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  #1  
Old 06-27-2020, 07:19 AM
Carl Froehlich's Avatar
Carl Froehlich Carl Froehlich is online now
 
Join Date: Dec 2007
Location: Dogwood Airpark (VA42)
Posts: 3,250
Default Some data for efficient cross country

Some flight data for you guys that like such stuff.

Just ~1 hour to go for the 40 hour test period. Yesterday was the high altitude data run (up to 17.5K?). As part of this run I wanted some raw data to develop cross country cruise setting. At first blush it looks like ~14.5K? is where, for the same speed, efficiency starts to fall off.

For these typical high speed cruise settings I got 27.3MPG at 14.5K?, then slowly dropping off to 26.5MPG at 17.5K?.

I?m sure I could enhance the MPG numbers at slower speeds, but shoot fire, we fly RVs!

14.5K? screen shot attached.

Carl

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  #2  
Old 06-27-2020, 09:41 AM
PilotjohnS PilotjohnS is offline
 
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Location: Southwest
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Default Wow

Wow.

Extra words added.
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WARNING! Information presented in this post is my opinion. All users of info have sole responsibility for determining accuracy or suitability for their use.

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  #3  
Old 06-27-2020, 10:16 AM
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DanH DanH is offline
 
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Quote:
Originally Posted by Carl Froehlich View Post
For these typical high speed cruise settings I got 27.3MPG at 14.5K?...
27.3 looks like knots converted to statute, or 23.7 NMPG.

Temperature probe appears to be running warm. Dunno about yesterday, but temperature at 14500 is forecast to be 32F all weekend.

Good performance. What engine/prop is that?
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  #4  
Old 06-27-2020, 10:25 AM
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Carl Froehlich Carl Froehlich is online now
 
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Quote:
Originally Posted by DanH View Post
SNIP
Good performance. What engine/prop is that?
IO-360-M1B and Hartzell BA prop.

Carl
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  #5  
Old 06-27-2020, 09:24 PM
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RV10inOz RV10inOz is offline
 
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Default

I am with Dan on the temp question. You should have been at or almost at the freezing level.

If your OAT probe is on the fuse anywhere, I bet it is getting heat from the exhaust. That will mean your TAS is reading a few knots faster.

Also were you slightly ROP and the EMS has been confused by leaning process you did? That flow at that DA looks more than 10dF LOP as a guess, based on scaling the RV10 engine.

And last of all have you done a GPS box to verify the TAS vs GPS, and hence any static error?

Otherwise that is one impressive speed for an RV7 on a 180HP engine.
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  #6  
Old 06-27-2020, 11:14 PM
lr172 lr172 is offline
 
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Location: Schaumburg, IL
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Default

Quote:
Originally Posted by DanH View Post
27.3 looks like knots converted to statute, or 23.7 NMPG.

Temperature probe appears to be running warm. Dunno about yesterday, but temperature at 14500 is forecast to be 32F all weekend.

Good performance. What engine/prop is that?
We were flying at 14K yesterday over nebraska and colorado. Oat was 33 - 35.

Larry
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  #7  
Old 06-28-2020, 06:43 AM
Capt Capt is offline
 
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Plugging in those indicated figures on a TAS calculator from the Net shows 177 TAS so pretty much spot on. It sure is warm outside at that height though. Plugging in ISA Std temp at that Alt only changed the TAS lower by 4 kts.
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  #8  
Old 06-28-2020, 06:47 AM
BillL BillL is offline
 
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Quote:
Originally Posted by RV10inOz View Post
Otherwise that is one impressive speed for an RV7 on a 180HP engine.
It sure is, esp at 14.5k! At max power, 2600, 8k (DA), my 180 hp 7 is the same but higher FF. The BA prop is faster than my composite.

But - - I think Carl is has an 8, it's faster yet!
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  #9  
Old 06-28-2020, 07:09 AM
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emsvitil emsvitil is offline
 
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What am I missing..........

Isn't the Ground Speed (GS) under the TAS? and why is it only 137?
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  #10  
Old 06-28-2020, 07:40 AM
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grubbat grubbat is offline
 
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Default Guess

Probably because ground speed takes into consideration winds.

Carl, did you happen to try different RPMs at that altitude? Was the ~2400rpm the best all around efficiency wise? The CAFE reports ( who remembers those) would show different rpms and for the -9, if I recall, they were able to get similar MPG at high rpm and also at lower rpm at altitude. I recall an old twin Comanche racer would run her engines at 2700rpm everywhere all the time. Just leaned them at altitude and 75% power. Just asking for your perspective.
Good stuff. Thanks for sharing.

Quote:
Originally Posted by emsvitil View Post
What am I missing..........

Isn't the Ground Speed (GS) under the TAS? and why is it only 137?
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