A

Anthony W

I'm New Here
Hello, this is my first time posting. I am sure fuel consumption has been discussed plenty, but I have not found anything on cost per distance. I am interested in puchasing an RV-4. I would like to know what the highest MPG is for an O-320 equipped RV-4. From what I understand, most fuel consumption discussion is based on GPH which is referenced to percent horsepower. I have found a few alt/%hp examples, but I have not been able to find any fuel consumption performance curves in any POH's available online. Just the O-320 manual, which only gives GPH for HP. I realize the highest MPG may be at a very low speed, maybe as low as 110kts. I know that not many pilots build RV-4's to fly around at the best efficiency. But I am still curious, what is the best combination of power setting, altitude, etc... that will produce the highest MPG for the average RV-4?
 
Last time I attempted to get good fuel mileage I managed about 27 MPG in mine. I have an electronic ignition and flew high over a 800 NM round trip to Sun-n-fun.

I have no idea of the % of power but I was at 9500 to 11500 and running about 2400 RPM. This was not WOT for me but not far from it. I'm usually in a hurry to get there but this time there was weather over KLAL I was waiting to move out.
 
I get about 27 mpg at 2300 rpm low altitude. Two mags and a carb. Stock RV-4 O-320. MT fixed pitch prop. 157-163 mph
 
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Some basics on mpg

Your best mpg in a no-wind case is usually at your speed for best L/D. For the -6A that's 106 mph. You can determine yours with the methods that you can find in the spreadsheets on the page linked in my signature. It is NOT the same as your best power-off glide. When there is a wind you would have to change a little, depending on the wind velocity as a percent of your best L/D speed. For that, also on the page linked below, you will find: Analysis of glide in a wind. The same principles apply for level flight.

Most people want to go faster than that. It is widely accepted that Carson's speed is the best compromise between speed and economy. That is 1.32 times your best L/D speed.

All the above speeds are CAS. The higher you fly, the greater the gain in TAS over CAS. For example, at 12,500 density altitude your TAS will be about 21% higher than your CAS. The only fly in this ointment is the potential for headwinds.

Lastly, engine performance and prop efficiency can vary with altitude and with RPM. A fuel injected engine has the potential to fly LeanOfPeak (LOP) and that can save a significant amount of fuel. Generally, this is a smaller variance than the above factors, though. A highly modified RV-4 prepared and flown by Dave Anders is the CAFE record holder for overall efficiency. Lots of potential there.
 
I've got an O-320 with 2 mags, fixed pitch wooden prop. My best so far was this year going to OSH. Flying between 9500-11500 at 2400rpm got 26.47 mpg...170 mph...6.6 gph.
 
I would also recommend reading up on Dave Anders. Although Dave used a larger engine, what he did to his RV-4 is noteworthy. Here’s an outline.

Note, at 14,000’, he achieve 190 mph ground speed, resulting in 4.5 gallons per hour, which translates to 42 mpg.

My reason for choosing the RV-4 was because of the efficiency it could possibly achieve with its lower frontal drag area. I want to pay attention to many of Dave’s modifications including fastback to the airframe, but without the bigger engine, higher compression, and just concentrate on the 0-320 engine. I’m just working on my empennage at this stage though, so a long ways from starting to have to concentrate on that stuff.

Also consider Kent Paser's "Speed with Economy" who also achieved similar results on a Mustang II.
 
Thanks for the responses with many good resources to look at and things to think about. I do not have an RV-4 myself, so it is hard for me to determine the information needed for the calculations. 27MPG seems close to what most people are burning, but almost every time I hear an MPG close to this, it is around 160MPH.

Hevansrv7a response makes sense, best range (efficiency) is near L/D coefficient which for the RV-6 is 106MPH. That is not anywhere close to 160MPH. The Vans RV-4 Performance page states that at 55% power, a solo RV-4 cruises at 171MPH and range is at 790sm. Might it be safe to assume that if someone were to painfully reduce their speed 65MPH to 106MPH (or appropriate RV-4 L/D), then the MPG should increase substantially? If so, any ideas of what the MPG is at that speed?

