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Old 11-12-2017, 09:37 PM   #1151
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Yeah, I'll bet he would be an educational guy to talk to Neil. Got any pictures of anything under the cowling?


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Old 11-13-2017, 03:14 AM   #1152
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Default Cameron's Christen Eagle II Build Thread

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Between the the 174 mph run a few weeks ago, and yesterday's, DA was close, but not exact. I didn't record atmospheric conditions. Just going from memory of the day and using a DA calculator, it was about 2000'. Yesterday, DA was about 1500'.

I guess I should be testing this type of stuff with the altimeter set at 29.92" and using the same pressure altitude?


Unless you have a Dynon or other glass that has DA readout if not Yes set the altimeter to 2992 and record OAT (take digital kitchen thermometer and stick it out the canopy or vent). Once you establish what the DA is try and repeat that altitude if you can. There are quite easy ways to normalize the data to any altitude or weight that I can go into if you want but you are going to need manifold pressure too. Measuring a couple of knots is tricky and when you add up all the errors in data and the way itís flown 2-3 knots can be in the noise.

I measure my improvement using fuel flow as my top end never changes because Iím fixed pitch so the I cap out at 2700 and measure the fuel flow at the same density altitude. I have firewalled it before but at 3300 RPM for a minute is cringing. I have seen 180 MPH indicated at 2000 da before, but I spend my time really getting the test point at 2700 rather than minutes letting everything stabilize at 3300 I like my engine and donít want to be mean. I let it get to 3300 often during Akro but only quick transients.


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Old 11-13-2017, 04:37 AM   #1153
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No dynon or glass except for an iPad. My other instruments are all steam gauges except for a 4 place CHT/EGT monitor.

I'd be interested to hear how to normalize the data and also how best to collect it. Matching the DA for every run makes sense.

Ive been doing top speed runs, mainly because I just want to see how fast it will go.

This is all interesting stuff. I know an Eagle will never be a super fast airplane but I think there is room for quite a bit of speed increase. Just depends on how much work I want to do.
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Old 11-13-2017, 01:22 PM   #1154
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I had always thought the four air vents on the eagle create quite a bit of drag? I used naca vents thinking it would help? I wonder if you made a temporary cover in front of them you may pick up some speed. You have eliminated antennas right, the fuel drain could be faired in. I think I saw a nice fairing Smizo made in front of the fuel drain. Tail wheel fairing and your ready for Reno.
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Old 11-13-2017, 02:12 PM   #1155
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All good ideas. I'm sure I'll get around to most of those eventually.
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Old 11-13-2017, 05:42 PM   #1156
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Fantastic work Cameron! I’ve got a copy of “Personal Aircraft Drag Reduction” by Bruce Carmichael. He makes several comments on the inlet and exit:

“The design of the passage between the inlet and the upper plenum has a large effect on the performance of the cooling system. The job of this so called diffuser is to slow down the high velocity inlet flow, converting its dynamic pressure to static pressure with a minimum of energy loss. For the case of a smooth diffuser with a constant diffuser angle, flow separation can be avoided up to a divergence half angle of 6 to 7 degrees. Dumping from the end of the diffuser into the upper plenum can cause large losses when the area change is too abrupt.”

“Cylinder fin baffles must be closely tailored and penetrations of these baffles should have tight fitting grommets. The exit area should should approximate the total flow area through the fins. The entry of any passages should have rounded lips of 20% of the entry diameter.”

I can’t see much more improvement on your lower exit your fairing looks great. The inlet side is much more tricky, particularly the inlet with the prop governor sticking out in the breeze. I’ve spent quite a bit of time staring at my own installation trying to imagine how to improve it and get a smooth gradual transition from the cowl inlets to the plenum above the engine. A custom plenum out of fiberglass would be ideal but lots of work. One more project on a long list of projects.

One final thought - have you considered a thin sheet metal airfoil shape around the exhaust sticking out the bottom of the cowl? Or something attached to the belly panel just behind the exhaust. A round shape is absolutely horrible for drag.

I’ve thoroughly enjoyed your build thread. Always great to see your work.
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Old 11-13-2017, 05:55 PM   #1157
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I think we need (I would like) someone smarter than me to keep this on a back burner for next Oshkosh. I would love to go look at some of this black magic but need to know where to go, to look. Don't need any snide remarks on where to go either, I already have people lined up with suggestions on that! I don't need speed but cleaning up the drag would help on loops which seem to take an extraordinary amount speed to accomplish because of the induced drag at higher speeds.
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Old 11-13-2017, 06:29 PM   #1158
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Thanks Paul. I'll have to see if I can get a copy of that book. I've got Kent Passer's "Speed with Economy." Lots of good stuff in there too.

I have considered fairing in the exhaust. Like you said, round objects don't move through the air that easily. Luckily, the exhaust is tilted back so the profile that the air sees is more elliptical. Kent Passer changed his exhaust so that it pointed more rearward, and he tapered the pipes to increase the exhaust velocity to add some thrust. I thought about at the very least changing the collector so that it points more rearward, but I'm still not sure about it. I've read that it makes the interior much louder.

At any rate, the exhaust is an item on the list of stuff to look at. There's enough items on this list to keep me busy for years.
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Old 11-14-2017, 02:16 AM   #1159
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That's interesting about the noise level. It looks to me like the raven exhaust is pointing more downward than the sky dynamic. I wonder if the SD is going to be louder inside the cockpit?


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