Heli wobbles during flight
 

I have a Falcon 40 heli which I've been using for flight practice and I'm having a problem. The heli has developed a terrible wobble motion which can be observed as soon as any throttle is applied. I recently crashed so I've done some work including leveling the swashplate, adjusting the flybar and paddles and I've got new and balanced blades. The main shaft doesn't look bent but I think I'll order a new one anyways since I've crashed this heli at least four times now. I don't know what else to check. Does anyone know why it's doing this? I've provided a video below.

[youtube]http://www.youtube.com/watch?v=rSRh4SQfQRE[/youtube]

RE: Heli wobbles during flight
 

looks like it might have a bent main shaft or a feathering shaft. you should take them out and roll them on a flat surface, that way you can see if one of them are out of round. if so, replace it
i'm kinda new to heli's, but that's my guess. hope it helps

RE: Heli wobbles during flight
 

Dude - I just went through that on my falcon 40. I had what I call a hard landing, not a crash, and then the same wobble. I checked the blades for balance (on a digital scale), I replaced the main shaft (it wasn't bent but if I take it out I put a new one in). I checked and double checked everything. The paddles were level, the flybar was straight and centered (same distance from the rotor shaft to each paddle). I could not see any damage to the mainframe. These are all things to check and fix.

Out of desperation and just to proove they weren't damaged I replaced the blades and bingo - the wobble was gone.

The old blades were not damaged in any way that I could see, they both weighed exactly the same, the cg on both blades was no more than a 16th inch different if that much, and I swear they look almost new. And they did not strike the ground in that hard landing. Blades are cheap - try a new set.

RE: Heli wobbles during flight
 

It is pretty much a given to replace the main shaft on a crash. It takes soo little to bend it just enough to wobble.

RE: Heli wobbles during flight
 

As a general rule I agree. But I've crashed the falcon more times than I can count over 2 years (including smacking a rain gutter and dropping 10 to 12 feet onto cement, then straightening the paddles and going back in the air) and never had to replace it. And it didn't appear to be bent this time, I've saved it as a backup.

The falcon is just flat out a tank and doesn't suffer damage like most other helis do.

RE: Heli wobbles during flight
 

I'd say replace the main shaft and the spindle/feathering shaft. IMO they are the two big things that will cause a really bad wobble. Try a set of blades like karlik said too.

RE: Heli wobbles during flight
 

Thanks for all the speedy replies. I took off the main shaft today and noticed that it was bent right where it meets the rotor hub. I also noticed that the main drive gear is torqued. I've ordered replacements and I'll let you all know if that fixes everything.

RE: Heli wobbles during flight
 

Overly tight blade grips have caused this for me. Just thought I'd bring it up.

RE: Heli wobbles during flight
 

Don't any of you know how to balance paddles and blades? Get a long hollow cf tube(30") and attatch small hooks, xmas tree bulb hooks work on smaller blades. No other way is as accurate to weigh a set of blades. With the hooks in place check the balance of the device. Next drilla smallhole in it's center point and push a xmas tree bulb hook through it. This wire will be wrapped around something solid, get creative. Now take the blades anlay themalong side each other as they lay on another rod. If one tip is heavier markit. Now weigh them on your new cf scale. One will likely be heavier, even in new blades!Now ya gotta think a little about how to change the tip weights and overall weights. Take the lighter one and spray paint on the bottom, for light adjustments, or sand the heavier onetill they match. It's great to have evenly weighted blades but having the weight in the right places has a huge effect too. If ya add all the weight to the tip and the blades spool up, that tiny bit of weight will get surprisingly large. Ya gotta get real good at balancing paddles and blades if ya fly a chopper.

RE: Heli wobbles during flight
 

DanMN, I have my blades loose enough to allow for self correction on spin-up.

GuitarPlayer, I balanced my blades and paddles before I attached them and I used a digital caliper to adjust the flybar to make sure it is perfectly centered. Everything that can be adjusted is adjusted and double checked on this heli as of today.

RE: Heli wobbles during flight
 

What the heck is "self correction?" Hey your' the one standing in front of it when it spins up. Don't try and convince me. Loose grips WILLNOT change the weight of a blade!!!! They will make for some sloppy pitch angles!!! My birds do not shake at all at any RPM. I would hate to be around a chopper as it blows apart near me. Do you know what the tip speed of a blade is at takeoff? It changes with the length of the blade with realation to its length, it's called angular velocity. Here's the formulas;



http://www.engineeringtoolbox.com/mo...las-d_941.html

RE: Heli wobbles during flight
 

Here's probably the easiest to understand explanation of tip velocity.

http://www.lcrc.org/stu22.htm

RE: Heli wobbles during flight
 

Ummm - everybody who knows the falcon 40 is a fixed pitch raise your hand.

RE: Heli wobbles during flight
 

Pitch is of no concern here. And any one who knows those blade can still cut right through the softer parts of your body raise you bloody stump. I'm done here.

