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  #21  
Old 01-27-2014, 04:10 PM
rvbuilder2002 rvbuilder2002 is offline
 
Join Date: Jul 2005
Location: Hubbard Oregon
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Quote:
Originally Posted by RFSchaller View Post
True, Scott, but for planning purposes on a long cross country 4.5 GPH seems to work out within a few tenths of a gallon. The few 12 owners I've met at the airfield say that's what they are seeing too.
With experience flying many 3000+ mile (round trip distance) cross countrys in RV-12's, that has not been my experience.
As I already said, fuel flow all depends on how fast you go / how much power you are producing. Power produced is a function of MP to RPM.
If you cruise cross country at anything near 120 TAS (which the RV-12 is capable of doing), the fuel burn wont be anywhere close to 4.5 GPH.
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  #22  
Old 01-27-2014, 04:27 PM
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KALEWIS KALEWIS is offline
 
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I am seeing an average of 5 to 5.5 GPH. that is usually cruise of 5300 Rpm, 116-118 KTS TAS. I always PLAN on 6 GPH. cruise at 5100-5200 RPM does not change the TAS that much.
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  #23  
Old 01-27-2014, 08:02 PM
sandpiper sandpiper is offline
 
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Haven't done any 3000 mile trips but, just beating around Oregon in my CT in loose formation with my neighbor in his -12, I seem to burn about 4.7 gph at 5200 whereas he burns a little less. Probably because he runs a little less rpm so I can keep up.
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  #24  
Old 01-27-2014, 08:38 PM
RFSchaller RFSchaller is offline
 
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Stop buying gas at K-Mart, Scott!

I'll stick with what works for me.
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  #25  
Old 01-27-2014, 09:02 PM
rvbuilder2002 rvbuilder2002 is offline
 
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Location: Hubbard Oregon
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You guys seem to fail to get the point
I could easily fly cross country in an RV-12 at 3.5 gallons per hour. So do I win?

The point is, telling the world that my airplane burns bla bla GPH is not providing information of any value beyond to demonstrate that the airplane can stay in the air if the engine is burning at least 4.5 GPH.

I believe in providing factual useful information. I have always tried to do so on this forum, and Van's does so with all advertising literature.

I think it only fair that prospective builders know that an RV-12 doesn't fly at the top cruise speed as advertised by Van's, while burning only 4.5 GPH.
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  #26  
Old 01-28-2014, 12:36 AM
Mounz Mounz is offline
 
Join Date: Oct 2010
Location: Germany
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Quote:
Originally Posted by rvbuilder2002 View Post
You guys seem to fail to get the point
I could easily fly cross country in an RV-12 at 3.5 gallons per hour. So do I win?

The point is, telling the world that my airplane burns bla bla GPH is not providing information of any value beyond to demonstrate that the airplane can stay in the air if the engine is burning at least 4.5 GPH.

I believe in providing factual useful information. I have always tried to do so on this forum, and Van's does so with all advertising literature.

I think it only fair that prospective builders know that an RV-12 doesn't fly at the top cruise speed as advertised by Van's, while burning only 4.5 GPH.
Co - rrect! The laws of physics have not changed. Fly fast burn more fuel. Drag increases as a square of the IAS. Your motor has to overcome the drag. There was an interesting article in the RVator some time ago when Van's flew their RV-9 next to their RV-12. The fuel burn on the RV-9 was slightly lower than on the RV-12 probably because of the flush rivets on the 9 and no wheel pants on the 12. So whether Rotax, Lycoming, Continental or Subaru, piston engines burning gasoline have very much the same fuel efficiency. Of course the airframe does play a major role as we see the CT being more draggy than an RV-12 and an RV-9 being cleaner than the RV-12 without wheel pants.
To quote Van; "every aircraft is a compromise". The RV-12 is obviously an excellent design in its class. Good speed, excellent useful load and the legendary RV handling qualities. You wanna go fast! You will burn more fuel - there are no free meals! The fuel burn numbers as published will stay as they are with this airframe.
The bottom line is the RV-12 is pretty efficient but flying 120kts IAS will see you burning around 6gph. If you want better economy, fly high and you might see see 120kts TAS at a much lower fuel burn as you will have a much lower IAS.

Last edited by Mounz : 01-28-2014 at 12:49 AM.
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  #27  
Old 01-28-2014, 02:34 PM
RFSchaller RFSchaller is offline
 
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Oh, I think we get your point, Scott.
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  #28  
Old 01-30-2014, 02:51 PM
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ScottSchmidt ScottSchmidt is offline
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Location: Salt Lake City, Utah
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Default Fuel Flow

I do think my fuel flow is slightly high. I am still tweaking the k factor. I don't think it is off by much though.
It is much easier calibrating the -10 when you can burn 40 gallons and fill exactly to the same spot.

No matter how you look at it, the -12 is a great plane. Fun, responsive, fuel efficient and cheap to fly. Yes, the -9 may burn less for the same speed but the savings burning auto gas will probably make it cheaper. We typically save over $2/gallon compared to 100LL. As a comparison to the -10, I can fly my -10 with 4 people, at 158kts and 10.5gph, right around 17 mpg (zero wind). So 10.5 gph times $5.50/gallon = $57.75 divided by 4 people = $14.43/person. Not too bad. About $14.50 /person to go 180 miles.

The -12 is 5.5gph times $3.20 = $17.60 divided by 2 people = $8.80 / person.
To go the same 180 miles it would be around $11.50/person in the -12 buying auto gas. But if you have to buy 100LL for $5.50/gallon, the -12 is about $40 in fuel or $20/person.
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  #29  
Old 01-06-2019, 11:22 PM
NinerBikes NinerBikes is offline
 
Join Date: Dec 2018
Location: Granada Hills
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Quote:
Originally Posted by rvbuilder2002 View Post
You guys seem to fail to get the point
I could easily fly cross country in an RV-12 at 3.5 gallons per hour. So do I win?

The point is, telling the world that my airplane burns bla bla GPH is not providing information of any value beyond to demonstrate that the airplane can stay in the air if the engine is burning at least 4.5 GPH.

I believe in providing factual useful information. I have always tried to do so on this forum, and Van's does so with all advertising literature.

I think it only fair that prospective builders know that an RV-12 doesn't fly at the top cruise speed as advertised by Van's, while burning only 4.5 GPH.

Assuming summer time heat, and flying at 7500 to 9500 ft, 110kt TAS, with the prop set for cruise not climbing performance, what type of GPH do you see, real world, in your plane.


I understand the relative density of air is less at elevation and in summer heat... Assume 50F air temps at 9500 feet.

And next question is GPH in the new 912 iS FI motor without the Bing Carbs.
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  #30  
Old 01-06-2019, 11:52 PM
Harvey rv12 Harvey rv12 is offline
 
Join Date: Apr 2015
Location: Olympia WA
Posts: 156
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Hello Scott;
Did you record your static runup RPM at full throttle?, or rpm achieved during climb out?.
I'm always interested in other folks numbers. I am trying to satisfy the Rotax service letter SL-912-016R1 (no less than 5200rpm at 29.1" hg MAP), while also allowing max rpm in level flight of no more than 5800rpm.
I am getting a static full throttle runup of about 4920rpm, DA -1386', 43 deg f, 29.9" MAP

Thanks
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Olympia WA

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