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

[Awful_Charlie]

When I put my JPI in, I deliberately put the OAT sensor downstream of the airfilter - that way it would record the change in temperature when the alternate door opened. As it's a turbo, I also have the CDT (temperature out of the turbo) and IAT (temperature after the intercooler), and also have the ship gauge and Aspen for OAT.

 

I discovered that on the Bravo, opening the alternate air in the cruise made no difference to the OAT on the JPI. However, the one time I have had the alternate door open automatically, then the JPI measured OAT did rise a good few degrees. I put this down to the NACA duct on the cowl having a high capacity, so opening the alternate air when in the cruise just runs air through the filter into the void between the engine and the firewall as well as feeding the engine.

[Healthpilot]

On 2/6/2015 at 9:17 AM, Jeff_S said:

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.

Happening to me as well since the last time the A&P cleaned the air filter on my O. Just a couple of weeks ago. 

[A64Pilot]

My J also shows a significant bump in fuel flow with ram air on,  which has me a little confused as I didn’t think our fuel control compensated automatically for manifold pressure, but it must or the FF wouldn’t change.

I don’t usually cruise at high power so I don’t use mine, but don’t see the need to remove it. I don’t see it wearing out and causing problems if it’s not used?

However it seems that while the ram air may not be a turbo, it seems to add at least as much if not more speed then many expensive speed mods.

Edited August 21, 2021 by A64Pilot

[A64Pilot]

On 2/11/2015 at 8:59 AM, Piloto said:

 

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

Wouldn’t that negatively effect Magneto’s? Although I have heard that an impact can cause a magnet to lose its magnetism, never see it but have read it.

[PT20J]

Permanent magnets don’t lose significant magnetism until heated to the Curie temperature which is several hundred degrees Celsius depending on the material. If it gets that hot in the engine compartment, you’ve got other problems.

The RSA fuel injection used on a M20J regulates fuel flow according to the airflow through it rather than the manifold pressure.

Skip

[buddy]

8 hours ago, Healthpilot said:

Happening to me as well since the last time the A&P cleaned the air filter on my O. Just a couple of weeks ago. 

 

[buddy]

I’m also using a K&N air filter with the 310 hp. I don’t think the alternate air door opens very much just enough to turn the light on.

[Ragsf15e]

2 hours ago, A64Pilot said:

My J also shows a significant bump in fuel flow with ram air on,  which has me a little confused as I didn’t think our fuel control compensated automatically for manifold pressure, but it must or the FF wouldn’t change.

I don’t usually cruise at high power so I don’t use mine, but don’t see the need to remove it. I don’t see it wearing out and causing problems if it’s not used?

However it seems that while the ram air may not be a turbo, it seems to add at least as much if not more speed then many expensive speed mods.

It gives about a .75” of manifold pressure bump on the older airplanes (e/f).  I cruise at low power too, but I definitely use the Ram air (this thread was about alternate air which is different).  If you’re at 9,500’, and full throttle in an NA airplane, you’ll still be at low power with the Ram air open.  It adds about 2-3 kts.  The early Js had a better intake though, so probably helps less.

[kortopates]

Alternate air doors on the modern Mooney's has nothing in common with Ram air on the Vintage and early J Mooneys. Alternate air doors pull air from inside the engine cowling, not directly from outside like Ram air. Their only thing in common is the air bypasses the induction inlets and air filter.  The alterate air door is spring loaded to open fully once the suction force overcomes the magnet - can't imagine it opening only slightly.

[ArtVandelay]

It gives about a .75” of manifold pressure bump on the older airplanes (e/f).  I cruise at low power too, but I definitely use the Ram air (this thread was about alternate air which is different).  If you’re at 9,500’, and full throttle in an NA airplane, you’ll still be at low power with the Ram air open.  It adds about 2-3 kts.  The early Js had a better intake though, so probably helps less.

I think the hole for ram air when shut off results in additional drag, removing it seem to result in same speed as when I had it open.

[A64Pilot]

45 minutes ago, ArtVandelay said:

 

I think the hole for ram air when shut off results in additional drag, removing it seem to result in same speed as when I had it open.

 

It might, but I’m pretty sure it wouldn’t be measurable, if your getting an increase in speed, it’s from an increase in HP.

If your LOP it could simply be from a richer mixture, LOP power is determined by available fuel and .4 GPH isn’t trivial. Using my newly learned HP formula LOP 15x.4= 6 HP, and 6 HP is pretty significant.
Assuming the fuel control does add fuel with increased airflow, then the additional airflow to add .4 GPH isn’t trivial either.

I think it’s over correcting and your moving closer to peak and that’s where the additional speed is coming from, When I tried  mine, I re-leaned and got no significant difference in airspeed, but maybe I over leaned and lost the power the ram air gave to me?

[Shadrach]

2 hours ago, Ragsf15e said:

It gives about a .75” of manifold pressure bump on the older airplanes (e/f).  I cruise at low power too, but I definitely use the Ram air (this thread was about alternate air which is different).  If you’re at 9,500’, and full throttle in an NA airplane, you’ll still be at low power with the Ram air open.  It adds about 2-3 kts.  The early Js had a better intake though, so probably helps less.

Down low in the winter it give nearly 1.5”. If I open it while running high power LOP it will push EGT 25-30 further to the lean side. 

[Ragsf15e]

3 hours ago, ArtVandelay said:

 

I think the hole for ram air when shut off results in additional drag, removing it seem to result in same speed as when I had it open.

 

Don’t you have a J?  I think the RAM air didn’t help nearly as much when they improved the intake on the J.  It’s worth it on the F, especially if you fly up high.

Edited August 21, 2021 by Ragsf15e

[ArtVandelay]

Don’t you have a J?  I think the RAM air didn’t help nearly as much when they improved the intake on the J.  It’s worth it on the F, especially if you fly up high.

It didn’t help much after I replaced my dirty air filter. I think removing the ram air inlet from the cowling improves aerodynamics as much as ram air helps, at least on the J, so I have no regrets removing it.