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Ram Air Boost?

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jchang10

Joined: 05 Jul 2006
Posts: 227

Posted: Sun Feb 19, 2012 12:45 am Post subject: Ram Air Boost?

Just out of curiosity, has anyone else noticed getting any kind of ram air boost in MAP? I am stock plans, engine, etc.



Specifically, i notice a little boost when pitching over to start a descent from cruise. I noticed this a few times now where I am cruising along at 22" x 2200 rpm or so at 3,000ft and 145 to 150 KIAS. Shortly after pitching over a bit and having only lost 500ft of altitude but now showing 160 KIAS, i will notice i am running oversquared at 24" x 2200 rpm for instance. How did i gain 2 inches all of a sudden?



I wonder if the MAP reading is accurate? The plane doesn't know it's pitched down per se, so is there something special about 160 KIAS? Sanity check?



Jae

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_________________
#40533 RV-10
First flight 10/19/2011
Phase 1 Done 11/26/2011

Mauledriver(at)nc.rr.com
Guest

Posted: Sun Feb 19, 2012 7:21 am Post subject: Ram Air Boost?

I know nothing about ram air, MAP, etc, but intuition has me believing 

that this is as it should be.  That we do have a ram air inlet, that a 

forward facing inlet gives us a positive boost in MAP at all speeds, and 

that if all things are equal, a 10 knot increase in speed would result 

in some increase in MAP.  The pitch angle is not really involved, it's 

just speed.



But I don't have a clue....



"Curious" Bill



 	  Quote: 	
		   



 Just out of curiosity, has anyone else noticed getting any kind of ram air boost in MAP? I am stock plans, engine, etc.



 Specifically, i notice a little boost when pitching over to start a descent from cruise. I noticed this a few times now where I am cruising along at 22" x 2200 rpm or so at 3,000ft and 145 to 150 KIAS. Shortly after pitching over a bit and having only lost 500ft of altitude but now showing 160 KIAS, i will notice i am running oversquared at 24" x 2200 rpm for instance. How did i gain 2 inches all of a sudden?



 I wonder if the MAP reading is accurate? The plane doesn't know it's pitched down per se, so is there something special about 160 KIAS? Sanity check?



 Jae

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partner14

Joined: 12 Jan 2008
Posts: 540
Location: Granbury Texas

Posted: Sun Feb 19, 2012 8:10 am Post subject: Ram Air Boost?

I think if you monitored the MP closely/continuously, you would see that part of the increase is due to altitude change, and part is due to increased airspeed.  I continually reduce my MP on decent,,, usually maintaining somewhere between 18 and 19".Don

  From: jchang10 <jc-matronics_rv10(at)jline.com>

 To: rv10-list(at)matronics.com 

 Sent: Sunday, February 19, 2012 2:45 AM

 Subject: Ram Air Boost?

 --> RV10-List message posted by: "jchang10" <jc-matronics_rv10(at)jline.com (jc-matronics_rv10(at)jline.com)>

Just out of curiosity, has anyone else noticed getting any kind of ram air boost in MAP? I am stock plans, engine, etc.

Specifically, i notice a little boost when pitching over to start a descent from cruise. I noticed this a few times now where I am cruising along at 22" x 2200 rpm or so at 3,000ft and 145 to 150 KIAS. Shortly after pitching over a bit and having only lost 500ft of altitude but now showing 160 KIAS, i will notice i am running oversquared at 24" x 2200 rpm for instance. How did i gain 2 inches all of a sudden?

I wonder if the MAP reading is accurate? The plane doesn't know it's pitched down per se, so is there something special about 160 KIAS? Sanity check?

Jae

--------

#40533 RV-10

First flight 10/19/2011

Phase 1 Done  11/26/2011

Read this topic online here:

http://forums.matronics.com/viewtopic.php?p=366580#366580

t;

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Don A. McDonald
40636

rv10flyer

Joined: 25 Aug 2009
Posts: 364

Posted: Sun Feb 19, 2012 10:09 am Post subject: Re: Ram Air Boost?

I'll have to check that out next time we go up. 



The decrease in angle of attack exposes a slightly larger engine air inlet area. Then you have the airspeed increase, altitude decrease, propeller pitch increase that will also raise MP.



When I begin descent I slowly pull power back to maintain cruise airspeed and leave mixture alone until I get down close to pattern altitude.

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Wayne G.

jchang10

Joined: 05 Jul 2006
Posts: 227

Posted: Mon Feb 20, 2012 10:29 am Post subject: Re: Ram Air Boost?

I generally try to do the same. I am a bit of a speed addict, so sometimes i just push over first, let speed increase a bit then adjust the descent speed with power.



It is generally right after the push over that i notice the gain in MAP.



Jae



 	  rv10flyer wrote: 	
		  I'll have to check that out next time we go up. 



The decrease in angle of attack exposes a slightly larger engine air inlet area. Then you have the airspeed increase, altitude decrease, propeller pitch increase that will also raise MP.



When I begin descent I slowly pull power back to maintain cruise airspeed and leave mixture alone until I get down close to pattern altitude.

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Use the List Feature Navigator to browse the many List utilities available such as the Email Subscriptions page, Archive Search & Download, 7-Day Browse, Chat, FAQ, Photoshare, and much more:

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_________________
#40533 RV-10
First flight 10/19/2011
Phase 1 Done 11/26/2011

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