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Smooth bottom cowl system???

smooth cowl

Chuck:

I want this "smooth" cowl for my 7A as well. My understanding is that I have to go with the horizontal induction engine. The consequence of this is that the engine intakes air from one of the front cowl intakes. As a result, you probably lose any ram air benefit that would be had from a more forward facing intake like the snorkel (or Checkoway's modified forward intake). In addition, the twists in the inlet duct to take the air from the cowl intake to the engine intake most likely further reduce the velocity of the incoming air. Finally from what I have heard the ability of the engine to intake air during steep angles of attack is impaired if you use intake air from the cowl intakes rather than the snorkel.

I hope one of the experts in this area chime in to either correct or corroborate what I have said.
 
Chuck I believe you are confused.
The smooth bottom cowl has no "scoop" but I guarantee you it has the snorkel.
 
Maybe dazed but not confused.....

Look at the picture of the yellow RV8 in the first post.

Where is the air intake? Several others like this have been seen on here in the last few months, in particular a polished and red P51 looking -8 a month or 2 ago.
 
Chuck-

The "snorkel" refers to the fiberglass tubing that takes the air from the left intake ramp down to a horizontal induction.

The "scoop" is for a vertical induction system, FAB, etc.

To go smooth, you need a snorkel...and from what I understand, most likely FI.

Joe
 
Horizontal Induction

Chuck

To use the smooth bottom cowl you need to have an engine equiped with horizontal induction. The intake on Dan's cowl was a modification done for ram air. If you have this type of setup you do not have to go with the ram air mod. The yellow RV8 you show in the pic for example is not using ram air. The air gets picked up thru a FAB snorkle under the cowling. The air comes in thru the the top of the snorkle that terminates at the baffle in the left intake.
 
Here's One Using the Vans FAB with Modifications

This is the setup on my Superior IO-360 Horizontal cold air induction. The paper towels are covering the K&N filter in the snorkel. The fit of the FAB was poor as I had interference with the Plane Power Alternator bracket and also the starter solenoid. I attempted to heat the fiberglass and make a bend, but couldn't get enough clearance. Eventually the FAB was cut and new fiberglass was layed up to provide clearance.

 
OK Now about the tradeoffs.....

So it looks really slick-all will agree to that I expect. What other advantages-disadvantages are there? Is it just another way to skin the cat?

Any effect on the cooling process?
 
A little history on Van's "smooth bottom Cowl" intakes:

Van's first use of an injected engine was the blue-green RV8 prototype. It had a 200hp Lycoming IO-360 with a forward facing injector body and first flew with a ram air inlet akin to the one on the Sam James cowl. On the production version the intake system was reconfigured to the present snorkel intake. The combustion air is taken from inside the cowl in front of #2 cylinder. While on first thought a straight ram air inlet would appear vastly superior, the snorkel intake has it's own advantages and performs very well (Van likes speed and efficiency). The air entering the cowling thru the inlets pressurizes the area above the cylinders and allows the engine to breathe this pressurized air supply. This architecture allows for the placement of an appropriate air filter resulting in minimum loss of air flow. Incorporating an adequate air filter in a straight ram air inlet given the physical lack of space under the cowl in that location might have been one reason the snorkel solution was chosen. An added benefit was the smooth looks of the cowl without a ram inlet snout.

Martin Sutter
building and flying RV's since 1988
 
The "cold air" advantage only applies if you are comparing it to an air intake source under the cowl that is taken from the rear baffle. Van's intake is located immediately behind the cowl inlet before the air comes in contact with the hot cylinders and is therefore cold also.

Martin Sutter
Building and flying RV's since 1988
 
Dan C's MP data is interesting. Theory says a good snorkel from the cooling air intake should get pretty close to the same MP as a straight front intake. The theory assumes good intake pressure recovery, a correctly sized filter, and no adverse twist and bends.

Dan's "snorkel" looks like it should work better than Van's. As I recall the stock fiberglass duct has a pretty sharp radius right before the throttle body. Dan used an alternate air duct from AFP which brings air to the front of the TB at less of an acute angle.

