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RV-8 Cruise Data

Scotty G

Well Known Member
I've been recording my RV-8's cruise data and power settings to get a feel for what it will actually cruise at.

Engine is a TMX-390 with a Whirlwind 74RV prop.

I'd love to see what other IO-360 and -390 people are getting at the cardinal altitudes for cruise.

I record MP, RPM, FF, TAS, IAS, OAT, % hp, LOP/ROP, and altitude. Measurements are taken after 4-5 minute of steady-state flight. I also record general W/B (fore, mid, aft) and DA.

I've recorded data at 24/24 up to FT/2,400 and 2,500 up to 11,500. It'll scoot at 2,500 RPM!

I'd love if some of you would share your data so I can ensure I'm not setting some dumb power/mixture setting. I like the infield of the ballpark.

Thanks in advance!
 

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You forgot to list your numbers! My -4 with an O-360 and fixe pitch Sensenich prop does 174 knots down low, burning 12 or so gpa, and falls off to 168 to 170 knots at 17,500 feet with fuel flows up there around 7gph.
 
I think it depends on what you are optimizing for.

Here are some recent numbers from my RV-8, io-360, Hartzell metal 2-blade:

DA: 9500
OAT: 44f
RPM: 2250
FF: 9.3
TAS: 172

DA: 9500
OAT: 44f
RPM: 2450
FF: 9.4
TAS: 174

DA:5500
OAT: 48f
RPM:2200
FF: 7.0
TAS: 144

DA:7280
OAT: 53f
RPM:2200
FF: 7.9
TAS: 159

One day I'll take the time to write or find a script to analyze all my data to find the optimal "get there quick" setting, "cover the most ground" setting, "stay in the air a long time" setting, and the "sightseeing" setting.

This is probably already known for my aircraft/engine/prop - so if you guys want to share it, cool!

PS: this data is with a gopro hanging out my right lower wingtip, and the subsequent left rudder requrired to keep the ball centered, so I guess I can get 1-2 knots better.
 
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Analyzing data

I made a list of every 1000 feet, and power settings from full throttle down in one inch increments, both Rich of peak and LOP. Then I divide TAS by FF to give me best MPG at each setting.
 
390 and Showplanes fastback.

First photo, being very fuelish, note EGTs...best power mixture:

70% Best Power w Flow Feb 2017.jpg

Peak EGT, 2500 RPM:

2500 RPM Cruise at Peak.jpg

Going for economy, a nonstop run from OSH to 08A. Works out to be 25.7 MPG:

Lean Cruise 23 deg timing OSH 08A 2018 800w.jpg

Typical. TAS ranges from 183 to 186 depending on weight, temperature, and bug load, with fuel flow around 9 GPH.

IMG_20210808_155421931 600w.jpg
 
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Sure, I’ll show ya mine…
 

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Here is a screen shot of a typical long cross country cruise setting where “I want to get there but not burn a crazy amount of gas”. This setting gives me a comfortable four hours plus IFR reserves. If the trip is more than 8 hours (one fuel stop) I tend to break it up into two days.

This is a stock IO-360-M1B with AFP injection and dual pMags, and a standard Hartzell BA CS prop running a little LOP. The injectors have been balanced. I sometimes burn 93 ethanol free unleaded when I can get it - perhaps as much as 50% mix with 100LL.

Go higher and fuel flow goes down a little. Go faster an fuel flow goes up a lot. I fly at the altitude that is best for winds (or mountains), but tend to not fly below 6,000’ or above 14,000’. I’ve tested up to 17,500’ and the plane did fine, but the reduce engine power is a significant downside for going that high.

I’ve played with RPM down to 2400 or so, but find for this prop 2500 RPM gets me a knot or two more for the same fuel burn. This is something to explore on your ship.

Carl

7-D185-E55-69-B8-46-F0-992-B-AF3188848-BC9.png
 
Very interesting, thanks.

I've flow NTPS three-leg runs multiple times, with excellent agreement to indicated TAS. Have you done similar calibration?

