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Intake Pressures

Not sure if this post is relevant anymore, but just going to park the info here for future reference.

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All that said, if Bob is indeed pulling 23+ inches at 9.5 altitude, I want me some of that!

Michael,

All still relevant, as we're still collecting data to analyze my MP results, and the possible impacts of my intake plenum and servo.

I did one flight to take delta P measurements requested by Dan and Steve, and to run a test for Dave Anders to compare our MP at 17,500' MSL.

I ran a prelim series of delta P tests, but didn't do it at WOT, so the conditions aren't really what they are looking for. This run did show an increase in pressure from the intake manifold to the MP line that goes to my JPI. It may show the Sky Dynamics plenum and intake runners are providing a benefit there. Dan and Steve want to see some WOT runs before any further analysis or conclusions. A drop was shown between the inlet to the FM-300 and the intake plenum, due to the partially closed throttle, as expected...but this skewed the rest of the tests, so I'll be doing them again. When I do, we'll post all the locations of the pressure taps and what is being compared.

After that test, I climbed up to 17.5K and tried to match speed with a recent test Dave had run on a X-C flight. He sent me a photo (pasted below) of his -4 making 142 MIAS/ 192 MTAS, at 5.7 GPH. That's 33.7 mpg, at nearly 200 mph...wow!!

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Dave's power was WOT @ 16.3" MP (very good MP at 17.5K), and 2200 RPM. My previous test at 17.5K was at 2400+ RPM, and 211 KTAS, where I saw 17.1" MP. He asked me to go up and see if I could match his speed while still at WOT, by winding back RPM. His goal was to see how our MP's compared at similar speeds, to take out the effect of additional ram air (he also has a SD plenum...and lots of other cool stuff under the hood).

I was not able to match his speed at WOT unfortunately. The prop hit the low pitch stop at 2120 RPM, and I was still at 197 KTAS (226 mph true)...so I still had 34 mph of ram effect on Dave. MP was 17.1". Not sure what that impact to MP would be, but my guess is Dave and I are getting fairly similar results, in terms of MP. My FF was 9.6 gph, so about 23.5 mpg. Not bad at that speed, but Dave crushes me in efficiency!

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I ran it back up to 2440 RPM, and it accelerated to 215 KTAS (247 mph), at 11.1 gph, for 22.3 mpg.

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While the MP numbers appear believable, yet still subject to further tests, my IAS and TAS readout appear to be a bit high. During flight test, I was typically indicating 3 knots faster than my chase. I've done two 4-way GPS runs, and showed 9 fast on the first, and 6 fast on the second...ughhhh. On that second test day, I was chased by F1Boss Mark Frederick, and my IAS was 3 knots above his, so that's two separate chase aircraft with the same result, and the delta from Mark was the same from 140 knots to above 210 knots, where he ran out of throttle (sorry Mark ;)). So am I reading 6+ high, 3 high, or ??? Mark was a legit 260 mph racer at Reno, and I had opening that day. My 4-way tests showed 231 KTAS (265 mph) on the EFIS, but the spreadsheet says less. More testing needed for sure.

I've since swapped washers under the static ports, from a pair of -L washers (1/32") to 1/64" washers that Georgetown bud Brian "Showplane" Decker had.

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I haven't had the chance to test the new static port or do more delta P tests, due to pop-up maintenance. You know that kind...where you change out the static ports, then, ah, what the heck, lets fix that wheel pant that is rubbing on the tire ever-so-slightly. Turns out it was a cracked wheel pant bracket...and while taking things off, the crack in the upper intersection fairing reveals itself...and why is the gear leg fairing open in the back? Oh those 3 pulled out rivets are the culprit. And yep, there's two on the other side too...dang it. So a couple quick fixes turn into 4 glass items to paint, just like that! Ah so what the heck, lets take the floor off and adjust the angle of the stick like I've been wanting to do...and while in there, fabricate some boots for the aileron sticks like Steve has been encouraging me to do. Can you say "mission creep"? :rolleyes:

Some pics...so the excuses aren't too hollow!

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Hope to be airborne this week to wrap those tests up, and get some good data to the team!

Cheers,
Bob
 
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Bob,

The calc for q to add to ambient MAP is based on IAS. So you would have .3" more MAP at 17500' than I do due to q. It would then appear your MAP is higher than mine at that altitude by .5" more. However you know that I have said the MAP taken at the primer port on the head isn't accurate for comparisons with other aircraft due to dissimilar induction runner lengths and runner taper ratios between aircraft unless they have the "same inductions and MAP pick up location". The reason is that the pressure at the back of the valve with your tapered runners may/is a higher mean value than the mean value of the induction plenum. So the reading you have at 17.1" (assuming it's correct) isn't the reading the engine induction system is actually seeing. It's only that cylinder for certain.

I know that sounds goofy.

The fact is I have taken data from my primer port with my tapered induction runners and compared them to my plenum that uses a Bernoullis' ram tube. The head mean pressure was 1.2" higher than the plenum. I assume that is due to my tapered runners, and it was consistent with the Ricardo Wave Program results. So in my case even though I indicate 16.3" up there, then if I added the q difference of .3" for your higher airspeed I'd have 16.6" in the plenum. However, at the head the mean pressure would be 16.6 + 1.2 = 17.8". But this kind of a comparison is not valid. We need to see what MAP you get in the plenum under the same test conditions.

Do you have a MAP port in your plenum so you could compare it the the head primer port?

Dave
 
Dave,

Makes sense, thanks! I'm doing delta P testing for Dan and Steve right now, and have a tap on the intake plenum. When that testing is complete, I'll look more closely at the photos of your set-up, and work on setting that test up.

Cheers,
Bob
 
Bob,

The calc for q to add to ambient MAP is based on IAS.

IAS?

The fact is I have taken data from my primer port with my tapered induction runners and compared them to my plenum that uses a Bernoullis' ram tube. The head mean pressure was 1.2" higher than the plenum.

DeltaP using the same measurement device, or separate measurement devices?
 
Back in the aughts, I did a lot of this on my RV-8 (Nuisance). I was trying to get the most pressure recovery I could at the inlet to the fuel servo by shaping the inlet airbox. The pressure available there is proportional to the mach number of the airspeed, and is appoximately 1" at RV speeds. This does not count any mysterious "wave" effects etc.
I would record the manifold pressure reading before engine start, and then do a low pass over the runway (10 ft. or so), and compare the readings. This was supposed to eliminate transducer errors.
At 7650' field elevation and 2400 rpm it was basically cruise power.
With an airbox shape that gradually increased cross-section area from the cowl inlet to the servo inlet (about triple) I could get about .75" of pressure recovery.
It seems to me that the upper deck pressure is much the same situation. If the inside of the inlets are smooth to reduce turbulence there, the pressures should be pretty close.
Steve, I find it interesting that you are looking at more instantaneous pressures over a single revolution of the engine? You think there might be something to gain there? Looking right at the intake valve chamber?
Have fun, John
 
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