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Intake Pressures

DanH

Legacy Member
Mentor
Rather than muck up the Carbon Fiber Wings thread (https://vansairforce.net/community/showthread.php?t=133700), I've started another here specific to combustion air intake.

Bob posted
Cruise at 9500', WOT (23.3"), 2300 RPM, 12.4 gph (slightly LOP, 14.9-15.2 AFR), came in at 218 KTAS.
which caught my attention because 23.3" hg under those conditions would be really, really good. I asked Bob for more info, and being a generous soul, he shared much here:

https://vansairforce.net/community/showpost.php?p=1659550&postcount=153

I posted
23.3" seems high for the conditions a few posts back. Breathing through a 3" inlet, at 9500, 54F, 230 RPM, 0.95 VE, and 218 KTAS, static pressure should be 20.98" with a pressure rise of 1.09", a total of 22.07" before the throttle body. Typically there would be some subsequent downstream loss for the intake plumbing (it's about an inch for my 390). Here, for 23.3 to be valid, the taper pipe manifold would have to be doing something interesting, perhaps due to increased velocity at the port (the taper), or better wave action, or both...an increase rather than a tract loss.

A differential manometer would tell. One static tap at the tube in front of the FM300, and one at a primer port, or better, an accumulator tapping several ports.

I had previous rigged pressure taps, primarily to look at the differential pressure across the nozzle bleeds on a constant flow fuel injection. The common belief was that pressure, assumed to be positive on the upper plenum side, could go negative, reducing or reversing the flow through the bleeds. There were two different experimental setups, one being a Big Picture view, and the other being a detail view, deltaP through a 720 degrees of crank rotation (0.05 sec at 2400 RPM) after the installation of turbo injector shrouds.

The Big Picture setup placed an aquarium bubble rock next to each injector nozzle, tapped into the top of the airbox, and tee'd into the manifold pressure line for the EIS. All the tubes led to the cockpit where I could connect a manometer as desired.

I've attached a data sheet. Line 17 was the test focus; average upper plenum pressure was always higher than average manifold pressure at the port, thus bleed air would be flowing as desired. No surprise here; the point was to determine how much. Not shown on this sheet but of equal interest, plenum pressure in the immediate vicinity of all nozzles was relatively even. That may not be true for all cowl setups.

Line 18 is the measurement of interest in the context of Bob's Sky Dynamics manifold. The values on the sheet reflect an FM-200 on a stock Lycoming horizontal intake sump, the manifold on the M1B parallel valve as well as most IO-360 angle valve and 390A's. The pressure loss (manometer deltaP) between the airbox and the primer port measured 14.5 inches H2O at 2500 ft, with the loss being reduced with altitude gain. Since I already had a pretty good idea of the loss for the airbox and FM-200 (from AFP's flow bench), the loss in average pressure for the Lycoming parts works out to be about 9.5" under the given conditions. Pressure variation across two crank rotations (the detail view) is more interesting, but that's a subject for another thread.

Lines 22 through 25 was a different approach to the same question. Line 30 reflects on the accuracy of another spreadsheet for calculation of pressure recovery at the combustion air intake.

The 14.4" H2O loss is about an inch of manifold pressure (1.0592" Hg). A better manifold would minimize that loss. If the 23.3" Hg Bob reported is true, the SD manifold not only negates the loss, but boosts pressure at the port. It would be really, really interesting if true.

So, Bob, that's what I did, and after you finish all the wing testing, and if you too are curious, well, all it really takes is two pressure taps...go for it! And Steve, comments welcome.
 

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I think this has the makings of a really interesting discussion.

I've been chatting with Mike Robinson (TOOBUILDER) about his various experiments in air box design. He is handcuffed by an updraft sump, at least for now (which I think has way more loss than the horizontal sump Dan and I have) but is trying to get all he can upstream of that.

The other VERY interesting subject will be what the pressures look like throughout the crank rotation, at both the primer port and in the induction plenum just behind the throttle body. I think this is where the Sky Dynamics design may show some interesting things. One of the related aspects for race tuning is what effect the 'tuned breathing' has on the change in GAMI spread at different RPMs. Everyone usually does our injector tuning at cruise conditions, but then at full RPM on the race course, we get indications that some cylinders are leaner than others. Would really like to have all the oars pulling the most they can at race conditions. SDS has a great solution for that, but for those with Bendix-type FI, it means we need to fiddle with injector size based on race data, and we ain't leaning to peak at those conditions! so it has to be inferred from CHT, EGT trends. Probably could go up high and do real GAMI spread at full RPM -- implicit in this is that the dominant effect on changes to GAMI spread is the RPM change, not the MAP change (which seems to me to be the case)

It also begs the question of whether there is benefit to adding volume downstream of the throttle body, which circles back to TOOBUILDER's configuration with a filtered air box downstream of the fuel servo.

Dan, what kind of instrumentation is readily available that would allow recording of the pressures through the crank rotation?
 
