This picture shows the throttle at the wide open position.
I then e-mailed a copy of my AutoCAD drawing to Ken Krueger at Van's to see if they would be willing to produce the bracket out of 4130 steel since I did not have the capability to do so myself. Ken was very helpful and he made up a few prototypes of the bracket and assigned it Van's Part Number VA-182.
When I received the bracket from Van's, I had to slightly increase the bend on the mixture tab to get the mixture all the way to full rich. The cable is almost at the limits of its adjustment in order to get to full rich but the alternative of moving the tab closer to the mixture arm would make the tab so long and flimsy that a gusset would have to be welded in to make it stiff enough. I was trying to avoid having to weld in the gusset to keep the cost down. I don't know if this bracket would work on any other engine/airframe combination.
I should also mention that the 45" mixture cable (#CT RED VMIXTURE 45) was too short to work in this installation, so I ordered the 49.5" one from Van's and it works okay (48" would probably be ideal but Van's doesn't stock that length).
This picture shows the throttle at the wide open position.
This picture shows the throttle at idle.
This picture shows the mixture at full rich. This was the most difficult position
to obtain. The cable is near the end of its adjustment range but there are still
about nine full threads engaged on the female rod end bearing. The Bendix servo
came with an offset mixture lever which interfered with the lower cowl. I replaced
this with the straight lever shown in these photos to avoid having to glass
in a "bump" on the side of the cowl air scoop to clear the mixture lever. The
part number of this straight mixture lever is Precision Airmotive #2522004 (list
price $118.16). It just clears the cowl but I still may have to glass in a small
"bump" on the side of the air scoop depending on how much the engine
moves on its rubber mounts. I also drilled a second hole where the cable attaches
to the mixture lever which is slightly closer to the pivot point in order to
better line-up with the cable and to make it easier to reach the full rich position.
This picture shows the mixture at idle cut-off. Also, note the 90 degree fuel
inlet fitting above the mixture lever. I replaced the straight fuel inlet fitting
that came with the servo with this 90 degree fitting to keep the fuel line from
getting too close to the exhaust. I didn't want to use a 90 degree hose end
here because the fuel pump end of the hose also required a 90 degree hose end.
It has been my experience that it is difficult to get two angled hose ends installed
at the correct angles with respect towards each other. The straight hose end
at the servo eliminates this hassle. However, the 90 degree inlet fitting was
not cheap (list price $214.93!!!). The part number of the fitting is Precision
Airmotive #2538044.
Here is a detailed view of the mixture tab. This photo was taken before the
bracket was primed and before I changed the fuel hoses to the integral firesleeve
type. There is not much room for error here. The cable comes close to the nose
gear support and the servo body itself. However, the clearance appears to be
adequate in this particular installation. I had to increase the bend angle of
the mixture tab from 40 to 50 degrees to get to full rich. I emailed this information
to Ken Krueger and he said that he would update the drawing to show the 50 degree
bend angle.
This photo shows my spring-loaded alternate air door. It bypasses the filter
and is screened to keep anything large from getting sucked into the engine.
Preliminary testing with a large shop-vac and a water manometer shows that I
will loose about 0.5 inch Hg. of manifold pressure with the air intake blocked
in addition to the loss of any ram effect. I will do further testing after the
first engine start. I would have liked a larger door but it wasn't possible
using Van's airbox design. While the engine may not develop full power if a
bird or heavy snow gets sucked into the air scoop, at least the engine won't
quit. The twin torsion springs used to keep the door closed are captured in
a way that prevents any metal from being ingested by the engine even if the
springs were to break. The airbox was mounted as far toward the right as possible
for three reasons:
1. To align the airbox with the cowl air scoop.
2. To insure that the airbox does not interfere with the mixture lever.
3. To leave as much room as possible for the alternate air door.
This link shows some additional pictures of the Alternate Air Door.