Jump to content

N200LZ: Chapter 23 - Cowling & Cooling


Recommended Posts

I see a lot about the NACA type scoop vs. the P-51 style scoop.

What is the bottom line when it comes to performance and drag trade-offs. I know that Waiter swapped out his NACA style on his rebuild but that was based on a Lycoming power plant.


My plane will be using a mazda rotary with the radiator in the area below the engine so the armpit/downdraft solution is out of scope here.

T Mann - Loooong-EZ/20B Infinity R/G Chpts 18

Velocity/RG N951TM

Mann's Airplane Factory

We add rocket's to everything!

4, 5, 6, 7, 8. 9, 10, 14, 19, 20 Done

Link to comment
Share on other sites

A proper NACA *should* give you less drag, all other issues aside. However, the "other issues" (like shoving air through a radiator) can't be tossed aside. There's a good reason the P-51 doesn't have a NACA on the belly... ;)


Keith Spreuer recently replaced his NACA with a "P-51" male scoop due to inadequate dP across his radiator (Subaru). He posted this to the Cozy list...


"My conclusion is that the P-51 style scoop with 3:1 expansion and

less than 11 deg expansion rate is key. The P-51 scoop is much more

compatible with a radiator installation. This is because the fine fin

arrangement of a radiator requires a higher delta P than the wide fin

spacing of an air cooled engine. The P-51 scoop does a much better

job of delivering that pressure."


Pics and graphs and such are here (look under "P-51 Scoop" and get a cup of coffee because it takes an eternity to download anything):




The graph shows twice the dP, 73%+ dT, and he reported no noticeable loss in performance (increase in drag). Plus, his plane looks more like a P-51 now. :cool2:



Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

  • Create New...

Important Information