I took a look at what Dave Anders has done, it is very impressive. Does anyone know if the 190MPH at 4.5GPH is consistent or was it over a single flight with very good wind? Either way, same principle applies; what if Dave were to slow his super-efficient -4 down to L/D, shouldn't his MPG go through the roof? I'm looking for best MPG at best lift/drag for the average unmodified RV-4.

This info is presented clearly in the Longeze and Varieze POH's, but those are aircraft built around efficiency. This might be something more easily tested with an airplane equipped with a fuel flow meter. Thanks for the responses in advance.
 
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I managed 22.7 today in a real world scenario. I trued out at 175-178 MPH over a 620 mile trip. We played over the beach and then had to zig and zag to get on top on the way out so that wasted a bit of fuel.

My advice is to let the Dave Anders of the world worry about getting 50+ MPG while the rest of us go fly. I admire what he has done but there is no telling how many hours he spent doing it.
 
I am having a hard time explaining myself.

I am specifically not talking about Dave Anders RV-4. Just the average RV-4.

Very simply put, 2 questions:

What is the best L/D coefficient (glide speed)?

What is the fuel burn at this speed (not at glide, but if this speed were to be sustained in level flight)?
 
A friend who has since sold his RV-4 IO-320 C/S prop, told me he routinely cruised at 5gph and that yielded 150mph...or 30mpg.
 
It's the same speed

Anthony W said:
What is the best L/D coefficient (glide speed)?

What is the fuel burn at this speed (not at glide, but if this speed were to be sustained in level flight)?
Click to expand...

It is a key, proven element of my methods, on which my worksheets are based, that the best L/D speed applies in a glide or in level flight. Where it does not apply is when there is prop drag. It does apply when there is any positive thrust. That is why it can easily be found out. Emphasis added in the quotation.

I would love to have this kind of data for the RV-4 so that I could publish another version of the worksheet.
 
I cruise at 27mpg.....

I normally get just over 7 miles per litre which is about 27mpg. (Thats little US galls., not proper ones.)

The AFS,, plus a macro I wrote, graphs it all for me. Hopefully I have managed to attach it. The grey line at the top is the miles per litre, and you can see it dancing around a bit above 7. It is computed from the fuel flow and IAS. The cut offs (the vertical grey lines ) are where the altitude abruptly changes, in this case noise in the system (gusts) because as you can see the altitude is pretty steady at 2400'. on the second flight.

So this is an RV4, O-320, MT c/s 2-blade prop with dual p-mags. In the cruise its set up for 2000rpm, 21lph and 22", or as close as I can get it. This usually returns 156mph if the air is smooth.
Or+Oakshott.bmp


I very much look forward to having the opportunity to do some longer cruises at higher altitudes, but life does not permit that right now. I expect to get better results.

One other thought, my RV seems a tad slow. Now this might be down to the big tyres it is dragging along, or I might just be under reading on the ASI, but I just dont have the oomph to do any more on that right now.
If it is actually going a little quicker than I think the MPG is proportionally better.

Hope that gives you a few answers.

PS One spectacular thing this graph shows is the jump in efficiency when everything is leaned out correctly. Somewhere around 9:28 or 9:29 I further leaned the engine and as you see the EGTs closed right up. Simultaneously the MPG jumps u quite a bit. The MP and RPM are unchanged. Exactly the same thing happens at the start of the return journey at about 12:41.
 
What about 180 HP?

Hi Anthony . . .

I know I'm not answering your exact question, but I bring this up only for interest. I recently flew a few legs in formation (7 hours total) with two other RV-4s and an RV-8. The RV-8 was 180 w/ a Hartzell CS, I have a carb'd O-360 w/ a Sensenich, and the other RV-4s had 150 or 160 HP w/ fixed wood or composite props.

I was surprised to see that the the RV-8 and I burned less per leg than the other RV-4s with the smaller engines (about 1 gal/hr less). My best guess as to why is propeller efficiency and our electric ignitions (which the "8" and I both had). It also seemed the higher we went the more advantage we had with the higher HP and electric ignitions (at cruise, not just the climb).

I seemed to average 180 MPH true airspeed with a 7.0 GPH fuel burn for just over 25 MPG at cruise. I've seen 24-27 MPG based on winds, and I usually fly at 8,500-9,500 feet at 51% power and about 180 MPH true.

