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Real world cruise speeds at 10k

Toddsanderson

Well Known Member
Hello,

If anyone would share their real world TAS/fuel burn at 10k ft it would be appreciated. LOP and ROP if possible!

Thanks!
 
Speed - Gross Weight
Top Speed: 203 mph
Cruise: [75% @ 8000 ft] 193 mph
Cruise: [55% @ 8000 ft] 169 mph
Stall Speed: 56 mph

ROP is best power.
LOP is less power than best power, deduct a few mph.
 
RV-14 Taildragger - 390 Thunderbolt Non-EXP

1760 lbs weight
8100' density Altitude
WOT (76% ROP) - 209 mph
65% ROP - 196 mph

What should the fastest altitude be?
 
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A pix of my recent flight that gives us all the numbers. My last week flight which was at 7500, same settings but ROP was cruising at 177K.
 

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Thank you for the replies. The 14A I am looking at has regular io-390, cold air induction, eflyii system 32 or injection and ignition.

The seller has the fuel injection balanced perfect with all cylinders peaking at the same time. This plane also has full de-ice on the wings and tail along with a 3-blade MT prop. He selected this prop because it had de-ice boots.

Plane does 173 MPH/7.5 GPH LOP at 10k and 183 MPH/11.9 GPH ROP. Appears to be 10-15 MPH slower than average. Seller seems to think the 3 blade MT is the factor. I would tend to agree as I don’t think the thermal deice has that much drag.
 
A pix of my recent flight that gives us all the numbers. My last week flight which was at 7500, same settings but ROP was cruising at 177K.

Thank you for that pic. Looks like 166 knots at 11500. -50DLOP is pretty good at 8.2. I think the one I am looking at would be a little faster as it was overly LOP at 7.5GPH and 2600 RPM. Also, your oil temps look real good. This one is pushing 210F.
 
At density altitude of 10k I get 172 kts at 0 LOP and 8.5 GPH or 175 kts 50 ROP and 9 GPH with oil temp 185-190 in cruise in most configurations. 14A with thunderbolt non-exp 390. My airspeeds are approximately the same from 8000 - 11000 feet. Best performance for airspeed at peak power settings in my plane was measured at 9000 density altitude 60 degrees ROP.

I would not want the de-ice equipment or prop since I would not fly in possible ice conditions. Im curious what price is asked, and if it would permit the expense of a prop swap to start.

I’m also curious if the de-ice can easily be removed from the prop because those props should not be a main cause of poor performance?
 
I’m only interested in this plane because of the De-ice. Just looked again and TAS as recorded by the G3X is 146 knots/167MPH. This is at 7.5 GPH, which should be very lean at 2600 RPM and 10k. I don’t have any data on how far LOP it is, but with the perfectly balanced injectors I suppose you can get real lean and still stay smooth.
 
Thank you for the replies. The 14A I am looking at has regular io-390, cold air induction, eflyii system 32 or injection and ignition.

The seller has the fuel injection balanced perfect with all cylinders peaking at the same time. This plane also has full de-ice on the wings and tail along with a 3-blade MT prop. He selected this prop because it had de-ice boots.

Plane does 173 MPH/7.5 GPH LOP at 10k and 183 MPH/11.9 GPH ROP. Appears to be 10-15 MPH slower than average. Seller seems to think the 3 blade MT is the factor. I would tend to agree as I don’t think the thermal deice has that much drag.

It’s been my experience that MT props, in general, are slower than other props. I’m sure the TAI in the wings isn’t helping either. Do you also have anti ice on the tail? How about the windshield? Heated fuel vents? Heated static ports? I’m all for IFR capable planes, but without ALL of these anti ice protections, (and tested in actual icing conditions) I wouldn’t fly it in ice. These just aren’t the planes for that mission.. I would remove all the ice stuff, put on a Whirlwind CS prop, and return the plane to a fun, fast RV.. the way it was designed.
 
Thanks Tom. I can’t use the plane n Indiana without de-ice. While I try to avoid it, we have ice most of the winter. It is usually only 3k thick and can be avoided much if the time, but when you get into ice it is nice to have some tools. Having $300k in a plane that has a very limited mission ability is not what I want. Even planes with heated static and fuel vents can be poor ice performers. My non-FIKI Baron with TKS and no heated fuel vents or static ports would fly through freezing rain without a problem. My FIKI P210 was horrible in the ice. Again, really don’t want to get into a debate about de-ice on a RV, just trying to figure out why it is so slow.
 