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Dan,

On your spreadsheet, the pressure delta labeling is a bit confusing, because it shows ratios rather than differences. (e.g. MP/Airbox). Am I correct in interpreting this as (P_airbox - P_primer port) ?

The other question I have is how much of that 14.5" of loss is due to the filter? What happens if you repeat with the filter removed?
 
The larger plenum volume of the SD intake combined with the tapered runners should be somewhat more efficient than a small plenum with straight runners.

Dave Anders has seen some good numbers with his modified SD manifold.
 
The larger plenum volume of the SD intake combined with the tapered runners should be somewhat more efficient than a small plenum with straight runners.

Dave Anders has seen some good numbers with his modified SD manifold.

Ross, care to comment on the RPM effects?

It seems like since the runners are not all exactly the same length (I think?), then the wave timing is slightly different on different cylinders. And then, at different RPM, the wave timing obviously changes. Is it reasonable to expect that the GAMI spread will change from, say, 2300 RPM to say, 2800 RPM?
 
Ross, care to comment on the RPM effects?

It seems like since the runners are not all exactly the same length (I think?), then the wave timing is slightly different on different cylinders. And then, at different RPM, the wave timing obviously changes. Is it reasonable to expect that the GAMI spread will change from, say, 2300 RPM to say, 2800 RPM?

The stock SD tubes are pretty close in length but Dave has adjusted the lengths of the bells inside his plenum to get the best results. Fixed lengths are a compromise, best at only one rpm.

First 2 photos are stock SD, 3rd is Dave's modified one.

I believe Dave has less than 3% trim overall between all 4 cylinders to get the GAMI down to around .1. I'd have to ask if he sees a change in trim required as rpm is varied. With SDS, Dave can alter the amount of fuel to each cylinder individually in flight.

For those who don't know, Dave has instrumented his plenum/ runners to look at the phase (timing) and amplitude of the intake pulses in order to optimize runner lengths and shapes. He knows more about this than almost anybody as related to Lycoming AV engines.
 

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The stock SD tubes are pretty close in length but Dave has adjusted the lengths of the bells inside his plenum to get the best results. Fixed lengths are a compromise, best at only one rpm.

More variation in length on the six-cylinder intake.

Seems like there would be some benefit to even a short, wide-angle diffuser from the throttle body to the plenum.
 
AMEN!!!

For those who don't know, Dave has instrumented his plenum/ runners to look at the phase (timing) and amplitude of the intake pulses in order to optimize runner lengths and shapes. He knows more about this than almost anybody as related to Lycoming AV engines.

I did some lab/test work on I-6 engines (mid 80's) to pulse charge the intake systems with resonance between the front 3 and rear three cylinders. It yielded 120% volumetric efficiency at the target point.

I spoke with Dave about his results a few times and quickly came to your same conclusion. IMO Dave is the expert. He would not say that, but he is very modest.
 
Timely thread, as indeed Steve has provided me some beneficial heading checks as I bounce between the guardrails on my own induction journey.

I did add a "filtered plenum" as a scab on to my otherwise stock updraft sump and relevant to this discussion picked up a significant MP boost in cruise. Also, to Ross point,the GAMI spread tightened up a bunch as a result. So much so that I had to zero my previous injector trim settings and start over.

I was going to comment on Dan's observation of Nasty's 23.3 MP, as I had similar numbers teed up and ready to share - until I realized he was at 9.5 altitude vice my (in this case) 8.5. HOWEVER, I made these numbers with the induction inlet buried within the LH cooling scoop. I do plan to test out a "pure" pitot style scoop shorty and see what kind of numbers I get.

Good thread - hope it stays alive.
 

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Also bear in mind folks that Bob is completely unfiltered ram system. Some of you are showing really good numbers even with a filter in the system. I think a filter is worth about 1/2 in. hg?

The other wrinkle to this is that in the past, when Bob had the old VM1000 and used to quote these seemingly too-high MAP levels, I sort of dismissed it as transducer error. But he just installed an EDM-350 and is still showing those kinds of numbers. So it seems like it is real.
 
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Seems like there would be some benefit to even a short, wide-angle diffuser from the throttle body to the plenum.

Could be worth trying as this is common in restricted classes like FSAE where we see lots of effort and simulation expended to develop the very best design. Would also increase effective plenum volume.

One has to remember that flow through the TB and plenum itself isn't steady state, it starts and stops at high frequency so there are inertial and acoustic effects.

The TB is capable of flowing a lot more than any single runner. Once the plenum volume gets close to 1/2 the total engine displacement, you don't need such a large TB and each cylinder can draw air from the plenum with minimal pressure change.

Lots of time spent on this stuff in the automotive world. This is the '23 Z06 setup. Note the sharply tapered runner and large velocity bell to reduce wall separation and obtain maximum velocity at the port for best filling. It's a beautiful casting:
 

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With really big filters, we see nearly imperceptible drop on the flow bench. For something you can reasonably fit in an RV, maybe about 5 inches H20 which is .37 in hg.
 
