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  #11  
Old 02-04-2019, 07:19 PM
rv6ejguy's Avatar
rv6ejguy rv6ejguy is offline
 
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In flight measurement won't take 4 hours and you'll know the whole truth without any guesses.

Like I said, on my airplane, air is certainly flowing from out to in on the spinner gap, otherwise my OAT sensor would be reading cowling air temps instead of ambient. Your plane could be different which is why you should instrument and find out as Dan Horton and I both did.

Post your results whatever you find out. Always enlightening.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #12  
Old 02-04-2019, 07:56 PM
scsmith scsmith is offline
 
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Quote:
Originally Posted by rv6ejguy View Post
In flight measurement won't take 4 hours and you'll know the whole truth without any guesses.

Like I said, on my airplane, air is certainly flowing from out to in on the spinner gap, otherwise my OAT sensor would be reading cowling air temps instead of ambient. Your plane could be different which is why you should instrument and find out as Dan Horton and I both did.

Post your results whatever you find out. Always enlightening.
I guess since you have mentioned it, I can't resist satisfying my academic interest too. My original plan for the diffuser and the cowl nose seal was just to do what I know would make it "better" without really knowing how much better. But it would be fun to know.

So -- where do I get a measurement system that can read something like 5 pressures and maybe a temperature or two? For how much money?
I'd have to mount it in the cockpit somewhere, and get power to it, and a ground. I'd have to route some pressure tubes through the airframe somewhere, penetrate the firewall (Or I suppose I could route them outside throught the canopy skirt and tape them onto the outside of the airframe with some duct tape).
This all seems like a substantial project on its own -- I can't image getting it installed in under 4 hrs, but maybe.

The dividend would be that once installed, it is there to make other measurements too, so for instance, when I start closing off the cowl exit, I can measure lower cowl pressure and exit flow velocity. Again, here I was just going to do things I know will make it "better" without being able to say really how much, other than airspeed change, if any.

So I'm open to recommendations on an instrumentation system. I don't really want to build a multi-tube manometer. Lord knows I've sprayed enough Meriam Fluid on the lab ceiling already in my life. And besides, that would take more than 4 hours.

I don't doubt that the "net" flow around the spinner is probably from outside in. Just saying it is a fairly complicated flow and not going inward everywhere. Spillage out the top is bad. Flow bypassing the engine cooling baffles to go into the lower cowl from outside is bad. A nose seal will be good, regardless of which way the unsealed flow is going.
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Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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  #13  
Old 02-04-2019, 08:48 PM
rv7charlie rv7charlie is offline
 
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One differential pressure sensor:
https://www.nxp.com/docs/en/data-sheet/MPXV5004G.pdf

Analog voltage output, could be fed to a spare analog input in an EFIS or engine monitor.

Temperature sensor:
http://www.johnloomis.org/ece445/sta...ag/st_ap29.pdf

LM34/LM35 for F/C measurement, also analog output.

Charlie
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  #14  
Old 02-04-2019, 09:03 PM
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DanH DanH is offline
 
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Quote:
Originally Posted by scsmith View Post
So -- where do I get a measurement system that can read something like 5 pressures and maybe a temperature or two? For how much money?
Ahh, the Chinese menu dilemma: fast, cheap, good...pick any two.

FWIW, I have a row of miniature bulkhead fittings installed in my firewall. Buy a length of 10-32 threaded rod. Cut it into 1-1/2" lengths. Chuck it in the lathe and machine a half inch of threads off each end, leaving a half inch of threads in the middle. Center bore with something small. Now drill a 3/16" hole in the firewall and fasten with a plain nut on each side. 1/8" tubing pushes over the threadless ends.

I have something similar installed in the rear baffle wall, four lengths of brass model airplane tubing soldered in a brass plate.

In an attempt to read static pressure only, I usually go with piccolo tubes, but you know more about that stuff than I'll ever learn.

This cheap electronic manometer is all over eBay:

https://www.ebay.com/itm/US-Ship-LCD...frcectupt=true

Easy temperature probes are LM34-ND top hat cans soldered on the end of a shielded 3-wire cable. The shield is purely physical armor, no electrical value, since the result is a tiny temperature probe on a wire you can move anywhere in the engine compartment.

The nice thing about an LM34 is the 10mV per degree F output. For example, 1.45 V = 145 F.

http://www.ti.com/lit/ds/symlink/lm34.pdf

All you need is power, ground, and your digital voltmeter. Or you can grab a handful of these:

https://www.ebay.com/itm/5PCS-Mini-B...g1i:rk:20:pf:0

When I built the airplane, I ran six blank wires through the firewall with the rest of the instrument leads. Those six go to a terminal block on the firewall so I always have an easy experimental hookup back to the cockpit.

Quote:
The dividend would be that once installed, it is there to make other measurements too, so for instance, when I start closing off the cowl exit, I can measure lower cowl pressure and exit flow velocity.
Come on, do it, you know you want to......

