Does alternate air help improve climb rate on take off or cruise climb?

[M20S Driver]

I was wondering if anyone has experimented with high density altitude take offs with Alternate Air open to bypass the filter?  

My guess is that the hot air around the engine will do more in reducing the HP than additional HP from bypassing the filter.  I may test it this summer but any experience/data on this would be appreciated.

[Piloto]

Are you sure is engine alternate air or static system alternate air?

 

The engine alternate air that I have seen is non pilot controllable but automatic.

The static alternate air valve vents to the cabin instead of the fuselage static ports when pulled out.

 

José

[M20S Driver]

Are you sure is engine alternate air or static system alternate air?

 

The engine alternate air that I have seen is non pilot controllable but automatic.

The static alternate air valve vents to the cabin instead of the fuselage static ports when pulled out.

 

José

 

It is the engine.  

 

I can open it or it will open automatically if there is a blockage of the air intake.  if manually opened, an amber annunciator light will come on.

[Lood]

It will probably give a slight increase in MP, but not a good idea to bypass the air filter on or near the ground. Chances are very real that you might suck dust and/ or other foreign material, directly into your engine - not good.

"Ram air", on older Mooney's is basically the same, but the recommendation is only to use it up high, where the air is clean and free of anything that could hurt your engine. Ram air, apparently, gives 1" extra MP.

[MB65E]

I would try a few and experiment with it. I'm not sold on the entire air filter thing. I've worked on and flown several airplanes with no filtratition. The Pitts I worked on had no filter on it and it made it to TBO. I would be more worried about a piece of the ram air door coming apart, than ingesting any amount of dirt or other fod. Not exactly the same thing but Jet engines swallow a lot more air, dirt, birds, etc. no filters there. However, if you work off of grass, dirt, sand, gravel, I'd take a filter if I could have one.

-Matt

[N201MKTurbo]

The ram air boost is proportional to speed. At takeoff and climb speeds it is less then 1/2 inch of MP. Hardly worth the effort.

[Guest]

I was wondering if anyone has experimented with high density altitude take offs with Alternate Air open to bypass the filter?  

My guess is that the hot air around the engine will do more in reducing the HP than additional HP from bypassing the filter.  I may test it this summer but any experience/data on this would be appreciated.

If the S model alternate air control is like the other long body airframes, air is taken from within the engine cowl. Warm cowl air is less dense, therefore lower power out put.

Clarence

[Awqward]

Interesting that on the newer Mooneys it is possible to manually open the alternate air door...on my J it is spring loaded closed and would only open if the air filter became clogged with ice say.... I also have the Ram air but have never used it...mainly for fear of the event mentioned above....ie ingesting the rubber seal

AQ

[blaine beaven]

My 78J has had the ram air removed by STC and the alternate air is automatic as described above. I don't even have an indicator for when it activates.

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[orionflt]

with some of the newer air filters the restiction is very minimual. I installed a challenger finlter on my C model and gained an inch of manifold pressure at altitude. was well worth the cost.

brian

[carusoam]

A few thoughts come to mind...

(1) MP is measurable during the T/O run...have somebody collect data from the MP gauge while you fly the plane.

(2) there is an STC available to increase the HP of the Eagle. Known to improve T/O run by giant leaps...

(3) there is an app that can help you measure T/O performance with the alternate air door open and closed....

This assumes you have the 244hp of the original Eagle?

Best regards,

-a-

[ArtVandelay]

My 78J has had the ram air removed by STC and the alternate air is automatic as described above. I don't even have an indicator for when it activates.

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Any regrets doing removing the ram air, what are the benefits?

[jetdriven]

You only gain .1 or .2" of manifold pressure inflight with the J ram air. Then you have the intake air leaks and the boot that can tear. It only gives you 1 horsepower in cruise. On previous models, opening ram air gave you 1 or 2" of manifold pressure. But it wasn't truly ram air. That would be higher than ambient air pressure. It simply gave yu back what you were losing due to a very inefficient air box setup. The J air box was redesigned to be nearly optimum. Ram air didn't help it.

Doing the service instruction and deactivating it does away with all that.

[Jeff_S]

This topic is near and dear to my heart...it turns out that I can test this on nearly every takeoff.  Something that I discovered after purchasing my O is that the Alternate Air door likes to open on its own accord at full power takeoff in "standard" atmosphere conditions. In other words, when I'm pulling 2700 RPM and maximum MP (like 29" or thereabouts...can't remember what the exact number is) the door opens up. I've had Joey replace the magnets and check everything imaginable, and no one at Mooney or anywhere has ever heard anything like this. We've checked the filter of course.  About the only thing we can determine is that it seems even the new stronger magnets aren't putting much hold on the door, as though the door itself has somehow gotten demagnetized.