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More food for thought- BMW S65 aftermarket carbon intake/plenum. Yummy:

All the whizzy automotive stuff uses tapered runners. They show about an 18% increase in flow over straight runners.
Sky Dynamics does this too. I'd like to see how they form those from metal...
 

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I understand that the taper in runners reduce separation turbulance and maintain the boundary layer.

This was explained by a friend, Wes King, who is a real talent in porting heads.

The fairly straight runs were welded fabrication.

Curved intakes would take more attention (and talent) but are doable.

One-offs are problematical. Small production runs find an answer and develop the process.

FWIW
 
Dan,
On your spreadsheet, the pressure delta labeling is a bit confusing, because it shows ratios rather than differences. (e.g. MP/Airbox). Am I correct in interpreting this as (P_airbox - P_primer port) ?

You are correct. Sorry, poor notation on my part.

The other question I have is how much of that 14.5" of loss is due to the filter? What happens if you repeat with the filter removed?

Going back to old flow bench data at AFP, the large area filter (K&N 33-2124) and airbox adds a drop of 1.9" H20 at 1400 PPH, and 2.7" H2O at 1800 PPH, as compared to the standard bench test bell mouth alone.

Dan, what kind of instrumentation is readily available that would allow recording of the pressures through the crank rotation?

My notes say a Honeywell SSCDRRN005PDAA5-ND, fed by an LM78 5V linear regulator. Analog output went to a Dataq 1100 feeding my laptop. And of course, you'll a helper to sit in the back seat of the -8 and run the capture.

Glued the components to a piece of formica. Mounted it on a valve cover screw so it was real close to the primer port; didn't want to introduce lag due to sensor tube length. It's a little board mount sensor, pretty fragile for this app, but a few flights was all I wanted.

DeltaP was one leg on the back end of a turbo bleed rail, one leg on the primer port. Used a second channel on the Dataq to record a voltage spike from a spark plug. With fixed timing, it gave me a marker from which I could derive TDC.

Fun and informative, but for now, we can learn a lot without the wave data, and all that takes is a manometer and a few tubes. Are those taper runners worth the swap?

https://sps.honeywell.com/us/en/pro...ount-pressure-sensors/trustability-ssc-series

https://www.dataq.com/products/di-1100/

With really big filters, we see nearly imperceptible drop on the flow bench. For something you can reasonably fit in an RV, maybe about 5 inches H20 which is .37 in hg.

Bwahahahahahaha! ;)
.
 

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Dan,

Thanks for doing this! I'll read this more closely, and work on a tap plan. Will likely have questions as I do that. I posted some higher altitude cruise performance numbers on the wing thread just now, but here is a compilation of the early cruise data photos I have taken (9.5, 10.5, 13.5, 15.5, 17.5). Still getting used to the leaning function in the new JPI EDM-350, and still checking the accuracy of the FF and totalizer.

Cheers,
Bob

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Congrats the new wings and performance, guys.
I'm hoping to piggy back off your knowledge. My ship isn't an RV but your data on the ram air is fascinating. by design we have an airbox built into the cowling and forward facing servo, but no filtering at all. Our cowlings use a small rectangeler opening at the bottom the cowling. some builders have put the cone shaped k&n and a bit of snorkel but we haven't attempted any of the science you are putting into your efforts.

If this intrusion is unwelcome, I understand

Paul
 
Interesting thread.
The dissimilar induction tube lengths do not allow making use of a properly timed N wave, and even the 4 cylinder SD lengths vary considerable, in terms of inches. That difference makes it certain that all cylinders can't have the same volumetric efficiency . By using Kevin Murrays' SD #2 tapered induction runner for all the cylinders with a tunable elliptical inlet in the plenum they are all the same length and by using Ricardo Wave Program I was able to determine the optimum runner length and increased th.e fuel flow 13% at the same rpm and AFR as I had in the original SD system. 13% increase in VE due to tuning the length of the runners.
 
... I was able to determine the optimum runner length and increased the fuel flow 13% at the same rpm and AFR as I had in the original SD system. 13% increase in VE due to tuning the length of the runners.

Hi Dave.

I'm told a stock angle valve (13864 sump and tuned length tubes) has a VE of about 0.875, and my own measurements suggest it's an accurate number. However, remember, that's sucking through an RSA-5 size flange, with stock ports and valve seats.

Increased VE decreases inlet pressure recovery, so did you see an indicated manifold pressure change?
 
Interesting thread.
The dissimilar induction tube lengths do not allow making use of a properly timed N wave, and even the 4 cylinder SD lengths vary considerable, in terms of inches. That difference makes it certain that all cylinders can't have the same volumetric efficiency . By using Kevin Murrays' SD #2 tapered induction runner for all the cylinders with a tunable elliptical inlet in the plenum they are all the same length and by using Ricardo Wave Program I was able to determine the optimum runner length and increased th.e fuel flow 13% at the same rpm and AFR as I had in the original SD system. 13% increase in VE due to tuning the length of the runners.

Dave,
Thanks for joining the discussion.

Is it correct that the tuning only works at one RPM? Is there a second RPM that works as a harmonic? (e.g. if you tune for 2700, would you also see some VE increase at 1350 RPM? (not that anyone would care))

How much drop-off do you see at other RPM? Is it as noticeable as, say, a 2-stroke engine with a tuned exhaust "coming on the pipe"?

If you get all the runners the same length, do you see a change in GAMI spread at different RPM? I would think not.
 
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Hi Dan,
I was always under the same impression the 200 hp sump had tuned equal length tubes. But due to their size and shape they never fit under my cowl so I always used SD. I calculated my new VE at 91% with my new sump and runners.
I looked back to my Savvy data and I don't have a direct comparison, but I have my last test data before I put on the new sump and tubes 12-18-2017.
2815 rpm, 29.9" MAP, 1646' Palt, 73F OAT, 14.4 gph fuel flow, 12.4-6 AFR, 248 mph TAS.
and 7-24-2022.
2907 rpm, 30.0" MAP, 1436' Palt, 82F OAT, 16.7 gph fuel flow, 12.4-6 AFR, 253 mph TAS.
The same rpm in 12-18-2017 would have produced a FF of about 14.8 gph back then. So that's about 13% more FF now, things being about equal. I couldn't see much change in MAP but the different Palts would make about .2" difference and the increase in q would also have made a tiny difference.
There were no changes in my plane, instruments or sensors during that time.
But if you play with the numbers it would appear the 29.9" would have been about 30.1" at the same altitude, and the 30" would have been only slightly lower at lower speed due to lower MAP due to q. But in don't think you can determine anything from that.
 
Hi Steve,
Yes you do tune them for the maximum rpm you intend to run so you can make maximum HP at that rpm.
I have 3 sweet spots when the N under is perfect 2100, 2400 and 2900 rpm.
At 2900 rpm I have a 5N wave, at 2400 a 6N wave and at 2100 a 7N wave, but HP doesn't drop off sharply on each side of those specific optimum wave lengths. It just slowly decreases until the .5 wave positions which is the worse location headed toward the plenum. You never actually feel those spots because as you increase rpm, due to the increasing rpm, you produced more HP anyway.
If you tuned 2700 rpm the N number, it will return at perhaps 2200-2250 again, and then too low for cruise.
The place I notice it the most is at max power and rpm, I think, and
It still does good at low rpm cruise (2190) because at around 192-195 mph TAS at 17500' I can run 16.7 AFR and considerable ignition advance, and get around 33-34 mpg at 5.7 gph FF. I do get 16.3" MAP up there under those conditions.
As for GAMI spread I think it is better, but I have SDS injection so I can tune each cylinder in flight, so they are identical when they all peak so there is actually no spread. REALLY close. You just do it one time, and write down the trim #s and you can set them in seconds to match your conditions.
I do know that if I had a better plenum it may even be better. The larger volume plenum has less MAP pull down during each intake cycle which is good, more hp too. But, since I have direct ram induction it changes as the speed increases, a bit, but all the cylinders seem to change about the same rate.
 
Great to see you post here Dave.

Though seemingly bizarre, some automotive race engines have purposely used fixed intake stacks of varying lengths (on the same engine) to broaden average power through their effective rev range.

What is really needed is something like the Mazda 787B used on their Le Mans Wankels- ECU controlled variable length runners so the intake length is optimized at any rpm. Not so easy to do on a Lycoming though.
 

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Hi Ross,
I've read about the variable engineering but i't's way past my ability and resources, and since we're basically steady state engines I tuned the lengths to be near optimum at the 3 rpms I use most. The primary reason for increased FF is ALL the cylinders now get the same charge, and it achieves the maximum pressure in the runner at the right number of degrees before the intake valve closes. it just so happens that it also works out to produce the maximum pressure at the back of the valve again before the intake valve opens.
 
Dave has asked me to do some comparative cruise performance tests, matching the conditions and engine settings he's shared with me. I just completed the Phase I flight tests with the new wings, so will embark on that soon, and Dave, I owe you a couple e-mails!

I will also work with Dan and Steve to instrument up a bit, and get some data to compare with Dan's data, to evaluate the validity of my MAP indications.

This thread really does have great info. How best to employ it is a next challenge.

I'm nearing time to work with Lycon on my next motor, and am thinking my best course of action would be to gather this brain trust to combine Lycon, SDS, AFP, and the intake and exhaust tuning we are discussing, to create the dream motor for Sport 49.

You guys game for such an adventure? I have plenty of room for stickers on my machine! :D

Cheers,
Bob
 
I'm nearing time to work with Lycon on my next motor, and am thinking my best course of action would be to gather this brain trust to combine Lycon, SDS, AFP, and the intake and exhaust tuning we are discussing, to create the dream motor for Sport 49.

You guys game for such an adventure? I have plenty of room for stickers on my machine! :D

Cheers,
Bob

We have a Reno racer discount program. Would be happy to supply and support you.
 