If you crank K&N's equation for filter size, the filter supplied with the Van's snorkel is undersized. Still, the pressure drop may not be significant.

I'm near enough to building a combustion air intake to be thinking about this stuff. At the moment (ha!) I'm inclined to take air from the left cooling intake, pipe it to a filter can in the lower left front cowl, and turn it into the AFP FM-200 with a 3" radius silicone hose. The filter can would accommodate a conical filter with more area than the standard flat filter, and would allow a water drain. The silicone hose would require a bump in the lower cowl; there's just not much room to work with in front of AFP's longer TB.
 
Last edited:
One-off snorkle intake duct & RSA5 adapter...

Pics tell the story best:

Machining the IO sump for frontal induction
engineoilsump04.jpg


We fitted an "IO"sump to an "O" top end. This required using IO360C intake pipes with a .250" thick adapter at the cylinder attach point. We liked the IO sump because of its smaller vertical profile, pseudo cold air induction, and frontal intake config.

"IO" sump fitted to "O" top end. Note intake pipe adapter.
intaketubeadapters08.jpg


The next trick was to design and fab an adapter to mate the RSA-5 throttle body to the sump.

Throttle body adapter
throttlebodyadapter05.jpg


Now a fiberglass S-duct was designed. Although it looks sort of crooked, it actually has a linear reduction in cross sectional area from inlet to nozzle. The duct also looks clean from the top because we hid almost all the attach hardware underneath the baffle floor.

Intake duct
inductionsystem07.jpg


The filter is a cut down K&N mounted in front of the #1 cylinder. It slides out the front for cleaning.

K&N filter
inductionsystem13.jpg


The view from underneath shows how it all fits.
engineunderside06.jpg


Just one way to do it... more pics posted at the Picasa web album.
 
Martin Sutter said:
The "cold air" advantage only applies if you are comparing it to an air intake source under the cowl that is taken from the rear baffle. Van's intake is located immediately behind the cowl inlet before the air comes in contact with the hot cylinders and is therefore cold also.

Martin Sutter
Building and flying RV's since 1988
Click to expand...
The cold air I am talking about is on the forward sump the air is not running through hot oil as in a vert.sump has nothing to do with the air pick up.
 
Rear baffle air

About taking air off the rear baffle:

Interestingly, on my RV4 I used air from the rear baffle as fresh air supply to the cockpit, AND for induction air to the engine. The pick-off point for the fresh air was about 1/2 way between the cylinder fins and the top of the baffle.

Result: Same temp as outside air, as far as I could measure. There was no measurable increase in temp at the rear baffle at all. I assume all the air flowing through the upper cowl plenum went down through the cylinder fins and out the bottom. None of the heat went up, as long as the plane was flying.

The induction air was taken from just above and behind the right rear cylinder. It ran through a 3" hose to the fuel servo, which was turned around backwards under the sump and *then* through a 90 deg elbow. My manifold pressures ran consistently the same (in formation) as a friend who had a straight-through gut shot into his sump, with a snoot right below the spinner. Maybe conventional wisdom isn't so conventional.

One data point... take it for what its worth.
 
Really pretty work Bill. Good data too (the rear baffle air source).

<<Although it looks sort of crooked, it actually has a linear reduction in cross sectional area from inlet to nozzle.>>

Student question please. Is there a specific reason for a linear reduction in cross section? Some bit of aero theory that suggests an advantage?
 
Dan, I was wanting to avoid rapid changes in pressure inside the duct. As we shaped the foam around the starter, it turned out that was also close to where we had minimum lower cowl clearance. The duct cross section thus began to get too small in that area, and the next thing the flow would encounter would the the 90 degree bend into the throttle body.

So, I decided to take a closer look at the duct's cross sectional area. I found that we had a minimum cross section right before the bend, and thats not good. There could be some flow separation or instability on the inside bend surface.

I was then faced with adding cross section in the critical area and needed to know how much, so I simply fit the area -vs- duct position to a linear function.

Short of doing a CFD analysis, this is a WAG at avoiding flow problems.

Bill
 
Bill Wightman said:
Dan, I was wanting to avoid rapid changes in pressure inside the duct. As we shaped the foam around the starter, it turned out that was also close to where we had minimum lower cowl clearance. The duct cross section thus began to get too small in that area, and the next thing the flow would encounter would the the 90 degree bend into the throttle body.

So, I decided to take a closer look at the duct's cross sectional area. I found that we had a minimum cross section right before the bend, and thats not good. There could be some flow separation or instability on the inside bend surface.

I was then faced with adding cross section in the critical area and needed to know how much, so I simply fit the area -vs- duct position to a linear function.

Short of doing a CFD analysis, this is a WAG at avoiding flow problems.

Bill
Click to expand...

Which is why I decided not to mess with the FAB to make it fit the AFP intake.

Interesting to read what Dan Checkoway had to say about this issue 4 years ago. I know he flew with his own FAB at the left intake connected with scat tube to the AFP "y", but I don't know if he abandoned it later. Seems like later photos of the airplane show the intake below the prop missing but it may have not been visible due to the angle of the shot. I do know he achieved great air flow with very little MP drop using his intake device and the direct ram air "y" may have been removed.
 
Snorkel

Disclaimer 1st! I'm not a engineer and know little about flow dynamics. The Van's snorkel has a large increase in x-sectional area just before narrowing to the throttle body entry. It always seemed paradoxical to me that pressure is low in a constricted area such as that (and flow velocity high). Downstream from the narrow area the pressure goes up and flow velocity down. Might this yield an increase in MP? As long as flow rate remains high enough, that sounds good. Van considered the snorkel lost minimal MP compared to the standard scoop intake but was a little cleaner, so about a wash overall. Anybody knowledgeable please comment/correct. Bill
 
Snorkel

Disclaimer 1st! I'm not a engineer and know little about flow dynamics. The Van's snorkel has a large increase in x-sectional area just before narrowing to the throttle body entry. It always seemed paradoxical to me that pressure is low in a constricted area such as that (and flow velocity high). Downstream from the narrow area the pressure goes up and flow velocity down. Might this yield an increase in MP? As long as flow rate remains high enough, that sounds good. Van considered the snorkel lost minimal MP compared to the standard scoop intake but was a little cleaner, so about a wash overall. His design surely does not have a linear decrease in cross-sectional area. Anybody knowledgeable please comment/correct. Bill
 
DanH said:
Dan C's MP data is interesting. Theory says a good snorkel from the cooling air intake should get pretty close to the same MP as a straight front intake. The theory assumes good intake pressure recovery, a correctly sized filter, and no adverse twist and bends.

Dan's "snorkel" looks like it should work better than Van's. As I recall the stock fiberglass duct has a pretty sharp radius right before the throttle body. Dan used an alternate air duct from AFP which brings air to the front of the TB at less of an acute angle.

If you crank K&N's equation for filter size, the filter supplied with the Van's snorkel is undersized. Still, the pressure drop may not be significant.

I'm near enough to building a combustion air intake to be thinking about this stuff. At the moment (ha!) I'm inclined to take air from the left cooling intake, pipe it to a filter can in the lower left front cowl, and turn it into the AFP FM-200 with a 3" radius silicone hose. The filter can would accommodate a conical filter with more area than the standard flat filter, and would allow a water drain. The silicone hose would require a bump in the lower cowl; there's just not much room to work with in front of AFP's longer TB.
Click to expand...

Ah, but there's one caveat with his MP numbers. His "y" has one butter fly valve. When the ram valve is opened, air flow is direct to the FM200 but also flows back up the plenum to the filter via the "y" connection. This would make it almost impossible to see much increase in manifold pressure and explains why those with the 2 butter fly set up see a jump in MP. Air flow is blocked to the filter.

When I talked with Don at AFP about buying this device, I did not know it came with 1 or 2 valves. Don said the one valve system will work and not only that, the filter will get cleaned by reverse air flow when the ram valve is open. :) I opted for the 2 valve deal and that's why there is a jump in MP when the ram air knob is pulled.

 
<<I opted for the 2 valve deal and that's why there is a jump in MP when the ram air knob is pulled.>>

(breathless with anticipation he asks <g>): How much does it jump?
 
DanH said:
<<I opted for the 2 valve deal and that's why there is a jump in MP when the ram air knob is pulled.>>

(breathless with anticipation he asks <g>): How much does it jump?
Click to expand...

It was about 1.5". The rpm went up from 2250 to 2400, I could hear and feel it.

(Sure will be glad when this winter is history. Several days ago we had 4" of snow on the runway, then it melted and there was mud, today it was frozen hard as a rock and rain is in the forecast this week end. It will be days until the frost is gone and things dry out. That is the down side of living with a grass runway.)
 
<<It was about 1.5". The rpm went up from 2250 to 2400, I could hear and feel it.>>

Holy cow. Is your filtered air like Dan C's (from the left cooling air inlet) or just from inside the lower cowl?
 
DanH said:
<<It was about 1.5". The rpm went up from 2250 to 2400, I could hear and feel it.>>

Holy cow. Is your filtered air like Dan C's (from the left cooling air inlet) or just from inside the lower cowl?
Click to expand...

It was from inside the cowl and too small. A second version uses an intake from the left baffle area and is better but needs improving. I did not read about the Dan C install until just a few days ago. I am finding out lots of other guys have done it similar and it works but each is a little different.

None of this is rocket science. Van has been down this road and what is in the plan is good stuff all based on Lycoming, Precision Air or a carb, and their FAB. The problem is it was not designed around AFP and some adjustments have to me made to use this very good system. I came away from OSH last year thinking the ram air inlet for AFP was a good idea and that's what's going on here. In a brief discussion, Van himself seemed to agree . They know what is offered in the kit will not fit that system.
 
I'm curious because I am considering a ram air system. When do you pull the lever for ram air? I assume it is when you are out of the "bug" zone? What is the logic for when you go to ram?

In considering a ram system, I've made the assumption that you want to open it up once you are reasonably safe from ingesting bugs. However, I've still seen bugs as high as 5-7K in the summer in the Midwest. If I fly at lower altitudes typically, I'm afraid I would never be able to open it. I must be missing something.
 
f1rocket said:
I'm curious because I am considering a ram air system. When do you pull the lever for ram air? I assume it is when you are out of the "bug" zone? What is the logic for when you go to ram?

In considering a ram system, I've made the assumption that you want to open it up once you are reasonably safe from ingesting bugs. However, I've still seen bugs as high as 5-7K in the summer in the Midwest. If I fly at lower altitudes typically, I'm afraid I would never be able to open it. I must be missing something.
Click to expand...

All very good questions and I do not have the answers. In fact I will add one more to the list - could a big fat high flying bug shut down the engine if it got into the intake of the FM200? From the AFP manual on the air section of the controller "A measure of the air flow consumption of the engine is accomplished by sensing inlet air pressure and venture throat pressure in the throttle body." Could these sensors be jammed by an ingested bug? Maybe Don Rivera could shed some light on the issue if he is tuned in.

I read Dan C's report on ram air one more time.
http://www.rvproject.com/20050426.html
He has proven it may not be worth the weight and complexity if one can get the air flow issues of filtered air worked out. He calculates ram air boosts MP .3". The MP comparisons at 5500' with 3 other airplanes seemed to confirm it. His filtered air MP was as good as ram air with his flying friends.

Obviously there is considerable pressure at the baffle inlet that makes this possible and it appears he achieved it even with the use of scat tubing. This may be why Van decided ram air was not worth it and leads one to believe the FAB unit with its smooth interior is a very good way to go with a Precision fuel controller. But it does not resolve the issue of doing it with AFP. Each pilot is coming up with his solution and until some vendor comes up with a dedicated AFP FAB, they will all be a little different.

With regard to opening the ram valve, I've been doing it at about 2000' AGL. The Dan C. report does address this issue as there is considerable dust to contend with in Southern California.
 
Ram rise data (theory only)

FWIW:

The "ram rise" we speak of here refers to the dynamic pressure imparted to the flow due to the speed of the airplane. This is simple to calculate:

Pressure = 1/2 * air density * velocity^2

At 8000 MSL, and standard conditions atmospheric air density is .0018678 slugs/ft^3.

Lets calculate the dynamic pressure (Q) for 200 mph, which is 293 ft/sec.

These conditions yield a theoretical maximum ram pressure of 80.17 lbf/ft^2 or .557 lbf/in^2.

My RV4 would get about a 1/2" rise in MAP when I switched from the alternate source in the lower cowl area to the ram source at the upper rear baffle. At my normal cruise speed/altitude, I found that I was getting 80-85% of the theoretical max ram recovery. Not too bad.
 
FWIW. I have the same setup as Dan C. I get a rise of .3 inches at
7500 ft WOT. You can see the setup here: http://rv7-a.com/ramair.htm
This is a single valve Y tube fed from the left forward baffle, K&N filter and
custom fiberglass snorkel.
 
Bill Wightman said:
FWIW:

The "ram rise" we speak of here refers to the dynamic pressure imparted to the flow due to the speed of the airplane. This is simple to calculate:

Pressure = 1/2 * air density * velocity^2

At 8000 MSL, and standard conditions atmospheric air density is .0018678 slugs/ft^3.

Lets calculate the dynamic pressure (Q) for 200 mph, which is 293 ft/sec.

These conditions yield a theoretical maximum ram pressure of 80.17 lbf/ft^2 or .557 lbf/in^2.

My RV4 would get about a 1/2" rise in MAP when I switched from the alternate source in the lower cowl area to the ram source at the upper rear baffle. At my normal cruise speed/altitude, I found that I was getting 80-85% of the theoretical max ram recovery. Not too bad.
Click to expand...




Um, yeah, I was told there would be no math...

Joe
:)
 
walter said:
FWIW. I have the same setup as Dan C. I get a rise of .3 inches at
7500 ft WOT. You can see the setup here: http://rv7-a.com/ramair.htm
This is a single valve Y tube fed from the left forward baffle, K&N filter and
custom fiberglass snorkel.
Click to expand...

I looked at your pictures, Walter, nice work and a lot of it. With just a .3" rise in MP going to ram air I am beginning to wonder if it is worth it.

There is another set up with AFP where a guy used a cone shaped K&N filter attached directly to the FM200 without the "y". He had a tube of sorts around the filter extending forward and brought ram air straight in to the device. More and more stuff to think about.
 
There is another set up with AFP where a guy used a cone shaped K&N filter attached directly to the FM200 without the "y". He had a tube of sorts around the filter extending forward and brought ram air straight in to the device.
Click to expand...

I know one guy who has that identical setup: Tom Stearman - with a 200HP C/S RV4. He and I flew tons of formation together. He was hangared at Wiley Post in OKC for years, now flys out of a private strip near Tulsa.

Tom and I had nearly identical ram pressure increases when flying side by side (we both could switch from ram air to non ram air). The increase was just under 1/2" MAP as I recall. A bit more than the .3" you're quoting.

Tom had what I called a "gut shot" straight through into the AFP system through a conically shaped K&N filter; I took air off the rear baffle also with a K&N. There was virtually no difference in ram recovery between our planes. And that makes sense since we're both taking the air and slowing it to zero speed.

At any rate, we're talking about roughly a 3% increase in MAP for doing this... I don't know how much HP that equates to but it does make a difference one can feel.
 
Bill makes a good point; there is only so much dynamic pressure available (1/2*density*V^2). The trick is to recover as much of it as possible. You have the same goal for a cooling air plenum. If that plenum has good recovery, then tapping combustion air from it is potentially as effective as a "ram" intake.

The real trick is delivering that pressure to the throttle body without loss. Bill made a point of ensuring his snorkel didn't suffer from an adverse pressure gradient due to an increase in duct volume following a "pinched" point near the starter. Dan C's duct is constant volume. If I understand theory correctly, the constant volume corrugated duct may suffer some loss of CFM compared to Bill's tapered duct, but it should not lose pressure. As long as CFM is adequate, it doesn't matter. We're interested in pressure.

BTW, if I understand Bill's earlier RV-4 intake correctly, it was also a scat tube duct.

Comments?
 
smooth bottom cowl

cawmd82 said:
Several RV8s have been seen lately with a smooth bottom cowl and no snorkel:
One example....several others seen on here lately.......
http://picasaweb.google.com/VansAirForce/52F_013109#5297553987192232914

Which induction system(s) work this way?

Any major disadvantages/advantages besides the clean look?

Exactly how does the air intake get plumbed?
Click to expand...

Look at my web www.ramairforhomebuilts.com
I sell a system for the forward facing sump/fuel servo and a 3" aluminum ring mounted in a fiberglass scoop/snorkel. My RV8 fastback is a good example of the system and can be seen on the web. Rod
 
<<I sell a system for the forward facing sump/fuel servo and a 3" aluminum ring mounted in a fiberglass scoop/snorkel.>>

As I understand the system, all filtered air is taken from inside the lower cowl. The air is hot and must work its way past the flapper valves, which means takeoff power is compromised if you're not willing to chance bugs and rocks and grass seed on the runway. The website reports a 1" rise in MP with the no-filter valve open.....which brings up a question. Is that 1" rise measured at cruise altitude and speed, or at ground level and low speed? Big difference.

Note the "velocity squared" input in the dynamic pressure equation. The potential dynamic pressure available for recovery at low speed is minimal. Here's a handy chart from "Aerodynamics For Naval Aviators. Compare 100 and 200 knots at sea level. The big jump (34 to 136 lbs per sq ft) is the result of velocity:



Now consider runway performance. Some quick calculator banging says given 50 knots as rotation speed, available dynamic pressure is 8.5 lbs per sq ft. That's only 0.059 psi, or 0.12 inches of manifold pressure (Hg).

A system with a 1.0" gain when run valve-open for takeoff isn't recovering dynamic pressure because there is almost none to recover. It is merely bypassing a compromised filtered air source. Using filtered air for departure probably lengthens the obstacle clearance requirement quite a bit.

Yes, I'm ignoring air velocity due to propwash, although I'm not so sure it makes any difference. David reported over an inch of loss using filtered lower cowl air, and that was with an AFP Y-valve (an open alternate throat, no flapper restriction). John Huft reports about 2" loss for a system similar to Rod's, although he also reports his flapper area as too small.

Any lower cowl air source starts out compromised. In rough terms we need about 2 lbs per second air mass to cool our Lycomings, which means a baffle pressure drop around 5 to 7 inches of water, or 0.35 to 0.5 inches Hg. Put another way, taking the filtered alternate air from the upper plenum should always net 0.35 to 0.5 more MP than a lower cowl source.
 
DanH said:
As I understand the system, all filtered air is taken from inside the lower cowl. The air is hot and must work its way past the flapper valves, which means takeoff power is compromised
Click to expand...

I talked to Rod yesterday, as I recall, the flow drop was only 3% loss from straight through, to filtered bypass.

400 cfm vs 388 cfm were the numbers I remember him stating.

This testing was done on a flow bench.

IMHO, if you NEED to be concerned about 3% takeoff power, then you are flying too close to the edge for me.

My main interest is for fuel savings at cruise, where the plane will spend the majority of its operational time.

Hopefully Rod will jump in here and confirm (or correct) my figures, and maybe give a better explanation than I did
 
When using internal lower cowl air as the source of filtered air, perhaps of greater concern than pressure is the temperature of that air, which is of course related. One would have to measure it to be sure but it would seem during summer months it could easily be 200F vrs 90-100F is using an external source. The cylinders are over 300 and the exhaust pipes over 1000 degrees, it is a warm environment. If anyone has measured forward lower cowl temperatures, it would be interesting information.
 
David-aviator said:
When using internal lower cowl air as the source of filtered air, perhaps of greater concern than pressure is the temperature of that air, which is of course related. One would have to measure it to be sure but it would seem during summer months it could easily be 200F vrs 90-100F is using an external source. The cylinders are over 300 and the exhaust pipes over 1000 degrees, it is a warm environment. If anyone has measured forward lower cowl temperatures, it would be interesting information.
Click to expand...

Really Eazy DECISION.

When in doubt open the ram air valve and have at least 1.5" over warm inner cowl air. Nice to use in icing. Don't use it the ram air unless you need it. Problem solved. A little dust will not cause that much damage if only for a few minuets.

Maybe a few "Extra Minutes on un-filtered air" (max HP) in a serious situation is better that no options at all. Who wants to get familiar with "terra firma"?

Why do RVr's increase compression ratio's and spend $$$$$ on speed mods that reduce the life of the engine for that extra edge when needed ? SECOND SUCKS that's why.

"Ram Air" is free..Use it when you need it. Close the valve when the air is dirty.

It may be interesting to note that 1/8" flange thickness on my ram air valve reduced the volumetric efficiency 8CFM (beveled and fixed) on a high end "FLOW BENCH" this week end. God forbid what 90 deg. turns and scatt tubing and filter off of the rear baffle does to air flow and volumetric efficiency.

What about the relative air of 200 MPH in flight directly on the servo that's
6" from the prop blast. Not avialable in the inner plenum.

Something to ponder...Why does a NAS car engine (360cu) produce close to700 HP. on NON supercharged engines. LYCOMING 360 produces 180 HP @2700 rpm. Volumetric efficiency for one thing.

My ram air filter system Flowed 400CFM (bench flows at 400 CFM) and when it was swithed to K&N filerted air it Flowed 388 CFM (4%loss). This was not in a warm air environment but it is a consideration when comparing it to an inefficient system such as lots of turns and angles. Throw in a scatt tube and a poor filter then compare to the incremental loss (.5") of warm air in the cowl. These are hard numbers that can be verified at LY-CON engine rebuilders in Visalia.

I still have alot to learn, but I have built a Starduster II, an RV3, RV4, two RV8's A STEWART MUSTANG, and six restorations and have learned all kinds of things with each project.

30 Years of problem solving and having fun building Experimental Aircraft is just a start in this wonderful hobby.

I have been verifying results on LY-CON'S flow bench lately and it has allowed me to focus on just one part of the incremental approach to improving volumetric efficiency.
It's hard to beleive what a little head flow work/indexing the cam/roller llifters(Lycoming) electronic ignition/ and higher compression will do. Add all of the above incremental improvements and cold air induction/ram air and $$$. WOW -

Dave Ander's addressed the cooling and airframe drag issues and his improvements showed what his RV4 machine($65,000 NASA prize) is capable of. Eat's Harmond Rockets for lunch.

LY-CON (Visalia, Ca) has spent over 10 years developing their engine improvements and now have an STC on engine case "O" rings. They have thousands of hours of adding and removing material in Flow Bench Analysis. They finally digitized the results and consistently replicate the optimum head flowing. The Haws CNC is 5 axis and is really awesome.

I have been reading the reply's on the Ram Air and find alot of Pepper Tree Analysis with out flow bench analysis or real field comparisons. (apples to apples.)

There are so many variations in each experimantal induction system in the field that unless a standard system is addressed and compared to "say a Van's airbox" the observations are meaningless.

Early on, when I was flying my RV4 I remember a trip back from Prescot Az, with Dave Anders RV4. I was having trouble keeping up at 12,500 ft. My RV4 had a smooth bottom cowl and the filtered air was taken off the right rear baffle. He had electronic ignition and an angle valve and I didn"t. I figured that I would kick the RPM up a thousand. (and lie alot). Guess what, I slowed down. Volumetric efficiency!!! Solution...went to a Van"s lower cowl scoop. Problem solved. Figure that . Before I tried ram air.

How many stories and good times in 30 years.. I have already gone on to long.

Want to go fast---- talk to Dave Anders. He De Guru on Dat stuff.

