How do you close off the cooling air to the avionics bay?

[AndreiC]

Hello all,

in my 1970 E-model I have a smaller diameter hose that goes straight from the passenger side NACA scoop to the avionics bay, for cooling purposes. I plan a flight next week in very cold temps (close to 0 dF), and I'd like to close off this hose -- avionics overheating will be the least of my problems  How does one do this?

On a related note, some people mentioned covering off part of the oil cooler with aluminum tape. What kind should I use? And what fraction of the cooler should I try to cover? I'd like to get the oil to normal operating temps.

Thanks!

 

[0TreeLemur]

9 minutes ago, AndreiC said:

Hello all,

in my 1970 E-model I have a smaller diameter hose that goes straight from the passenger side NACA scoop to the avionics bay, for cooling purposes. I plan a flight next week in very cold temps (close to 0 dF), and I'd like to close off this hose -- avionics overheating will be the least of my problems  How does one do this?

On a related note, some people mentioned covering off part of the oil cooler with aluminum tape. What kind should I use? And what fraction of the cooler should I try to cover? I'd like to get the oil to normal operating temps.

Thanks!

 

I'd be tempted to put a block of cut styrofoam into the NACA duct, and cover it with a bit of duct tape.

[Bolter]

Even with very cold ambient temps, my panel still has heat.  (Aspens and Avidynes, so lots of electronics)  I recall my 430 staying warm in low ambient temps, as well.  If you have modern avionics, any block you install would be best if it could be removed in-flight.  If you have an avionics fan, maybe just pull that fuse if you feel too much cold air is getting in, as an easy compromise between full cool and no cool.  

[N201MKTurbo]

9 hours ago, AndreiC said:

Hello all,

in my 1970 E-model I have a smaller diameter hose that goes straight from the passenger side NACA scoop to the avionics bay, for cooling purposes. I plan a flight next week in very cold temps (close to 0 dF), and I'd like to close off this hose -- avionics overheating will be the least of my problems  How does one do this?

On a related note, some people mentioned covering off part of the oil cooler with aluminum tape. What kind should I use? And what fraction of the cooler should I try to cover? I'd like to get the oil to normal operating temps.

Thanks!

 

My M20 F had a tiny lever near where the hose connects to the side wall. The lever was there to close the airflow when you are flying through the rain so you didn't get rain water in your radios.

[Shadrach]

I cannot speak to your plane specifically, but my 1967 M20F has a butterfly valve right at the passenger side NACA duct, just as @N201MKTurbo states above.  It's an "L" shaped piece of stamped metal. Aft of the valve a 1" diameter section of tube that runs behind the panel to a diffuser panel that is mounted on the firewall behind the radio stack. I don't know that it's for rain per say as I don't recall having an issue with moisture entering the cabin at the diffuser.  Some rain will enter at the NACA duct.  The first time I replace the CAT tube it was full of rusty bits of the spiral reinforcement wire from inside of the tube. It's a good idea to upgrade to SCEET or SCAT tubing over the CAT tubing the factory used.  

I will be at my hangar later. I will get a pic of the lever in both the closed and open position and post it here.

[N201MKTurbo]

[Shadrach]

7 minutes ago, N201MKTurbo said:

Did your F have outlets on the left scoop as described above? Unless I missed something, mine just has a Wemac vent.

[Yetti]

20 minutes ago, Shadrach said:

Did your F have outlets on the left scoop as described above? Unless I missed something, mine just has a Wemac vent.

I think that is poorly worded.    My F has louvered vent on the Left side of the skin near the baggage compartment. There is not a vent in the inside sidewall panel in the baggage compartment. So airflow would between the sidewall and the skin of the plane.   Thus creating airflow behind the panel from the right vent with the tube attached.

Edited January 10 by Yetti

[N201MKTurbo]

1 hour ago, Shadrach said:

Did your F have outlets on the left scoop as described above? Unless I missed something, mine just has a Wemac vent.

It did, they were all capped from the factory. When I bought that plane, it was just like it came off the showroom floor, so I don't think it was changed.

[GeeBee]

Why are you worried about an avionics under temp? I assure you the avionics can survive in much lower temps than you can stand. As for the cooling air effects on the cabin, your cabin heat should more than overcome its effects.

[Shadrach]

This is what it looks like in my 67 F from the footwell:

and from behind the panel:

Note the detent (red arrow)for open. There is a corresponding detent for closed not visible in the image.

[AndreiC]

I am of course not worried about the avionics being too cold. I am afraid of me being too cold! I want to close off all sources of cold air in the cabin. (The cabin is drafty enough as it is...)

The highs in the areas I will be flying through on Saturday are predicted to be around 0 dF on the ground. I suspect it will be much colder higher up. So I am trying to preserve as much as possible of the engine heat.

BTW, I did not hear any comments back about sealing the oil cooler. Any advice will still be very helpful.

@Shadrach: my plane does not seem to have the same system as yours. I looked more carefully today, the right scoop only has one (or more, can't recall) fittings for big hoses (3"? 4"?) and two small outlets for what I believe would be 1/2" or 3/4" hoses. One of those was capped with duct tape on my plane, on the other one was attached, with a zip tie, the 1" SCAT tube going to the avionics bay. I opted for simplicity: I removed the 1" SCAT tube and put a conical cork plug in the outlet. Hopefully it will hold.

 

[Shadrach]

32 minutes ago, AndreiC said:

I am of course not worried about the avionics being too cold. I am afraid of me being too cold! I want to close off all sources of cold air in the cabin. (The cabin is drafty enough as it is...)

The highs in the areas I will be flying through on Saturday are predicted to be around 0 dF on the ground. I suspect it will be much colder higher up. So I am trying to preserve as much as possible of the engine heat.