Same fundamental airframe, an 8 with a Showplanes fastback kit and Grove gear.

A TMX-390 is probably a 390A small main from the pre-Thunderbolt kit motor days, same as my Barrett, which was not hot rodded.

Prior to paint you were reporting 1166 lb. Mine weighed 1167 initially, with paint. Closer to 1175 now.

I have seals on the wheel pants and fewer antennas. You have Zip Tips and different induction, cowl, exhaust.

Got any photos with the cowl off?
 
Engine shots, prior to paint, obviously.
 

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Here are my speeds, IAS is checked and calibrated, I wish it was faster.
Engine low compression IO-375, they said 195HP, I believe it´s more like 180-185HP. Whirlwind 74RV prop, standard Vans cowl. Larger tires.

xyoiExe.png
 
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I've been recording my RV-8's cruise data and power settings to get a feel for what it will actually cruise at.

Engine is a TMX-390 with a Whirlwind 74RV prop.

I'd love to see what other IO-360 and -390 people are getting at the cardinal altitudes for cruise.

I record MP, RPM, FF, TAS, IAS, OAT, % hp, LOP/ROP, and altitude. Measurements are taken after 4-5 minute of steady-state flight. I also record general W/B (fore, mid, aft) and DA.

I've recorded data at 24/24 up to FT/2,400 and 2,500 up to 11,500. It'll scoot at 2,500 RPM!

I'd love if some of you would share your data so I can ensure I'm not setting some dumb power/mixture setting. I like the infield of the ballpark.

Thanks in advance!

Forget the numbers. I'm very much looking forward to that view in my next movement! Awesome picture.
 
Engine shots, prior to paint, obviously.

First photo tells the tale...seals with gaps in the wear marks. Whole lotta leakin' goin' on. Combined with conventional cylinder baffles, you're probably flowing twice as much cooling mass, while the large exit kills velocity and adds frontal area.

Pretty close to zero leakage here, with gasketed baffle wraps. The coal shovel is entirely gone...just enough belly bulge to cover the pipe.

The taped stuff is velocity and temperature measurement gear, since removed.
.
 

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Thanks for the detailed analysis of my plane, Dan. Now that you’ve established yours is nicer, maybe others can get back to the topic at hand.
 
Scotty, it's not a matter of which is "nicer". This is tech. I don't have any other photos for illustration. Would you prefer not to know?

I'd love if some of you would share your data so I can ensure I'm not setting some dumb power/mixture setting.

Ok, you're burning a lot of fuel running somewhere around 50 ROP. Won't hurt the engine if well cooled and kept below 75% or so, but it's definitely a hard way to not fly fast. Here the CHTs are very high for an angle valve cylinder at cruise power...partly due to poor baffle sealing and partly due to mixture. If you're also running a bunch of ignition advance, well, yeah, it might be called a dumb setup.

BTW, the CHTs are also highly unbalanced; some of the spreads are almost 50F. It's not strictly necessary that they all be close, but 50F should make you curious.
 
Thanks for the detailed analysis of my plane, Dan. Now that you’ve established yours is nicer, maybe others can get back to the topic at hand.

When comparing speeds isn't documentation of the speed robbing/increasing elements a good thing to know when asking for other data points? It would appear that you could gain 3-4 kts with some minor changes. Your speed sure looks to be in the upper percentiles already.

I will keep my numbers (10kts slower) for a -7 thread. ASI corrected.
 
See, it's all in the delivery.

Sure, I appreciate input. But that's not really what the question was. I wanted to see if I was in the ballpark on running the engine properly, and as a side-note, how do I stack up with other -8s.

Clearly - clearly - my airplane's baffling and cooling can use some work. It's on the list, but other things have taken priority since it's airworthy, cooling, and running well.

I installed a plenum on my Lancair 360 racer, so I understand that aspect of drag reduction and cooling. I just haven't reached that part of the program on my -8 yet.

Thank you for the input; I do appreciate it.
 
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