Confusion about DWG 19 firewall penetrations

[IowaRV9Dreamer]

I need to drill holes for throttle and mixture cables for my 9A. I’m using an RSA fuel servo, with throttle on the left and mixture on the right. It will be vertical on the bottom of what was an O-320. I see there are a few locations called out on the DWG 19 inset. I read the firewall forward kit instructions which say a vertically mounted Bendix servo should be treated as a carb.

For the throttle cable, the drawing says to use hole A (in the bumpout) for a 9A with an O-320. It also lists hole B (low, a little right of center) for a 7A with an O-320. Why the big difference? The fuselages are identical, same engine….

Similarly for the mixture cable: hole D (high/left) for 9A/O-320 vs. hole E (low/right) for 7A/O-320. Why the difference?

I like the idea of up high because all of the low spots go through the heat deflection cover which seems like a pain. Thanks for any insight. I’m only asking because I’ve found that when I don’t understand why the plans are a certain way, I often end up choosing the poor path…

 

[PilotjohnS]

Welcome to the OLD Vans way of doing things. I took the locations with a grain of salt. in fact, I had to cover up one of my firewall holes with a piece of aluminum and proseal, another with a bolt and nut that does nothing.

All my cable penetrations are at the bottom of the firewall relief (bucket) for the oil filter. They sit on top of the bottom shelf, are secured with cable clamps on the flat bottom of the "bucket" just before the cables leave the plane of the firewall.

 

[Ralph Inkster]

Note that the cable hole locations change if you have upgraded to the new style nose gear & mount.

 

[PaulvS]

It may help to hold off drilling the holes until the engine is installed and the proposed locations can be physically checked for interference, kinks etc. This is what I'm doing; the positions are marked on the firewall per the plans (there is some confusion there) but I won't drill them until the carburettor and exhaust are fitted and I can trial the control cable paths.

 

[johnbright]

Note that the cable hole locations change if you have upgraded to the new style nose gear & mount.

Right, we're talking about the RV-7, 7A, 9, 9A Firewall Bulkhead F-601 drawing 19.

For the A models, rigid nose mount is rev 4 of 12/01, elastomer mount starts at rev 5 of 04/30/2019 which AFAIK is the latest rev.

One needs to specify the rev in order to talk about these drawings because holes have moved and designators have changed (A, B, C, etc).

 

[IowaRV9Dreamer]

One needs to specify the rev in order to talk about these drawings because holes have moved and designators have changed (A, B, C, etc).

Thanks John! You are right. I'd been looking at a PDF of R5. I also have a PDF of R4, and my kit came with a paper copy of R3. It looks like Vans has been revising this over time, and the latest revision presumably works with any nose gear as the holes don't have a callout for NG type.

That being said, I may just go with the Pilotjohns approach above and put throttle & mixture through the oil filter bump out. Prob seems like it can stay in the Vans specified locations as it doesn't seem to have moved in all the revisions.

I still don't know why Van's moved the cables between 7A and 9A with the same engine.

 

[Draker]

Note that the cable hole locations change if you have upgraded to the new style nose gear & mount.

Yup. I drilled my control cable firewall passthrough holes before the new style nose gear was available, and then decided to go with that style. The routing for the throttle cable was... let's say very problematic.

 

[PaulvS]

Welcome to the OLD Vans way of doing things. I took the locations with a grain of salt. in fact, I had to cover up one of my firewall holes with a piece of aluminum and proseal, another with a bolt and nut that does nothing.

All my cable penetrations are at the bottom of the firewall relief (bucket) for the oil filter. They sit on top of the bottom shelf, are secured with cable clamps on the flat bottom of the "bucket" just before the cables leave the plane of the firewall.

That location on recess sounds interesting. Do the cables need to curve much FWF to reach the throttle/mixture bracket? And does your engine have carb or FI?

 

[PilotjohnS]

That location on recess sounds interesting. Do the cables need to curve much FWF to reach the throttle/mixture bracket? And does your engine have carb or FI?

No I think it actually works out well.

 

[PaulvS]

No I think it actually works out well.

That's what I am thinking also, it would avoid going through the lower cover plate, will need to check on my installation that is O-320 with carburetor.

 

[PilotjohnS]

That's what I am thinking also, it would avoid going through the lower cover plate, will need to check on my installation that is O-320 with carburetor.

There is an S bend in the cable, but it seems the bend needs to be either firewall forward or in the cockpi; I chose firewall forward. The S bend firewall forward also provides stress relief for the “wet dog shake”