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Tell Me About Range

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PilotjohnS

Well Known Member
I am flying my RV9A with a IO320 on cross countries.

Vans lists the range as 850 miles.
But I cant see how anyone can get this. I can probably get 600 out of mine, but no where near the Vans numbers.

Is there any data to support the Vans listed range?

What is a reasonable range?

Does cruising in the teens allow more range?
 
PilotjohnS said:
Yes but still doesnt add up, unless one runs the tanks to the bare minimum of vfr reserves
Click to expand...

That's pretty much exactly what you would do for maximum range, along with running LOP at altitude. And yes, altitude is definitely your friend for max range, see below. I'm running long range tanks, but still the important thing to notice is the fuel flow versus true airspeed.
 

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Yes!

airguy said:
That's pretty much exactly what you would do for maximum range, along with running LOP at altitude. And yes, altitude is definitely your friend for max range, see below. I'm running long range tanks, but still the important thing to notice is the fuel flow versus true airspeed.
Click to expand...

Those numbers are similar to mine. I didnt run as low as 46% power because i was fighting a 12kt head wind the whole way home today.Good to se similar data. I still need to add upper intersection fairings.

I ended up climbing at 300 fpm, 50 rich of peak and it seems to be best. Climbing lean of peak just didnt work.

Pretty amazing plane
 

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That is good 2gph too high of a fuel flow for that speed and altitude.. my old -7A was in mid 5's for same parameters.. (LOP of course)
 
Radomir said:
That is good 2gph too high of a fuel flow for that speed and altitude.. my old -7A was in mid 5's for same parameters.. (LOP of course)
Click to expand...

Im inclined to agree. We lean out at 7.5 gph for 155 true. If we leaned out to 140, it would probably be in the 5 gph range.

So doing the math, we burn on average 15gph for 15 minutes to get to altitude, that's 3.75 gallons. With the standard pickups, there's roughly 0.5 gallons unusable on each tank, and a 30 minute reserve is another 3.75 gallons at cruise. Take those 8 gallons away from 42 and you get 34 gallons (4.5 hours) of cruise or 697.5 nautical miles (802 statue miles). I didn't include anything for the runup, but I also didn't include any distance covered in the climb, so the numbers come out pretty close to advertised for our setup.
 
PilotjohnS said:
Yes but still doesnt add up, unless one runs the tanks to the bare minimum of vfr reserves
Click to expand...

If you were in sales, would you add more reserves and cut the advertised range in the marketing materials?

Also I'd assume they were flying with no baggage, solo, in a plane without 25 pounds of sound deadening insulation, leather seats, 10 pounds of spare oil, etc.
 
blaplante said:
Also I'd assume they were flying with no baggage, solo, in a plane without 25 pounds of sound deadening insulation, leather seats, 10 pounds of spare oil, etc.
Click to expand...

Note that Greg has about 311 lbs (51.8 gals) of fuel on board and is getting 24.5 nm/gal (28.175 statute miles/gal)(no wind) in his screenshot.
Van's numbers for the RV-9A show only 1 mph difference in cruise speeds between solo weight and gross weight (350 lb difference).

John is getting 18.2 nm/gal (no wind) at 7.9 gph.
% power calculations (EFIS) are within 0.5 hp considering the different size engines.
Greg is running SDS ignition and possibly injection as well. That helps.

Those upper intersection fairings and LOP operation will probably help.
 
I think I managed 4 hours on the way back from OSH one year.
That was max bladder time.
I think I can match the Van's numbers if I tried.
155 kts @ 6 GPH 36 gallons
 
I've heard one can get more range when throttled back. Don't know as I've never been able to do that personally.
 
Soaring magazine

agent4573 said:
That one's easy:
Green arc: <2 hours
Yellow arc: 2-3 hours
Red arc: >3 hours
Click to expand...

There was a article written by a physician that was published in Soaring magazine a while back. He talks about how to get long bladder times. The number one culprit was the American diet. Too much salt and caffeine. I avoid salty foods, preserved foods, and caffeine the day before and I have no trouble lasting 6 hours, with just a few bottles of water with me to counter the dehydration. One of the things he said in the article, is if you feel thirsty, you are already dehydrated and must drink a bottler of water right away to avoid potential medical problems while flying. The salt is the worst ingredient in modern foods. JMHO
 
Max Range / Max Endurance

FWIW,
I still need to further test my numbers, but from preliminary data, here's what I get:
Maximum range at +/- 4000 ft is 105 KIAS . I need to test at other altitudes.
At that speed I burn 3.6 gph 50°LOP. I could test even leaner to 100°LOP but have to weight in the loss of speed vs. the lower fuel burn.
Theoretically, at 105 KIAS and 3.6 gph, no wind and full tanks, allowing a generous 2.5 gallon taxi/takeoff/climb burn, 1 gallon unusable fuel, yeilds a bit more than 10.5 hours. Remove the 30 minutes reserve and that leaves 10 hours at slightly more than 105 (KTAS) depending on T°, that's above 1000 NM.
Boring flight maybe but way long... Remember this is what a C172 cruises at 4000 ft and 2300 RPM.
Maximum endurance is at 91 KIAS. There, I burn 3.2 gph. That's slightly lower than a C152 cruise speed...

It's nice to know if I need to really stretch a leg or stay in the air for some reason.
 
