Hesitation During Pitch Reversal

[WhirlingBladesOfDeath]

Now that I'm trying to do some flips and rolls, I've noticed there is a pronounced hesitation in thrust when I change from negative to positive pitch (or vice versa). I really noticed it tonight when I tried my first tic-tocs. I'm trying not to slam the collective, but I inevitable ended up at full negative trying to get the heli to flop back over. I would hit full negative and you could hear a "womp WOMP". The first womp coincided with the pitch change, but then there was a momentary delay until all the "slop" was worked out and the blades bit in with the second WOMP. Does that make sense?

After a few of those, I tried just pumping the collective up and down while in a hover, and got the exact same thing transitioning to positive pitch. The heli would slow it's descent a bit (womp), pause, and then WOMP the blades would really bite in and thrust the heli back up.

After landing, I checked the head and there's no obvious problems (to my untrained eye). Otherwise the heli is flying fine. I had a minor crash my 3rd time out, and (knock on wood) no other ground events for the 50 or 60 flights since. Not sure if the problem has always been there, but didn't notice until now, or could something actually already be wearing out?

I'll be taking it to my LHS tomorrow and see if they can find anything.

Thanks,
Jason

[Finless]

Are you running woods or CF blades? Trust me this makes a difference... After running the new Align CF's for awhile now I had a crash and didnt have any blades other than the woods... YUCK! I cant believe I flew the woods that long but after flying good stiff CF blades there is a very noticable dead area going from positive to negative with the woods which is almost gone with the CFs.

Bob

[Jermo]

What's the cheapest decent CF blade out there? I recently tried a set of Radix CF mainblades and loved them but at $48 a pop I felt really bad when I broke them practicing inverted hovers.

[key]

Will plastic blade grips cause the same sort of hesitation?

[WhirlingBladesOfDeath]

Yea, I'm using the stock 325 woodies. But I'm finally starting to get over my fear of wreaking and slapping on some $50 blades would probably make me all nervous again!

Also forgot to mention, I'm using the 11T gear. I haven't measured my head speed yet (running 100-90-100 TC), but would bumping the head speed up with a 12T or 13T possibly help this problem? Now that I mention it, could that also be the reason I always end up banging the collective? Since I have a lower head speed, the blades don't make enough thrust at the -11 / +11 range?

Thanks,
Jason

[key]

When I ran a 11T with my 430L it seemed like I had no power.. I moved to the 13T and have been much happier, even running a 90-85-80-85-90 TC. In idle2 I run 100-98.5-95-98.5-100 and it's crazy, but the battery goes down fast like that.

[infinity005]

Originally Posted by Finless

Are you running woods or CF blades?

Finless, are these available anywhere? I searched online, no luck!

I think I found the part number.
AGNH325CFW

[WhirlingBladesOfDeath]

Are these the new Align CF blades?
http://www.helidirect.com/product_in...oducts_id=2819

[Funky]

Originally Posted by WhirlingBladesOfDeath

Are these the new Align CF blades?
http://www.helidirect.com/product_in...oducts_id=2819

Yes

[WhirlingBladesOfDeath]

Oh Boy, promise not to laugh?

I've still been having the hesitation problem. After tonight's couple of flights, I sat down to re-check everything, and install the 13 tooth gear and some Align carbon fiber blades. I didn't really thing either was the real problem, but figured what the heck. So I'm there admiring how perfectly my head is all lined up when I noticed....... my Gorilla paddles were on backwards!

Not sure what that would do, but could that be causing my problem? Other than the hesitation thing, the heli seems to fly just fine for me? I've been doing rolls, flips, tic tocs and tonight started doing my first loops!

I can't wait to try flying it tomorrow! I'm half tempted to put the woodies and 11T pinion back on and try with the paddles the right direction to isolate that one change. Agh, too late now anyways, I'll just fly it and see as it is now. :mrgreen:

I'll let you know....

Thanks,
Jason

[Y@nkee]

My flying buddy is complaining over his rex having that hesitation problem.But only going from positive to negative pitch, its ok the other way.
And we cant find anything wrong in his setup.
And his paddles is mounted the right way.
His rex is an XL with the same blades/motor setup that i have one my SE at about same headspeed, and i dont have that problem.

