DonFromTX

DonFromTX

Well Known Member
I have a need to put a fresh (combustion) air intake to the engine on top of the cowl. I don't seem to find any information on how to design this for best performance and least drag, or even how big it needs to be Anybody have any references to doing this that might be helpful?
 
Besides the obvious problem of connecting it, I think you would be better served by a NACA vent (properly sized) located mid right rear side of lower cowl. Many aircraft use this location for oil cooling.......

I guess I didn't answer your question. But at least your post moved back up to the top..............:D
 
Don,
Since HP is pretty much a function of air flow, you could use the cross sectional area of the RV carbureted intake snout as a guide.

That snout appears to work well for 160 to 200hp engines.
Scale it based on HP ratio. (is the Honda ~ 100 hp?)
If so, the RV inlet area could be cut in half. 100HP/200HP
Assuming a circle, the new diameter would be 72% of current diameter.

A friend of mine has the first Sonex with this Viking engine. He likes it a LOT better than the V-dub he replaced. Nice looking outfit.
I don't remember what his intake arrangement is. I'll try to break into his hangar and look tomorrow.
 
You must be speaking of Casey Lyon, I have talked with him about airflows, he has done some experimenting. A NACA vent did not provide the airflow needed, so he just turned it upside down and made it a scoop! Was fairly new at Sebring, but seemed to work well for him.
 
Look at lots and lots of pictures of WWII fighter planes and bombers with V-12 enignes. Over the conflict, a wide variety of scoops and inlets were used.
From my point of view, avoid anything that obstructs your view over the nose.
Turning the NASA scoop upside down and backwards is cute. A faired scoop with divergent pressure recovery, who'd a thunk it? :confused:
 
Keep in mind that in a steep climb, the top side of the engine cowl is often a low(er) pressure area.

An RV-12 is already flying with a Viking engine. Why would yo need to design your own induction system? I thought a FWF installation was supposed to already be available for the engine?
 
rvbuilder2002 said:
Keep in mind that in a steep climb, the top side of the engine cowl is often a low(er) pressure area.
Don,
This is the reason North American went to a longer carb inlet scoop on the Allison powered P-51/A-36/P-51A. They found that the nose was blanking the carb inlet in climbs. The original scoop stopped just about mid-way along the nose...just about over the middle of the Allison, and the longer scoop extended to just about an inch or so behind the prop disc to also provide some ram air capability.

This is something you will want to keep in mind for your 12.
Best of luck with your scoop!
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There are at least three RV12's flying with a Viking, but I am looking for ways to improve things. Using heated air from the radiator to provide combustion air is not my idea of the best way to do things, this is caused by a late improvement to the intake manifold.. The Sonex improved things with a simple scoop above the air filter, but decreased flow in climb rears its head, probably moreso on a 12.. The cowling is designed to produce a heated low pressure area at the intake, since ALL air passes thru the radiator. I was looking for those that would like to brainstorm the situation a bit looking for an improvement. At the present, it seems to me that a "snorkel" type intake up just behind the prop may well be the best answer (besides that would really look cool too!). Any comments welcome!
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QUOTE=rvbuilder2002;753619]Keep in mind that in a steep climb, the top side of the engine cowl is often a low(er) pressure area.

An RV-12 is already flying with a Viking engine. Why would yo need to design your own induction system? I thought a FWF installation was supposed to already be available for the engine?[/QUOTE]
 
Scoop

Don - I have just what you need!!!! Since you're using an auto conversion why won't an auto scoop work? I know that viking puts out the ponies so why not feed them well? I went out to the shop and pulled a scoop I used to run on my race car. It looks to be the perfect size for that RV. All you'll have to do is make a cutout in the top cowl, do a little fiberglass work and presto an awesome air intake scoop that any auto conversion guy would die for. I'll cut you a deal on this one or you might find something better on Ebay. If you want mine $25.00 delivered will do it and I'll throw in a couple of Crower Cams stickers I also found. Ted

http://i48.tinypic.com/10qar7b.jpg
 
It's been done a couple of times on rotary powered rv's.

Here's a dirty looking but effective version:
http://www.rotaryaviation.com/renesis_engine.htm

He has a much cleaner version on his 3-rotor powered RV-8, but I can't find a photo for you.

Basically, the chin inlet for a vertical induction sump lyc is duplicated *in spirit* (but much smaller) on the top cowl where ever it suits your needs. The intake tube is extended forward to near the prop, kinda like a machine gun in the cowl. That gets the inlet away from the boundary layer, & there's a flow divider between the tube & cowl, similar to what you see on Van's 'chin' inlet.

The actual inlet can be slightly smaller than the throttle body inside diameter, if you taper the inlet tube for pressure recovery.

You'll obviously need a plenum around the air filter. (One would think that you'd also need a plenum between the throttle body & the 4 intake tubes too, but what do I know....)

Charlie
 
I think that has RV6A written all over it, better keep it for yours.