We have a Reno racer discount program. Would be happy to supply and support you.

That's really generous of you Ross, and I look forward to working with you. I've watched Andy and a few others closely, and admire the quality and performance. Next time I come up to visit Bill and Ralph in Calgary, it'd be fun to visit your skunkworks.

The concept of combining your ignition and FI with Dave's research, and combining it all into one of Kenny's engines is enticing, to say the least! Sounds like Dave's...and his results are amazing!

Cheers,
Bob
 
Hi Bob,
For normally aspirated engines there is a greater benefit in a tunable injection than one may imagine. With the ability Ross can provide of getting the best atomization, the best timing, and the maximum power from each cylinder that it can produce at the same time at maximum rpm, you'll never have made more power under similar conditions before.
This last year before the AVC race I discussed tuning at high power with Kenny Tunnell. I had never tried to trim the individual cylinders with the SDS above perhaps 50% power. Ken said as long as you approached it carefully and didn't see any cylinder temp changes it may be OK. I tuned the injectors to stoichiometric for each cylinder by dialing in the #1 cylinder on the SDS to 1470 F degrees, then plused and minused each injector 1% at a time until the maximum EGT for that cylinder occurred. It is VERY sensitive. I did it at around 90% power, 26" map and 2900 rpm. It took about 7 minutes and was done on a heat soaked engine. The CHTs on the hottest cylinder went from 343 to 354 F during that time. It ran really good.
 
Guys, I too am interested in wave tuning, but for the sake of the larger audience, maybe we could discuss plain 'ole indicated manifold pressure. Does the tapered tube manifold, as purchased, boost that average gauge pressure at the port, as compared to a standard tuned Lycoming intake?

The question requires relatively simple deltaP measurements rather than wave recording.
 
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Guys, I too am interested in wave tuning, but for the sake of the larger audience, maybe we could discuss plain 'ole indicated manifold pressure. Does the tapered tube manifold, as purchased, boost that average gauge pressure at the port, as compared to a standard tuned Lycoming intake?

The question requires relatively simple deltaP measurements rather than wave recording.

Dan,

Sorry for the thread drift...back to your original question. I've completed the phase I testing on the wings, and though I'm continuing to evaluate performance and expand the envelope, I have more flexibility to work this into the mix.

I re-read the thread, and just spoke with Steve about how to accomplish this. My MP tap is off the #6 cylinder, and I have a sniffle valve in the bottom of the SD plenum.

So Q1: If I "T" into the MP line and run that hose to one side of the D-Manometer, and replace the sniffle valve with a barbed fitting and run that hose to the other side of the manometer, will that get you the delta-P data you are looking for?

Q2: Or are you looking for pressure prior to the FM-300? In that case, I may be able to put a tap in that 4" silicone tube I have leading to the servo.

Q3: Can you post a link to the manometer you are using? I want to ensure I'm using a common tool, with proper ranges, so I get valid measurements and provide good data for this effort. Others reading this, that wish to replicate the efforts, would benefit from the proper tool info as well.

Thanks mucho!

Cheers,
Bob
 
Bob, the drop or rise we want to measure is between a point upstream of the FM300, to the intake port. A tap in the big silicone tube and another tee'd into the MAP line should do it. Restrictors in both taps may be helpful.

As for an manometer, it depends. I have two. The cheap one (search "manometer HT1890" on eBay) is quite accurate. However, don't make the above connections at idle, as you might break it; the specs state the max deltaP is 10 psi, about 20" Hg. If you connect it in flight and disconnect before landing, it will be fine.

Also have a Dwyer 475, with a range of 1' H20 to 150 psi, but those cost more.

Really, the cheap one is probably better for low pressures. The expected range of interest is less than 2" Hg, ballpark 1 psi, or 27" H2O.

If desired, a deltaP between a tap into the aircraft static system and the big silicone tube will tell how much dynamic pressure rise (ram) you're getting with the 3" intake ring. That number might be informative later, if you go to a larger intake. It' easy to calculate, but backing the calc with a measurement is better.
 
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Hey Dan,

I bought a manometer to do the under-cowl pressure measurements to compare with your data, instrumented using your 'white paper'. I think it is the HT1890, but I'm not sure. (its at the hangar so I can't check right now) I found that the displayed pressures are so erratic that you can not even do an eyeball average. I made up some gust filters with 0.020 tube restrictors bonded into some barb fittings with a short section of pipe in between to add volume downstream of the restrictor. This improved the unsteadiness some, but still it is far from a solid measurement of average pressure.

Any advise on how to appropriately filter the pressures to get steady average measurements? Maybe I just need longer segments of pipe to increase the volume downstream of the restrictor, or need a smaller tube for a restrictor (A hypo needle maybe....hmmm, where did I leave my stash?)


Bob, the drop or rise we want to measure is between a point upstream of the FM300, to the intake port. A tap in the big silicone tube and another tee'd into the MAP line should do it. Restrictors in both taps may be helpful.

