WANTED: M20J ram air cable

[ArtVandelay]

It would be interesting to know the drag associated with the ram air inlet, I’d be willing to bet a beverage that the drag is greater than the power boost at cruising speed.

[EricJ]

12 hours ago, John Martindale said:

What I am unclear about is that if there is moisture in the air at a temperature conducive to icing in the pump body after the automatic alternate door then why doesn't that same air cause problems after going through the normal air filter. Is that filter really fine enough to remove molecules of water? What makes the ram air entrance so different, it's the same air after all. Also, if it is such an issue why isn't removal of the ram air inlet mandated in all models or a mod available to add hot air if needed like a carburetor engine?  Regards John

Ice builds up on leading edge surfaces like wings, tail leading edges, etc.   If the ram air door is open it has a straight shot to build up on the fuel servo ram tubes (which provide pressure to help regulate fuel flow) and the throttle plate, etc.   It won't do that after a bend, and a lot of dirt/debris loses its way after a bend as well.    Ice may build up on the air filter, but if it does the automatic alt air door opens and allows air in that way.

Carb heat is to compensate for the temperature drop due to the carburetor venturi, which doesn't exist (as much) in a fuel servo.   

[carusoam]

Two sources of cold temp in a carb Venturi...

1) decrease in pressure, removes energy... appears as colder air...

2) fuel evaporation, removes energy... appears as colder mixture... 

Cold enough to drop warm air to below freezing...

Just add moisture...

Best regards,

-a-

[sdflysurf]

I also have a need for a RAM air cable in my 1968 F model.   In my model is it worth it or should I just remove it?  Also if it is worth it does anyone have one here or should I go to Mcfarland?

[carusoam]

It is worth it to update to the newer style intake... safer, better, and minimizes the benefit of having the ram intake...

The old system with the 1”mp benefit has a more restricted intake, and doesn’t have the updated Alt air system...

... so maintaining what you have vs... getting an update.... up to you... both are worth it...  

PP thoughts only, not a mechanic...

Best regards,

-a-

[Mooney in Oz]

16 hours ago, sdflysurf said:

I also have a need for a RAM air cable in my 1968 F model.   In my model is it worth it or should I just remove it?

The Mooney Service Instruction (M20-93) that authorises removal of the ram air system is only applicable to J models.

https://cdn2.hubspot.net/hubfs/4147179/technical_documents/service_instructions/sim20-93-1.pdf

[RobertGary1]

17 hours ago, sdflysurf said:

I also have a need for a RAM air cable in my 1968 F model.   In my model is it worth it or should I just remove it?  Also if it is worth it does anyone have one here or should I go to Mcfarland?

Ram air is very helpful in an F model. Gives you about 3/4” a free mp at altitude. In a J the cowl design reduces the bends in the intake so ram air has almost no effect. 
 

-Robert 

[Bartman]

My J has an off field landing due to loss of engine power in her history and the FAA records indicate the pilot had flown thru icing conditions as the cause.  When I first read it many years ago I remembered my primary training and know about carburetor icing, but I didn’t understand how a fuel injected engine could develop induction icing. Later I joined Mooneyspace and read about the Ram Air and realized it was not just induction icing, but icing of the fuel servo and that  2+2=4. 

In 13 years of ownership I have never opened the Ram Air but have fought with the gasket that goes between it and the cowl many times. For these reasons when my rebuilt engine is installed later this month it will be without the Ram Air.  

Edited May 11, 2020 by Bartman

[tmo]

A fellow flying a TB20 has also reported suspected fuel servo icing - without flying through ice, just quite high up in below-ISA temperatures, and with low power.

[Cyril Gibb]

On 4/30/2020 at 11:57 PM, EricJ said:

With the ram air door open on a J model (or I think an E or an F, but I'm not positive on those), the ram tubes in the fuel servo, and the throttle plate, are both in the direct air path.   This means cold/freezing moisture can accumulate on them just like on any leading edge, but when ice accumulate on the ram tubes the fuel injection gets fubared.    All of that is downstream of the automatic alternate air door, so it won't help.   I don't know whether that has ever happened....

Yes, it has happened.  Only took a few seconds of freezing drizzle to kill the engine.