Pictures Ram Air System

[Brian2034]

Okay, not looking to start the good/ bad ram air debate!
I’m interested in the system and would like to see photos showing the details of the system. My 1963 C doesn’t have it.

[PT20J]

Here’s a drawing from the M20J IPC. All it does is create a direct path from the front of the cowling into the air intake on the fuel injector servo with a butterfly valve to open and close it.

[Brian2034]

Thank you

I have that parts diagram for the J

Did the C have a similar setup?

 

[hammdo]

No, never really had ram air for the carb version.

-Don

[EricJ]

12 minutes ago, Brian2034 said:

Thank you

I have that parts diagram for the J

Did the C have a similar setup?

 

+1 that I think C models never had it.    It's a straight shot from the intake filter to the carb, so it probably isn't needed (i.e., you kinda already have ram air, and it's always filtered, which is good).

 

[Brian2034]

2 minutes ago, hammdo said:

No, never really had ram air for the carb version.

-Don

That would answer the question , why I couldn’t find any C model pictures of the ram air setup.

[Vance Harral]

The system is substantially different on the E and F models vs. the J, due to the different cowl.  A page from the parts manual and a picture of an M20F are attached below.  It's a little hard to follow the parts manual picture, so start with the picture of the actual airplane.  In that photo, the ram air port is the rectangular hole directly below the spinner and directly above the air filter.  The important thing to understand in the E/F models is that the fuel servo air intake is directly behind the ram air port, but somewhat above the air filter and the air box behind the filter.  Therefore, when air enters via the normal intake path, it passes through the air filter, then it must travel an S-shaped path through the air box to get to the fuel servo.  If the ram air door is opened, then not only is the air filter bypassed, but the incoming air also has a direct path to the induction system.  This is why ram air is somewhat effective in these models.

In the J model, the normal induction path is more efficient, hence less benefit from ram air.

 

[Brian2034]

2 minutes ago, EricJ said:

+1 that I think C models never had it.    It's a straight shot from the intake filter to the carb, so it probably isn't needed (i.e., you kinda already have ram air, and it's always filtered, which is good).

 

I was hoping for a ram air set-up with no air filter interference.

From my homebuilt side of aviation, the ram air without filter gives an additional inch of manifold pressure.

[Brian2034]

4 minutes ago, Vance Harral said:

The system is substantially different on the E and F models vs. the J, due to the different cowl.  A page from the parts manual and a picture of an M20F are attached below.  It's a little hard to follow the parts manual picture, so start with the picture of the actual airplane.  In that photo, the ram air port is the rectangular hole directly below the spinner and directly above the air filter.  The important thing to understand in the E/F models is that the fuel servo air intake is directly behind the ram air port, but somewhat above the air filter and the air box behind the filter.  Therefore, when air enters via the normal intake path, it passes through the air filter, then it must travel an S-shaped path through the air box to get to the fuel servo.  If the ram air door is opened, then not only is the air filter bypassed, but the incoming air also has a direct path to the induction system.  This is why ram air is somewhat effective in these models.

In the J model, the normal induction path is more efficient, hence less benefit from ram air.

 

Thanks Vance that looks more like it.

If the C didn’t have factory ram air, I wonder if this can be adapted.

Can anyone provide pictures of this setup?

[EricJ]

1 minute ago, Brian2034 said:

I was hoping for a ram air set-up with no air filter interference.

From my homebuilt side of aviation, the ram air without filter gives an additional inch of manifold pressure.

Sometimes that's an indication of a suboptimal air box design.    The M20J got a redesigned airbox and there was so little gain from bypassing the filter that after a few years the factory deleted the ram air.    Mooney made a ram-air delete kit for the previous J models and we installed that on my airplane.   Flying in rain or any dust is not good without the filter, and can wind up signficantly impairing the fuel servo. 

I doubt you'd get much gain on a C model by bypassing the filter, especially if the filter is kept clean.

[Joshua Blackh4t]

If you delete the ram air, do you still have an alternate air? I thought that was required. 

[Vance Harral]

24 minutes ago, Brian2034 said:

If the C didn’t have factory ram air, I wonder if this can be adapted.

It seems to me that the geometry of the components prevents this.  If you look at that parts manual diagram above, the lower images are for the carbureted engine.  The carburetor airbox is directly inline with the intake path through the air filter.  Any mechanism that bypasses the filter would have to take a roundabout route to get to the airbox.  I don't think there is room in the cowl for such a mechanism, but even if there was, it would create the same kind of circuitous route the E/F have through the normal intake path, and thereby reduce the benefit of the ram air.

[Vance Harral]

18 minutes ago, Joshua Blackh4t said:

If you delete the ram air, do you still have an alternate air?

The alternate air mechanism in the E/F is completely independent of the ram air port, and I suspect it's the same in the J.  I've circled it in red in the figure below, clipped from the parts manual picture above.  It's a round door at the back of the air box, which is ordinarily held closed by spring pressure.  If the air pressure inside the air box gets sufficiently lower than the air pressure outside the air box (presumably because the normal intake path through the air filter is blocked), the air pressure difference overcomes the spring pressure and opens the door, drawing air from inside the engine cowl.  The mechanism is completely automatic, there is no control in the cockpit for it.  The mechanism should be periodically checked (annual, oil changes) for freedom of movement against the spring.

Note that if you're in conditions which you suspect might clog the intake system (ice, volcanic ash, whatever), it is critically important to keep the ram air door closed.  Opening the ram air door directly exposes the impact tubes of the fuel servo to an unfiltered air stream.  If ice or dirt or whatever in that air stream clogs those tubes, the fuel servo stops working as designed, and it's pretty much game over.  You can't fix it by closing the ram air door, and the alternate air door won't do you any good.  I'd argue that the ram air port is actually the antithesis of "alternate air", since its use is more likely to cause an intake emergency than it is to bail you out of one.

 

[EricJ]

39 minutes ago, Joshua Blackh4t said:

If you delete the ram air, do you still have an alternate air? I thought that was required. 

On the J model the alt-air inlet is not affected by deleting the ram air.   You can see how the air box works in the M20J diagram posted above.   The alternate air inlet remains the same.