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  #301  
Old 12-22-2018, 10:57 AM
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DanH DanH is offline
 
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I'm gonna put this one up just because I like the numbers. Groundspeed is nice (221 knots) but check the TAS vs fuel flow, 192 at 9.8. Settings are simple; WOT, adjust RPM for an indicated 65%, and lean to peak at 23 degrees BTDC.

Pressure recovery for the combustion air intake is pretty good. 21.4 Hg is measured at the usual #3 intake port. Static pressure for this altitude and temperature is 20.98, so delivered MP increase due to ram is 0.4" Hg after all intake tract losses, here including a filter which hasn't been cleaned since last January.

How much intake tract loss? Total pressure at this PA, temperature, and velocity is 22.3 Hg, but you can't recover all of it for several reasons. In the case of an engine intake (and just like cooling air), the noteworthy factor is that the "pitot" is not a closed end system. At 2500 RPM, if we assume engine VE is 90%, the calculated total pressure inside the airbox, before the filter, would be 21.9 rather than 22.3, so the overall intake tract loss for the 390, with filter and FM200, appears to be about 0.5" Hg.

Please excuse the crappy photo. The sun was at an entirely wrong angle.

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  #302  
Old 12-22-2018, 11:24 AM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DanH View Post
Settings are simple; WOT, adjust RPM for an indicated 65%, and lean to peak at 23 degrees BTDC.
Whhhhhatttt.......

Only 23 degrees BTDC?

You don't need the fancy ignition system gear for good fuel economy?
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  #303  
Old 12-22-2018, 10:00 PM
BillL BillL is offline
 
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Just taking some other data this morning, and did a quick run up to get on the board.

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  #304  
Old 12-23-2018, 09:46 AM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by rvbuilder2002 View Post
Whhhhhatttt.......

Only 23 degrees BTDC?

You don't need the fancy ignition system gear for good fuel economy?
Keep in mind that this is "Peak" EGT and the flame front is still moving pretty rapidly. Go LOP and the advance requirements change quickly.

Also keep in mind this is an angle valve with a better combustion chamber AND higher compression than standard, to boot. 23 degrees is a relatively steep advance.

If you are to add the 5 degrees to compensate for the less efficient parallel valve combustion chamber, a few more to make up for the higher compression, and then the 4 that I add when going 30 LOP, sudenly you have your advance in the low 30's.

If you want to throw in another wrinkle, consider that Dan is running a dual system. If you want parity with all those guys running an electronic on one side and a mag on the other, you have to add ANOTHER 5 or so degrees. Now you are up in the high 30's, knocking on the door of 40. Yet this same engine at a sea level TO power will need ~ 22 degrees. Do you know of a "simple" ignition that offers that range of adjustment in normal operation?

So as it turns out "fancy ignition gear" IS a required tool for good economy.

Dont mean to turn this into another ignition thread, but the "cheap shot" needed a response from someone who has done the flight testing and knows better.
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Last edited by Toobuilder : 12-23-2018 at 10:18 AM.
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  #305  
Old 12-23-2018, 10:39 AM
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You're both right, and it wasn't a cheap shot. Technically speaking, it's not a fancy ignition system (a Ford module with a sub-$200 timing controller), and it is 23 degree fixed timing when running on this ignition map. I have two, switchable in flight, but a fella can probably do it with mags if given the other airframe changes.

I can run this angle valve for more economy, and if chasing economy alone, I'd be at less RPM, LOP, and out around 27~29 degrees, which is the other ignition map. However, I would also be slower. This is a speed thread. The point is 190 plus KTAS on less than 10 gph. It makes 200 knots GS a near sure thing for the windward leg of most flights, without breaking the bank. I like it.
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Last edited by DanH : 12-23-2018 at 11:55 AM.
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  #306  
Old 12-23-2018, 12:04 PM
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Toobuilder Toobuilder is offline
 
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Quote:
Originally Posted by DanH View Post
You're both right, and it wasn't a cheap shot. Technically speaking, it's not a fancy ignition system (a Ford module with a sub-$200 timing controller), and it is 23 degree fixed timing when running on this ignition map. I have two, switchable in flight.

I can run this angle valve for more economy, and if chasing economy alone, I'd be at less RPM, LOP, and out around 27~29 degrees, which is the other ignition map. However, I would also be slower. This is a speed thread. The point is 190 plus KTAS on less than 10 gph. It makes 200 knots GS a near sure thing for the windward leg of most flights, without breaking the bank. I like it.
I believe Scott's intent was to diminish the importance of a "fancy" variable timing system.

In sharp contrast, here is but one post on a flight from a couple years ago which very clearly illustrates the value of variable (and most importantly "correct") timing.

http://www.vansairforce.com/communit...2&postcount=53

For those who dont want to read it, let me summerize: thanks to the correct timing curve I was able to match your speed AND FF in my heavy, loaded to the gills 540 Rocket on a hot day. I saw 191KTAS @10 GPH - could not have done that without direct control of the timing bump needed for LOP ops.

So to return this thread back to the boasting about speed:

Congrats Dan, you have managed to get your slick, highly refined speedster to match my overloaded, coarsely built and significantly overpowered Rocket for speed and economy!
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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.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C

Last edited by Toobuilder : 12-23-2018 at 12:06 PM.
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  #307  
Old 12-23-2018, 01:19 PM
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Toobuilder Toobuilder is offline
 
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To be fair, my OAT was 70 degrees that day... At cruise altitude...
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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.

Michael Robinson
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Harmon Rocket II -SDS EFI
RV-8 - SDS CPI
1940 Taylorcraft BL-65
1984 L39C
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  #308  
Old 12-23-2018, 09:19 PM
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rvbuilder2002 rvbuilder2002 is offline
 
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Quote:
Originally Posted by DanH View Post
The point is 190 plus KTAS on less than 10 gph.
And that was my point as well.

I'm fully aware that the quoted fuel flow isn't as low as it could be if ultimate range economy is the goal.....
The point was that considering the speed it is still impressive fuel economy without advanced tech like automatic variable timing, etc.
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Opinions, information and comments are my own unless stated otherwise. They do not necessarily represent the direction/opinions of my employer.

Scott McDaniels
Hubbard, Oregon
Van's Aircraft Engineering Prototype Shop Manager
FAA/DAR
RV-6A (aka "Junkyard Special ")
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  #309  
Old 01-04-2019, 02:47 PM
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Didn't get a picture, but we hit a ground speed of 231kts on my very first flight in my newly purchased 6A on our way home from California. Nice way to start things out.
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  #310  
Old 01-04-2019, 04:47 PM
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Ed_Wischmeyer Ed_Wischmeyer is offline
 
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Suppose Van's did come out with a fabric covered Super-Cub-ish plane, with rib stitching. That could give the 200-knot club a whole different meaning...
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