As for an manometer, it depends. I have two. The cheap one (search "manometer HT1890" on eBay) is quite accurate. However, don't make the above connections at idle, as you might break it; the specs state the max deltaP is 10 psi, about 20" Hg. If you connect it in flight and disconnect before landing, it will be fine.

Also have a Dwyer 475, with a range of 1' H20 to 150 psi, but those cost more.

Really, the cheap one is probably better for low pressures. The expected range of interest is less than 2" Hg, ballpark 1 psi, or 27" H2O.

If desired, a deltaP between a tap into the aircraft static system and the big silicone tube will tell how much dynamic pressure rise (ram) you're getting with the 3" intake ring. That number might be informative later, if you go to a larger intake. It' easy to calculate, but backing the calc with a measurement is better.
 
I had good success testing PDs with Dwyer/ Magnahelic gauges as Dan mentioned. Made in many different scales and types. Very stable readings. Need a camera to log but that's easy these days.
 
Any advise on how to appropriately filter the pressures to get steady average measurements?

I've never bothered to get them absolutely steady, but it's easy to damp them a lot. Doesn't have to be a drilled restrictor plug. At the brute force end of the scale, just kink the tube between your fingers, or squeeze it flat with a little clamp. At the fancy end, try dial-a-restriction; search "fish tank valve" on eBay.

The meter has an averaging function.

I'm surprised MAP sensors last like they do.
 
Fuel filter

I think I've heard of using small (lawnmower) or paper fuel filters to dampen pulses in air lines. There are also such dedicated filters in some car vacuum lines.

Finn
 
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Lemme see if I can parse this multi-quote enough to ask good questions...

Bob, the drop or rise we want to measure is between a point upstream of the FM300, to the intake port.

So we want the pressure before the servo, to best estimate any rise we get from the SD Plenum and intake runners, correct? Steve and I were thinking the sniffle valve would show plenum pressure, just before the intake runners, so the delta P from sniffle valve/plenum to MAP would show the runners' impact. Is there value to tapping both, and comparing them each to MAP, and to each other? I reckon that would show the drop through the servo...though I know you said earlier you had that number from Don's bench tests. Thoughts?

A tap in the big silicone tube and another tee'd into the MAP line should do it.

Any recs on how best to place a tap here? Perhaps a 1/8" NPT elbow with a barbed fitting, or a small NPT to press-to-fit elbow? You likely have an even more simple idea...open to all.

As for an manometer, it depends. I have two. The cheap one (search "manometer HT1890" on eBay) is quite accurate. However, don't make the above connections at idle, as you might break it; the specs state the max deltaP is 10 psi, about 20" Hg. If you connect it in flight and disconnect before landing, it will be fine.

Hey Dan, I bought a manometer to do the under-cowl pressure measurements to compare with your data, instrumented using your 'white paper'. I think it is the HT1890, but I'm not sure. (its at the hangar so I can't check right now)

Through the magic of Dan Horton and Jeff Bezos, this will arrive tomorrow...how's that for instant gratification! Steve, this may also help you recall if that's the one you have.1 HT 1890.jpeg

Restrictors in both taps may be helpful.

I found that the displayed pressures are so erratic that you can not even do an eyeball average. I made up some gust filters with 0.020 tube restrictors bonded into some barb fittings with a short section of pipe in between to add volume downstream of the restrictor. This improved the unsteadiness some, but still it is far from a solid measurement of average pressure.

Any advise on how to appropriately filter the pressures to get steady average measurements? Maybe I just need longer segments of pipe to increase the volume downstream of the restrictor, or need a smaller tube for a restrictor (A hypo needle maybe....hmmm, where did I leave my stash?)

I've never bothered to get them absolutely steady, but it's easy to damp them a lot. Doesn't have to be a drilled restrictor plug. At the brute force end of the scale, just kink the tube between your fingers, or squeeze it flat with a little clamp. At the fancy end, try dial-a-restriction; search "fish tank valve" on eBay.

The meter has an averaging function.

I'm surprised MAP sensors last like they do.

Also arriving tomorrow...

2 Fish tank valve.jpg

So just place this in line near the manometer, and turn it down until the reading is less jumpy? Should anything be placed on the tap end?

If desired, a deltaP between a tap into the aircraft static system and the big silicone tube will tell how much dynamic pressure rise (ram) you're getting with the 3" intake ring. That number might be informative later, if you go to a larger intake. It' easy to calculate, but backing the calc with a measurement is better.

That's a good idea for the future comparison, and easy to add to the mix.

Cheers,
Bob
 
Through the magic of Dan Horton and Jeff Bezos, this will arrive tomorrow...how's that for instant gratification! Steve, this may also help you recall if that's the one you have.View attachment 37033

Mine looks like that, but seems to behave differently. Mine does not have an averaging function.

Also arriving tomorrow...

View attachment 37034

So just place this in line near the manometer, and turn it down until the reading is less jumpy? Should anything be placed on the tap end?

