Need help on the Hawk Pro>>>>>>

[traeside]

Help!! I built this Hawk Pro for my friend but all he had was regular servos (not digital) and an old mechanical gyro. I balanced the blades and set the tracking and yet still right as it gets light on the skids it starts shaking like when you start spooling up with the blades too loose. I am thinking that the Gyro has something to do with it as I am having to fight the tail back and forth. One other thing he has an old Futaba radio that is a lot harder to program then the new ones. The bird seems to react the correct direction to the swash but I was wondering if there is something that is going to surprise me if I get it in the air. Short of getting all new stuff any suggestions? :dontknow
PS: I told him to go get a 401 combo to start with.

[Ray Fernandez]

Help!! I built this Hawk Pro for my friend but all he had was regular servos (not digital) and an old mechanical gyro. I balanced the blades and set the tracking and yet still right as it gets light on the skids it starts shaking like when you start spooling up with the blades too loose. I am thinking that the Gyro has something to do with it as I am having to fight the tail back and forth. One other thing he has an old Futaba radio that is a lot harder to program then the new ones. The bird seems to react the correct direction to the swash but I was wondering if there is something that is going to surprise me if I get it in the air. Short of getting all new stuff any suggestions? :dontknow
PS: I told him to go get a 401 combo to start with.

First of, you are mentioning that the heli starts to shake as you power up. That really has nothing to do with the gyro. It has to do with something that is unbalanced. Usually, when you power up and the heli spins abruptly, that is an indication of the gyro being reversed. Check to see if you measurements on the flybar are equal. You might also have a low headspeed and will need to get the RPMs up.

BTW, what model is the "old" Futaba gyro? Also, how old is the heli. No mention if it was new or used. If "used", had it been in a crash? Are mainshaft and spindle straight?

[traeside]

Sorry,
It was a new build and after the clutch is fully engaged it spins smooth for a few hundred more RPM but then as it starts to lift off it starts vibrating. I just thought of it maybe there is to much slop in the dampeners. The main shaft is true the fathering shaft is good. I am within .001 grams on the blades but it took a ton of tape to get them there. And yes I checked the COG on the blades and weighted them there. The gyro is an old Futaba 125? I will look again. It was reversed but it is going the right way now. This all good info thanks!

[RAV50]

Check your rotor head hub.

I was helping a fellow with his a couple of weeks ago and we had a similar problem. On closer inspection we found the hub was defective (molded a bit off center). First time I had seen it, on many that I had helped in the past.

No problem, as it was exchanged at N/C by our LHS. He said that Century always made good on any defects for him.

[traeside]

Okay I will check that thanks. Luckily I live about 20 miles from Century so I can take it there if all else fail. Okay so I rest up all the linkage per JustChris’s link he sent me. I was surprised how different they were from the book. But it got me to almost the same place but the aileron bell cranks on either side of the collective arm. Are not level at all I would half to shorten the aileron links up by maybe 15mm. I will have another look tonight as I see the instructions now say to remove both the aileron links and the collective link. Either way it goes as it is now it still sounds like the head is spinning over 2500 RPM and it is still on the ground. I am now at 3.5 positive pitch at 50% stick and the throttle is ½ open. What blades are people using? I would like to get a second set to eliminate that.
Thanks again for all the input.

[RAV50]

If you have your collective pitch set properly and the heli does not lift at a high rotor speed, that usually means that the two washer/spacers on the end of the feathering spindles are not mounted in the proper order.

The smaller one should go inside to ride against the INNER race of the bearing and the larger one on the outside of it to ride against the locknut.

If these are not mounted properly, as the head comes up to speed, the centrifugal force will cause the large washer to bind against the OUTER race of the bearing and your servo will not be able to rotate the blade grip enough to give adequate collective pitch to lift the heli.

But if you are only 20 miles from Century, I would take it to them to take a look at it all.

[Ray Fernandez]

Either way it goes as it is now it still sounds like the head is spinning over 2500 RPM and it is still on the ground. I am now at 3.5 positive pitch at 50% stick and the throttle is ½ open.

Usually, your pitch should be +6 at mid stick (50%). Are you using a tachometer to check the head speed?

[JustPlaneChris]

Usually, your pitch should be +6 at mid stick (50%). Hmm.... I guess there are two schools of thought there. I personally do not like my helis configured that way (mid-stick hover) since it causes you to essentially "re-learn" your stick positioning when you progress to flying in idle-up. IMO, it's preferable to set zero pitch at mid-stick in all flight modes, that way you can seamlessly switch between them in flight (and mentally too). I guess it's whatever you get used to, or whether or not you ever plan to fly in idle up. :)

For what it's worth, my Hawk (Toki 40) needs well under half throttle at mid-stick to keep the RPMs reasonable at zero pitch.

