REFLECTOR: Auto pilot challenges

Sun Nov 18 11:36:38 CST 2007

Al,

Let me know when its "take it out on Chuck" day and I'll make sure I'm out of town.  :-)    The $1000 invoice is interesting and very odd.  A lot of times, I figure vendors add 50% to my bill just for having to put up with me, but a bill that big seems pretty high for a nice guy like you.  :-) !!!!

There must be a disconnect or something on the charge as its been my personal experience that TT is at the way-low end of aggressiveness for billing for maintenance, support or on general principles.  Like GRT, sometimes its kind of hard to get a bill.

Al, I had no idea you were so suseptible to sales pitches.....I think the pitch about "going back to straight and level at approach speeds" if you happen to fall asleep during base leg was followed by "the Velocity will dog fight with the best of them."   I still laugh myself silly whenever I think of that one!!!

So, if you think you may have a little weakness for pitches, be sure to delete those emails from Nigeria before reading!!!!!

Chuck

-----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of Al Gietzen
Sent: Sunday, November 18, 2007 12:24 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Auto pilot challenges

Subject: Re: REFLECTOR: Auto pilot challenges

Come on; Chuck, yesterday was my 'take it out on TruTrak' day. Now you want me to justify it:-)? (Remember, I had just opened the bill for $1000 for the servo I had already returned).

Interesting observations, but I'm curious...why do you care about the drag on either the ailerons or elevator on the ground. 

I don't really.  When I first installed the servo, and felt the drag, it seemed a little nonsensical to have made special effort to get everything aligned and tight so there was very little drag, or play; and then connect a servo that added a bunch of drag. 

.  When the A/P is disengaged in the air, I doubt that the the drag from the servo is even noticeable compared to air forces on the elevator and ailerons.

Before changing from the "C" to the "B" servo, I found that is was definitely noticeable at pattern speeds; and especially for the small corrections on very short final.  Now with the stronger roll trim springs and "B" servo, I don't know. Of course the control forces required are now higher, but I'm getting used to that. I'm sure partly it was having flown for over 40 hours without the servo connected, and getting used to the very light control forces.  I just gave me a better "feel" for the airplane at low speeds.

As far as putting the aircraft into a roll and letting go of the controls and expecting the plane to go back to level (and maybe I have my wires crossed) but I thought in a roll, with no input to the controls, the plane will stay in a roll, yes?  

OK; you must not have gotten the full Velocity sales pitch:-). Paraphrasing; "At speeds above about 120 you put it into a bank and it stays there; but at pattern speeds, if you get crooked, you let go of the stick at it returns to straight and level.  That's why it's an incredibly stable IFR platform, etc. etc."  (At least that's what I was told back in the mid 90's before I bought my kit).  I believed it, and I found that it was true - well; sort of. Once I connected the servo; at approach speeds the controls did not return to neutral, and it wasn't true. 

The lateral control issues you cite sounds like either one of two things, 1) you need to tweak the "lat act" activity a little or, 2) check to see if your servo is hooked to the cable or directly to the ailerons. 

I'm expecting we can that figured out. It is true that I have the servo connected to the bellcrank at the back of the keel.  When initially installed, I had essentially zero 'play' between there and the ailerons (I used full diameter bolts, etc.).  I reasoned that was the best environment in which to install the servo, and that connecting it to one aileron simply doubled the play to the other - which may not matter. I haven't checked the play in the system since, and it could be a factor.

Thanks,

Al

 -----Original Message-----
From: reflector-bounces at tvbf.org [mailto:reflector-bounces at tvbf.org]On Behalf Of Al Gietzen
Sent: Saturday, November 17, 2007 8:20 PM
To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Auto pilot challenges

Subtitle: Me and My TruTrak

Back in about 2000 I bought an S-Tec S-30. The servos were already installed when in 2001 my project ran into about a 2-year delay.  When I got things going again I re-designed the panel around the use of GRT EFIS.  The S-Tec worked off analog input, and the EFIS systems are totally in the digital age.  It would have cost many hundreds of additional bucks for the converter, and meanwhile TruTrak came with the digital age AP at a very reasonable price.  Decision: Sell S-Tec, buy Trutrak; have money in my pocket. I went with single axis Pictorial Pilot as a starter.

The S-Tec servos have clutches that release entirely when the unit is not active - zero drag.  When I got the TruTrak servo (C-version) I was sure something was seriously wrong because the stepping motor had no clutch, and had serious drag even when not engaged.  When installing my control system, I had made sure there was very little drag in the aileron system; now I had a servo that added serious drag, so bad that stock roll trim springs were meaningless and could not overcome the drag.  OK, it turned out there was a gear mesh problem, and TT replaced the servo.  Now the drag was maybe 20% less but still many times the drag in the system without it connected.  I was assured by TT that it wouldn't be a problem in flight conditions; and whatever, they would make it right.

Fast forward - 2006.  I left the servo disconnected through the Phase 1 testing.  When I let go of the stick, controls returned to neutral.  That was nice, particularly at pattern speeds.  I then connected the servo.  Major difference.  Push it into a roll at pattern speeds and let go; it would not return to neutral control. Otherwise the AP seemed to work fine coupled with the GRT EFIS.

I told TT that it was unacceptable.  They told me to put in stronger roll trim springs, and they would replace the "C" servo with a "B" servo - smaller and less drag. I found some suitable springs with roughly 3 times the spring rate, and the "B" servo has less drag; so I'm not delighted but it's OK.  I returned the "C" servo, and got the delivery confirmation about 10 days ago

Following their suggested procedure, I had the "activity" level set at 3 or 4.  In flying a flight plan I found that it seemed to track Ok, but near a waypoint it wandered quite a lot.  A higher level setting seemed to help that.  But I find now that it will slowly wander from the course; and then make a fairly aggressive correction back toward the course, then a nice transition back onto course; then repeat.  I will discuss with TT about what action to take.

Yesterday I received a bill from TruTrak for $1000.00 pending return of the defective unit.

The Trio system looks r-e-a-l-l-y good to me right now.  Their servo has a clutch release.

YMMV,

Al

To: 'Velocity Aircraft Owners and Builders list'
Subject: Re: REFLECTOR: Auto pilot challenges

Is anyone using the the TT autopilot with a different set up (other than GRT and the 480)?  Is the response the same?  

How about the Trio Avionics A/P in a Velocity?  Is the experience similar to that of the TT autopilot?  Thanks

Regards,

Jorge Bujanda
Velocity XL FG 

Palmdale, CA
Website:  http://members.dslextreme.com/users/jbujanda/

"Make your best case... not the best case."
"Spare the noise... convince through silence."

                                                                         JB

Subject: Re: REFLECTOR: Auto pilot challenges

On the GRT EFIS A/P settings, I set all of the gain values to "1".  

The correct setting on the A/P is for "Vert Act" to be set to 2 or 3 in most instances.  One gets into the setup mode on the A/P by pushing and holding the right button I believe it is (if that doesn't work, then it is the left button :-) )--for the circular A/P...I'm not sure which button if you have the radio stack version.

After holding the right button and the menu items come up, push "next" until you see Vert Act pop up, then try it at 2 or 3.  No airplane will fly correctly at a setting of "0" and a large setting of  4 or above usually results in pretty aggressive altitude hunting.

Even with my old settings, the A/P flew the plane straight and level very well--it was just in the turns or turbulence that it started having Fundamentalist behavior.

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