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Old 04-23-2017, 08:31 AM
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DanH DanH is offline
Join Date: Oct 2005
Location: 08A
Posts: 7,295

Keep swinging Andy! You're doing fine.

Originally Posted by crabandy View Post
Ground run and subsequent test flight went well. The boot does transmit quite a bit of vibration to the oil cooler and the fiberglass duct at idle, above 1000RPM it barely moves.
Remember, your eyes can't see vibratory movement higher than a certain frequency. It's a lot like not being able to see the flicker due to 60 hz AC.

I have an adjustable-rate strobe for looking at vibrating objects. Tuning a strobe to the exact frequency of movement freezes the object so it appears motionless. Tuning just a bit higher or lower puts the vibration in apparent slow motion, allowing visual observation of the entire vibratory cycle or repeating motion.

I have seen propeller blades twisting torsionally as they rotate. I have seen the center of a control pushrod describe a circle about 3" dia at one particular engine RPM; it appeared perfectly still when I released the strobe trigger. I have watched the sides of a fuselage pump like the gills of a fish under the influence of propeller inflow (it was a pusher). And I've watched an entire engine move through its vibratory cycle on the mounts...and it appeared motionless without the strobe.

Point is, although your "no relative motion" observation is probably correct, don't bet on it if failure has a consequence. Put another way, seeing is believing, but your eyes can lie.

Part of me thinks I should re-design the boot to be more flexible, part of me thinks it doesn't shake any more than the standard oil cooler location/baffle material/fiberglass airbox. My guess at any failure points would be the adel clamp mounts to fiberglass duct attach points which isn't a safety of flight issue. I plan on more flight time and keeping a close eye on it.
Works for me.

I haven't been able to measure any pressure difference in the lower cowling under the cylinders compared to several locations around the firewall.
There's no reason to believe you'll find a pressure variation between any two points inside the lower cowl volume.
Dan Horton
Barrett IO-390
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Old 06-12-2017, 09:09 PM
crabandy crabandy is offline
Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 1,781

Several tanks of fuel later, #4 cylinder dropped 15* and is now right in line with #3 in climb and all cylinders in cruise. Oil temp is close to the same, the lower duct was consistently showing .25 inch H2O less pressure than the lower cowling at cruise speeds. No speed difference was found, structurally everything as installed.

One difference noted, oil temp increases with a power reduction and increased airspeed in descents. I need to measure the upper face of the oil cooler and see how it compares to upper plenum pressure.

I modified the lower duct from mostly constant area to an expanding duct, I sliced off a portion of the duct leaving the attatchment and cowling/engine mount interference points.

There's a Smooth On dealer a couple blocks from work, I grabbed a sample pack of their 3lb density pour foam.

I tapped some damns on my duct and used chunks of pink foam as a "bulk filler." If you use "bulk filler" make sure it is stuck in place, mine wasn't and the pour foam floated the chunks of pink foam to the top as it expanded and I had to do a second pour.

I attempted to make the new lower duct a divergent duct to see if I could increase the pressure differential across the oil cooler.

RV 7 200 hours and counting
12/17 donation
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Old 06-13-2017, 12:44 PM
crabandy crabandy is offline
Join Date: Jan 2010
Location: Ottawa, Ks
Posts: 1,781

New lower oil cooler duct installed.

The junction of the oil cooler duct and lower cowling.

I installed a piccolo tube in the upper oil cooler duct so I can measure the pressure on the front side of the oil cooler.

RV 7 200 hours and counting
12/17 donation
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