warlock1174

My Feedback: (23)

DELETE!!!

flmgrip

My Feedback: (2)

what is your problem?

warlock1174

My Feedback: (23)

As I said in the original post, it is just hanging up. I can find no reason why... The whole rotor head assembly moves as smooth as silk, but when it is actually in the air, it will hang up in fore/aft flight. Like, if I am backing up to myself, and I put some forward to it, it'll keep coming backward for another couple of seconds before it will grab and go forward. Not only is this frustrating, but possibly dangerous.

flmgrip

My Feedback: (2)

ahh... now we're talking, just didn't know what you meant...

i had the same problem once, found the problem to be a STRIPPED servo gear !
is any part of the swashplate binding at full cyclic input? check that with a full rotation of the head...

that's all i can think of this moment...

warlock1174

My Feedback: (23)

I have tried checking if there is binding in the swashplate. It does seem that at full fore/aft cyclic the inner race that the shaft bearing is set in will rub a little on the main shaft. I am unsure of whether this may be an issue, but it seems that when i have it sitting in front of me with the engine off that even at this full fore/aft position, the servo will still effectively move the swashplate back into position. Also, when the engine is off, and I apply full fore/aft and let go of the stick, the servo as well as the swashplate will resume it's normal centered position. However, if I bring the rpm's up to almost-hover speed and perform the same maneuver, the servo/swashplate will not resume to it's center position. I am so completely baffled by this. The poor tech support guys at heli-world are so sick of me they probably wish I would shove this helicopter up my....... well... you get it...

Lift

My Feedback: (1)

Warlock1174,
What you are describing to me sounds like a weak servo. What are you using?

On the bench there is no resistance to change like there would be when the machine is spooled up. So, you need to test that servo under load.

You can do this by placing the blades parallel with the boom. Now, hold the flybar control arms with your hand and give FORE cyclic. Is there enough torque to make it difficult to stall? I don't mean that you to have strong arm it but it should put up a decent fight.

Now, this time we want to check the strength of the servo as it returns to center. Give FORE cyclic again without resistance but hold it there with the transmitter stick. Hold the flybar control arm again and let the transmitter stick return to center. Is there enough torque to make it dificult to stall? It shoud feel the same as the prior test.

Ok, you now have a baseline as to what that servo is putting out. Now compare it to the Aileron servo by placing the flybar parallel with the boom and repeating the same tests.

If the servo is weak you will notice a slight difference. Not necessarily night and day difference but a slight difference.

This tip is assuming that as you said there is no binding and you can move the elevator assembly easily. I hope you meant by taking the link of the elev servo arm and manually checking for binding. It shoud move freely with NO break-away feel.

Hope this helps. Let us know.

BimmerM3

My Feedback: (6)

It sounds to me like it could be stripped servo gears as mentioned earlier. Hold the elevator servo arm with your fingers while giving fore/aft inputs with the radio. Hold it tight enough to cause resistance. If a gear is stripped, you'll feel it slip.

rotordoc

My first choice would be that of some of the others here.I would lean towards the stripped tooth out of one of the servo gears theory. The "load check" suggested by Lift should also show this up, but the real test would be to change servos and see if the problem repeats itself.

Ditto for a bad servo pot. One with a dead spot in it.

Another thing that can cause "pitch change sticking" is if you have installed the washers improperly when installing the blade grips in the feathering spindle. Be sure that you have the two washers that fit between the nut and the feathering spindle in the proper sequence. The smaller M4x 10 unit fits to the inside against the radial bearing and the larger M4X12 unit will fit on the ouside of this one against the nut. If they are installed in reverse in either blade grip, it can cause the outer bearing to lock up at speed (the centrifugal force of rotation is now pulling outward at a few 100 pounds and the inner race will be pushed outward while the outer race is held inward by the larger washer). But usually this is felt more in the collective then in cyclic pitch changes.

warlock1174

My Feedback: (23)

Ok guys, thanks for the tips, but, I had this problem BEFORE I replaced the servo. It has a brand new servo in it, and I have tested all of the servos connected to the rotor head very thoroughly.... If the flybar paddles were misaligned would that cause any problems? and how would I know?

BimmerM3

My Feedback: (6)

Do you have a lot of weight on the flybar? It almost sounds as if there is some sort of gyroscopic thing happening. I know I'm reaching here, but I'm stumped. I have a Hawk IV and it doesn't behave like that.

If I understand correctly, when the head it rotating at flying speed and you give an aft cyclic command and then release it, there is a delay before the head returns to a nuetral position. Have you actually observed this? I mean can you look at the heli on the ground, give a cyclic command and then actually witness the swashplate not return to level after you release the stick?

The natural tendancy of the rotor disk will be to return to a nuetral state. A force must be applied to move it (fore, aft or side to side). When the force is removed, it will "want" to nuetralize. But something is preventing it from doing that.

Are the flybar paddles square to each other? One paddle being offset might cause this. Have you checked your setup against the instructions? Could a linkage rod be on wrong? Are your batteries putting out enough juice? Have you checked them?

Lift

My Feedback: (1)

You will know if the paddles are not aligned by looking at the flybar "disk" to see if it is running parallel to the main rotor "disk".