Jrskygod said:
Don - I have just what you need!!!! Since you're using an auto conversion why won't an auto scoop work? I know that viking puts out the ponies so why not feed them well? I went out to the shop and pulled a scoop I used to run on my race car. It looks to be the perfect size for that RV. All you'll have to do is make a cutout in the top cowl, do a little fiberglass work and presto an awesome air intake scoop that any auto conversion guy would die for. I'll cut you a deal on this one or you might find something better on Ebay. If you want mine $25.00 delivered will do it and I'll throw in a couple of Crower Cams stickers I also found. Ted

http://i48.tinypic.com/10qar7b.jpg
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Don

Agree with Dan. Based on your location taking air off of the front inlet would be your most effecient way.

If you are set on the top scoop, then best avoid the car flush ramp scoops, you do not want to ingest boundry layer air. I have pictures but only in books. If it opens past the nose, you want raised lip for clean air and a way to divert the boundry layer around the scoop. Imagine a p-51 radiator inlet with the rear end like the rear half of an RV-3 cheek cowl. If you bring the scoop to the front end of the cowl it can be flush.

Unfortunately, I had to go the top scoop route for my oil cooler bandaid. Not fond of the looks, but I hope the drag penalty will not be too much. Hope to find out this weekend.
 
Saw a show on the B-25 last night. Even though the B-25 used radial engines, the top of the cowling on each engine had an air scoop that was not unattractive, to me anyway.

Thought of this thread and thought I'd call your attention to it.

P.S. Ooooo! Just looked on the internet and apparently there were different designs for the air scoop on the B-25. The one I spoke of is the smaller one. The bigger one would be unattractive on an RV-12, IMO.
 
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The B25 scoop is pretty much the same as the P40 one. This photo shows what I am talking about.
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rv7boy said:
Saw a show on the B-25 last night. Even though the B-25 used radial engines, the top of the cowling on each engine had an air scoop that was not unattractive, to me anyway.

Thought of this thread and thought I'd call your attention to it.

P.S. Ooooo! Just looked on the internet and apparently there were different designs for the air scoop on the B-25. The one I spoke of is the smaller one. The bigger one would be unattractive on an RV-12, IMO.
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I don't think it will interfere enough to be worth mentioning. However, this was my first choice, but I never could figure out how to make them match each other and finally gave up on it.
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David Paule said:
Why would you want anything to interfere with your field of vision?

Dave
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Don,

If you're looking at P-40 style inlets, there just happens to be a certain F1 Rocket with just such a scoop feeding an IO-550. Heck, its even painted like his favorite Warhawk! Perhaps F1Boss Mark would be a resource in your quest! He can probably tell ya about the "goods and others" of his design. Here's a pic:

Boss%2520and%2520Bob.jpg


Cheers,
Bob
 
Hey that looks familiar! Although my scoop isn't tested yet it is sized specifically for the Rotec engine. The ram air effect of the scoop should provide some boost for the engine. Many of the ideas I've used for the cowling and engine were stolen from the Reno guys. Lots of information out on the web.

Brian

Www.facebook.com/radialconversions
 
At LSA speeds there is not much potential manifold pressure increase due to "ram air". The maximum available Q for 125 knots is about 0.75" Hg at sea level. Since we don't fly at sea level and the maxQ figure assumes a zero flow inlet, you probably shouldn't expect more than 0.3" in actual use. Point is, simply supplying cool inlet air may be a better approach if fabrication or maintenance is simplified. An NACA inlet would be fine.

I'm just sayin'.
 
I have already decided against any gains from ram air, not at my speeds. Cool and adequate is my only goal. A friend with the same engine tried the NACA vent, they apparently only give small flow, not enough to feed the engine adequately (he took it off, turned it upside down to make a scoop effect, made a world of difference..

DanH said:
At LSA speeds there is not much potential manifold pressure increase due to "ram air". The maximum available Q for 125 knots is about 0.75" Hg at sea level. Since we don't fly at sea level and the maxQ figure assumes a zero flow inlet, you probably shouldn't expect more than 0.3" in actual use. Point is, simply supplying cool inlet air may be a better approach if fabrication or maintenance is simplified. An NACA inlet would be fine.

I'm just sayin'.
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DonFromTX said:
I have already decided against any gains from ram air, not at my speeds. Cool and adequate is my only goal. A friend with the same engine tried the NACA vent, they apparently only give small flow, not enough to feed the engine adequately (he took it off, turned it upside down to make a scoop effect, made a world of difference..
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A properly sized and placed NACA vent can actually supply a lot of air, but just sticking one someplace convinient will often result in poor performance.

If it is located on a surface in a low pressure area or with a thick boundry layer, it will not perform very well (if at all). I know of instances when people experimenting with NACA vents found that the installed location resulted in flow in the reverse direction from what was needed.
 
I think you hit the nail squarely on the head there. The location appeared to be in just such an area.

rvbuilder2002 said:
A properly sized and placed NACA vent can actually supply a lot of air, but just sticking one someplace convinient will often result in poor performance.

If it is located on a surface in a low pressure area or with a thick boundry layer, it will not perform very well (if at all). I know of instances when people experimenting with NACA vents found that the installed location resulted in flow in the reverse direction from what was needed.
Click to expand...
 
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