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  #321  
Old 11-29-2015, 08:17 PM
crabandy crabandy is offline
 
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Quote:
Originally Posted by DanH View Post
We can do things to improve heat transfer at the baffles. For example, I see you've already been busy with glass wraps.
Yes, when I installed new lycoming nitrided cylinder assemblies I also made some silicone baffle wraps similar to yours. Really easy to apply with everything off the engine. I really liked the flexibility/durability of the material and they stuck VERY well to the cylinders.

As I was breaking in the cylinders I kept waiting for the CHT's to stabilize at my old CHT temps. Old cylinder CHT data here: http://www.vansairforce.com/communit...=112941&page=5)
Anywho the oil usage stabilized around 8 hours but at 25 hours the new cylinders where about 40 degrees hotter than the old ones. Filing the casting slag on the cooling fins between the valves was worth about 10* cooler and removing the baffling wraps from the cylinder barrels between the cylinders was worth about 10* as well. I also removed the remainder of the baffle wraps from #1,#3 cylinder with no change, I previously had used Van's black baffle material between the curved baffling and lower aluminum baffling. At 50 hours the new cylinders are still 20 degrees hotter than the previous ones, mixture distribution seems to be way different as well.

Since things were apart and I don't have baffle wraps on #1 and #3, I was also thinking about changing the baffling a bit as described here:
http://x-jets.com/Design_for_optimum...efficiency.pdf
Lots of stuff in the way underneath, but if I could stick the baffling wraps to the baffling around the inlet/exit curves and also design an outlet duct with a different capture system than the rod.
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  #322  
Old 11-30-2015, 08:59 AM
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Quote:
Originally Posted by crabandy View Post
"I made 2 flights 4 hours apart at approximately 2000 Pressure Alt. and 78*F with plenum pressure differential measured between static pressure in in/H2O. Here's the rough averages:
115 knts IAS-upper plenum 7.5 In/H20-lower plenum 1.4 In/H2O
130 knts IAS-upper plenum 9 In/H2O-lower plenum 1.5 In/H2O
160 knts IAS-upper plenum 13.25 In/H2O-lower plenum 2 In/H2O"
Convert IAS to TAS, then determine dynamic pressure for that TAS and density, then divide upper plenum pressure by available dynamic pressure to determine upper plenum pressure coefficient. Check my math, but I get:

115 IAS = 121.0 TAS = 8.66" H2O 7.5/8.66 = 0.86
130 IAS = 136.7 TAS = 11.0" H2O 9/11.0= 0.81
160 IAS = 167.9 TAS = 16.7" H2O 13.25/16.7 = 0.79

Even if the inputs are off a little (for example, uncalibrated IAS), it doesn't change the big picture...the stock Vans inlet is pretty good in this level flight condition. Although level flight Cpu might be tweaked for a gain, the real reason for a change (for example) might be to improve Cpu in a high power, high AOA condition, or because it provides a mechanical path to better sealing, or for drag reduction.

Two observations.

Those lower cowl pressures are quite low. There's nothing very restrictive about your exit.

In the other thread you listed 5.5 " H2O for 100 knots IAS in low power level flight, and 6" H2O upper plenum pressure for a full power, 100 knot IAS climb. If that climb condition is apples to apples with your level flight measurements (notably same OAT and altitude), you're not picking up much boost in dynamic pressure due to propwash. That's interesting, given that climb cooling is a big deal. Let's look at that.
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  #323  
Old 11-30-2015, 09:35 AM
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I put this in a separate post, as it deserves a disclaimer. This where we get experimental...I don't have any supporting documents on this subject, so the following is theory and opinion until proven. Comments please.

Oh yeah, Andy, before we get going too much, was that climb condition measurement in fact apples to apples with the level flight measurement?

Dug up a photo of your prop:

http://www.vansairforce.com/communit...&postcount=198

The Catto has good airfoils at the blade root, as I would expect. So why is that airfoil not increasing inlet pressure at full power?

My guess is twofold. One, it might rise if the inlet was closer to the prop. I think Tom and I have the same opinion here. On my own cowl, I moved the inlets forward to minimum clearance at coarse blade pitch

Two, the slot inlet is subject to significant radial flow across the length of the inlet, i.e. pressure at the outboard end of the inlet is significantly higher than at the inboard end. Such flows wastes pressure. Craig might have some sort of calculated pressure map of the outflow that we could look at. The outflow illustration in CR3405 says there is a considerable radial pressure gradient. If true, a round inlet moved as far outboard as possible would have a major advantage in the high power climb case. FWIW, I've recorded a 33% gain (6" vs 9") with such an inlet.

BTW, it wouldn't matter if such a reshaped, relocated inlet was high or low Vi/Vo.

Stock and relocated inlets side by side:



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Last edited by DanH : 11-30-2015 at 09:39 AM.
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  #324  
Old 11-30-2015, 12:10 PM
crabandy crabandy is offline
 
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"There's nothing very restrictive about your exit."

Nope, my plan was to play with the exit after the inlet/plenum side. I was trying to change 1 thing at a time so I could have a better idea what the changes were doing.
Since I was eventually going to reshape the outlet I did cut the aft edge of the stock Van's exit forward approximately 3/4-1 inch in an effort to reduce CHT's while I was playing around with the other things. CHT's were unchanged, lower cowling pressure lost about .5 in H2O and I lost 2 knots. The airspeed loss was noted from my TAS on the EFIS, 4 leg NTPS shows my TAS readout to be just under 2 knots slow.


"Oh yeah, Andy, before we get going too much, was that climb condition measurement in fact apples to apples with the level flight measurement?"

