My dilemma came down to whether I was going to install the autopilot or not...and I thought I would have to make the decision prior to closing up the wings. I assumed that I would need access to the front of the wing spars in order to attach the required hardware -- whether that was nutplates, mounting brackets, whatever. I thought that I might get squeezed into spending a bunch of cash now just to have the servo(s) regardless.
I contacted TruTrak and they sent me an information packet. It didn't have any more information than their web site provides, but it did come with installation diagrams. I've scanned them in and made them available here for other builders who are in the same decision predicament, so you can see what the installation entails.
From what it looks like, no additional attachment hardware is necessary other than the bolts for the aileron bellcrank brackets. It appears that those bolts end up becoming dual-purpose. I suppose it's possible you have to fabricate the brackets yourself, but that's no sweat. At least the spar doesn't require any modifications, and more importantly, it looks like you can install this sucker easily through the inspection hole on the underside of the wing after the wing is already completed. I assume you'd need to remove the bellcrank in order to set up the servo pushrod attachment, but at least nothing structural has to change or be added. Still, I could be wrong. But I'm running with these assumptions and not bothering with the autopilot until after the fact.
I scanned in the TruTrak installation diagrams for the RV-7 in case anybody finds them helpful.
NEW! Laird Owens, builder/owner of RV-6 N515L, is installing a DigiTrak autopilot and he sent me these two pictures of the parts:
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Update: August 23, 2002 Laird completed his DigiTrak installation and gave me these photos to post. FYI, this was done on an RV-6, which has a different bellcrank than the RV-7.
Update: December 15, 2002 Tom Prokop, another local builder of an RV-6 that has been flying for a while, emailed me a photo of his DigiTrak installation. Tom wrote:
Dan,
I thought you might be interested in this picture of my installation of the Digitrak auto pilot servo in my -6. Trutrak has a fuselage mount which I am using.
The thought of running 7 wires out to the wing tip thru a 1/2 inch pvc conduit (installed during my wing construction) did not appeal to me. I made the harness for the a/p on the bench and will install
it next week (my panel overlay is being remade by Werner Berry) when i reinstall my panel. The only concern I have with the fuselage servo mount is the possibility of "pitch bump" but the folks at
Trutrak did not think it would be a problem and after installing the servo, I don't think it will be either. At full up or down elevator there would be pitch bump but how often do have the a/p on
and full up or down? Never I would hope. Anyway, the Digitraks are now shipping with GPS course following at no extra charge. I'll let you know how it works when I'm flying again.
Tom (Redtail)
And here's Tom's installation photo:
Update: January 6, 2003 Tom Prokop completed his installation, and here's what he wrote:
Thought some would be interested in my experience installing and
using the Trutrak Flight Systems Digitrak Auto Pilot. A picture of
the servo installation is on Dan's www.rvproject.com web site in the
Trutrak section. Much has been said about how nice the components
are of this system. At $1795 it is more expensive than the NavAid
system. The control head can be ordered with either a 2 1/4 or 3 1/8
face plate. Although I think the 2 1/4 looks nicer, I had a 3 1/8"
hole (removed a g meter). The instructions and wiring diagrams were
easy to understand and the fuselage mount (supplied with the A/P,
just tell them when you order) fit perfectly and was easy and
straight forward to install. Because I mounted the servo under the
pilot side floor, I was able to make the wiring harness on the bench
(6' 5" long). I used 20 gua wire for the entire harness (7 wires to
the servo). Only one wire from the GPS was required for heading
info. I have a Garmin GNC 250 XL and it was pin 19 (RS 232 out). As
Laird had gone through this first, his comments were very useful and
appreciated. After enabling the RS 232 on the 250 XL in the set up
screen, I followed the set up instructions and then went flying. The
initial flight was straight forward and I followed the set up
procedure including the magnetometer set up. It was cool watching the
A/P fly the airplane to the four compass headings during the internal
compass set up. In the set up screens, my values are as follows:
screen #1 is 5, #2 is 7, and #3 is 96 (baud rate, set up on the
ground).
This thing is so cool. After more than a couple of test flights I
can say with confidence everything works perfectly. It will track a
GPS course with no drifting at all. On one test I was flying 90 deg
to the GPS track and engaged the A/P. It turned and made a 45 deg
intercept angle and then shallowed the intercept as we got closer,
flew slightly thru the course, and then turned back, after about 1
minute of small course changes it was locked on. John Hughes and I
flew to Boulder City NV for an extended test and the Digitrak worked
flawlessly never varying off course. One note however, as you fly
these RV's the fuel usage causes a trim change in the roll axis.
After about 20 minutes or so I could see the A/P making constant
adjustments. Turning off the A/P momentarily, retrimming and
reengaging the A/P did the trick. I could have let it fight the out
of trim condition, it still held the course perfectly, but chose to
re trim. Did I say how much I love this thing? Now I will be able
to read the chart AND stay on heading, just ask the guys who followed
me to Oshkosh this summer how good I was at that!
Redtail
Here are the scans of the TruTrak installation diagrams for the RV-7:
