The Extra Inch...

[bjdecker]

Originally Posted by Carl Froehlich

I did a beta test of a new snorkel before Oshkosh. I did the same data runs with the orginal snorkel and the new one.

Hey Carl,

Do you happen to know the part number for the new snorkel? Is it VA-132-3? or VA-271-1? Or...something else??

Cheers,

B

[Carl Froehlich]

As far as I know the new snorkel is not yet in production.

Carl

[mr.sun]

I have been thinking on this for quite a while and here was my approach. Put a 2” slide valve on the rear vertical baffle above #3 cylinder operated from cockpit. Route a 2” piece of scat tubing under cylinder 1 & 3 to the starboard side of the snorkel with a 2” flange attached over a 2” hole in the snorkel. Bend and fiberglass into place with no air leaks. Then above 1000’ pull the slide valve open to augment air coming thru the filter and increase MP by at least the pressure loss thru the filter. Since I have no alternate air valve, I figured this would also do double duty and get me air to the engine if the filter got plugged in flight. Not full power with it only 2” but partial power is better than none. Have not built any of this yet. Opinions.?

[DanH]

Originally Posted by mr.sun

Opinions.?

I doubt you'll see a manifold pressure rise for three reasons.

The flange entry and long hose will exhibit pressure loss just like the filter, probably more.

The Cp plots in 3405 suggest slightly lower pressure available in the rear baffle zone, as compared to just inside the inlet.

The legacy snorkel flows poorly around the sharp bend at the lower neck, and you're still stuck with it. The neck is a significant change on the new snorkel.

[bjdecker]

Thanks DanH, Carl, Carl, Bill, others...

I spent some quality time with Savvy this afternoon and analyzed a dozen or so flights since the Condition Inspection. What jumped out at me was the fact that my MAP has been steadily decreasing since last October. Why is that significant? It happens to be the last time I cleaned & recharged my K&N air filter.

The Data, gathered at 6500ft - 30.02"Baro, 2500RPM, WOT, 50°F ROP.:

Fresh Filter -> 23.9" MAP
11 month filter (<60 hours) -> 23.4" MAP

So there's .5" of MAP lost sucking through a dirty filter, who'd a thunk it...

[Radomir]

I just put a new filter and I saw no change in MAP.. I looked back 6 months and compared with similar flight a week ago and they both show 20.0 inches at 11,500ft.. so for me, brand new filter did not seem to make any difference. Old filter was of unknown "history" (unknown to me.. no idea when it was cleaned last time)

[bjdecker]

Originally Posted by Radomir

I just put a new filter and I saw no change in MAP.. I looked back 6 months and compared with similar flight a week ago and they both show 20.0 inches at 11,500ft.. so for me, brand new filter did not seem to make any difference. Old filter was of unknown "history" (unknown to me.. no idea when it was cleaned last time)

Assuming a local baro of 29.92" (std.day), your 20" MAP is .6" above "ambient" or "free stream" air pressure. Not too shabby...

[pa38112]

To the OP: Your filter is too close to your scoop, and you have a bad transition of shapes. The key to air flow is to keep the airflow laminar. There are many engineering rules of thumb for this, like the number of diamaters between transitions, and the air-to-cloth ratio of the filter size. I look at your design and I see turbulance. A few sugestions if you are going to stay with your current pick-up location:
1. Reloacte the filter to an area where you can put a good transition in and out of it.
2. Make your scoop round, like the old ship air inlets.
3. put an air flow straightener after your pick-up. You are capturing turbulant air there and need to settel it down.

The Sam James cowl has a very good design. I forget my numbers, but get good MP with mine. I had to rework the filter box to get better tranitions. and I installed airflow straighteners after my filter.

Having said all of that: your current performance seems fine. You are not going to get a noticable preformance increase with this work. Unles you are racing, I would spend the extra time flying.

[Pilot135pd]

Originally Posted by bjdecker

I fabricated a "hood scoop" to sit on top of the air filter...

I need to learn how to work with fiberglass, that scoop looks like something factory made !

[Carl Froehlich]

Originally Posted by bjdecker

Assuming a local baro of 29.92" (std.day), your 20" MAP is .6" above "ambient" or "free stream" air pressure. Not too shabby...

I did a careful calculations of actual MP on the ground with the engine off (correcting for field elevation and local barometric pressure). I ended up inserting a correction factor of -0.4” into the SkyView EMS to get a more accurate MP readout (as in before the correction the MP pressure was reading 0.4” higher than actual).

Assume the whatever you are reading for MP is off unless you calibrate the sensor.

Carl