried to come up with some solutions, but I'm out of ideas at this time.

If any of you have a suggestion, I'd love to hear it.

Thanks,

e

[MrMel]

Tailblades ENHANCE the vibes, not needed to be the cause.

Most common? Gearmesh or that tail gear is mounted at an angle (tailboom)

[egaus]

I've been striving to get that mesh and angle perfect and from what I can see, it is. Not too snug, not too loose. I'm using a digital bevel box. I took the head off the main shaft, measured the main shaft to be 0 degrees. The boom is at 89.8 and the main gear is at 89.8, give or take a tenth of a degree.

Here's the spec with tail blades on:

[MrMel]

Cracked tail case if you using plastic tail case is a common one if you have flown with vibes, hairline fracture just in front of the lever-armholder.

[egaus]

Thanks. I'm running a new CF tail box.

Now I am thinking of tearing the whole thing down, getting some new frames and tail block as it is getting difficult to align the tail into the frames because the eight holes that hold the tail in a getting worn in, the tail seems to settle into the same place each time I adjust it.

Do you think there are any other parts I have not mentioned that should be replaced? Everything on the main shaft appears to be doing fine, perhaps the one-way? This crash I am rebuilding from was not very hard.

e

[egaus]

I will add that it is possible to also gauge the backlash/gear mesh from both the top and bottom by eye using a small flashlight. I would assume if the gear mesh looks the same from both the top and bottom that the angle of alignment would be in the ballpark, this is confirmed by digital level.

e

[egaus]

I've started disassembling the helicopter more fully to examine some of the other parts.

Two things I've found:

1. The top main shaft bearing is a little notchy, not completely smooth. I'm replacing this.
2. The lower main shaft bearing is installed into the motor plate facing down. The instructions for the 400SE do not ever show this bearing and on one page it looks like the silver motor mount should be installed so the bearing is placed into the hole from the top, then on page 7 the illustration looks completely different, making it look like the bearing is installed from the bottom into a black plastic motor mount. I don't think it really makes a difference, should I be concerned about which direction this bearing is fitted into the mount? When the shaft is all tightened up, there's no way it is coming out.

That's all I've found, the swash is nice and smooth, the main shaft is true.

Could this single bad bearing be the cause of my problems? (maybe)

One more thing, does the shaft collar go on with the ridge facing up or down? I had it facing down.

Thanks,

e

[Jays200]

Ridge on collar should face down towards the bearing. The ridge is designed to sit against the inner race of the bearing.

The bearing in the silver motor mount should face down so that when you put the main shaft retaining collar on it is effectively clamping the main shaft against the two bearings with the collar and one way bearing, preventing any possible axial movement of the main shaft.

In theory, if you don't have the bearings facing out from the centre of the main shaft, there could be a chance of the bearings coming out of their holders.

As for notchy bearings, I replace them without giving them a second thought. They're cheap.

Spectrum analyser will usually indicated where the vibe is and then I "test" suspect bearings by putting in a shaft and side loading using my hand and you will feel if it's bad. Compare the same bearing to a new one using this process and there will be an obvious difference if one is worn.

Yes it is highly likely one "bad" bearing can cause issues with Vbar and vibes.

[egaus]

Sweet. Thanks, Jays. Sounds like I had the build right, but that bearing went bad. I can't see anything else that would prevent me from getting rid of the vibes as far as parts replacement goes, so once I get the replacement bearing(s) I'll give it another go. Rebuilt the tail assembly, everything looked good. Double checked the orientation of the thrust bearings and all looked good. Tail assembly is perfect, boom is new, hopefully I can make some improvement on my next spec analysis.

e

[egaus]

Here's the method I've used to get the tail on the Logo 400 seated just right into the frames.

You will need:

Logo 400 with tail sitting loose in the frames (barely tighten the 8 M3x12 screws)
6 cell battery
deck of cards
digital bevel box

1) Place the helicopter on a level surface.
2) Place the battery directly under the vertical tail fin.
3) Zero out the bevel box on the main shaft (remove head)
4) Place bevel box on boom.
5) Add cards a few at a time on top of the battery until they just begin to make contact with the tail fin.
6) Continue adding cards with slight down pressure using your hand on the boom until the bevel box reads 90 degrees.
7) Check gear mesh between front tail pulley and main gear, adjust if necessary - use a flashlight from the top you can see this.
8) Tighten the 8 screws while keeping slight downward pressure on the boom with your hand.
9) Bevel box should read 90 degrees. Voila.
10) Check bottom and top gear mesh by eye with flashlight to check that they appear the same. You can use the strip of paper through the mesh method to adjust backlash as well.

That's the method I've been using. I check the bevel box on the main shaft, 0 degrees, the boom at 90, the top of the motor at 90 and the underside of the main gear at 90. You should be able to get all those within .1 degree using this method.

Hope someone finds this to be useful.

e

[Bullfrog98]

Good idea to use the playing cards, I never thought of doing that.

Getting my tail boom at 90 degrees normally involves a combination of blind luck and bruit force.

I'll give your method a try soon enough as i want to swap my Logo 10 (560mm) boom on my 400 for a Logo 14 (620mm) one so I can run 523mm Edge blades on it. Only thing stopping me at the moment is the fact that my current boom is so perfectly set up I don't want to touch it.

[egaus]

So that's how I got my tail adjusted. I don't think my vibe issue is related to this because the measurements I have made read straight up perfect numbers using a digital bevel box as described above. The mesh is not tight and not loose, it's right where it should be.

I've replaced main shaft bearings, main gear, pinion gear, front tail assembly - complete including bearings, pulley, pin, block.

I replaced the boom and bought a new CF tail box. New tail output shaft. New pitch slider. New tail blades balanced on the hub. I have built two separate tail assemblies (hub/grips/blades) and have tested both. Same result. Mad vibes at final RPM, HS = 2100 using Readyheli headspeed calc with calibrated throttle.

Attached are two screen shots - 1 with complete tail assembly, one with no tail assembly.

MrMel has indicated to me that adding the tail assembly amplifies vibes that may have been present without the tail assembly. My screen shots seem to confirm this. That spike is nasty. Of course, putting on the tail assembly could also introduce its own vibes if not balanced or assembled correctly. I've gone over this multiple times.

I am hoping someone can suggest where I should go from here. I'm out of ideas.

I've built a Logo 600 which flies beautifully, no vibration issues. I took the tail off of it and put it on the 400 (with shorter blades) - same result.

I am no expert, but I know my way around my models pretty well. I've built and rebuilt several and they all fly great. I thought this one was flying great until it flew itself into the ground due to an apparent unknown (was running Express) vibration problem. Funny how I got like 5 great flights out of it and then it went down. User error for sure.

Thanks to anyone that can offer me a path that leads to my 400SE flying again!

e

[Bullfrog98]

All i can suggest is putting some tape on the one blade and spooling it up on the analyser and checking the vibes.

If the vibes are worse then put the tape on the other blade and try again.

It's a bit of a slow trial and error way of doing it, but by adjusting the amount of tape on the trouble blade you should be able to reduce the vibes significantly or at least zero in on the problem.

[egaus]

Thanks BF. I'll give it a try. Got the assembly balanced on a magnetic prop balancer with a piece of tape, but I can try moving it around I guess.

Glad you liked my tail setting method with the cards! Makes that chore super easy.

e