Vibration w/ higher H/S

[prototype3a]

I could use some help diagnosing this. My lepton is running 5s3700 Kora 15/14 and Jazz 80 and at 60% throttle it seems to fly ok but if I go above about 65% it starts to vibrate fairly violently. When I say vibrate I'm not just talking about the tail, I mean the entire helicopter. My bird has never been crashed and I'm using the MAH blades.

Thanks

[mudbogger2]

Something is likley to be bent or out of balance. Check the balance of the main blades, the head assembly and tail assembly. Check the mainshaft for straightness as well as the spindle. Next you may want to try a diffrent set of main blades.

I ran my lepton at over 3000 rpm and it was smooth as glass.

[Helder22]

I had the same problem when I ran the rpm up to about 3200+ by mistake. Its only at very high speeds though, and the vibration is very very bad. And theres nothing out of balance cause 3000 or under theres no hint of vibration.

[prototype3a]

Well I balanced my TR yesterday and that definately made the bird fly nicer but it didn't fix the problem. When at 100% throttle I tached it at 2880rpm so I don't think I'm anywhere near 3200. I just finished checking the main blades and they were spot on. I suppose I'll check the main shaft and feathering shafts just in case.

[TMoore]

I just finished checking the main blades and they were spot on.


How did you check the main blades?

TM

[prototype3a]

a razor blade to compare the CG's and a balancer to compare weights.

Doubt it'll fix it but I found a ball link in the head I aparrently put on backwards so it was quite a bit tighter than it should be.

[toyturbo]

Try switching the blades to the opposite grips. I have the same blades and got vibrations, switched the blades around and it was gone. For some reason, the blades have a sweet spot that you have to find with either grip.

[Helder22]

OK one more thing. The measure the distance between the hub and the grips on either side. I noticed that the rubber dampers are so tight on the spindle that it will actually hold the spindle more towards one blade than the other sometimes. Its just an itsy-bitsy difference but its more than enough to cause the vibration.

[TMoore]

Did you balance spanwise and chordwise.

I have two sets of MAH and there were deadnuts.

TM

[prototype3a]

I measured the grips and no issues there.

Just lengthwise. I don't have the patience for the other way. I found that the tight head link issue resolved some of the vibration. I got a pm from the original owner saying to check that (what I'm gonna call) the tail boom support block is not extremely tight. In checking this I found that it was broken. I CA'd it in the mean time. I'll see how she flies this afternoon.

I hope microheli, duzi or someone else will make a cnc version of this part as the design really leaves me scratching my head. Seems like a poor design and easy to break. It would have been better if they had made the "straps" that go around the boom the full width of the "block". I hope if they do cnc machine some, they'll machine a pair of grooves into it to accept a pair of o-rings that'll actually grab the boom and hold it tightly.

[CRAZYKEV]

OK one more thing. The measure the distance between the hub and the grips on either side. I noticed that the rubber dampers are so tight on the spindle that it will actually hold the spindle more towards one blade than the other sometimes. Its just an itsy-bitsy difference but its more than enough to cause the vibration.

I had the same problem with my grips being off to one side more. Check the distance from the grips to the hub. Mine was off enough that I could move the grip in and out a bit.

[prototype3a]

Well I think the broken tail boom support block was the cause. Boy does this bird fly nicely. Still kinda touchy on landings though.

[tday]

Yeah, this thing has some serious collective response. I ended up making my pitch curves slightly "expoed"--5% pitch on each side of middle and turned pitch expo smoothing on (DX7). Also, have a pretty low head speed normal for that purpose too.

Tom

[prototype3a]

Found that Helidirect has a CNC version for the HDX 500 so I think I'm gonna get it as it's only $3 more than the hirobo part. I'll let you guys know how it turns out when I get it.

[prototype3a]

Well it showed up and seems to be much higher quality than the *other* HDX parts. It has a hook on the bottom as a tail control rod support which I broke mostly off with a pair of pliers and then filed the rest off. Also you'll probably need new tail boom supports as the balls mount horizontally on this part. It grips the boom too tightly, causing vibration, so I inserted the black washers that are supposed to be used with the tail servo mount as spacers between the two halves then locktighted everything and then it flew nicely again. All in all I think this is a must have part for the lepton as the stock part breaks entirely too easily.

I thought up a new sort of "trick" during this. I scratched the anodizing or whatever on the boom right against the tail boom clamp so when ever I loosen the boom I can get back to the same belt tightness and such fairly easily. I suppose pictures might make this a little easier to understand and as such I may shoot a couple tomorrow evening.

Now if someone would just make a swashleveler like the one for the trex 450.

[CRAZYKEV]

:) I also scratch the tailboom so it can be lined up much easier.