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Performance Data

JDA_BTR

Well Known Member
Started some test flights for performance data. It is hard to control all variables. Especially density altitude!!! But here is some preliminary data below. I didn't do the best job controlling EGT on this, so there is some variability in power at each level but not a lot.

6000-7500 feet seemed to be the sweet spot for TAS. I'm going to work in that area some more and play with power settings.

It is 2000' Pdens on the ground here right now.....

DensAlt RPM   MAP   TAS   
10084 2500  21.8  170 All approx 100 ROP
    2400  21.8  167   
    2300  21.8  164   
9570  2500  22.2  171   
   2400  22.2  169   
   2300  22.2  167   
9083  2500  22.7  172   
   2400  22.7  170   
   2300  22.7  167   
8605  2500  23.1  173   
   2400  23.1  170   
   2300  23.1  170   
8152  2500  23.5  173   
   2400  23.5  171   
   2300  23.5  169
7650  2500  24  173
   2400  24  169
   2300  24  167
7180  2500  24.4  175
   2400  24.4  173
   2300  24.4  168
6600  2500  24.9  174
   2400  24.9  170
   2300  24.9  169
5980  2500  25.3  174
   2400  25.3  170
   2300  25.3  167
5400  2400  25.8  172
   2400  25.8  169
   2300  25.8  166
4990  2500  26.4  172
   2400  26.4  170
   2300  26.4  166
4450  2500  26.8  172
   2400  26.8  169
   2300  26.8  167
4020  2500  27.3  173
   2400  27.3  169
   2300  27.3  165
 
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I went up today and focused on the best efficiency density altitudes.

1. One trend is that things seem worse at 150ROP compared to 100ROP. They
certainly don't get better! So no reason to be more than 100ROP so far as I can tell.

2. Not a big difference at 100ROP or Peak in this range of altitudes. My data is a snapshot and would benefit from a lot more averaging in some different weather. I will probably do this again in the winter.

3. My conclusion is for best performance operate 6500-8000 density altitude, and more bang for the buck out of raising RPM at peak EGT than in going ROP to boost speed.

4. Best speed/dollar benefit of going 50-100ROP is at 2400 RPM; not much benefit at all at 2300.

5. Best speed is 100 ROP at 2500 RPM.

6. Best density altitude to fly 2300RPM is 7500 and 50ROP there gives a nice speed boost. 171 kts at 10.1 GPH.

7. Another good compromise is 7500', 2400 RPM at Peak EGT. This looks to me like the 7000-8000 density altitude sweet spot for keeping the gas flow low and the plugs clean.

8. When I got it more than 5-10 degrees LOP I got a big drop in power; easy to hear and feel. I won't be running LOP I think. My ear could pick out the peak in most of these cases.

PHP:
DAlt	RPM	 Peak	 50 ROP	100 ROP	150 ROP
6500	2500	172/10.8	174/11.1	175/12.3	175/13.5
	    2400	168/9.6	173/10.6	172/11.5	171/12.2
	    2300	166/9.5	167/10.1	168/11.4	169/11.7
7000	2500	172/10.0	174/11.0	176/11.9	176/12.0
	    2400	172/9.9	173/10.6	173/10.9	172/11.9
	    2300	167/9.0	167/10.4	168/11.5	168/12.0
7500	2500	172/9.7	174/11.0	176/12.0	176/12.0
	    2400	172/9.9	173/10.6	175/11.1	171/11.1
	    2300	167/9.7	171/10.1	170/10.6	169/10.8
8000	2500	173/10.2	174/11	176/11.7	176/11.8
	    2400	172/9.6	172/10.4	172/10.6	172/11
	    2300	166/8.9	169/9.3	169/10.1	167/11.4
 
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Great info, thanks for sharing it. The advance timing will make a difference, if you have options to play with that.

During my last x-country trip, I learned the best bang for the buck is to go high. I was getting a slightly better speed for about .8 G less.
My TAS was 163 @8.3G at 12500 vs. 164k at 7.5G at 17500. The plane had no issues climbing at 500 fpm at 16500.
 