That's the data point I was curious about.... $300K. I debate selling my 14 to finance completing my 8 but then I would miss flying too much.
 
Thank you for that pic. Looks like 166 knots at 11500. -50DLOP is pretty good at 8.2. I think the one I am looking at would be a little faster as it was overly LOP at 7.5GPH and 2600 RPM. Also, your oil temps look real good. This one is pushing 210F.

Just some additional feedback that this is EXP engine which consumes a bit more fuel than the standard.
My nozzles are also have been balanced to about .1G and all numbers (TAS, Fuel flow, etc) all have been calibrated and verified. My CHT delta typically is about 10F.
My last RV which had a standard IO390 consumed about .5G less fuel but also was a bit slower. My top speed in this plane has been 191k with cowl flap open. Closing cowl flap usually gives me 2-3 knots.

In regards to the three bladed prop, yes they are typically a bit slower and much harder to remove/install cowl. But I would also pay attention to the CG as 14s need a bit more weight up front.

Good luck.
 
I received some PMs about the de-ice not being acceptable on the RV. Again, I am not wanting to debate de-ice. I have been flying 35 years and find that all tools are welcome. The draw to the 14A is the speed and efficiency along with having deice. If I am going to buy a plane without deice I would buy another Glasair III or Legacy as I really don’t need the short field performance and they are 50 knots faster than the RV. I could deal with 170 knots, but 150 would drive me crazy. Like anything, there is no free lunch. I need to think this out a bit. I appreciate all the replies.
 
Consider the following factors regarding LOP power versus speed:

1. Lean of peak, you get (regardless of fuel flow) 14.9HP per GPH
2. Using the example you shared for the airplane in question, 7.5 GPH x 14.9 = 112 HP
3. For the IO-390 (210 HP version) this is 53% of rated power
4. The aircraft in question is seeing 150 kts (173 MPH) at 53% power - not bad and in line for an RV-14/14A. According to Van's website, cruise at 55% power is 172 MPH or about 149.5 kts
5. If you want to push the power up to 70-75% (depending on altitude - limited to less at 10K) you should see around 170 kts (Van's performance data says 75% power, cruise is 195MPH or 169.5kts).
6. One data point: the RV-14A I built saw 168 kts LOP with FF of 9.6 GPH: 9.6 GPH x 14.9 = 68% power.

Regarding "how far lean of peak": once you're lean of peak, going farther lean of peak gains nothing in efficiency as power goes down in proportion to fuel flow. The primary purposes of lean of peak operation are to gain efficiency (especially above 7500 feet where you are safely out of the red box) and protect against possible damage (below 7500 feet if operating at high enough power setting to be in the red box). Both are achieved at EGTs 25 or so LOP for just about any power setting in typical cruise flight (does not apply at high/power/lower altitude, where you should operate ROP anyway): going farther LOP doesn't really achieve anything pulling the throttle back won't (again assuming LOP).

References: https://resources.savvyaviation.com/wp-content/uploads/articles_eaa/EAA_2012-12_red-box-red-fin.pdf

https://youtu.be/h3bATVXMHQg
 
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I agree with you completely. All of my NA planes were most efficient around peak to -20 LOP. My turbocharged planes were most efficient around 50-70 DLOP depending on power setting. At 65% or less you are out of the red fin and can run as lean as you want, but going excessively lean is counterproductive.

With that said, I have received multiple replies where people are getting at least 165 knots and most are getting 170+ knots LOP around 8.5 GPH. The plane in question is around 147 knots. Now, this plane is likely a little heavy with deice, big extra alternator, 2 batteries, etc, but flight test was done with 1/2 fuel and just the pilot.

Even at 11.9 GPH it would only eke out 157 knots. Has to be a drag issue.
 
I agree with you completely. All of my NA planes were most efficient around peak to -20 LOP. My turbocharged planes were most efficient around 50-70 DLOP depending on power setting. At 65% or less you are out of the red fin and can run as lean as you want, but going excessively lean is counterproductive.

With that said, I have received multiple replies where people are getting at least 165 knots and most are getting 170+ knots LOP around 8.5 GPH. The plane in question is around 147 knots. Now, this plane is likely a little heavy with deice, big extra alternator, 2 batteries, etc, but flight test was done with 1/2 fuel and just the pilot.

Even at 11.9 GPH it would only eke out 157 knots. Has to be a drag issue.


