The more I learn, the more question I have.

[kentb]

Today Oregon has great weather, so I took a day off from work and flew my plane.

I did performance testing and collected the following data:

Testing was done at 8000 pressure altitude. 100 degrees ROP. OAT 53 F degrees, full throttle.
"TAS Lite" is the TAS computed by my BMA EFIS Lite (G3).

rpm map TAS Lite FF
2690 22 160 10.3
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
150 129 146 210 180 309 166

rpm map TAS Lite FF
2600 22 158 9.7
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
151 233 188 349 149 128 165

rpm map TAS Lite FF
2550 22 158 9.5
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
154 124 149 224 178 311 166

rpm map TAS Lite FF
2500 22 159 9.2
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
181 322 146 208 153 99 162

rpm map TAS Lite FF
2400 21.9 154 8.8
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
157 94 144 194 177 318 162 74% pwr

rpm map TAS Lite FF
2300 152 8.2
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
173 319 143 208 158 78 158 70% pwr

rpm map TAS Lite FF
2200 22.3 149 7.6
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
166 54 135 170 162 293 155

rpm map TAS Lite FF
2100 22.4 147 8
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
164 300 135 200 149 85 152 richened to smooth engine

rpm map TAS Lite FF
2000 22.4 144 7.6
speed 1 Track 1 speed 2 Track 2 speed 3 Track 3 TAS
154 70 132 194 157 283 151

Now the questions:

I am surprised that running at 2690 (full prop) and 2600 were not faster then 2550. Why would this be? Did I make a mistake in my measurements?


Why would I start getting roughness at 2100 rpm?

Vans predicts 195 mph for 160hp engine. What do I need to do to see this number? Fly down low at full throttle?

When I did this testing I flew from 170 ft MSL to 8000 MSL at full throttle and on takeoff I was turning 2700 RPM and when I reached 8000 ft I was turning 2660 RPM. Is this to be expected? After leveling off I turn the prop up to full which was 2690 and then using my AFS2500 engine monitor found the peak EGT and the richened to 100 degrees.
As I tested with slower RPM I kept leaning to keep the same temp on the EGT. Is this the correct way to do this or should I refine peak EGT of each RPM setting?

Kent

 

[Bob Brown]

wheel pants/gear leg fairings

Hi Kent,
You don't say if you have wheel pants and gear leg fairings on.

There are two brand new 9A's flying here at Independence. You should come down and get together with these guys to see how they compare, performance wise.

Contact me offline and I'll put you in touch with them.

 

[Tandem46]

Kent,

For clarification: Are your test speeds in mph or kts?

 

[Bryan Wood]

Kent,
The pitot system in the 9A has the potential to read low. If you were to read the CAFE report the factory 9A was off a bit too. My plane was always showing around 5 knots less indicated than people that I would fly with so I had it tested the last time my transponder was certified. The crazy thing is that it was very accurate when a positive connection was made to the pitot. With a simple change to the bend of the pitot tube my speeds came up and now the illusion of flying faster makes me feel better. It now closely matches others in flight. So Kent, what is your indicated airspeed at 8K'?

As point of reference my 9A will do 160 knots at 8K' full throttle and 2300rpm. At 2450-2600rpm it is considerably smoother and gains around 2 or 3 knots for each increase of 100rpm. (Dynamically Balanced Hartzell) The added fuel burn for the slight speed just doesn't pay off though. I flight plan for 8 gph block time. (climb and runup included) This is a conservitive number and the plane usually beats the fuel burn to get 160 knots.

Are you painted yet? Paint seemed to help mine even though is got heavier.
Also, when you do the Linda Blair thing and look at your elevator counter weights in level cruise how much are they sticking up into the wind? If it is a lot try loading up the baggage compartment enough to move the CG back and try again. The elevator will be more in trail and the speeds will reflect it.


Good luck,

 

[kentb]

More information about my testing.

All fairing are on and the plane is painted (white). The wheel and gear leg fairings are not painted yet and there is a little fiberglass work to do on them yet, but they are very smooth.

All speeds are in knots. I don't know why VAF looses the format, but the columns in my post looked good until I hit the submit reply button. Anyway the last number in the line is the answer to TAS for the excel spread sheet that computes it off three GPS speed/tracks.

I have borrowed a very expensive machine to calibrate my pitot and static system so I am confident that the instruments are reading right. A point to consider here is that the procedure does not take into account any errors due to the ports them selves. This is because the machine is attached to the lines and not the the ports during calibrations.

Bryan, I know it is hard to read my chart above, but the 8000 ft 2300 rpm indicated TAS from the EFIS Lite is 152 kts and the GPS computed air speed is 158 kts. Fuel burn at 100 degrees ROP at this point is 8.2 gal/hr.

Don't know if my old neck is up to doing Linda's trick, but I will try to see the tail. Maybe I should just carry a mirror with me.

Kent

 

[RV9798]

Keep working on this post

This is an interesting post and we need to keep working on it to get some numbers for our 9's. May be we should make a protocol so we can compare similar data. Since I am not an expert on protocol, but like to participate, we should call on a more knowledgeable brother or sister to give us guidance in this matter

 

[kentb]

Hello Pete

I save my data in an Excel spread sheet, and could post it or email it to anyone interested.

I think that part of my problem is that although I was at 8000 ft pressure alt that because of the warmer temp (53F) I should have done my flight at about 6300 ft.

Kent