It is dual pmags set for 29 degree advance with -7 initial set point. I copied others on the setting
 
Dudley,

When you set peak EGT, are you doing it slowly, and by reference to the raw EGT values, not the fish finder's textual "PEAK" indication?

I ask because I noticed something. Your 7000 ft and 8000 ft fuel flows at peak and 2400 are 9.9 and 9.6 GPH. There was a new RV-14 owner at the last Petit Jean gathering reporting similar fuel flows (if I recall correctly!), the oddity being that Marvin and I both thought them higher than we see with our 390s. I flew a three leg speed check with him, which offered an opportunity to play with leaning; flow was in fact higher than mine for the same settings. The difference was a few tenths, no big deal, but more.

Here is a snapshot from this spring, some where over Virginia on my way to Mom's house. I'm very slightly LOP, not enough to creep into the power loss. Peak would be typically 9.1~9.2 at this altitude. Ignore the speed; the RV-8 is just faster, no surprise. The point of interest is the fuel flow (here 9.0) at peak and 2400. What is your indicated manifold pressure at 7000 and 8000?

4_13_19%20Cruise.jpg
 
A few tenths difference in indicated fuel flow could easily be the level of precision that the FF computer is calibrated too.......
 
I found peak manually. I dont know any other way on my G3X.

My MAP there is about 24. So a little more power and fuel than what your pic shows. Do you know the density altitude of your example? My numbers are DAlt. Temps here are very hot. 68 degrees at 5500 press alt.
 
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I found peak manually. I dont know any other way on my G3X.

My MAP there is about 24. So a little more power and fuel than what your pic shows.

That would explain a lot. I'm throttled to hold 65~66% in the photo.

Do you know the density altitude of your example? My numbers are DAlt. Temps here are very hot. 68 degrees at 5500 press alt.

Sorry, no.
 
Sorry, no.

The data is there. Dan shows true airspeed (186 kts) and IAS (164 kts). The square of 164/186 is equal to the current air density divided by standard sea level density. Find a chart of density vs standard atmosphere altitude, that will tell you density altitude.

Edit. Or use the following approximation: He’s indicating 7500’, and 48 F. OAT. 48 F = 9 C. Standard temp at 7500’ is 0C. Multiply difference by 100, 9x100 =900, his density altitude is about 900’ higher than indicated, e.g., 8400’.
 
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Thank you for posting your data!

I went up today and focused on the best efficiency density altitudes.

1. One trend is that things seem worse at 150ROP compared to 100ROP. They
certainly don't get better! So no reason to be more than 100ROP so far as I can tell.

I came to the same conclusion. I could find no speed advantage above 100ROP.

2. Not a big difference at 100ROP or Peak in this range of altitudes. My data is a snapshot and would benefit from a lot more averaging in some different weather. I will probably do this again in the winter.

I think your gut feeling of needing more averaging is good. In post #6 DanH asked how you were finding peak. He may be on to something. If you subtract your PEAK fuel flow from your 100ROP fuel flow at each altitude and RPM the delta varies from 0.9 to 2.5GPH, but the variation is not linear with either altitude or RPM. I had the same issue until I started finding PEAK very very slowly. It may take 30 to 45 seconds between adjustments which feels like an eternity when your doing 3 RPMs at each of 4 altitudes:).

3. My conclusion is for best performance operate 6500-8000 density altitude, and more bang for the buck out of raising RPM at peak EGT than in going ROP to boost speed.

I agree. My ROP data looks best around 8000 possibly 9000DA. If you look on the Vans aircraft website, they publish cruise speeds at 8000’. They don’t specify DA or PA, but I suspect DA. I found even higher to be best for PEAK and LOP cruise. The RV14 wing seems to be very efficient in the low to mid teens.

4. Best speed/dollar benefit of going 50-100ROP is at 2400 RPM; not much benefit at all at 2300.

Harmonic vibrations always concern me. I chose the IO-390 and Hartzell blended airfoil prop combination because Lycoming had tested that combination and found it acceptable. However, that testing was with standard magnetos. The only Lycoming data I could find for electronic ignition was on an IO-360. As a result of that testing, Lycoming recommended a minimum cruise RPM of 2350. For my plane I decided to just use 2400RPM or more. Since you found no advantage to 2300RPM I can feel better about my choice.