The 11.9GPH example is ROP however, where you can't apply the 14.9 HP per GPH: the richer the mixture the less efficient. If there is a big drag problem, how can you explain on-target performance LOP at 53% power??

I don't think 170Kts at 8.5 GPH is realistic at all: this would mean they are getting the same performance at 60% power that Van's sees at 75% power. It's more likely there is a measurement error somewhere.

The only way to know is to go flying in the airplane, fly LOP at 10K feet, at highest / best GPH setting, fly in multiple directions and average the groundspeeds versus demonstrated TAS. (That's what I did to calibrate airspeed in my airplane). Also - measure fuel use over time compared to what the totalizer says: I had to adjust the K factor in mine to correct some error (not huge but not insignificant).
 
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I thought the OP reply about 7.5 GPH and 2600 rpm was interesting. When I want to save engine life or gas I drop the rpm to 2300. I climb at 2500 and cruise at 2400 and poke around at 2300. It never occurred to me to aggressively lean out at very high RPM.
 
The 4-way GPS ground speed average worked out to 153 knots at 10k and 2600 RPM. Unfortunately, it was done as a combination of LOP and ROP. I’m not sure if he had the wing deice on during this time, but that alternator develops about 8000 watts of power which is about 15 HP if it was being used. Also, 7.5 GPH is way too lean at 10k and 2600 and 11.9 is way too rich. Would be interesting to see it run at the correct mixture setting and ensuring that deice was off.

The engine also seems to run hotter than those that have posted here. Cylinder temps were in the high 300s whereas many of you have posted low 300s. Also this plane has 5” oil cooling scat tube, yet still pushes over 210 on the temp.
 
I thought the OP reply about 7.5 GPH and 2600 rpm was interesting. When I want to save engine life or gas I drop the rpm to 2300. I climb at 2500 and cruise at 2400 and poke around at 2300. It never occurred to me to aggressively lean out at very high RPM.

In a NA engine you get better volumetric efficiency at lower RPM, but I always climb at full RPM and full throttle unless the engine has a HP time limit at full power. Within 5 minutes or os in the climb you are not able to make much more than 70% power anyway, so the HP time limit is rarely a factor.
 
The 4-way GPS ground speed average worked out to 153 knots at 10k and 2600 RPM. Unfortunately, it was done as a combination of LOP and ROP. I’m not sure if he had the wing deice on during this time, but that alternator develops about 8000 watts of power which is about 15 HP if it was being used. Also, 7.5 GPH is way too lean at 10k and 2600 and 11.9 is way too rich. Would be interesting to see it run at the correct mixture setting and ensuring that deice was off.

The engine also seems to run hotter than those that have posted here. Cylinder temps were in the high 300s whereas many of you have posted low 300s. Also this plane has 5” oil cooling scat tube, yet still pushes over 210 on the temp.

If it's 210 in cruise, something definitely off on cooling. The ONLY time I saw CHTs high 300s on my 14 was first couple of flights, after that anything over 350-360 was rare. Oil temps could hit 220-225 in climb on a hot Florida day but usually around 185-195 in cruise (with original oil cooler and SCAT tubing design - would likely run much cooler with bigger tubing etc).
 
If it's 210 in cruise, something definitely off on cooling. The ONLY time I saw CHTs high 300s on my 14 was first couple of flights, after that anything over 350-360 was rare. Oil temps could hit 220-225 in climb on a hot Florida day but usually around 185-195 in cruise (with original oil cooler and SCAT tubing design - would likely run much cooler with bigger tubing etc).

Bigger tubing has little affect. In my last 14A, I changed it from 4" to 5" and saw very little improvement, about 5F and others have reported the same. But I agree with your comment about CHT or the oil temp of the said plane.
 
The 4-way GPS ground speed average worked out to 153 knots at 10k and 2600 RPM. Unfortunately, it was done as a combination of LOP and ROP. I’m not sure if he had the wing deice on during this time, but that alternator develops about 8000 watts of power which is about 15 HP if it was being used. Also, 7.5 GPH is way too lean at 10k and 2600 and 11.9 is way too rich. Would be interesting to see it run at the correct mixture setting and ensuring that deice was off.

The engine also seems to run hotter than those that have posted here. Cylinder temps were in the high 300s whereas many of you have posted low 300s. Also this plane has 5” oil cooling scat tube, yet still pushes over 210 on the temp.