Nothing at the tap end. Ideally you would use a fairly flush orifice on the inside of your silicon tube, like one of those machined static taps we just installed in your fuselage. You can order those from Cleveland Tools, or see if the guy in Georgetown has more.
 
So we want the pressure before the servo, to best estimate any rise we get from the SD Plenum and intake runners, correct?

Correct.

Steve and I were thinking the sniffle valve would show plenum pressure, just before the intake runners, so the delta P from sniffle valve/plenum to MAP would show the runners' impact.

I should pull out a textbook here, but my current understanding is that the plenum volume has a role to play in the result. As such, I'm more inclined to treat the servo, plenum, and runners as a system.

Is there value to tapping both, and comparing them each to MAP, and to each other? I reckon that would show the drop through the servo...though I know you said earlier you had that number from Don's bench tests. Thoughts?

More data is better. You could get all three deltas at one power setting, which is valuable.

Airbox vs static - dynamic pressure rise.

Airbox vs intake plenum - carb loss through the FM300 at the then current PPH

Airbox vs primer port - gain or loss for the manifold system.

Same baseline for all three, here the big silicone tube. Reduces variables, and makes tubing management easier in the cockpit. You're only swapping one leg of the manometer.

Any recs on how best to place a tap here?

I'm pretty sure Steve knows how to tap static pressure. I think I machined a little barb fitting from a screw, photo first post. Business end was near flush, like a fuselage static port.
 
I mentioned wave tuning in our side email to illustrate the stability of the pressure source for MAP indication. The plenum is a more stable source and the size of the plenum does have an effect on MAP. The larger the plenum, the less MAP drawdown on each cylinder intake. For instance on a continental 550N with that really neat looking set of runners on top of the engine, they connect to a manifold not a plenum. They are all dissimilar lengths: the shortest being 15" and the longest being 16.25" which means the volume in the runners vary a lot to the face of the servo, with the maximum volume in runner #3 of 67.6 cubic inches. Each cylinder intakes 91.66 cu ins in about 0.014 of a second and the maximum volume of that runner is 67.6 cu ins so that requires around 24 cu ins (more on the other cylinders) to be drawn from the adjacent runners so they start on their cycle with a "net" lower pressure.
Sorry for the drift
 
RV-8 Intake Design

This is the RV-8 I built way back in 2000 -2002, here in Australia.

I too am a dedicated "Total Performance" kinda guy so was motivated to gain some free HP all for the sake of research and putting that into practise to enhance the power output. My research focused around the P51 (why not) as we all know the success of Edgar Schmued’s design. For his day he was quite innovative and thought well outside the square. For me I was a professional aviator, not an aeronautical engineer, however this is all there for the want of research.

The design parameters revolved around gaining the maximum available thrust from the Propellor feeding into the intake, thus you will note the intake is placed almost directly behind the position of max cord of the blades. I had to set it back far enough so as the blade would still clear the scoop when at max pitch angle, that clearance being slightly less than 10mm (1/2”) at max pitch angle. I also adopted the “Smilie” intake since it absorbed a large radius as the propeller rotated, ie maximum exposure. Being a three bladed MT Propellor, it would have required a “mouth” of 120 degrees to reduce pulsing pressure and obviously that would not have been achievable. The P51 having a 4 bladed Propellor only required 90 degrees of intake arc to achieve this.

Initially it resulted into a higher-than-expected fuel consumption, however in consultation with Bart Lalonde, it was pointed out that since we had effectively "Turbo" the engine he advised we needed to add the Turbo Injector modules to each injector. Once they were in place, I saw the true results of my endeavours and "The Boy" turned into a real performer. The original engine was an Lycoming AEIO-360-M1B and with O2 onboard I quite often flew at F/L's (normally F/L 120-130 and up to F/L 180 on one occasion) and you certainly need a good AP up there (I had a Tru-Trak 2 SVGV fitted).

Utilising LOP, I could observe F/F's of 28-30 Litre/ Hr. Apart from that, time to climb to say 10,000ft was significantly reduced.

Jon Johansen manufactured these units for a time, however for whatever reason only sold a few units through his company "Flymore". We called it the "RAIS -Ram Air Induction Scoop". I think that back then it may have been too innovative maybe.

The engine power was certainly enhanced by the RAIS and by applying the formula of 1.67 x rise in MAP per Cylinder would suggest: - 1.67 x 1.8 x 4 equates to a HP gain of 12.024 HP due to Ram Rise effect from the RAIS. Considering I also installed Dual LSE Plasma 11 EI & AP Fuel Injection, I guess I was gaining "Total Performance" (to coin a phrase).

There were improvements to be had, however once I got it in the air, I guess I was happy with my achievements and since I lived Overseas, time back in Aust was limited.

I’m keen to get my butt into building and flying a RV-15 and will more than likely angle for enhanced performance from an IO-360-M1B, with some form of forward induction feeding via a cold induction sump, flow ported, balanced injectors, tuned exhaust etc.