5. Best speed is 100 ROP at 2500 RPM.

Yep, I found even better speed at 2700RPM, but it takes a lot of fuel:). I just accept 2400RPM.

6. Best density altitude to fly 2300RPM is 7500 and 50ROP there gives a nice speed boost. 171 kts at 10.1 GPH.

7. Another good compromise is 7500', 2400 RPM at Peak EGT. This looks to me like the 7000-8000 density altitude sweet spot for keeping the gas flow low and the plugs clean.

8. When I got it more than 5-10 degrees LOP I got a big drop in power; easy to hear and feel. I won't be running LOP I think. My ear could pick out the peak in most of these cases.

This surprises me. The main advantage of electronic ignition advance is during LOP operations. Even a standard magneto can reasonably go farther LOP. Somewhere on this message board RVBuilder2002 posted a factory RV14 cruising at 10,500 to 11,500 at 0.5 gallons LOP (about 25LOP) with standard Slick magnetos. I suspect you will get better results next time you find PEAK.

PHP:
DAlt	RPM	 Peak	 50 ROP	100 ROP	150 ROP
6500	2500	172/10.8	174/11.1	175/12.3	175/13.5
	    2400	168/9.6	173/10.6	172/11.5	171/12.2
	    2300	166/9.5	167/10.1	168/11.4	169/11.7
7000	2500	172/10.0	174/11.0	176/11.9	176/12.0
	    2400	172/9.9	173/10.6	173/10.9	172/11.9
	    2300	167/9.0	167/10.4	168/11.5	168/12.0
7500	2500	172/9.7	174/11.0	176/12.0	176/12.0
	    2400	172/9.9	173/10.6	175/11.1	171/11.1
	    2300	167/9.7	171/10.1	170/10.6	169/10.8
8000	2500	173/10.2	174/11	176/11.7	176/11.8
	    2400	172/9.6	172/10.4	172/10.6	172/11
	    2300	166/8.9	169/9.3	169/10.1	167/11.4

My replies are bolded within your quoted post because I’m not very good at message boards. Thank you for taking the time to post your data I like to look at trends and your data gave me a good comparison.

For looking at trends within one aircraft my next two questions are not necessary; however, you did a great job of comparing Altitude and RPM so I would like to know two things.

1) Did you test for a K factor on your fuel flow and do you like the results when you compare calculated fuel burned to what you pump back into the tanks?

2) Did you do a GPS calibration of your TAS?

Neither of those questions matter for your chart, they only allow me to compare across aircraft.
 
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My red cube is very much on the money. I've had it be within a few tenths of a gallon on every fillup; likely more accurate than my level approximation to the vent overflow at the tank!

I didn't correlate TAS with GPS. Too much wind variability to know. I feel like the computed value in the G3X is pretty close to right but I didn't prove it.

Your comments about vibration... at 2300 the "feel" isn't as right as at 2400 in my plane. There is a definite difference in vibration at the lower RPM. 2350 is better than 2300 in it too. I'm planning to dynamic balance once I'm done with the break-in. I'll probably balance for 2400.
 
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My red cube is very much on the money. I've had it be within a few tenths of a gallon on every fillup; likely more accurate than my level approximation to the vent overflow at the tank!

I didn't correlate TAS with GPS. Too much wind variability to know. I feel like the computed value in the G3X is pretty close to right but I didn't prove it.

Kevin Horton has a link to a 4 leg GPS TAS calibration spreadsheet. I have a G3X system with the standard Vans pop rivet static port. The TAS error is less than 1KT. It may be a test you would enjoy.
 
Your comments about vibration... at 2300 the "feel" isn't as right as at 2400 in my plane. There is a definite difference in vibration at the lower RPM. 2350 is better than 2300 in it too. I'm planning to dynamic balance once I'm done with the break-in. I'll probably balance for 2400.
Mine feels far more smooth at higher RPM and as I go below 2500 RPM, I easily feel the vibration, which is relative to the higher RPM. I did a dynamic prop balancing and it was surprisingly so balanced to the point that he could not add any weight or adjustment to make it better. He recommended to leave it as is which I agreed.
 
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