M20J Ram Air - Performance?

[DC_Brasil]

Hello guys!

My M20J has the RAM AIR intake. Last flight, cruising at 10,000 feet I could see a 0.2'' MP increase with the Ram Air open. I believe I could only see that because of the digital G3X engine gauges. If it were an analog dial, I doubt I could have seen any difference. Since the manual doesn't have any data, I wonder if anyone here can share their experiences with the Ram Air.

[Vance Harral]

Our M20F has ram air, and it's benefit is higher than the M20J due the less optimal induction path with the older cowl.  If I'm paying close attention, I can see just under 1" of MP increase by opening the ram air door at varying altitudes.  However, the resultant change in cruise speed and/or climb rate is negligible - basically too small to see.  The "benefit" is so uninteresting that everyone in the partnership quit fiddling with the ram air control a long time ago.  All it seems to do is present an opportunity to forget to close it toward the end of the flight, and thereby ingest unfiltered air into the engine during descent.  It also causes us occasional maintenance grief when the rubber seal on the door dries out, or the cable needs to be lubricated, or the warning annunciator circuit gets out of whack.  We maintain the system because we want everything on the airplane to work as designed, but if someone offered free parts and labor, we wouldn't hesitate to have it deleted.

The benefit with the M20J cowl is even less than on older models, which is why the factory deleted the feature in later years.

[Paul Thomas]

I've opened mine and did not see any difference but others says it does add a couple knots.

[KSMooniac]

It is so useless on a J that Mooney eventually removed it from later production models and issued a Service Bulletin or Service Instruction to show how to remove it from existing airplanes.  I did that before getting my plane repainted since the hole in the cowl needs to be filled/patched.  The best part is getting rid of that very expensive (and maybe currently unobtainable) seal behind the cowl that is subject to lots of movement due to engine vibration and cowl movement.  It can be torn and/or worn and allow unfiltered air into the intake all the time instead of just when the ram air valve is opened.

[ArtVandelay]

I've opened mine and did not see any difference but others says it does add a couple knots.

Any extra horsepower the ram air will give you is eaten up by the extra drag of the hole on front of the cowl. Remove the ram air, fix the cowling, and remove a possible failure point.

[EricJ]

My J is an early 77 and had the ram air, but I deleted it.    Don't miss it, and now I worry less about crap getting in the ram tubes in the servo.

[toto]

The only time I ever open the ram air on my J is when I’m flying with a terrible headwind and I want to make myself feel like I’ve tried everything.

[DC_Brasil]

Thanks for the answers. 

Just curious about the removal of the Ram Air: is it considered a minor our major alteration from a maintenance point of view?

[Bolter]

1 hour ago, DC_Brasil said:

Thanks for the answers. 

Just curious about the removal of the Ram Air: is it considered a minor our major alteration from a maintenance point of view?

These are the instructions for removal:

ram air removal M20-93.pdf

And a video of my former J, before and after opening the ram air (barely moves the needle):

https://www.dropbox.com/scl/fi/0tnwmhsjppo96pf5hfg80/M20J-Ram-Air-Demo.3gp?rlkey=prlkdyd9g2f3d80fshqklsqzu&dl=0

[EricJ]

1 hour ago, DC_Brasil said:

Thanks for the answers. 

Just curious about the removal of the Ram Air: is it considered a minor our major alteration from a maintenance point of view?

We did this on my airplane before I had my A&P, and my grumpy, anal, overcautious IA at the time did it as a logbook entry.   I don't think it meets the requirements of a major alteration, either, especially since there's a service bulletin showing how to do it.   Strictly speaking, the installer determines whether it is major or minor, so talk to your IA.

[Shiroyuki]

in my 77J, opening the ram air gives and extra half inch of manifold pressure.

Can hardly tell if there is any difference in performance

[201Steve]

Delete Delete Delete

watch your silicon levels in oil disappear

have one less system to work on and inspect

never forget to close it

all at the expense of nothing (well, money). 
 

I just plated over my air box, and back side of cowling, then once I had an opportune time to fiberglass the cowl, did it later. 

[A64Pilot]

Of course your altering the aircraft, but as it’s covered by factory drawings your maintaining the aircraft IAW it’s Type Certificate by removing the thing. Otherwise it would be a Major.

I still have mine, but just don’t use it. I think the drag on a closed hole is insignificant.

The break even point for ram air on motorcycles is roughly 100 mph, that’s the point where performance increase exceeds the drag, I’d expect the same for an aircraft.

Ram air does work, look at the inlet of most turboprops for an example. 

I suspicion that it’s not very effective on a J because if you look at where the air filter is mounted, it appears it’s in the airflow and therefore is getting a ram effect so opening the ram air doesn’t do much. Just my guess.

If you want to see if it works, watch fuel flow, if opening it increases fuel flow, then it works. How much HP does it add?

Well assuming your LOP and if 1GPH is 14 HP when LOP, then it stands to reason if opening it increases fuel flow by 1 GPH, then your adding 14 HP.

Opening it on mine doesn’t seem to effect the EGT by much if any, but I don’t have a monitor so my single probe just isn’t a precise instrument so it might.

I do get a not insignificant increase in fuel flow though