The difference between my and his heli is:
He ofc have the servos connected to swash via those #¤%&#* bellcranks(reason that i switched to the SE frame).

I got the 220mm flybar with lighter paddles, he got the stock XL flybar/paddles.But mine didnt do this with the stock XL flybar /paddles.

He got the plastic head, i got the alu head.Both got same dampening.

And i got HS65 servos, and he got HS56 servos.

Blades we are using : http://www.elefun.no/webshop/aspx/pr...kategoriID=128

My heli is flown quite a bit more so i got some more slop in the head than he got, maybe it could be links that is to thight?(even tho we find them nice and loose on his heli to)

[redgiki]

Check his collective pitch mixing arm. If he has had a hard crash, this arm gets cracks in it quite easily and they are tough to see without moving the arm by hand and looking for them.

Yep, I played that game. Major hesitation because the servo would move the arm, and the strain would open up the crack, then the plastic mixing arm would catch up and close the crack again. Very irritating until I got it sorted out, but it had similar behavior to what you describe. However, it would mostly just slow down the collective response, though in my case the way the crash was it would slow more negative to positive than the other way around.

[WhirlingBladesOfDeath]

Well it didn't make any difference really. Heli flew about the same, but maybe with slightly less bogging, which I attribute to the higher head speed more than the paddles.

About the cracked servo arm, that would only cause this problem on an XL, not a SE, right? If I had a cracked arm, wouldn't I get a bunch of interaction along with the hesitaion?

As close as I can tell, I get the exact same thing going positive to negative and vice versa.

Should I have someone "load" on my blades by hand while I cycle the collective to see if something is broken? I gotta get a video going so I can show you what it actually looks and sounds like.

Thanks,
Jason

[redgiki]

Yes, the cracked mixing arm only applies to the XL HDE. Another thing you may want to be aware of is that if you are descending into your own rotor wash, the turbulent air can result in a loss of lift for your blades. This is really common when you are doing a fast "elevator" descent with the wind and then attempt to push positive from negative. It takes a second to "bite" the air because you were flying into your own downwash.

A video would help to troubleshoot it, for sure.

[chevpro]

When your descending with negative pitch, is the wash not above the rotor blade??

[redgiki]

Originally Posted by chevpro

When your descending with negative pitch, is the wash not above the rotor blade??

http://en.wikipedia.org/wiki/Vortex_ring

Modest descent at positive, neutral, or slightly negative pitch can create this situation. We mostly see it in our helicopters as a bit of a stutter at the end of an elevator-style descent. Try it yourself... it only takes 3-6 feet to get out of the vortex ring with our T-Rex helicopters. Flying *with* the wind (not against it), initiate an elevator-style descent with a forward speed at approximately the ambient wind speed. About 10-20 feet above the ground, apply positive pitch. The bird will continue to descend, clawing at the sky through the turbulent air it just created in its descent, increasing the spin rate of the donut of air it just created until it "pops" and gets some clean air several feet of descent later.

BTW: I don't think this is what is happening with the top post. If you can easily reproduce the behavior every time regardless of wind direction or descent rate, and identical behavior by the same pilot in a very similar heli won't do it, it's only logical to assume that it's due to a difference between the two birds that you should isolate.

[WhirlingBladesOfDeath]

I'll play around with this some more tonight. I think it has happened at other times, but to be honest, I notice it mostly when I'm just hovering in front of me and pumping the collective. It very well could be what you're describing?

And now that I think about it, I don't get any hesitation if I'm in a stable hover and punch it, just pure zoooom.

I'll try to do some collective pumping while in FF, into the wind, and see if I notice it still.

Thanks!
Jason

[Longwing]

I have also had this ame problem;

I have also had this same problem it appears the servos are just a tad slower then the movement of the stick therefore you have a slow pitch change. Added with woodies the pitch changes are a quite slow. I’ve always associated it to slow servos. Running higher voltage might be the answer in the future for me. I am also running 56’s except for the tail. Anyone else have any ideas? They are not as fast as some of the vieos I've seen out ther of guys making very quick flips and tick tocks!!


Blake.