Tail servo

[pilotmotor]

Here is a pic of my tail setup. It's very smooth mechanically but very hard to move push rod when up to speed. Thrust bearings are good. I flew it yesterday and it was much better , but still does not have the tail authority that my spectra g has . (both use the same furaba 9254 tail servo) With the smaller servo wheel and the loosing up of the grip links in can now piro in slow foward flight ,before it would do nothing with full left rudder input. It still needs more nose left travel

[Intrepid175]

Originally Posted by pilotmotor

Here is a pic of my tail setup. It's very smooth mechanically but very hard to move push rod when up to speed. Thrust bearings are good. I flew it yesterday and it was much better , but still does not have the tail authority that my spectra g has . (both use the same furaba 9254 tail servo) With the smaller servo wheel and the loosing up of the grip links in can now piro in slow foward flight ,before it would do nothing with full left rudder input. It still needs more nose left travel Attachment 674870

Ok, I don't see anything in the picture that looks out of place. Chris might see something I'm missing. I can't remember the last time I saw a belt drive on a Bergen. That's not your problem but it's interesting to see one again.

You say the Bergen and your Spectra G are running the same tail servo. Are they running the same gyro? The 401, while a great "bang for the buck" gyro in it's day, is still a relatively basic gyro. Please excuse me if I'm stating the obvious here but I'm just trying to cover the basics since I can't look at the bird directly with you. On top of the gyro are two rotary adjustment pots. Delay and Limit. The delay one you want at 0. The limit allows you to adjust the end points of the servo so that it's not binding at the extremes. One of the limitations to the 401 is that it doesn't allow you to set a separate end point adjustment for left and right tail. If you turn down one side, you'll be turning down the other side too by an equal amount. That makes it very important that the tail control linkages from the servo back be centered when everything is neutral. So if you're getting full right on the tail, mechanically, but very little left, then that neutral needs to be adjusted mechanically. Ideally, you'll want a servo arm that allows full mechanical throw in both directions with the limit adjuster on the gyro as close to 100% as possible. I hope this makes sense!

[pilotmotor]

Hi Steve
Yes this intrepid is old!! ive had very good luck with it over the years , about 15 or so . Never had a major crash with hundreds of flights . The worst incident was months ago when i lost the origonal tail servo and wiped out the tail after a pretty poor auto. This intrepid has a G23 and never even burped in flight , so not much auto skill!!
The gyro on the spectra is a spatran .The wheel on the spectra tail servo is the large round one and the ball is out at least 20mm-30mm from the center , a considerable (2-3 times )further than the bergen and the tail is insane on that thing!!!It also has 105mm tail blades compared to 95mm on the bergen???

I know about the delay and limit pots on the 401. The limit pot is adjusted correctly but delay pot is at about 10 or 15 . I wanted to see if it would make a difference in how hot the tail servo got . I did have it on zero though at one point. I will put it back to zero.
The throw is almost even on the tail , just about 3/16 or so less to the left and as you said the gyro cant adjust the limits differently on both sides.

What i have been doing with the pitch slider is to get the tail stable in a hover in rate mode , land it and see how far off center the slider is. Adjust the grip links in or out to get the slider centered and then adjust the push rod to center the servo wheel with the trim centered. The only problem with that is the the tail shaft is only so long and it dosent allow much nose left travel.

Just so you know many years ago my tail shaft broke in a hover and MR Bergen Senior said their was a problem with the original design tail shaft and sold me a shorter shaft and redesigned grips putting the links further out past the center line of the blade.

I think that is the problem because centrifical force wants to make the grips go nose right with lots of force. Most all other hellies ive seen have the links to the grips centered with the blades presumably so the forces to move the blades will be the same both ways. I still cant believe how hard it was to move that push rod by hand !!
Steve thanks again for you insight and tips i really appreciate your opinion.

[pilotmotor]

Steve
oddly enough while searching for something totally unrelated this is what i came across

https://www.helifreak.com/showthread...&highlight=tre

seems to explain exactly what im experiencing

[Intrepid175]

Originally Posted by pilotmotor

Steve
oddly enough while searching for something totally unrelated this is what i came across

https://www.helifreak.com/showthread...&highlight=tre

seems to explain exactly what im experiencing

Now that's impressive. Thanks for sharing. I guess for me, in your case, what's confusing is that your problem is so atypical for Bergen machines, at least by my experience. I've flown them a lot since the mid 90's and never had one display the symptoms you're having and most were using the 401/9254 combo. Something like that bolt setup, if you can find it, or make it yourself, will no doubt help. I wouldn't mind giving it a try on my birds even though I'm not having this issue.

I'm pretty sure that Chris Bergen has made some improvements in the blade grip designs since the one's your using were first made. In fact, the entire tail assembly from the gearbox out is different from what you're using, even if you didn't have the belt drive. Give him a call. Who knows.

Please let me know how it works out and best of luck with it.

Fly Safe,
Steve R.

[cbergen]

Of note is the angle of the arms on the tail blade grips, as you stated, all of the other manufacturers use a straight arm in the position.

We originally did as well. We then felt that since the tail blades do NOT stay at zero degrees of pitch for hover, we redesigned the tail grips to put in a certain amount of pitch so that in a neutral pitch slider and tail servo position, the tail rotor would hold the tail still.

It worked great with the TT drive systems. The belt drive systems however, just didn't give the same locked in feel.

Bearing in mind though, at the time, we considered belt drive systems were for "basic" models, and not intended for use in more abusive aerobatics besides the basic loops and rolls..

We also then felt that the angle we were using was a bit too much, so we redesigned them with a smaller angle (6 degrees), which is what we use today.

Here's a video explaining this newer design.

New Tail Blade Grips (1 min 55 sec)

Some things that "may" help in your bird, longer tail blades (if they'll clear the mains), and possibly upping the head speed. You haven't mentioned what head speed your running. If it's on the lower end of the recommendation, then your going to see less tail authority.

HTH,

[pilotmotor]

Ok Chris thanks for the insight. I'll see what i can do. What is your thoughts on the push rod forces and these thing called "Chinese weights". I linked a video in the previous reply.

[cbergen]

It's been awhile, and my memory ain't what it used to be, but I think we found that Chinese weights really didn't offer much improvement.

I sent one of our gearboxes and tail assy to one of the bigger proponents and testers of the Chinese weight systems and he could offer no improvements over our latest 6 degree offset blade grips.