Quote:
A nose seal will be good, regardless of which way the unsealed flow is going.
Soft foam block seal if you have the propshaft space. The Rocket gang knows about them. The flap seal I use is still fine after 850 hours. I've thought about detailed pressure measurements in the gap behind the spinner, but it's pretty far down my list for the very reason you state.

Mini bulkhead fittings for manometer tubing, tygon small engine fuel line from NAPA:



LM34 on a wire, here determining the air temperature near the variable exit servo:



Trusty Fluke in the cockpit. LM34 10 mV per degree means 140.4 F. Orange tubing is for manometer:

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RV-8 SS
Barrett IO-390

Last edited by DanH : 02-04-2019 at 09:35 PM.
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  #15  
Old 02-05-2019, 01:48 AM
scsmith scsmith is offline
 
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Quote:
Originally Posted by DanH View Post
Ahh, the Chinese menu dilemma: fast, cheap, good...pick any two.

FWIW, I have a row of miniature bulkhead fittings installed in my firewall. Buy a length of 10-32 threaded rod. Cut it into 1-1/2" lengths. Chuck it in the lathe and machine a half inch of threads off each end, leaving a half inch of threads in the middle. Center bore with something small. Now drill a 3/16" hole in the firewall and fasten with a plain nut on each side. 1/8" tubing pushes over the threadless ends.

I have something similar installed in the rear baffle wall, four lengths of brass model airplane tubing soldered in a brass plate.

In an attempt to read static pressure only, I usually go with piccolo tubes, but you know more about that stuff than I'll ever learn.

This cheap electronic manometer is all over eBay:

https://www.ebay.com/itm/US-Ship-LCD...frcectupt=true

Easy temperature probes are LM34-ND top hat cans soldered on the end of a shielded 3-wire cable. The shield is purely physical armor, no electrical value, since the result is a tiny temperature probe on a wire you can move anywhere in the engine compartment.

The nice thing about an LM34 is the 10mV per degree F output. For example, 1.45 V = 145 F.

http://www.ti.com/lit/ds/symlink/lm34.pdf

All you need is power, ground, and your digital voltmeter. Or you can grab a handful of these:

https://www.ebay.com/itm/5PCS-Mini-B...g1i:rk:20:pf:0

When I built the airplane, I ran six blank wires through the firewall with the rest of the instrument leads. Those six go to a terminal block on the firewall so I always have an easy experimental hookup back to the cockpit.



Come on, do it, you know you want to......



Soft foam block seal if you have the propshaft space. The Rocket gang knows about them. The flap seal I use is still fine after 850 hours. I've thought about detailed pressure measurements in the gap behind the spinner, but it's pretty far down my list for the very reason you state.
Thanks Dan,

All pretty good ideas. Certainly would have been tons easier to do all this while building. On a finished airplane, ARRGH!

So either one buys several of the manometers, or you sit and switch tubing around in flight (not simultaneous readings, but OK) or make sort of a manifold with manual pressure switches on each input to select which input goes to the manometer, and always be sure only one switch open at a time. Need a co-pilot to log data.

Wouldn't it be great if there was a small box with 5 pressure transducers and 2 thermocouple junctions, plus power supply and signal conditioning, and a USB output to a thumb drive. All you have to supply is the power, ground, and hook up the pressure tubes and thermocouples. I imagine that such a box is available, probably in the $1500 range?
__________________
Steve Smith
Aeronautical Engineer
RV-8 N825RV
IO-360 A1A
WW 200RV
"The Magic Carpet" Flying since Sept. 2009
Hobbs 700
also
1/4 share in 1959 C-182B (tow plane)
LS6-15/18W sailplane SOLD
bought my old LS6-A back!!
VAF donation Dec 2020
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  #16  
Old 02-05-2019, 07:04 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by scsmith View Post
So either one buys several of the manometers, or you sit and switch tubing around in flight (not simultaneous readings, but OK)....
I switch tubing around. Hey, you asked for cheap

Quote:
Wouldn't it be great if there was a small box with 5 pressure transducers and 2 thermocouple junctions, plus power supply and signal conditioning, and a USB output to a thumb drive. All you have to supply is the power, ground, and hook up the pressure tubes and thermocouples. I imagine that such a box is available, probably in the $1500 range?
Just finished installing a single differential pressure sensor, but not for ease of use or less installation time (frankly both are worse), but because I want to look at intake tract and injector bleed pressures at 2400 RPM. In other words, I need a very high sample rate. So, I hope to do it with a laptop, a Dataq DI-1100, and somebody to manage it in the back seat.



Not as all-encompassing as the desired box, but it looks like some of the Dataq kits have channels programmable for thermocouples.

https://www.dataq.com/data-acquisiti...ource=homepage
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  #17  
Old 02-05-2019, 08:30 AM
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rv6ejguy rv6ejguy is offline
 
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These are the Magnehelic gauges, can often find them used on Ebay but new they are cheap anyway. Available in different models and scales. 0-15 and 0-20 in H2O are probably the most useful scales for RVs. These are way more stable and practical than liquid manometers, especially in rough air. Record with your phone or on a kneepad. Old school but worked for me.