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Welcome Ray!

(Anyone seen Mike? He must be on sick leave)

...by applying the formula of 1.67 x rise in MAP per Cylinder would suggest: - 1.67 x 1.8 x 4 equates to a HP gain of 12.024 HP due to Ram Rise effect from the RAIS.

Ray, what were the conditions? Full throttle, climb at low forward airspeed?
 
Welcome Ray!

(Anyone seen Mike? He must be on sick leave)



Ray, what were the conditions? Full throttle, climb at low forward airspeed?

Dan,
Thanks for asking.

That was at a Sea Level airport on the coast,
18 deg Celsius (64 F),
QNH 1013 (32" Hg).
Full Power for Take-off and approx 50Kts (57.5 Mph).

Had I completed it properly by fairing the internal scoop (removing potential vortices) I may well have seen another 0.5" MAP gain.
The installation was with initial build and only a few months later I got to trial next to a similar powered RV-8 with a 2 bladed Hartzell. Time to 10,000ft was approx 1.5 mins improvement over that A/C.
Next time I go see the new owner, I'll get some "behind the cowl" pic's

RayJ
 
I believe that Dual LSE, AP Injection, Port Polished and a 4 into 1 Tuned Exhaust Pipe would also have contributed to the improved performance. Next build (RV-15) will also include Sky Dynamics Cold Air Intake & Sump.
 
I believe that Dual LSE, AP Injection, Port Polished and a 4 into 1 Tuned Exhaust Pipe would also have contributed to the improved performance. Next build (RV-15) will also include Sky Dynamics Cold Air Intake & Sump.

In the context of manifold pressure, the AP servo has a bit less loss compared to the equivalent RSA style. You may have also worked in a larger filter.

The manifold pressure increase due to propeller outflow is maximized at very low forward airspeed, and minimum near max airspeed. MP increase due to forward velocity is near minimum at low forward airspeed, and maximum at max airspeed.

All the same for any intake pointed pointed forward. The interesting question in your case revolves around blade passage. Does the smile shape boost average pressure, as compared to a more typical round intake?

Some of the aero guys might say no, as they typically treat the area behind the prop disk as a uniform pressure field. I think not, having strobed fabric airplanes in the dark, and watched the sides pulse like the gills of a fish...
 
All the same for any intake pointed pointed forward. The interesting question in your case revolves around blade passage. Does the smile shape boost average pressure, as compared to a more typical round intake?

Dan,
Correct.
Obviously by pure physics, blade passage does have a positive effect on Ram Air into the intake. Vans "Rhino Horn" intake works well, however blade passage is very limited and so relies on aircraft velocity (bonus). As is obvious in pics of my intake, blade sweep Ram Induction was significantly improved over the Rhino Horn.
In my opinion, the FAB-Horizontal Induction system offered suffers to many internal vortices etc to be of any real advantage, in-fact I would suggest it suffers significantly because of directional and aperture changes creates a turbulent flow. Only advantage maybe a clean profile on lower cowl.
Anyhow I am not an aerodynamic engineer and do not profess to be same. Just quote what is obvious.
RayJ
 
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Timely thread, as indeed Steve has provided me some beneficial heading checks as I bounce between the guardrails on my own induction journey.

I did add a "filtered plenum" as a scab on to my otherwise stock updraft sump and relevant to this discussion picked up a significant MP boost in cruise. Also, to Ross point,the GAMI spread tightened up a bunch as a result. So much so that I had to zero my previous injector trim settings and start over.

I was going to comment on Dan's observation of Nasty's 23.3 MP, as I had similar numbers teed up and ready to share - until I realized he was at 9.5 altitude vice my (in this case) 8.5. HOWEVER, I made these numbers with the induction inlet buried within the LH cooling scoop. I do plan to test out a "pure" pitot style scoop shorty and see what kind of numbers I get.

Good thread - hope it stays alive.


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

As established in my original post, my new airbox configuration picked up a significant MP number (thanks Steve), but I was still drawing air from the LH cooling inlet through a free flowing round duct. As promised, I have dispatched with that duct and went with a short, straight pitot style ram air duct. Yes, its cobbled together from a handy wipe bottle, a plastic cupholder (providing a reasonable form of inlet bellmouth), and masking tape - all inserted through a hastily cut hole in the front of my cowl, but does provide a close approximation to the maximum benefit I can see from the pure ram air.

If one looks at the MP of "my" Dynon display and compares it to Bob, I still come up significantly short. That said, I am pulling my MP sense from the case of the airbox, not the individual cylinder, I'm running a filter, AND I also question the repeatability of the display of the MAP through the GM sensors used. For example, I route this single pressure tap to a manifold that feeds (3) of these GM MAP modules - one is for the Dynon, and the other two feed the two SDS ECU. If I look at the SDS display for MAP, I routinely see the display .7 inch or so HIGHER than the Dynon. Which is right? I don't know and don't care. It seems this is not laboratory grade equipment, and absolute values are suspect.

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

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