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1. 05:56 AM - Re: Ram Air! (rob ray)
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--> RV4-List message posted by: rob ray <smokyray@yahoo.com>
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@london.edu> wrote:
--> RV4-List message posted by: "Steve Sampson"
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.
----- Original Message -----
From: "rob ray"
Sent: Wednesday, January 25, 2006 1:38 PM
Subject: RV4-List: Re: RV4-List Digest: 1 Msgs - 01/24/06
> --> RV4-List message posted by: rob ray
>
> Steve, I didn't use the FAB on my RV4 as I built my own tunnel ram
> equipped with Ram air for normal flight and a K&N filter by-pass for
> ground operations. Hasn't let me down in 10 years. This allowed me to run
> the early stock cowl and scoop with a carb. My cowl was from pre-FAB days
> when the plans called for a setup similar to mine. In 95' the FAB came out
> and they enlarged the scoop to handle it, although the carb intake
> location isn't the same on all 320 sumps and the FAB won't work on every
> engine without some serious cutting. Van's sells the larger scoop you can
> attach to the cowl, I bought one and it is still sitting in my attic,
> never used. Which injector throttle body are you going with?
>
> I too like the looks of the 320 cowl and scoop and haven't changed it
> one bit...
>
> RR
>
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