Rod
 
Hello Rod,
Thanks for checking in. Don't get the idea you're being singled out. The discussion is about the pros and cons of various intake configurations; none are perfect. I've suggested your particular configuration has one major drawback, a large loss of manifold pressure when operating on filtered air for takeoff. It is in all other respects a nice piece.

<<When in doubt open the ram air valve and have at least 1.5" over warm inner cowl air.>>

Are you confirming the system has a valve open/closed difference of 1.5 inches at runway speeds?

<<My ram air filter system Flowed 400CFM (bench flows at 400 CFM) and when it was swithed to K&N filerted air it Flowed 388 CFM (4%loss).>>

Probably a good SuperFlow bench with FlowCom and a motor controller for automatic test pressure regulation, so both CFM numbers were taken at the same test pressure (probably 28") ?
 
DanH said:
Hello Rod,
Thanks for checking in. Don't get the idea you're being singled out. The discussion is about the pros and cons of various intake configurations; none are perfect. I've suggested your particular configuration has one major drawback, a large loss of manifold pressure when operating on filtered air for takeoff. It is in all other respects a nice piece.

<<When in doubt open the ram air valve and have at least 1.5" over warm inner cowl air.>>

Are you confirming the system has a valve open/closed difference of 1.5 inches at runway speeds?

<<My ram air filter system Flowed 400CFM (bench flows at 400 CFM) and when it was swithed to K&N filerted air it Flowed 388 CFM (4%loss).>>

Probably a good SuperFlow bench with FlowCom and a motor controller for automatic test pressure regulation, so both CFM numbers were taken at the same test pressure (probably 28") ?
Click to expand...

Dan, over the last 3 years my system has gone through several changes. John Huff supplied the ram air valve and it was mounted directly to the tapered K&N filter. This allowed for ram air when open and warm filtered air in the closed position.
My first experience with this system resulted in a loss of .5" on the ground using inner cowl air. The flight showed a gain of 1". After flying it and removing the cowl I noticed that the treatment oil had blown onto the inner cowl surface.
This was remedied by a fiberglass cannnister to contain the overboost and resulted in a 1.0" gain at crusing altitude. If you subtract the .5" loss with filtered air the net is close to what others on this site are experiencing.

My next change was to create a bridge between the filter cannister and the 3" tube that supplied the ram air. This solved the inner air problem as both the ram and filtered air came from the same source. Problem fixed. Well almost as the package , though compact, created install problems for builders and required alot of fiberglass rework.

This led to the current aluminum cannister system and most of the install problems were resolved. There is a trade off with the inner cowl temps but not a great loss in MP rather a small loss as experienced by my customers.

I flew my first leg to OSH from Visalia to Provo UT and climed to 13,500 ft with the filtered air activated and noticed no performance issues. I also activated the filter at 14,500 ft on the way to Arlington, WA due to smoke and still had no issues. When I open the ramair at that altitude and at 2500 rpm I got fuel burn down to 6.2 gph and showed a 160k tas. Close to 30 mpg.
At 6500 ft going to West Coast flyin and 25 sq my advanced flight system showed a 191 kt tas cruise at 9.5gph

I am still learning about my new plane and can only offer my experience with my plane and point to my web testimonial of Ron Keilin in Florida(RV8). Ron flew my fiberglass system with the outside filtered air for several years and then replaced it with the alum cannister that utilizes the inner cowl air. Ron has lots of experience with both systems now and would be happy to field any questions. Gets pretty hot in Florida and Ron has not seen as a problem.

The beauty of this induction approach is the simplicity and time it takes to install. My goal is to supply a quality product that minimizes the work needed to have a flying airplane. I have just finished a complete bolt on system for the RV-10 that can be installed in one morning and the fiberglass scoop takes less that 30 min to cut and glue in. Try installing Van's filter system and keep track of the time it takes.

I have quite a few systems flying now and will share the results as they come in.
By the way the flow work was at 28" and it was really an eye opener when we tested the RSA5 and the FM200 fuel meters. I am in the process of making a video of the flow work at LY-CON and will post on my web soon.

Rod
 
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