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Massaging the last Knots out of the "School Bus"

Wesael

Well Known Member
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 :eek:

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.

IMG_20130131_174639.jpg


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

IMG_20130201_063825.jpg


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:D
Density Alt 0
MAP 29.4
RPM 2800
Mixture Approx 175 Rich of Peak
GPH 27.5:eek:
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 :D:D

IMG_20130201_062937.jpg
 
For comparison, what were the results prior to all your taping? How many knots did the taping buy you? Just curious......

bob
 
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 :rolleyes:
 
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?
 
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.
 
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,
 
OK,

If those are knots not MPH....:eek:

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 :eek:

What am I doing wrong?
 
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,
 
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
 
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! :)
 
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.
:)

There are a few things that we did different very early in the build trying to get the most speed possible in a practical manner. I was not out to make an all out race plane but something that I can use and service in a practical manner.

The cooling system was modified using a plenum with fiberglass transitions molded to capture all of the air and force it into the plenum without leaking into the lower cowl.

IMAG0216.png

IMAG0229.png


Under the engine we tried to provide a transition to smooth the airflow flowing out the exit side of the cowl. (not shown in the pics. all of the gaps were sealed with RTV)

IMAG0220.png

IMAG0222.png


This along with a modification to the lower cowl to slightly increase the outlet area provides enough cooling to keep the engine cool without using the factory "louvers" under the cowl. I think they are draggy but the effects are unknown to me.

We closed all of the ends on the control surfaces.

IMAG0787-729497.jpg


Closed the hinge gaps like this

IMAG0803-726757.jpg


Also we sealed every hole that we could find in the wing root area. control rods, spar web gap etc. This is to keep air from in-filtering from the tail and exiting the low pressure area in the wing root and door area..

The wheel fairings are extra tight around the tires.

I only have 1 comm antenna on the belly and 1 transponder blade. the rest of the antennas are internal.

I ordered new ECI cyl's that were flow matched. worth it? i dont know..

The area that Pierre talked about on the spinner is cut very close to the blades.

The spinner is very close to the cowl (really its to close but its not rubbing so i left it like it worked out).

It is not really 1 thing that makes airplanes go faster. It is a lot of small things that finally add up.

Also note that I accept a slightly higher CHT that some do. My limit is 400 F in cruise so I MIGHT be accepting accelerated engine wear due to heat???? In my case I accept the risk--not for everyone.
 
Wow that's fast. Good work! I will definitely keep these in mind later on in my build!

Thanks!
 
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Great time for me to ask about this!

We closed all of the ends on the control surfaces.

IMAG0787-729497.jpg

This would not be hard to do right now since I'm glassing in the control surface FG tips. I've considered it on the -6A for 20 years but never gotten around to it. Seems like a no-brainer on the -10 project, but I thought I'd ask if the weight/cost/time is worth it. Is there an extra knot to be gained doing "this one weird trick":D by itself, maybe?
 
This would not be hard to do right now since I'm glassing in the control surface FG tips. I've considered it on the -6A for 20 years but never gotten around to it. Seems like a no-brainer on the -10 project, but I thought I'd ask if the weight/cost/time is worth it. Is there an extra knot to be gained doing "this one weird trick":D by itself, maybe?

Few things.....make sure whatever you use to fill from the last rib to edge is not something heavy and will not turn to powder (some types of foam). One posible idea is use balsa wood secured with a large area fender washer bolted to a plate nut in last rib then covered in fiberglass. Understand the risk! If something comes loose you could have a jammed control and go down.

Also consider mosture intrusion. If you get any moisture inside an enclosed cavity it will freeze and swell at altitude!
 
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The best speed test is to fly beside another aircraft at known power settings, then matching speeeds. Now make your change, one at a time, then fly with the other plane , same power settings and compare. Speed gains, or losses, can be seen. Any other method requires multiple runs and temperature corrections.
For me this was the quickest, most reliable method of checking speed mods.
I flew countless four leg trials before I realized that horsepower at different temperatures had a big effect on speed. Data without horsepower corrections due to temperature change are unreliable, useless was my experience.
 
There is always some error when measuring airspeed, so it can be difficult to determine the effect of an individual modification. Just because we can?t measure it doesn't mean it doesn?t have an effect, it just tells us that the effect is smaller than our measurement error. But the cumulative effect of many small individual tweaks and attention to details can be significant. Bottom line for me is to use our understanding of physics to make small tweaks that should improve airspeed, and not worry too much about measuring their individual effects.

Weasel, now that this old thread is revived, I got to say that I really admire what you have accomplished with your -10. It really shows what a stock setup can do when you focus on the right details.
 
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