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Ram Air!

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smokyray(at)yahoo.com
Guest

Posted: Fri Jan 27, 2006 5:56 am Post subject: Ram Air!

Steve,

   

    I went with a carb on my RV4 for several reasons. Many moons ago I flew Scouts and Super Cubs up in Alaska. Reliability and simplicity was an issue and still is with me. Every fuel injected airplane on the ramp was hard to prop start in the backcountry, expensive to fix when it broke (injectors, throttle body) and had problems with auto gas. The Carbureted Lycoming is alot less suseptible to carb ice by design than Continentals, the carb air is routed through the sump full of hot oil. In all my hours over the tundra I rarely used carb heat except during visible moisture or when I saw indications of ice. In 1500 hours of RV4 operations, I have used carb neat twice, both times above 10,000 feet in Idaho flying through visible moisture below 45 degrees F. Even then, the engine was running fine, just a slight drop in RPM. Since the K&N filter has a metal chrome housing and sits 2" below the very warm sump (on top of the ram air intake), it is surrounded by warm air inside the

 cowling. I use it as an alternate air source along with filtering during ground operations. It cleared up my carb ice symptoms both times. For normal operations I take off with the flapper closed and open it when safely airborne, giving a nice "shot" of power on climbout. 

     For the Carb air intake box I enlisted the help of my master craftsman friend Arvil Porter who constructed the airbox per my drawings. I simply read page 11-3 in the RV4 builders manual and from that drew up my design. It is a square-shaped tunnel with a flange welded on top to mate to the carb on the aft end and reaches within 1" of the cowl intake in front. Centered on top is a welded 2" scat duct where the K&N motorcycle filter attaches. In front it has a cockpit selectable trap door for closing during ground operations or in the rare case of carb ice. When closed a 1" drop in MP is noted at SL, 2" at 8500'. Van actually used to sell a very close match to my design but since everyone started flying "newer" RV's, the ram air intake has gone the route of the dodo bird. You might contact Van's and see if they still have one gathering dust on a shelf somewhere.

    For me and my "KISS" principle basics, the ram air, original cowling and carb are a simple, effective and very reliable setup.  Good Luck..

   

  Rob Ray



Steve Sampson <SSampson.SLN21(at)london.edu> wrote:

  



Rob - I am totally unfamiliar with the set up you have.Never heard of K&N 

but I have never understood why we need to filter the air once airborne.



My plan was to go with the Silver Hawk injector, mostly because that is what 

everyone offered if FI. Reason for going FI was here in the UK carb ice is 

frequent and I presume the injected engine is smoother and more frugal on 

fuel. However the things stacking up the other way are:

- I really prefer the look of the O-320 cowl

- the air inlet is presumably matched to the engine

- VANS can supply the brackets for the carb but not FI and the O-320 FAB 

will fit

- there are not so many aircraft to copy how things are done near me. I have 

built a carb -9A before and feel more confident.

- there was also an interesting old post at Vans Airforce "Carb vs Fuel 

Injection" by Stein Bruch which go me thinking that perhaps the money is 

better in my pocket.



Feel free to tell me I am making a mistake if you feel strongly.



If I go back to a carb I guess I have to understand if I want a Marvel or 

someting else. Is there any other carb I should consider? If so what does it 

offer?



Cheers, Steve.



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SSampson.SLN21(at)london.
Guest

Posted: Sat Jan 28, 2006 6:59 am Post subject: Ram Air!

Rob - thanks for that. Yes I am moving increasingly to the standard 

approach. I cant quite understand why VANS moved away from your ram air 

design. Sounds good.



I am just left frustrated that it will be hard to balance the fuel to each 

cyl.



Thanks, Steve.

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smullins(at)drury.edu
Guest

Posted: Sat Jan 28, 2006 8:46 am Post subject: Ram Air!

Hey Rob, 



Do you have any drawings or photos of your ram air/KN setup that you would

share?? 

Steven D. Mullins

Associate Professor of Economics

Co-director 06-07 Convocation Series:     http://www.drury.edu/post911

 

The Breech School of Business Administration

Drury University

417.889.5609 (Home)

417.873.7299 (Office)

 

 



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smokyray(at)yahoo.com
Guest

Posted: Sun Jan 29, 2006 9:34 pm Post subject: Ram Air!

Bottom line on carbureters.....they work!



Steve Sampson <SSampson.SLN21(at)london.edu> wrote:  



Rob - thanks for that. Yes I am moving increasingly to the standard 

approach. I cant quite understand why VANS moved away from your ram air 

design. Sounds good.



I am just left frustrated that it will be hard to balance the fuel to each 

cyl.



Thanks, Steve.

---

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