Too much advance would explain the higher temps. If the advance is excessively high you would get higher temps and lower speeds. I would try again with an ROP advance of 23BTDC and a LOP advance of the same 23BTDC or up to 28BTDC.
 
Too much advance would explain the higher temps. If the advance is excessively high you would get higher temps and lower speeds. I would try again with an ROP advance of 23BTDC and a LOP advance of the same 23BTDC or up to 28BTDC.

Thank you for that info. Doesn’t the EFII system 32 automatically adjust timing for MAP and altitude?
 
around September 2022

-14A, IO-390 Thunderbolt
9500 south bound overhead Savannah, GA

+/- from memory +/-

peak egt
full throttle, 2350 - 2400 rpm
8.5 gph
172 kts TAS
 
Data

Thank you for that info. Doesn’t the EFII system 32 automatically adjust timing for MAP and altitude?

Here is my fuel mapping file name OUT_IGN and readable as an xls file. I never changed this and used the one in the system. It can be modified pretty easy. It will be on the SD card. Also, typical speeds what I call LOP (-25%) on the display. Flow was 8.1 GPH and AFR was 15.8. (At least that is what the O2 sensor stated) but I would not bank on that number. The issue is going to be one man's LOP will be different than another's. My 3 bladed WW prop seems happiest at 2,400 and other than take-off that's where I run it. Harmonic data also shows this is a good RPM. Phase 1 tested it from 2,200 to 2,600. By richening the engine, I can get another 8 - 10 knots and if I go more lean (AFR 16.8) I can lose 8 - 10 knots with flow rates in the low 7's. With EFI systems you can run pretty lean and still very smooth. Changing flaps 3 degrees does not change anything.

I'm using a 4 in SCAT tube and oil temps in the low 180's in cruise.

Thought I saved the G3X screenshot to my thumb drive but apparently not. The data was almost an overlap of Mehrdad's screen shot. I insert later.
 

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Performance data at 8,500 and 10,500 14A

Had to dodge some cumulous today, typical Florida afternoon.

Early 390 Thunderbolt, 210 hp, Stock compression. WWW300 3 Blade. (Cowling removal very easy) 1,820 Lbs gross, 84.25 CG
 

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Yes, too efficient

Wow! That is efficient!

I went back and checked my logs on Savoy as from memory these did look to good. Now seem to be using almost a gallon per hour less flow on take-off and a little less than 0.4 gals less in cruise than flights made before I updated to 9.22. I had issues with 9.22 changing set parameters but mostly were obvious and easy to fix. One was a AirInc parameter change that I had to have help from Garmin. I was told they have seen this before. I didn't record my K factor from before, but I get a duplicate reading on the EFI display for GPH and can check that. Typically, don't cross check that reading to the EFIS display. I apologize for the confusion. (My airspeed indicator has been verified correct.)
 
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Here is another 14A with 390-119, new style cowl, slick mags. 170 knots at 10k 20.9MP/2500RPM using 9.9GPH. Assuming this is ROP, but don't know how much since the pilot did not indicate. Guessing 75-100 ROP, thougts? EGTs 1350-1410 CHTs 325-328 OIL 191. I believe this was with the cowl flap fully closed. Definitely plenty cool.
 

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Here is another 14A with 390-119, new style cowl, slick mags. 170 knots at 10k 20.9MP/2500RPM using 9.9GPH.

Since this thread was about real world cruise speeds, it's worth noting that the PFD image shows -150 fpm descent rate and path vector a bit below the horizon. That probably adds several knots compared to level flight (unless it was turbulence induced just prior to taking the picture).
 
I logged 2 cross-countries yesterday (about 2 hours each) with some time to measure and record. Here is my data:

9000 MSL, 11300 density
Sweet spot cruise (slightly LOP, 2400/WOT 22.3) - TAS 170 kts, 8.4 gph
Fast cruise (ROP, 2500/WOT 22.4) - TAS 176 kts, 10.7 gph
Max (ROP, 2620/WOT/22.4) - TAS 178 kts, 11.3 gph
Economy cruise (full LOP) - don’t use it, didn’t try or measure

10000 MSL, 12300 density
Sweet spot cruise (2400,WOT 21.5) - TAS 169 kts, 8.8 gph

(These are typical values selected as middle range - I had some better, some worse - the 10000 performance doesn't appear to be as good - I believe it's just variation and I didn't record as many points.)

Some other minor factors:
IO390 with Superior cold air sump, Vetterman trombone exhaust, tunnel cooling flap (EXP 119) installed/closed
 

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