Altitude to Open Ram Air?

[201er]

What altitude is a good minimum for opnening the ram air? Besides air polutants I'd imagine getting bugs in there isn't great either. Does the time of year or DA affect this decision? How high you want to be before opening ram air?

[The-sky-captain]

I wouldnt even worry about opening it on a "j" model. The ram air was originally a band-aid for a bad design and those flaws got cleaned up with the "j" model. If you do decide to you use it you may see 1/4" of extra manifold pressure wheareas the pre J's will get an extra inch. Its not worth the hassle for me.

[201er]

If it's nothing more than hassle and it does yield a knot or two on a mutli hour flight, I figure heck why not? But what I need to know is how high I gotta be before doing it cause I don't thin contaminating the engine justifies the 1/4" of MP. Now someone here proposed that it yields lower CHTs and that's almost worth more than the 1/4" of extra MP.

[David Mazer]

I checked with several knowledgeable people, including and A&P who owns an M20F, and the consensus was 1,000 ft.

[David Mazer]

Sorry, that was for an M20F.  I can't imagine it would be different for a J.

[Piloto]

When properly rig you can get up to 1/2"MP increase. On most M20Js I have seen the RAM air vane does not open completely thus having some restriction. When properly rig the vane would be perpendicular to the air flow. To accomplish full opening the clamps that holds the actuating cable to the airbox should be routed to the left side of the attaching bolt. The theoretical speed gain for 1/2" increase is 1.5kts and about 50fpm climb increase. The RAM air should only be open in clear air (no clouds or precipitation).

José    

[Shadrach]

I open mine as low as 300 ft depending on conditions... If it's mayfly season, snowing, flying into a sand storm ect... leave it closed. My oil analysis has never shown an abnormalities because of anything taken in through the Ram-Air. IMHO there is little risk to your engine from airborne particulate. It's the fuel servo that is the concern...a bug or piece of foreign matter could clog one of the impact tubes in the intake. This could have a noticeable affect on the servo's fuel metering ability, depending on the severity of the obstruction...

As for the J vs F Ram Air and induction system. I have read comments in the MAPA articles that suggest the same thing that Bodie has said.

However, I've also read in MAPA log publications that it's best to lean to 100ROP in the climb above 3000ft and that 50ROP is a "good balance" between best power and economy...as well as other recommendations and other Mooney truisms that I think are horrible advice and untrue.

So give it a shot and report back.  I've never flown a J model with Ram-Air...  I am skeptical that bypassing any type of "useful" air filter would not yield a noticeable increase (relatively speaking), it certainly does in my F.

Moreover, the folks at Lopresti thought it useful enough to include in the design of their "Super 210 Cowl".  I'm guessing that the primary reason Mooney did away with it because mfg and install was a pain in the a$$. I'm guessing that it added 2-5 hours to the build time...

Do let us know how it shakes out!

[Shadrach]

Jose, makes a very good point. The Ram-Air design (on the F anyway) is not the most sophisticated system. Mine was not opening completely when I first started flying this plane.  Having R&Rd my lower cowl many times, I understand why. It requires patience and time to get the linkage, cable and travel just right. It's quicker with 2 people...especially if you're familiar.  It's the kind of work where someone who's not flying the airplane might be inclined to say "good enough" even when it's not.   

[DaV8or]

Out where I fly in the San Joaquin valley, there is almost always a haze layer that extends up to about 4500 ft. Much of that is particulate from all the agriculture going on down below. So, I open mine above 5000 ft as a rule. I have read that dirt particulate is bad for you engine and I suppose it's why we have filters. I choose to be conservative with the ram air usage.

As to the ram air design itself, I think in the case of the vintage Mooneys it is a fix for a poor induction design, but in the case of the J, it's just the opposite. I think in that case the ram air was designed poorly. The concept of the ram air induction is sound and the LoPresti claims 1.5" MP with their new system without a butterfly valve. I really like everything about their cowl except the price. I really wish it were cheaper.

[jax88]

I opened the ram air on my 75 F at 10,500ft on a recent trip from San Antonio to Las Vegas and got just more than a 1/2" of pressure from it.

[201er]

Is there ANY sort of consensus of a minimum altitude to safely open the ram air? I've heard everything from shortly after takeoff, to 10,000ft, to not at all!

How about this. Has anyone ever had a problem as a result of opening it too low?

[Bennett]

I have the LoPresti owel on my M20J, and I use the ram air function whenerever the air appears clear, almost always about 5000' or above.  To appreciate how ram air works on the LoPresti cowl set-up see: 

 LoPresiti Speed Merchants claims an increase of 1 1/2 " MP, and my experience is that this is not unrealistic.  I generally see over 1" increase and often 1 1/4" increase in MP. Really helps keep HP up at higher altitudes.  This is an expensive mod, but the spped increase is impresive, and I really like the ram air feature. 

[Shadrach]

As I stated earlier, No problems... I do not operate it in the rain, (although I'm not entirely sure why yet), snow or when bugs or particulate are present.  Our past oil analysis has traditionally shown very low silicon (<2.5) and insolubles (<.03)...

Moreover, I had the displeasure of R&Ring our engine because of a crankcase crack. Upon inspection, the internals looked very good at 11yrs and 830SMOH.  We replaced anything that had signs of wear (which turned out to be exhaust valve guides and lifters) and put it back together with an OHd case.

The "consensus" between myself, my partners and the owners of the engine shop was that the engine looked great, save for the crack on a "bolt boss" just aft of the generator.

Let me ask you this... why would the altitude matter? The question you want to ask is...is the air my engine is breathing clean? The air does not care how high it is...

It seems to be our nature as pilots to look for "rules of thumb" and they get spoken, handed down and taught as scripture... and are memorized until they become rote... Rote behavior is good for things like formulas, cockpit organization, emergency memory items, etc...  I try to think of operational questions more critically.  YMMV

[DaV8or]

Bennett-

I really like the Lo Presti cowl. The ram air they have devised looks to be much better than the stock. One thing I was wondering about it is ease of removal of the lower cowl for annuals, maintenance, etc. One thing I really like about the vintage Mooney cowl is the quick release cheek panels.

[Bennett]

In my opinion, no more difficult to remove than the stock lower cowl, but a second person is really helpful.  If you also have the Power Flow exhaust system (highly recommended), the LoPresiti cowl still works fine, but some spacing is a bit tighter. The actual exhaust pipe has to be carefully adjusted when exiting the cowl so that they don't rub together  - not a big deal, but something to be aware of.  I'll post a photo of the exhaust exiting the cowl on in my gallery.