Rick
 
MPG RV-4

Hi All
My on the last trip from CXP to Burning Man the MPG was
10500" alt
136kts IAS 163TAS
2500 rpm's
7.5 GPH
about 24.9 kmpg 28.6mpg
most of the time I am running 22-24 kmpg or 25.3 to 27.6mpg
O320,2 p-mags
 
This thread was my effort to get that data. I was able to run all the way down to 3.7 gph in my 6 at 93 KIAS at 8000'. But that was not practical and did not yield the best MPG. The best MPG was at about 109 KIAS and computed to about 27 MPG.


http://www.vansairforce.com/community/showthread.php?t=56061&highlight=data+lop

There might be better combinations of power, airspeed and altitude, but the 1.32 L/D max at the most efficient RPM and engine settings is a real good gouge point. And anything better will probably only be marginally better. In a reasonably stock RV anyway. Drag reductions are where the increased efficiencies lay.
 
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gereed75 said:
I was able to run all the way down to 3.7 gph in my 6 at 93 KIAS at 8000'. But that was not practical and did not yield the best MPG. The best MPG was at about 109 KIAS and computed to about 27 MPG.
Click to expand...


Gary, your first set of numbers totals out to 28.9 mpg with the 93 knots (X 1.15 = statute) figure burning 3.7 gph, which is better than your 27 mpg figure with the 109 KIAS speed.
 
Altitude vs efficiency

Dayton Murdock said:
Hi All
My on the last trip from CXP to Burning Man the MPG was
10500" alt
136kts IAS 163TAS
2500 rpm's
7.5 GPH
about 24.9 kmpg 28.6mpg
most of the time I am running 22-24 kmpg or 25.3 to 27.6mpg
O320,2 p-mags
Click to expand...

Dayton, I think you're on the right track. As has been explained exhaustively elsewhere on the forum, our carbureted engines have higher efficiency if the throttle is wide open. If you keep the throttle at 100%, mpg should continue to increase up to some practical limit. I suspect that limit for many of us is the requirement for oxygen above 12,500.

163 ktas at 28.6 statute mpg is remarkable by any standards. Can't wait to see how my bird performs up there.

M
 
foka4 said:
Dayton, I think you're on the right track. As has been explained exhaustively elsewhere on the forum, our carbureted engines have higher efficiency if the throttle is wide open. If you keep the throttle at 100%, mpg should continue to increase up to some practical limit. I suspect that limit for many of us is the requirement for oxygen above 12,500
M
Click to expand...

One of the ways that you can get better mpg if you have a carburetor is by using carb heat. The heated air reduces the density of the charge going into the cylinder, the so-called volumetric efficiency, which reduces the engine's power. BUT, increasing the induction temperature actually increases the engine's thermal efficiency, its specific fuel consumption. On a recent flight I got 4.9 gph at 180 mph TAS using carb heat, 36.7 mpg. Give it a try, give-it-a-triers!
 
0-360 RV-4 C/S Fastback

Dayton Murdock said:
Hi All
My on the last trip from CXP to Burning Man the MPG was
10500" alt
136kts IAS 163TAS
2500 rpm's
7.5 GPH
about 24.9 kmpg 28.6mpg
most of the time I am running 22-24 kmpg or 25.3 to 27.6mpg
O320,2 p-mags
Click to expand...

This past winter I turned my 1992 RV-4 into a fastback using 3 Harmon Rocket bulkheads, and a turtledeck skin, plus a Todd's Harmon Rocket canopy. A fairly easy conversion. Another plus, the rear passenger gets zero air from the back of the canopy, which is normal on a -4.

I did not keep accurate figures of my speeds with the standard canopy, but with the fastback I can consistently get 169-170 nautical miles per hour true airspeed at 9,500 feet, burning 7.5 gallons per hour. The speed is confirmed by my GPS ground speed considering the head or tail wind. Also my EI fuel flow is accurate when refueling. I'm carbureted and was running WOT.

I consistently used less fuel at each fuel stop in a flight to Oshkosh this year compared to my friend with an RV-4 (C-FHUM) running an 0-320, Ellison throttle body injection with a Sensenich fixed pitch. A prior RV-9A - 0-360 I built, the same RV-4 used considerably less fuel on each flight. Different airplanes, but just a comparison.