Yes, I took all the measurements on the same flight.
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Last edited by crabandy : 11-30-2015 at 12:12 PM.
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  #325  
Old 11-30-2015, 01:03 PM
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Quote:
Originally Posted by crabandy View Post
Since I was eventually going to reshape the outlet I did cut the aft edge of the stock Van's exit forward approximately 3/4-1 inch in an effort to reduce CHT's while I was playing around with the other things. CHT's were unchanged, lower cowling pressure lost about .5 in H2O and I lost 2 knots. The airspeed loss was noted from my TAS on the EFIS,..
Loss of low cowl pressure = loss of exit velocity = drag increase. Nicely matches theory.

Quote:
...4 leg NTPS shows my TAS readout to be just under 2 knots slow.
Not nearly enough to skew conclusions. Two knots = Q of less than 0.01" H2O

Quote:
Yes, I took all the measurements on the same flight.
Yeah, but did you grab the upper plenum pressure very close to when you passed through 2000 PA in full power climb?
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  #326  
Old 12-01-2015, 09:19 AM
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Andy, returning to your stream tube question, and intake area ratio...

First establish known parameters. For this example we'll assume that we're climbing at 120 KTAS through 2000 feet on a standard day, and mass flow (from the Lycoming cooling chart) is expected to be 2.4 lbs per second.

120 KTAS = 202.53 feet per second
2.4 lbs per second / 2 inlets = 1.2 lbs per second per inlet
Standard density 2000 ft = 0.072098 lbs per cubic foot
1.2 lbs / 0.072098 = 16.6440 cubic feet

The necessary math is based on the usual formula for volume:

volume = area x length

or

volume = radius^2 x pi x length

We know the length of the stream tube (202.53 feet) and the volume (16.6440 cu feet), so just flip it around and solve for R^2:

volume / pi x length = R^2
16.6440 / 3.14 x 202.53 = 0.02617

That's radius squared, so its square root is the actual radius of the stream tube...

sqrt of 0.02617 = 0.1618 feet

Two times radius is diameter, so:

0.1618 x 2 = 0.3236 feet

And last, 0.3236 x 12 = 3.8832 inches stream tube diameter for one intake.

We're interested in area ratio, i.e. stream tube diameter / intake diameter, so we need area for each. Here I'll assume a 6" diameter inlet ring, since I don't yet know what you might choose:

(3.8832 / 2)^2 x 3.14 =11.837 sq in
(6 / 2)^2 x 3.14 = 28.26 sq in

11.837 / 28.26 = 0.4188 area ratio, which is the same as Vi/Vo

Yes, I've put it into a spreadsheet and sent it to you.

Plug in different altitudes and airspeeds. You'll see that Vi/Vo changes with each change of input. For example, at 175 KTAS the stream tube is longer for the same volume, so diameter is decreased, and area ratio becomes 0.2871.

Take particular note of the converse; area ratio rises when airspeed is reduced. It means for a high Vi/Vo inlet, low airspeed makes diffuser quality more critical...which is why some small inlets don't cool very well at low speed and high AOA. Any little design error or condition that pushes the inlet flow into separation tanks the Cpu value.

As always, ya'll check my arithmatic
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  #327  
Old 12-02-2015, 10:10 AM
crabandy crabandy is offline
 
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Dan,
That's exactly what I was looking for, I still have more homework to do to wrap my head around it. I think I was having more trouble keeping the units straight than anything.

As far as the plenum pressures taken at 100 KIAS level vs full power, those numbers were taken a year and a half ago and I honestly cannot remember for sure. I believe I was at 1800 level for the 100 KIAS where I took my readings, I then transitioned to a full power climb at 100 KIAS starting at 1800 pressure altitude but I'm sure it took at least 500-800 feet to get a stabilized airspeed and pressure so the pressure readings were most likely taken passing through 2500-3000 pressure altitdude. Next time I will start the climb low enough I can be established on airspeed and pressures passing through my target altitude.
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Last edited by crabandy : 12-02-2015 at 10:13 AM.
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  #328  
Old 12-02-2015, 11:31 AM
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Quote:
Originally Posted by crabandy View Post
Next time I will start the climb low enough I can be established on airspeed and pressures passing through my target altitude.
Never hurts to repeat a test. For now it's not a big deal. The difference in available dynamic pressure due to air density reduction is only about 0.10" per 500 feet.

For example, you previously listed level flight upper plenum pressure as 5.5" H2O for 100 knots IAS in low power level flight at 2000 PA, and 6" H2O upper plenum pressure for a full power, 100 knot IAS climb. If you were in fact passing through ,say, 2500 PA when you recorded the 6.0" figure, maybe it would have been 6.1" at 2000. Doesn't change the big picture; you're not getting much of a pressure boost due to prop outflow in full power climb.
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  #329  
Old 12-02-2015, 02:22 PM
crabandy crabandy is offline
 
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Pressure and temps from a month ago with the aft edge of the cowling exit cut forward and a temp probe in the lower cowling. The lower cowl temp may be off a tad, on the ground the EFIS OAT was 49 with the cold lower cowling 54.

Level flight
Pressure Alt 3500
OAT 32 *F at 3500PA

100 KIAS
Upper Plenum 5.8 in/H2O
Lower Cowl .81 in/H20
Lower Cowl Temp 107*F
CHT 294-302

160 KIAS
Upper Plenum 15.4 in/H2O
Lower Cowl 1.16 in/H2O
Lower Cowl Temp 108*F
CHT 348-382

100 KIAS = 103.5 KTAS = 6.56 in H2O 5.8/6.56 = .88
160 KIAS = 164.9 KTAS = 16.65 in H2O 15.4/16.65 = .93
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Last edited by crabandy : 12-13-2015 at 01:25 AM.
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  #330  
Old 12-02-2015, 02:25 PM
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