----- Original Message -----

From: Charlie Kohler

To: lml@lancaironline.net

Sent: Saturday, April 03, 2010 8:03 PM

Subject: [LML] Re: IV-P AC

Hi Bob,

It would be interesting to note whether your AC is the early version/or late. The difference is the dimension that the scoop extends down from the fuselage. I don't recall the exact figures but the next time you're at the airplane with a rule--- get the measurement from the center of the fuselage down to the top of the scoop. This will tell me whether or not you will gain anything from the conversion. The later models with the scoop tucked up close to the fuselage had very little drag.

At any rate-- if you do intend to make this change-- do a test flight before you start and get some indicated airspeed runs at various altitudes. Make sure the engine power figures are recorded also.

Then we can have definitive data to support this long-standing debate.

 

After I installed mine, I compared that data from a prop test I had done a year earlier for MT propeller--testing the three Blade versus the four blade. And compared that data with the AC data at the same altitudes in power settings. There is always some scatter but I found that 3 kn was the average penalty.

And--what you will be able to establish that I was not-- how much does the condenser cooling exhaust causes drag. As you can imagine if this exhaust air is strong enough you will have to trim the airplane nose up (causing drag). Also, very exhausting at 90° to the flow of air over the skin, will cause drag. How much we don't know.

At any rate it will be a very interesting test.

 Thanks

 

Charlie K.

 

See me on the web at

www.Lancair-IV.com

 

---

From: Bob Rickard <r.rickard@rcginc-us.com>
To: lml@lancaironline.net
Sent: Fri, April 2, 2010 2:06:28 PM
Subject: [LML] IV-P AC

IV-P Experts:

 

I am contemplating replacing my air conditioning unit in my IV-P from the under fuselage scoop to one that is installed in the tail.  Purely for speed benefits.  My unit works fine but I hear that it may slow me down by 10-20 or more knots.   What are your recommendations?  Is there already a thread on this?  I have the room in the tail, CG shouldn’t be an issue, but I want to know the bad news.  I have the airplane in Phoenix part of the time (yep, it’s really hot, and the current AC is adequate) and I need the system to work at least a little on the ground so I don’t die before takeoff – this is my major concern.  And I would love to hear if some of you have actually made this change and if so what speed benefit you have observed.  Lastly, is there more than one vendor option?

 

Thanks for your comments

 

Bob Rickard

IV-P ( I didn’t build it!)