=A0Installed sheet metal ‘baffle’ to form new upper = wall of the diffuser as shown in the photo.=A0 The idea was to assist in = maintaining attached flow, and to block leakage through the gap at the top.=A0 The = baffle was done in 3 pieces in order to insert past the divider/supports in the = scoop; each piece is about 7 =BD” wide.=A0 There are gaps between pieces = of about 3/8 – =BD” inch.=A0 The inlet pressure probe was placed at = point “D”.

Test flight showed no noticeable = difference in delta T on the oil.=A0 The pressure measured at “D” was = 3” H2O.=A0 Pressure behind the exit fairing was again -3/4”.=A0 The = pressures at C and D (measured at different times) are at about 6” from the = inboard end of the 22” long cooler.=A0 There may be some variation = axially.=A0 Because of the gaps in the baffle, and fitting around the end tanks, there is = still some air bypassing the cooler; but I don’t know how = significant.=A0 Given the 9+” H2O dynamic pressure out in front of the scoop still = indicates not good pressure recovery.

Nonetheless; it is certainly disappointing that there was no change (within the accuracy of the temp = measurements) in the effective cooling.=A0 This suggests that the wall shape and the = air leakage are not the problem.

Calculating back from the temp = changes in oil and air suggest there is only about 1000 cfm going through the = cooler core. The extrapolation of my measured data on air flow vs pressure drop = across the core suggests that at 3” H2O there should be about 2000 cfm = through the core. =A0Because of the centrifugal blower I was using for flow = tests I was only able to get data up to about 0.6” H2O and 700 cfm. =A0I fit = the data to Y=3Dax+bx² using regression analysis, which gave a very = good fit up to that point; but extrapolating out to 3” may be stretching = it.=A0 If I assume the pressure drop goes as the cube of the flow velocity, the = extrapolation is considerable different – about 1330 cfm at 3” = H2O.

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Al Gietzen
Sent: Friday, July 20, 2007 10:42 = AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = Oil cooler inlet

Well; I may end up with VGs and change in upper duct wall shape. My intention yesterday was to install VGs as a first step, test fly, measure pressure = and temps; then proceed with installing sheet metal upper duct wall = change.

In deciding where to put the VGs, I looked at things with the gear up = (Photo 1). The gear door has a bump, and there is some gap around the = door. Don’t know what all this does to BL. Ended up putting VG = toward the left side about 26” in font of scoop, and toward the right side = right on the gear door bump.

I then spent a bunch of time trying to get the pressure measuring tube = situated. The only access is through the scoop opening, and I can’t = get my hands in there; so it is very tough. Plus the tube going in there, = or along the surface in front will affect the flow behavior, so what affect = are we going to measure. Having multiple measurements would be great; but = very difficult to achieve.

While doing that, I spent some time looking in there with a small mirror. = What I noted was that initial gaps above and below the cooler (required to = slide the unit in and out) had changed a bit. The cooler is supported on = pads of ‘Cool-Mat’ insulation. Those have compressed just a = little, so now there is very little gap at the bottom, and 1/8”+ along the top. That is a fairly substantial leak, and the loss of pressure = at the top likely exacerbates the flow separation. I decided it = wasn’t worth going to test the VGs as long as that leakage gap was = there.

Taking the wing off (mostly getting it back on because of next to impossible = access to nuts), and removing the cooler looks a bit much right now. I = realized then; that by putting in a sheet metal ‘false’ upper duct = wall, I could extend it up into the gap at the top (photo 2), thereby changing = the shape, and (mostly) closing the gap at the top.

The false wall has to be in three parts for the three openings, and there = will be gaps between because of the supporting dividers; but it could make a substantial difference. I made the piece for the center, and = considered testing just that; but the upper gap concerns me enough that I think = I’ll try to get all three fit in.

Then go take a flight test. Unfortunately this combines three changes, VGs, = closing gap, and changing duct wall. I had hoped to test these one at a time. If there is a substantial change; it will be easy to remove = the VGs to see what that effect was.

Of course I’ll let you know when I get some = results.

Oh, the price of innovationJ.

-----Original = Message-----
From: Rotary motors in = aircraft [mailto:flyrotary@lancaironline.net] On Behalf Of Thomas Jakits
Sent: Thursday, July 19, = 2007 10:31 AM
To: Rotary motors in = aircraft
Subject: [FlyRotary] Re: = Oil cooler inlet

Okay,

Monty thinks the emphasis is on the = BL.

I believe (don't = know), the main-problem is the upper ductwall shape. Even if you have perfect BL = flow, the upper wall shape is still not good and will stall the flow. =

At the end of the game you want good flow at = all speeds and be able to close any ducts to limit excess cooling (when you hopefully get there).

Obviously BL will play a role in your = installation as the intake is rather narrow.

However BL or not - BL does not mean there is = no flow, just slower and more turbulent, but still generally going towards the = cooler.

Aerodynamics in the duct should be much the = same for laminar, turbulent, any flow, as long as there is = flow.

When things stall is when flow pretty much = ceases (in the stalled area ....), no matter how well things where at the = entrance.

The stall in this case is rather = "easy" to get, as the speed seems rather low already. Still may be good enough if = you can do away with the stall.

So I suggest to work on the duct wall first = and optimize it.

As suggested, with some kind of sheet, alu, fiberglass, etc. You can curve it more and more until you = peak.

Maybe pinched ducts (copyright Ed!!) are not = working here, but it may as well - if they work a Ed's theory explains = (energizes the flow...)

If this works, modify according to the best = shape found.

Then try to improve with VGs or sanding or = turbolator tape.

Then go for the exit - after all it is a = differential pressure game....

On = 7/18/07, M Roberts <montyr2157@alltel.net> = wrote:

Al,

I think you need to do = something to energize the boundary layer. If you can't divert it you need to put some = energy into it. It is probably getting slow and separating from the face of the = duct. That is what your data seems to indicate to me.

I like the shape that = Thomas proposes better than what you have now, however, I still think you will = need some VG's in front of the inlet.

I know it may seem counter intuitive, but turbulence may actually help in this case. You will not = get very efficient internal diffusion, but it will be a lot better than what you = have now. I don't think that putting a turning vane will help too much = without doing something to energize the boundary layer first. You'll just have a slow = thick low energy layer, and a high energy layer separated by a turning vane. =

It is really easy to duct = tape some aluminum VG's in front of the inlet and see what it does. =

You may need a combination = of Thomas' contour, VG's and a turning vane. Go with the easy fix and work = your way up in complexity.

Monty