If not, one side of the disk will be higher than the other. Also, refer to manual to verify the position of the mixing arms when the swashplate is at 0 degrees.

I don't know, but I am just throwing this out as well. These are the typical demons that we all have with helis. The must be found and stamped out. Hang in there.

warlock1174

My Feedback: (23)

Yeah, I've tried strangling the living S**T out of the demons in the heli, bet they're still there.

DavidH

Does the Hawk have thrust bearings in the rotor head? If it does there is a good possibility they are installed wrong . Then when the head starts turning RPM and in forward or aft flight the blades are locked into the pitch command they have been given and can't rotate. Do the blades have a tendency to go out of track when this happens?
This may not be your problem at all, but would be worth checking.

David

warlock1174

My Feedback: (23)

It is very interesting that you mention this. (Try to picture this all if you can....) On the main rotor head block, there are recesses on each side for the rubber dampers. I was having this problem with the heli hanging up in fore/aft, so I replaced the rubber dampers (which were looking pretty worn out) with bearings. This did not seem to help, or worsen the problem..... So, I am completely befuddled....

warlock1174

My Feedback: (23)

You can follow this link to see what I am talking about as far as the rubber dampers are concerned...

http://centuryheli.com/manuals/cn100xHawk4/step1_2.gif

DavidH

Warlock,
The rubber damperners are there for a reason. You should not replace them with ball bearings but with the rubber damperners. If you put ballbearings in place of the rubber damperners you have very dangerous setup now. The blade axle is not able to float in the head block now and could bend or break and the blades come flying and hit you or someone.
I looked at the drawings for the blade grips for the Hawk 4 and it does not have any thrust bearings, so having them put in backwards is not your problem. But you could be turning the head at too high a RPM and binding up the radial bearings. This can be a problem also.
I would think that with the ball bearings in place of the rubber dampeners that the heli oscilates really bad unless your turning a high speed in a hover.

David

syclic

WOW!!! Ignorance is bliss!!!

Thanks DavidH , you saved me a lot of typing. Please check out my post early on. Similar to the thrust bearing issue is the washer size issue......have you checked that?????

Before we go any further and waste any more of our time.....is there any other "changes of your own" from stock configuration that we have not been informed about????

warlock1174

My Feedback: (23)

Actually folks, I ASKED the fellows at heli-world about the degrading condition of the rubber dampers, and they advised me that I could use the same bearings (two for each side) that are used for the tail section, etc... in the rotor head... I thought this sounded weird too, but heck, I thought they know what they are talking about...

Lift

My Feedback: (1)

I am speculating here but I would be willing to bet that Century was advising you to use those washers on the spindle between the grips and the dampeners. This is probably to tighten up the dampening. Not, in side the headblock.

I couldn't imagine them advising you to put them in the head because that would lock the spindle in place and provide an EXTREMELY rigid dampening. If should I say NO dampening!

warlock1174

My Feedback: (23)

Forgive me for sounding condescending, but I must point out the obvious. They told me to substitute 2 bearings in each side of the headblock for the rubber dampers... Period.

bhelisN6

Hello Warklock1174,

Let me say that Century apologizes for misleading you into thinking that you should ever replace rubber dampers with anything else but rubber dampers.

We thank you for raising the various issues and situations where you have encountered problems, as Century does address the concern of the general flying public who use and have confidence in our products.

In this rather unique situation, Bryan was wrong to suggest using ball bearings however, I have four years experience in helicopter customer support. At times in the past, I have tried very hard to trouble shoot the problem over the telephone, only to find out that it was virtually impossible to find the source of the problem. Unfortunately in the exchange of the discussion between you and Brian a misunderstanding occurred and both Brian and you agreed at some level that bearings would fix the problem. If given the chance to relax and think clearly, I am sure logic should have won over. It did not, a bad recommendation was made and Century is interjecting at this point.

Moving on, absolutely re-install the rubber dampers and make sure that the smooth side of the washer is against the rubber. I have flown Hawks since they were first released, and I change the rubber dampers once per year.

Regarding your elevator control situation. I like many have never experienced a hesitation in the elevator servo. I agree with the other posts that the usual cause is stripped servo gears, however, I took a call once (a long professionally frustrating week of the same customer with a collective servo that seemed to hesitate) where I was unable to find or recommend a solution to satisfy the customer.

The actual problem was that he mixed servo brands on his Hawk, and accidentally attached a Hitec servo horn to his futaba servo. A simple and honest mistake but the slight difference in the size of the servo output splines was enough to cause this hesitation. On the bench, the servo worked flawlessly, even under finger load but in the air, when descending the horn would slip.

I do not think this applies to your situation as in your post you have checked the servo.

Our recommendations are:
1. Change the elevator servo, use a ball bearing servo with a minimum of 40oz of torque.
2. Exchange the aileron and elevator servo, if the problem shifts to the aileron control, then you need to change the servo. If the problem remains then we need to look deeper into your problem.
3. Slight rubbing of the swashplate against the main shaft indicates you can reduce the elevator ATV slightly. BTW, with a high head speed this much cyclic will easily tumble the helicopter, I would be surprised you use this much through in forward flight.

I sincerely hope that you find the problem that you are having and get on with having fun in this great hobby of ours.

Andrew Schoenherr