How much my fastback conversion helped me in my speed, I can't accurately say, but I'm happy with the result. I did it for the appearance and any speed gain was a bonus.

Jake Thiessen
Independence, OR
 
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Fast back is faster.

All of the above information is valid and well written. Stock, out of the box an RV4 performs extremely well compared to certified airplanes of the same HP. You can clean them up, fair them up and gain a few knots here and there or do what Dave Anders did. Regardless, even the most draggy, beat up, poorly faired RV4 performs well, way better than a 150HP C-172. You can land on fairly rough grass strips (like mine) nice short ones (like Steve Sampson's), climb out of Leadville (9927') with 2 aboard on a hot day and go 180 MPH all day long. Questions?
When eleven of my fellow squadron mates all had RV4's I had a chance to see up close and personal the efficiencies of different engine/prop combinations. The 180HP C/S RV-4 burns less fuel over a given distance than the 150HP FP at 75% cruise speed. However, at the lower end of the speed spectrum, (120 knots) the numbers are nearly identical.
Now for the kicker. All those long trips I took in my RV4 over the 12 years I flew it I kept track of fuel burns over a given distance. Amazingly enough my 285HP GAMI injected Harmon Rocket burns less fuel over a given distance than my 150HP RV4! 10.3 GPH at 185 knots true is pretty good efficiency. When I travel XC with RV's I usually put in less fuel than them on gas stops which always yields perplexed looks. It does have a foot and a half less wing and a longer fuselage (and mud caked on it) but still delivers amazing performance, especially at low power settings (<50%)which is down at RV cruise speeds. FYI, my buddy JJ's fastback four with 180HP and a Hartzell BA goes 180 knots true at just over 9 GPH.
Why? John Harmon knew long ago that the fast back is faster and less drag. It's also way more comfortable for the rear seater and they can sit taller in the saddle. So, if I was building a RV4 right now, it would be a fast back.

You wanna burn less fuel over a distance? Slow down, lean out, fly high. Around 120 knots in a four seems to work well for L/D although best glide in mine was 100 knots. In 1959 Max Conrad flew a stock Comanche (IO-540) from Casablanca to LAX flying most of the way at L/D max. (58 hours, solo @115 Knots) He emerged from the airplane at LAX in a tuxedo. Jon Johanssen on his RV-4 global jaunts also flew at lower speeds, around 140 knots TAS.

After all the drama was over, Jon set off for Bangor, Maine. The original plan had been to start the Atlantic crossing in St. John's, Newfoundland, but Jon had heard several stories about the expense and bureaucratic red tape of flying from there. He decided that his limited budget couldn't stand the gaff. Even though the trip to the Azores would be four hours from St. John's, he decided to leave from Bangor. Once again the weather gods smiled. After a short period of IFR, the skies cleared and he found he had a 10 knot tailwind. Careful records kept on this leg proved the efficiency of his airplane. True airspeed at 11,000' was 143 knots, running at 18" mp and 2200 rpm. Fuel burn was a miserly 22 liters/hour... about 5.6 US gallons. That works out to about 28 mpg. All in all the trip to the Azores was completely ordinary, if that is the word for a night Atlantic crossing in a single engined airplane.


http://en.wikipedia.org/wiki/Jon_Johanson

It works.
Smokey


http://soloflights.org/conrad_data_e.html
 
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MPG

Talk about mpg. The RV12 can do 120kts IAS and get well over 30mpg...with car gas! Thats better than my Honda! (But not the Prius...lol)
 
smokyray said:
Pete, There's alot to be said for 30 MPG on auto gas in an RV. My 150HP RV4 could do that as well at 120 knots, easily, in 1994!
Of course it could go faster :)

However, there are a few out there doing some amazing numbers.
http://www.lightspeedengineering.com/News/News.htm

Smokey
Click to expand...

I hear ya Smokey. One of the problems with the Rotax is they are not fuel injected and lord knows how much fuel is wasted with the "BMW" altitude compensation system. Just out of curiosity, how do the Lycomings handle ethanol? Rotax has approved them up to 10% but I notice we are soon going to E15. Petersen's make no allowance for it in their certifed STC's.
 
Get off the Alcohol!

