What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Cowling Dilema.

Drifteral

Active Member
After mounting the engine and mount to the firewall, I temp installed the cowling to the airframe and noticed there is about 1/2" from the front of the ring gear to the front edge of the cowling.

I noticed my cowling has the "CS" marked on it and i'm using a wood prop.
Is it normal to have to trim the back of the cowling to get the fit needed for the prop/spinner?

I was under the impression that most 6's needed a prop spacer of some kind.
 
You need to get one of these spacers from Saber Manufacturing:

(Click to enlarge)

Then install the prop and spinner. Once they are in place, you fit the cowl to them, starting with the top cowl. Set it slightly low (About an 1/8" should be fine) so that when the engine sags, it will fall in line.

This picture is me fitting the bottom cowl.

(Click to enlarge)

Good luck!
 
Last edited:
Bill thanks for the reply.

I should have done a better job of explaining. In my situation any kind of a spacer more than say 3/4" the cowling will be to short.

In starting to think i have the wrong cowling.

Al
 
Originally there were two cowls offered, one for constant speed props and one for fixed pitch. At that time the fixed pitch cowl used a 4” extension. At some point Van’s switched to a 2 1/4 inch extension for fixed pitch which allows for the same cowl to be used for either type of prop. If you have a very old cowl it could be the shorter constant speed version. However, it sounds like any extension would be an issue with your setup. Maybe the back of the cowl was trimmed incorrectly at some point.
 
After mounting the engine and mount to the firewall, I temp installed the cowling to the airframe and noticed there is about 1/2" from the front of the ring gear to the front edge of the cowling.

I noticed my cowling has the "CS" marked on it and i'm using a wood prop.
Is it normal to have to trim the back of the cowling to get the fit needed for the prop/spinner?

I was under the impression that most 6's needed a prop spacer of some kind.

Is this a new cowl installation that you are just starting?

The aft edge of the cowl always requires some amount of trimming.

A cowl labeled CS means it is the constant speed or fixed pitch version (VS fixed pitch only) and requires that a fixed pitch prop be installed using a
2 1/4" prop spacer. Until that is done, you wont be able to accurately evaluate the fit of the cowl.
 
I see no evidence that the cowl has been trimmed or otherwise modified.

With a 2 1/4" spacer the cowl will be 1 1/2" to short.

Right now if I remove approx. 1/2" from the firewall side of the cowl it will be even with the face of the ring gear.

Maybe that's the way it's supposed to be. I don't have a problem with trimming the cowl to fit and also not having to use a prop spacer.

The only concern I have would be with clearance inside to cowl such as starter, alt and exhaust. So far it looks like there are no problems with the starter but I don't have an alternator or exhaust yet.
 
I see no evidence that the cowl has been trimmed or otherwise modified.

With a 2 1/4" spacer the cowl will be 1 1/2" to short.

Right now if I remove approx. 1/2" from the firewall side of the cowl it will be even with the face of the ring gear.

Maybe that's the way it's supposed to be. I don't have a problem with trimming the cowl to fit and also not having to use a prop spacer.

The only concern I have would be with clearance inside to cowl such as starter, alt and exhaust. So far it looks like there are no problems with the starter but I don't have an alternator or exhaust yet.

Your clearance concerns are valid, but your description of the mis fit makes no sense.

The original (non constant speed) cowl used a 4 inch thick prop extension vs the 2 1/4 that is used with the CS cowl. What you are seeing makes it sound like you either actually have a 4" extension or you fwd fuselage was built incorrectly (doesn't have the fwd tilt of the upper firewall).
 
Not using a spacer is not normal, either the cowl is too short or the engine mount is non standard, assuming you are using a lycoming 4 cylinder engine.
If you can make it work without a spacer go for it.
 
...... or you fwd fuselage was built incorrectly (doesn't have the fwd tilt of the upper firewall).

I wouldn't call it incorrect...:)

The original plans had the firewall with no slope in the upper area. I had to splice metal on my F-646 parts to get the slope.

F-646 was significantly redesigned in 1999 (R7 on Sheet 30).
 
Check your engine mount

Just a guess , but is there not two different lengths of engine mounts ? One that gives you a 8.5 ? firewall to isolator mount centers and the other is 11? off the firewall for the lighter 0-290/ 235 powered RV 6?s,,,, you may have the long one !
Scott may enlighten us on the history here !
 
I wouldn't call it incorrect...:)

The original plans had the firewall with no slope in the upper area. I had to splice metal on my F-646 parts to get the slope.

F-646 was significantly redesigned in 1999 (R7 on Sheet 30).

I am aware of that Gil, but I think you know what I mean.
 
Just a guess , but is there not two different lengths of engine mounts ? One that gives you a 8.5 ? firewall to isolator mount centers and the other is 11? off the firewall for the lighter 0-290/ 235 powered RV 6?s,,,, you may have the long one !
Scott may enlighten us on the history here !

There is, but the long one was only developed for use on an RV-7 with a light engine and prop. It would never be shipped with an RV-6 finish kit unless someone specifically did a special order for it.
 
I wouldn't call it incorrect...:)

The original plans had the firewall with no slope in the upper area. I had to splice metal on my F-646 parts to get the slope.

F-646 was significantly redesigned in 1999 (R7 on Sheet 30).

Gil, I think your on to something. both of my front ribs "F-646" have been spliced to make up for the front slope and the middle rib doesn't come close to the firewall.

I cant rule out that the cowling has been pre-trimmed. But when i purchased this "project" there was no engine mount or engine so whomever never would have known where to cut the cowling.

At this point I think the only option is to order an exhaust and alternator, check for clearance problems and finish installing the cowling.

I have a fair idea that mine is going to be known as the "short cowl" RV6A and will be just a bit different from the rest.

Guess that's why they call them Experimental.
 
There is, but the long one was only developed for use on an RV-7 with a light engine and prop. It would never be shipped with an RV-6 finish kit unless someone specifically did a special order for it.

Scott I think you and Gil both get a cookie. My conical engine mount is approx 13" from the firewall to engine.

Now it's all starting to make sense.

Al
 
Back
Top