 

For now I just twist the prop knob back a turn or two on takeoff so I'm only showing 2600 RPM, and if I keep the MP below max the door stays closed. The only other thing we'll try is replacing the door entirely. Once I get airborne and say 1000' AGL (which is 2000' for me) then I can go to max power and the door stays closed. It has something to do with the system pulling max power.

 

I'm open to others' thoughts on this if you've got 'em.

[N201MKTurbo]

It seems that this thread is mixing the ram air used on the classic Mooneys and the early Js with the alternate air door that bypasses the air filter if it iceses over.

These are two different things. And the planes with ram air have both.

[M20S Driver]

A few thoughts come to mind...

(1) MP is measurable during the T/O run...have somebody collect data from the MP gauge while you fly the plane.

(2) there is an STC available to increase the HP of the Eagle. Known to improve T/O run by giant leaps...

(3) there is an app that can help you measure T/O performance with the alternate air door open and closed....

This assumes you have the 244hp of the original Eagle?

Best regards,

-a-

 

1- agreed.  I have not collected the data

2-I have the STC (Screaming Eagle) for 280 HP  from 244HP.  I get 800 fpm at 3100lb with DA at 8200 feet. 

3-App is a great idea.  What is it called?

[carusoam]

CloudAhoy is the app...

It used to be free. Some parts are still free. It helps to have a WAAS input (SkyRadar) for the iPad....

It is the only way I know to measure T/O distance with any level of safety and accuracy...

My O went from 1200' to 800'. By going from 280 to 310hp... Roughly speaking, at nearly sea level...

Expect the air intake of a modern Mooney to be pretty well designed. Accidently leaving alt air open is not expected to yield very much. Only data will tell...

Best regards,

-a-

[blaine beaven]

Any regrets doing removing the ram air, what are the benefits?

This is my first Mooney and the previous owner had the mod done, so I have no regrets haha. The benefits are as noted by Byron.

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[M20S Driver]

If the S model alternate air control is like the other long body airframes, air is taken from within the engine cowl. Warm cowl air is less dense, therefore lower power out put.

Clarence

 

Clarence,

 

you were right.  I tested it yesterday at 5000 feet and saw .2 inches of MP increase with alt air open compared to air going through my new filter (standard and not the high performance).  The climb rate change was not noticeable.

 

M20S Driver

[carusoam]

Interesting data collection, at least...

Thanks for sharing what you found.

Best regards,

-a-

[Piloto]

This topic is near and dear to my heart...it turns out that I can test this on nearly every takeoff.  Something that I discovered after purchasing my O is that the Alternate Air door likes to open on its own accord at full power takeoff in "standard" atmosphere conditions. In other words, when I'm pulling 2700 RPM and maximum MP (like 29" or thereabouts...can't remember what the exact number is) the door opens up. I've had Joey replace the magnets and check everything imaginable, and no one at Mooney or anywhere has ever heard anything like this. We've checked the filter of course.  About the only thing we can determine is that it seems even the new stronger magnets aren't putting much hold on the door, as though the door itself has somehow gotten demagnetized.

 

For now I just twist the prop knob back a turn or two on takeoff so I'm only showing 2600 RPM, and if I keep the MP below max the door stays closed. The only other thing we'll try is replacing the door entirely. Once I get airborne and say 1000' AGL (which is 2000' for me) then I can go to max power and the door stays closed. It has something to do with the system pulling max power.

 

I'm open to others' thoughts on this if you've got 'em.

 

Magnets tend to loose their pulling force with high temps and vibration like those in an engine environment. They should have used the spring mechanism like those in the M20J model.

 

José

[jlunseth]

I have not tried what the OP suggests, that is, using the Alt Air on takeoff, but I have used it at cruise.  My door opens automatically if induction icing is detected, or it can be opened manually.  I have done it both ways.  There is a loss of power because of the hotter air being ingested by the engine, it is not large, probably in the .5 -1MP ranged.  Not sure if that would apply on takeoff, since the engine compartment may or may not be warmed as much as it is at cruise, but at cruise there is a loss of power. 

[slowflyin]

With regards to Ram Air I initially didn't think it did much on my bird.   However, after I got digital fuel flow I could see a significant difference.  What was barely noticeable on the MP showed up as .5 gph on the ff without touching the big red knob.

[ArtVandelay]

With regards to Ram Air I initially didn't think it did much on my bird. However, after I got digital fuel flow I could see a significant difference. What was barely noticeable on the MP showed up as .5 gph on the ff without touching the big red knob.

I'll have to check that out next time, I think the effectiveness depends on the altitude, the higher the more effective It is

[ArtVandelay]

With regards to Ram Air I initially didn't think it did much on my bird. However, after I got digital fuel flow I could see a significant difference. What was barely noticeable on the MP showed up as .5 gph on the ff without touching the big red knob.

I played with it today, 6500', the FF does bump up, but then settled down after a minute about 0.4 higher, speed went up 3-5 knots, MP only went up 0.2"