[Ray Fernandez]

Hmm.... I guess there are two schools of thought there. I personally do not like my helis configured that way (mid-stick hover) since it causes you to essentially "re-learn" your stick positioning when you progress to flying in idle-up. IMO, it's preferable to set zero pitch at mid-stick in all flight modes, that way you can seamlessly switch between them in flight (and mentally too). I guess it's whatever you get used to, or whether or not you ever plan to fly in idle up.

I am in agreement with what you say, however, I am speaking on behalf of the newbies out there who are still learning and who probably will not be doing Idle Up flying. I for one, flew for a very long time using the "half stick" learning curve and became comfortable transitioning to 3/4 stick flying later in my advancement of flying RC helis.

[traeside]

Good thought on the washers I will check them as that was assembled when I got the heli from him. I have set my others at 0 degrees at 50% but I do like to lower the throttle curve so that for a rookie like me it is less touchy. For my Belt CP there is a dial on the remote so I can change the pitch while flying if it gets windy. I tried the hawk at 0 now at 3.5 so my LHS said maybe my head speed is to low. I don’t yet have a RPM gauge but what head speed should I be running just incase someone at the field has one? I did pick up the 401 combo last night so I will put that in to eliminate that and make me feel better.
Thanks again for all the help guys.

[JustPlaneChris]

1700-1800 rpm (or less) should be plenty for just tooling around and training.

[RAV50]

I like to set the pitch curves for beginners as follows:

Normal

-2/0/2/5/8 ... and match the throttle curve to maintain a 1550 to 1650 head speed (This will usually turn out to be about 15/45/60/65/85 on a more powerful engine like the OS37 or Toki 40, depending on fuel, muffler and altitude. This makes the collective and cyclic soft enough to not be intimidating, yet to give a hover at about 3/4 stick

Trainer Idle-Up (for learning FF)

-3/-1/0/5/9 with the throttle at about 40/45/50/65/90 - This should give a similar rotor speed that will not bleed off on descent at bottom stick, leaving the motor at a good RPM to stop it.

So now he is learning from the start to hover at 3/4 stick, without having too twitchy a collective or cyclic.

Then, when ready for more mild aerobatics, and to get him used to a higher rotor speed (e.g. 1850 to 1950) then the idle up can be set:

-3/-1.5/0/4.5/10 and the throttle points set to maintain the rotor speed desired. Probably 40/55/60/70/100

From there it will be an easy step toa 3D set up of -10/-4.5/0/+4.5/+10, again with the throttle curve points adjusted properly (about 100/70/60/70/100)

Note: At the higher rotor speed the gyro gain will probably have to be lowered to keep the tail from wagging an to maintain rotor speed in aerobatics, 40% or so of aileron to throttle and elevator to throttle mix will have to be used along with a bit (15% or so) of right rudder to throttle mix.

Just another way to skin the same cat.:-)

[traeside]

Okay,
I have not had time to go in and check the feathering shaft or get the linkage set. I am still at -2 0 +3.5 +5.5 +7.5 but that will all change once I get the aileron links set. I still cant see how I can get the aileron bell cranks on either side of the collective arms level and be anywhere near the measurements I have seen. What I did get done is I mounted the 401 and the digital rudder servo I also put a new battery on her and with that if nothing else I feel much better. is it going to be okay if I have to shorten the aileron links up by as much as 20mm?

[traeside]

Okay I lowered the throttle and then I realized I forgot the instructions so I did not want to adjust much more but it did make sure the swash was level threw the travel and it was so I started it up and was kneeling next to her looking at the swash to see if it was going to rock all over when it started to dance as someone had said it might be the servos failing. As I throttled up to where I thought it would start dancing I looked down and she was an inch off the ground! I quickly set her back down as being on the side of her with my head at swash level is not thee place I want to be when testing a new model. I got behind her gassed her up she took off very smooth and wanted to climb I only took her up to about 8 feet as there was about 15 MPH crosswind and I was having trouble telling if it was the wind or sub trim that was off. Also with the digital tail servo and analog on the elevator and aileron it felt wired I had to be slow and easy with my left thumb and quick and over compensating with my right. So I will head back to the LHS for 2 more digital servos. I was thinking Hitec to save him some money. Any suggestions?
Thank you all again for all your help.:thumbup:

[traeside]

Okay I put 3 JR digitals in and lowered the throttle curve and she now lifts off at around 1250 RPM (sure sound faster) but she hovers stable and seems to react good. I gave her back to her rightful owner and he seems happy. I told him I was not sure this was the best heli for a beginner but he is willing to try so I handed over to him with a copy of Radd's rotary flight school and watched him on his first tank.
Thanks again for all your help!

[RAV50]

Traeside,

It will make a wonderful trainer for him. That 1250 head speed seems very low. Is that what you tached?

[Fboss38]

I agree, mine w/OS37 tachs at 1800 at center stick and Tcurve is set for 0 at mid stick.