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  #1  
Old 02-01-2013, 10:53 AM
Wesael's Avatar
Wesael Wesael is offline
 
Join Date: Feb 2009
Location: Brooksville
Posts: 282
Default Massaging the last Knots out of the "School Bus"

I have always wanted to tape all the joints and fairings up on this airplane and see what speeds it will make in a semi-race configuration.

Yesterday afternoon I found time to completely wax the airplane man what a job. Reminded me of polishing a 38' smooth side aluminum dump trailer when I was trucking

I then taped up all of the seams and intersections to provide a smoother air flow across the joints and to prevent air from entering or exiting.



The method used for determining TAS during this test was per NTPS using there 3-way gps spreadsheet.



I started before daylight in an attempt to provide a more uniform air mass for testing. The sun did not have time to start warming the air and cause the air mass to start rising.

Test #1
Density Alt 8000
MAP 23.8
RPM 2700
Mixture Approx 175 deg ROP
GPH 18.5
TAS per ntps 189.3
TAS 189.8 per Dynon

Test #2 Note : I was trying for 75% power here but when I got back on the ground and did the calculations correcting for temp it wound up being more like 79% power.
Density Alt 9910
MAP 21.9
RPM 2700
Mixture Approx 175 deg ROP
GPH 16.9
TAS 186.7 per ntps
TAS 187.4 per Dynon

Test #3 Note : This is the same as above but running Lean of Peak
Density Alt 9910
MAP 21.9
RPM 2700
Mixture Average readings of 10 deg Lean of Peak
GPH 12.1
TAS 182.6 per ntps
TAS 183.0 per Dynon

Test #4 Note : This is at Sea Level with the hammer down
Density Alt 0
MAP 29.4
RPM 2800
Mixture Approx 175 Rich of Peak
GPH 27.5
TAS 193.1 per ntsp
TAS 195.5 per Dynon


This shows that the Dynon TAS may have a slight error on the high side but is well within my needs. 1-2knots is close enough for planning.

By the way......it was a lot of fun

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RV-4 715hr Sold
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  #2  
Old 02-01-2013, 11:01 AM
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rleffler rleffler is offline
 
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Default

For comparison, what were the results prior to all your taping? How many knots did the taping buy you? Just curious......

bob
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  #3  
Old 02-01-2013, 11:12 AM
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Wesael Wesael is offline
 
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Default Not a Lot

Maybe 1 knot....Maybe. It was not worth it other than I "had" to know.

If I had not done it I would always wonder
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  #4  
Old 02-01-2013, 11:41 AM
N427EF N427EF is offline
 
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Default Very impressive!

Thanks for sharing the results of your effort.
Approximately 1 gallon of gas for 1 knot of speed going from LOP to ROP.
Is your governor set to 2800 RPMs for this test or normally limited to 2700 RPM?
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  #5  
Old 02-01-2013, 11:53 AM
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Wesael Wesael is offline
 
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Default

Quote:
Originally Posted by N427EF View Post
Is your governor set to 2800 RPMs for this test or normally limited to 2700 RPM?
Normal operation is 2700 max but have it set for 2800 if needed.

DISCLAIMER: Never set your RPM to above max rated speed! You engine will probably blow up resulting in pieces flying everywhere, the prop will be trashed, it will cause financial distress, and ultimately push you closer to the nursing home at best and maybe even cost your life. you have been warned.
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  #6  
Old 02-01-2013, 02:30 PM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default It may be faster yet.

The high speed, hammer down, translates to almost 222 MPH! Mine does 217 MPH WOT, not taped, so you're doing really well. However, Alan Barrett mentioned to me that a lower prop RPM, with more 'bite' in the blades may make it faster...and Wow, went from 211 to 217 TAS, on the Dynon-100 at 2625 RPM and WOT.

Best,
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  #7  
Old 02-02-2013, 02:53 AM
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RV10inOz RV10inOz is offline
 
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Default

OK,

If those are knots not MPH....

I must have too many antennaes and stuff hanging off ours because I can get about 180 or so and 10-20 LOP about 165+/- a bit, but 183Knots TAS

What am I doing wrong?
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  #8  
Old 02-02-2013, 06:09 AM
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pierre smith pierre smith is offline
 
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Location: Louisville, Ga
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Default Dunno.

Hard to tell without looking at it David. Could be so many things. I only have two bent-whip comms out in the breeze, under the belly...all the other antennae are on the dash.

Lower intersection fairings are flush mounted and the uppers fit really tight too.

The space between the prop shank and spinner is so close that the blade almost touches the spinner at coarse pitch...this is a high-drag area if there's a big gap or one of those chrome spinners with a lip around the blade openings. The late Paul Lipps was adamant about a tight-fitting spinner/blade relationship and the F-1 and racing Bipes fill that area from inside the spinner with leather....and I've considered it on my -10. You could glue leather to the prop shank, just inside the spinner and centrifugal force would hold it against the inside of the spinner.

Dan Horton has done an amazing job of sealing the forward baffling against the rotating flywheel, upper and lower, to prevent any air from squirting out around the backplate/cowl junction for yet more speed.

Best,
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RV-10, 510 TT
RV6A (Sojourner) 180 HP, Catto 3 Bl (502Hrs), gone...and already missed
Air Tractor AT 502B PT 6-15
Air Tractor 402 PT-6-20
EAA Flight Advisor/CFI/Tech Counselor
Louisville, Ga

It's never skill or craftsmanship that completes airplanes, it's the will to do so,
Patrick Kenny, EAA 275132


Dues gladly paid!
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  #9  
Old 02-02-2013, 02:23 PM
BillOrcutt BillOrcutt is offline
 
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Default

I agree with Pierre....drop your rpm to 2600-2650 and you should pick up a knot or two. The reason is the blade tips are usually encountering turbulence at 2700 RPM. I've found this to be true on 2 and 3 blade scimitar hartzells.

Bill
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  #10  
Old 02-02-2013, 06:08 PM
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RV10inOz RV10inOz is offline
 
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Location: Brisbane Qld. Aust.
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Default

Its interesting stuff drag, because you can't see or measure it, well not easily in flight apart from speed.

I have a stubby Transponder, 2 x VHFs, GPS, Stormscope (huge) and the VOR/ILS rabbit ears in the tail. They will be all huge drag items for sure.

Spinner drag is an interesting one, and a very good point. I might have a look at that a bit closer and investigate sealing it.

We noticed about 4 knots in removing the tie down rings alone.

Pierre, I would be interested to see your TAS number for 65% at 11.3gph LOP at a DA around 8-9,000 and at a weight of say 2450-2500lbs. Which would be a typical 2 pob bag and full or close to full mains.

No rush, but when you get the chance. Pics always enjoyed too!
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