BTW, I did not hear any comments back about sealing the oil cooler. Any advice will still be very helpful.

@Shadrach: my plane does not seem to have the same system as yours. I looked more carefully today, the right scoop only has one (or more, can't recall) fittings for big hoses (3"? 4"?) and two small outlets for what I believe would be 1/2" or 3/4" hoses. One of those was capped with duct tape on my plane, on the other one was attached, with a zip tie, the 1" SCAT tube going to the avionics bay. I opted for simplicity: I removed the 1" SCAT tube and put a conical cork plug in the outlet. Hopefully it will hold.

 

Sorry the images weren’t useful. Duly noted that the 1970 model is different. As far as the oil cooler goes, aluminum tape works well for partially (or totally) blocking flow through the cooler. I do it every year. My heater works really well but at -30° It’s a good idea to have layers.

[AndreiC]

What kind of aluminum tape would be used? The kind that is used on dryer vent pipes? That seems a bit flimsy to me… Or is there some thicker, aviation version of that?

[AndreiC]

59 minutes ago, Shadrach said:

Sorry the images weren’t useful. Duly noted that the 1970 model is different.

Sorry @Shadrach, I should have said that the images were useful in understanding that I was looking in the right place, just for something that was not there… Thanks for the pics. 

[Shadrach]

12 minutes ago, AndreiC said:

What kind of aluminum tape would be used? The kind that is used on dryer vent pipes? That seems a bit flimsy to me… Or is there some thicker, aviation version of that?

Aluminum Duct tape is plenty strong enough to inhibit airflow through the cooler.

[PT20J]

I wonder if closing off the cooling to the radios is a good idea. My J doesn’t have that capability, so at some point Mooney quit doing that. A legacy stack can overheat pretty easily depending on what you have in there.

I would not block off the oil cooler unless you know from experience that it is necessary. And, I would fabricate a plate to do it right. Aluminum tape will deform into the oil cooler from the air pressure and be difficult to remove.

 

[ArtVandelay]

I wonder if closing off the cooling to the radios is a good idea. My J doesn’t have that capability, so at some point Mooney quit doing that. A legacy stack can overheat pretty easily depending on what you have in there.

My J does. I assume you have a blower?

[Shadrach]

11 hours ago, PT20J said:

I wonder if closing off the cooling to the radios is a good idea. My J doesn’t have that capability, so at some point Mooney quit doing that. A legacy stack can overheat pretty easily depending on what you have in there.

I would not block off the oil cooler unless you know from experience that it is necessary. And, I would fabricate a plate to do it right. Aluminum tape will deform into the oil cooler from the air pressure and be difficult to remove.

 

I and many others have been utilizing aluminum tape as a means of winterizing the cooler for decades. Several hundred hours of winter flying on my bird alone. It does not deform so much as contour to the surface of the cooler to provide a perfect seal. It is very secure, yet easy to remove. The cooler can be blocked to whatever degree the season dictates. For me that’s 30% in late fall/early winter. As temperatures drop well below freezing, I add more. We have fairly manic weather here in the winter; it might drop from the 40s to near 0° in just a few days and then back. I can think of no better solution that offers the same combination of adjustability, ease of application, low cost and low weight. A fine example of Occam’s Razor.

The design of the cowl and the oil cooler location makes for an cool running set up for IO360 powered airframes. Combination of low CHTs and direct airflow through the cooler mean that I think more about keeping things warm then how to cool them off.  I know from experience that without an oil cooler blank, I would be looking at oil temps in a 150 to 160° range.

You may be right about airflow to the Avionics. I don’t ever bother to close mine, even in very cold temperatures. However, there are rare occasions where it might be useful if not needed. I have a very good heater, but admit that I have not done a lot of flying in temps much below -20°.  I’m sure there’s an OAT where any cold air coming into the cabin is undesirable.

[PT20J]

I’ll certainly defer to Ross @Shadrach since he’s used the tape on the oil cooler successfully. I used aluminum duct tape once to temporarily seal some baffle gaps and the air pressure deformed and tore it and made it very difficult to remove, so I’ve been leery of it since.

 

[Shadrach]

28 minutes ago, PT20J said:

I’ll certainly defer to Ross @Shadrach since he’s used the tape on the oil cooler successfully. I used aluminum duct tape once to temporarily seal some baffle gaps and the air pressure deformed and tore it and made it very difficult to remove, so I’ve been leery of it since.

 

That's odd. I wonder if it's due to the location of the rear mounted cooler on the J and heat after shut down compromising the adhesive.  It's never been a problem for me with the front, lower cowl, mounted cooler.  One just needs to ensure they don't forget to remove it when the OAT is borderline.

[AndreiC]

@Shadrach: can you please post a pic or two of where you put the aluminum tape? Or say a few more words where you put it? On the outside of the cowling?

[Shadrach]

10 minutes ago, AndreiC said:

@Shadrach: can you please post a pic or two of where you put the aluminum tape? Or say a few more words where you put it? On the outside of the cowling?

I'll be at he hangar tomorrow. Will get some images then. 

[A64Pilot]

It makes one wonder why we don’t have a flap that can close off air flow through the cooler connected to a cable in the cockpit, rather than making us resort to un-approved methods. We can manage cowl flaps so why not oil temp too?

My 1946 C-140 has a winterazation kit that blocks off airflow, even had an asbestos blanket that you put on the oil tank 

This shows the covers, the ones under the prop blocked airflow from the bottom of the motor that’s for oil cooling and the others block airflow to the heads.

https://skyportservices.net/cooperjr/wntrkit.htm

[Pinecone]

I have seen kits for some airplanes that has a sliding Al door to set the airflow.  And the sliding part can be removed for summer time.