Pete,

Running MoGas all those years in my 4 I learned alot about fuel, systems and maintenance. One thing about ethanol, you don't have to buy it. Yep, most retailers will sell you larger quantities without the juice in it. Ask your local oil distributor how large a lot he would need to sell you non-ethanol laced 87 octane. My answer was 500 gallons. At a lot price of $1.87 a gallon, that's not too bad if you fly alot or have friends who do.
Carbs: My RV4 had an MA-4SPA on it. I installed a stainless steel needle and seat, with a metal float. I hand lapped the needle/seat and made all the gaskets myself from NAPA gasket material. Never had a problem. (Airflow Performance makes a nice MoGas capable injection system for the Lycoming and the 912. Check their site. Just Aircraft's Highlander has a system on it. )http://www.airflowperformance.com/v2/systems.html
My flying technique on hot days was long (1 min) run-ups at 1500 RPM to get good cold fuel in there. Never had a problem.
High altitude? I added CD3 (lead additive) Never had a problem.
Upper cyllinder lubrication? Marvel Mystery oil added per the instructions. Never had a problem.

Good Luck!

Smokey
 
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Thanks

Thanks for all the good info Smokey. I did see where airflow performance was making the system for Just. I'll have to look into that. I love the website you sent me on the fuel contests! 60mpg! That IS better than my Prius. Thx again.
 
Hard to beat...

This post from Klaus pretty much sums it up:

On Monday April 7th, just prior to Sun ‘N Fun, the weather looked great for a non-stop flight across the country, coast to coast, 2000 miles. I hopped in the Delaminator as early as I could bear and set out for Florida. The tailwinds were good but not quite as strong as predicted so I had to slow down a little to increase my range. It took 8 hrs and 58 min for the total distance of 1985 statute miles, SZP, CA to PFN, FL via ELP TX to avoid the restricted area.

Total fuel used was 25.8 gallons of the 29.2 carried in the standard tanks, leaving more than an hour worth of fuel remaining. Average fuel flow for the entire flight was 2.87 gph. Average speed was 220.6 mph. Tailwind average was around 30 mph at 17500 ft. The density altitude was above 19000 ft. Of course, I was on oxygen for the entire flight.

Now for the technical run-down on engine configuration and the methods used to achieve this level of efficiency. In the Delaminator, the maximum manifold pressure available at 17500 is almost 16”. See picture 1 and note the fuel flow of 4.2 gph at peak power giving a true airspeed of 204kts, resulting in 55.9 statute mpg. As shown in picture 2 taken during this cross-country flight, the throttle was reduced by almost 1”. While our custom FI automatically adjusts the mixture for all engine conditions, it can be biased just like the Plasma CDI timing. The automatic mixture adjustment was thus manually leaned to almost 300 degrees past peak EGT, where slight roughness occurs. Manual increase of timing advance returns some power lost under these conditions and eliminates any lean misfiring. As a result of these settings and lean burn, all temperatures are near the low limits, oil pump outlet temp is below 150 F and the cylinder head temperatures are all below 300 F. See picture. While leaning this far on the lean side of peak reduces power significantly, it is slightly more efficient to reduce power by leaning rather than by closing the throttle because the pumping losses of the engine are lower.

The best “no wind range” is normally achieved at best glide speed. For the Delaminator, this is about 100mph when fully loaded. Most of the trip was flown at 130 mph indicated at 17500 ft. Prior testing has shown that the airplane achieves well over 80mpg at best glide speed. Flying at 130 mph, the Delaminator still achieves over 60 mpg. The tailwind brought the mpg to nearly 80 mpg.

While I could think of a faster airplane with a higher wing loading and a bigger engine, such a configuration could not come close to the efficiency demonstrated here at high altitude. It seems that this combination of a highly optimized 0-200 engine and high aspect ratio wings offers a combination of efficiency and speed that simply cannot be beat.

KS

Smokey

Of course he can't land at the Swamp :)
 
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RV4 mpg

Around 1979-80 the RV4 prototype debut on the cover of Sport Aviation with an article written by Van.

He did extensive mpg testing using a separate calibrated one gallon tank, the results were part of this article. It would answer your mpg question at many power settings in a controlled test.

Does anyone have a copy of the article they could post, or post just the speed, power, fuel flow results?

(I looked online, no luck, but found the prototype empty weight was 890lbs.)
 
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