A couple of indoor/ outdoor thermometers, but need to find some which go to 100C which is more difficult. An ASI will give you a quick check on exit velocity (corrected for temp), should be lots of these around used with most folks using Glass today.

As an engineer, you'll find it interested to collect and crunch the data I think.

Dan's solution is more elegant, always nice to data log on a PC. You don't miss anything and you can concentrate more on accurate flying.
__________________

Ross Farnham, Calgary, Alberta
Turbo Subaru EJ22, SDS EFI, Marcotte M-300, IVO, Shorai- RV6A C-GVZX flying from CYBW since 2003- 450.6 hrs. on the Hobbs,
RV10 95% built- Sold 2016
http://www.sdsefi.com/aircraft.html
https://www.youtube.com/channel/UCiy...g2GvQfelECCGoQ


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  #18  
Old 02-05-2019, 09:09 AM
Tom Martin Tom Martin is offline
 
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In the rocket there just is not a lot of room to make an exit diffuser going to the bottom outlet. Ideally you would have a inlet and outlet that are dedicated to the oil cooler. These could be mounted in the lower cowling area. I saw this idea in practice on one of the MX aerobatic planes. The inlet was on the lower forward surface of each side of the cowling, with a small inlet and a long tapering inlet to the coolers mount on each aft lower cowling. The exit diffusers cleanly exited the cowling lower aft side. This completely isolated the oil cooler from the engine cooling air system.

I would like to do this some time but I decided to do a sort of hybrid system.
My oil cooler is mounted do the back baffle drawing air from the upper plenum, as per normal installations. I built a exit diffuser that curved 90 degrees and exited the cowling just ahead of the side hinge line, in the lower cowling. I then experimented with various "bluff bodies" until I got the lowest profile that would draw air from the cowling. As the shape of the bluff body could draw air from the cowling I did not have to be too fancy with my outlet diffuser, again I was challenged with the available room.
The last picture shows one of the prototype exits. It had the right size opening but "appeared" a bit draggy. The final version is much longer and more streamlined. Over all this solved my oil cooling issue and allowed me to continue experimenting with my cowl flap and exit air fences on the lower cowling. At the end of the day I never felt that I gained much, or any direct speed increases with these modifications. They did however, let me run at full power in a race without high oil temperatures, thus allowing for higher speeds.




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EVO F1 Rocket 1000 hours,
2010 SARL Rocket 100 race, average speed of 238.6 knots/274.6mph
RV4, RV7, RV10, two HRIIs and five F1 Rockets
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  #19  
Old 02-05-2019, 09:47 AM
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Toobuilder Toobuilder is offline
 
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Interesting and timely thread since I'm working on my cowl right now. Looks like I'm not as clever as I thought I was considering the same ideas I'm implementing are being discussed here.

Mr Martin: I have a similar oil cooler problem and I was looking to penetrate the cowl side just like you have done. I intend to duct the outlet back to the wing root near the point of max thickness to harvest that fat slice of low pressure that always shows up so well in CFD plots. A very simple flanged 3 sided duct could be bent up and attached with speed tape to the fuselage to validate the theory in no time. If you want to do that and report back, be my guest!

Also looking at the prop seal thing. Though Dans flywheel seal works, the Rockets have an extra long hub which provides plenty of real estate to seal. Not only is the overall sealing surface smaller on the Rocket, but the surface speeds are much lower on the small diameter hub. Both are good things. I plan on teflon tape around the hub and a dry felt seal media contained in a floating seal retainer.

Finally, I have added a underbody fairing which closes out the cowl "chin" on the Rocket. This fairing system includes a functional cowl flap as well as exhaust augmentor tunnels. I'm looking into a fully developed augmentor system to eventually replace the articulated cowl flap, but I need to get flying first.

Good stuff.
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WARNING! Incorrect design and/or fabrication of aircraft and/or components may result in injury or death. Information presented in this post is based on my own experience - Reader has sole responsibility for determining accuracy or suitability for use.

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  #20  
Old 02-05-2019, 10:25 AM
rv7charlie rv7charlie is offline
 
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OK, I'm going to demonstrate my untrained ignorance. If Bernoulli says that speed and area have an inverse relationship, and speed and pressure have an inverse relationship (redneck engineering expressions), then I'm struggling to see how putting an expanding cone on the exit of a heat exchanger (when it's located in a volume of basically static air) will reduce pressure at the heat exchanger exit.

When I struggle through books like Kuchemann & Weber, and Kays & London, 'diffuser' is the term used to describe an expanding duct that *slows the air and increases pressure*.

I totally get what Tom Martin did (matches descriptions in the above books, plus docs found on the CAFE website on cooling), but I'm struggling with an expanding cone that's contained within a cowl.

Please educate me.

Charlie
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