RE: Heli wobbles during flight
 

Ok - but can somebody show me the feathering shaft in the exploded view? You can download it here - [link]http://www.walkera.com/en1/fileDown.jsp?file=%2Fcn%2Fupload%2Fpicture%2FZ2004 2604_ex.jpg&la=en[/link]

Loose grips won't change the pitch (create sloppy pitch) unless you have them real real loose. The suggested setup for the falcon varies depending on the source but basically they need to be loose enough to straighten themselves out as the head spins. This link gives some pretty good instructions for adjusting the blade grips at the bottom, as well as a few methods to balance the blades. [link]http://www.rc-airplane-world.com/rotor-blade-balancing.html[/link] but it sounds like you have them about right. And the "self correcting" he's referring to means once the head is spinning the blades will "self correct" so they are 90° to the flybar or in line with the grips.

I prefer this method of balancing - this does static and dynamic in a couple of real easy steps. I got a digital scale from harborfreight.com for 10 bucks. And use trim tape - trying to sand the bottom of these hard undercambered plastic blades would take forever and possibly affect flight characteristics.

"tip speed" of the falcon blades changes constantly - since the pitch is fixed the only thing that the throttle changes is the head speed. But I will agree that you don't want to get wacked by one of these blades, and common sense says to practice safety on all rc helis, not just the "big ones". If you develop bad habits with the falcon, or even a small coaxial, they will carry over to when you get that trex 600.

There is a dedicated thread to the falcon here - [link]http://www.rcuniverse.com/forum/m_4826535/tm.htm[/link] And just about every problem/malfuntion the falcon/walkera4/honeybee fp is capable of has been discussed there. There are also lots of mods that make it more reliable.

RE: Heli wobbles during flight
 

*Raises hand* :D

By "self-correction" I'm referring to leaving the blades just loose enough in the grips to allow for centrifugal force to pull the blades out and straight on throttle up. And did I not say, three times now, that I balanced my blades and paddles?

karlik, the Falcon 40 doesn't have a feathering shaft. Instead it has the two bearings on the rotor head core (parts 52 and 49).

I don't know how the discussion on pitch, angular velocity, tip speed and bloody stumps happened.

RE: Heli wobbles during flight
 

Yeah, I know. But someone flying the falcon may be a very new novice and suggesting a feathering shaft is a lot like like suggesting a muffler bearing. Good chance you could have spent hours trying to identify a part that doesn't exist. From there things just started moving away from our toylike fp world where we just fly it and have fun and into the world of cp where you need a working knowledge of algebra, geometry, calculus and all 4 major fields of physics. (I just passed the test on Bernoulli's work with fluid dynanmics. I figure at my current rate I'll be ready to fly a collective in about 12 years)

And like I said, bloody stumps isn't really out of line. Although the falcon only has a fraction of the head speed a cp has, it can still do some damage, and safety habits have to apply everywhere.

RE: Heli wobbles during flight
 

My comments were based on the knowledge of a person that thinks "loose grips" will solve a balance problem. All the "simple physics" I wrote about were meant to scare this guy into taking heli setup seriously.  No heli should ever wobble at any head speed. Mine don't.

RE: Heli wobbles during flight
 

blades should be able to rotate in their grips... its why they give you a foam blade holder for transport, because the blades do rotate. atleast on CP, I imagine its the same for FP though.

obviously you straighten the blades out before you spin it up, but you'll never straighten them to absolute perfection, ever... the centrifigal force of the spinning will do the job for him within the first few seconds, which is what he says about autocorrection.

I honestly have no clue what the balance thing is with the CF rod and christmas tree hooks... every guide Ive ever seen involves some sort of small shaft(I use a spare main shaft), some tape, and then a blade balancer or scale... spraypainting? that seems incredably complicated, they make and sell balancing/tracking tape for this exact purpose.

OP figured out the problem already though, little warm in the main shaft and gear, swap em out and he should be perfectily fine.

RE: Heli wobbles during flight
 

Normally that kind of wobble is caused by too low a head speed. Do you have a throttle curve or even just a hovering throttle adjustment on your TX ?

           Let us know how you get on

                                               cheers
                                                       john

RE: Heli wobbles during flight
 

again, my birds do not wobble at any head speed.  I make my own balancer and always balance my blades tip to hole. Think about that next time you balance a set of blades.

RE: Heli wobbles during flight
 

The ideal tightness for the blades in their grips is when you can move them freely by hand but they cannot fall under their own weight when the helicopter is tilted on it`s side.

                                    cheers
                                             john

RE: Heli wobbles during flight
 

At that tightness, pitch will not be accurate. At well over 125 mph, blades will straighten out at higher grip strength and give more accurate pitch, even in fixed pitch birds.

RE: Heli wobbles during flight
 

Your right, some helicopters dont do it at all no matter how much you slow them down, my x-cell pro`s are like that, but my 450 size furion will start to 'settle' into one when the battery drops off and my hirobo sceadu`s will 'settle' into the wobble with only a small reduction in throttle.my old concept 30`s were quite prone to it as well.

I`m sure he will post the results when he solves the problem.

cheers
john

RE: Heli wobbles during flight
 

My last reply. Your' blades are not properly balanced then.