My dilemma

riseric said:
FWIW,

...Theoretically, at 105 KIAS and 3.6 gph, no wind and full tanks, allowing a generous 2.5 gallon taxi/takeoff/climb burn, 1 gallon unusable fuel, yeilds a bit more than 10.5 hours. Remove the 30 minutes reserve and that leaves 10 hours at slightly more than 105 (KTAS) depending on T°, that's above 1000 NM.
Boring flight maybe but way long... Remember this is what a C172 cruises at 4000 ft and 2300 RPM.
Maximum endurance is at 91 KIAS. There, I burn 3.2 gph. That's slightly lower than a C152 cruise speed...

It's nice to know if I need to really stretch a leg or stay in the air for some reason.
Click to expand...

This is my dilemma. When I get down to 3 gallons on the first tank, and have 6 remaining on the second, That's still theoretically quite a bit of range left. But I get nervous below 4 gallons on each side. If I am going home, or a place with guaranteed fuel, I will run one tank down to 2 gallons and then switch over to the fuller tank for landing. But 4 gallons is 140 miles!!!
 
There is a test in the EAA test manual that describes how to find the speed for the best endurance and the best range.

The test basically involved getting the fuel burn numbers at various speeds in TAS. Then plot the data, speed in X-axis, fuel burn in Y-axis. From the 2-D plot, you can find out the speed that will get your the max range and the speed for max endurance. I suspect the speed for max range will be lower than the high cruising speed that many RVs fly.
 
I didn’t build an RV to go slow. That said, not letting down for fuel could make up a significant amount of time depending on final destination.
Tortoise or Hare?

I have found Vans numbers to be spot on, for the configurations they tested, which few folks build to.
 
I remember flying with Dan Checkoway in his RV-7 and he told me when he just wanted to fly around without any particular destination in mind, he'd run way LOP (I forget the exact number of degrees but it was dramatic) and get like 120 knots TAS at 3.8 gph or some such number.

He had GAMI injectors. The fuel flow was extremely well balanced between cylinders, because at some point the mixture control functioned like a throttle. There was very little vibration, the engine just dropped power very smoothly. I think it would be hard to do that without a CS prop, because you can't set or hold power as precisely with a fixed pitch prop.

Best range speed is usually going to be pretty slow because drag builds up quickly as speed increases. Few of us got into RVs to go slow. :)

--Ron
 
Max L/D speed will be your best range. You won’t get there until next month, but it is the most inefficient. I fly my plane WOT/2500 everywhere when above 7k ft and about 20F LOP. I get about 17 NMPG or nearly 20 SMPG. 50 gallons useable and my personal minimum of 1 hour fuel gives me 4 hours range which is 800 statute miles. I could use a 10 gallon bladder tank to go nonstop, which I am considering since it is just me in the plane about 50% of the time and my bladder can take it. My wife can’t, so we stop after 2 1/2 hours anyway.
 
Ah! come on, I can't be the only one that has a gallon baggie with a bunch of cat litter in it.
There is always one in the back of my plane.
Great to have an auto pilot to make the process easier. But is doable with out one.
My luck varies Fixit
 
PilotjohnS said:
This is my dilemma. When I get down to 3 gallons on the first tank, and have 6 remaining on the second, That's still theoretically quite a bit of range left. But I get nervous below 4 gallons on each side. If I am going home, or a place with guaranteed fuel, I will run one tank down to 2 gallons and then switch over to the fuller tank for landing. But 4 gallons is 140 miles!!!
Click to expand...

I chuckle when people state range in terms of miles; it can yield a false sense of security.

The fact is, your “mileage” range is a function of how long the engine will run, not how many miles you will cover. Consider your example of 4 gallons and 140 miles. Into a 70 mph headwind, what is your mileage range? It’s not 140 miles. How about an extreme example: you are flying a 90 kt cub into a 90 kt wind. You have 3 hours of fuel on board. At the end of 3 hours, the engine quits and you land. Total mileage covered…zero. You end up where you started.

Another fact is that there is no excuse for running out of gas in an airplane!
 
JonJay said:
I didn’t build an RV to go slow. That said, not letting down for fuel could make up a significant amount of time depending on final destination.
Tortoise or Hare?

I have found Vans numbers to be spot on, for the configurations they tested, which few folks build to.
Click to expand...

+1. Exactly. IMHO the -10 really could have used a bit larger standard tanks. Running 75% power on a trip from home to Seattle requires a fuel stop, while 60% LOP makes it a comfortable non-stop, and the tortoise wins!
 
[email protected] said:
Ah! come on, I can't be the only one that has a gallon baggie with a bunch of cat litter in it.
There is always one in the back of my plane.
Great to have an auto pilot to make the process easier. But is doable with out one.
My luck varies Fixit
Click to expand...



I’m not sure I need a gallon bag but do have a quart one available.

Litter can spill. The lining of a couple of baby diapers in the bag is superior, weighs less, more absorbent, and folds up smaller. And a folded paper towel in the bag.
 
agent4573 said:
Im inclined to agree. We lean out at 7.5 gph for 155 true. If we leaned out to 140, it would probably be in the 5 gph range.

So doing the math, we burn on average 15gph for 15 minutes to get to altitude, that's 3.75 gallons. With the standard pickups, there's roughly 0.5 gallons unusable on each tank, and a 30 minute reserve is another 3.75 gallons at cruise. Take those 8 gallons away from 42 and you get 34 gallons (4.5 hours) of cruise or 697.5 nautical miles (802 statue miles). I didn't include anything for the runup, but I also didn't include any distance covered in the climb, so the numbers come out pretty close to advertised for our setup.
Click to expand...

The RV-9 only has 38 gallons, not 42 like the -7 or -8..
 
+1

BobTurner said:
+1. Exactly. IMHO the -10 really could have used a bit larger standard tanks. Running 75% power on a trip from home to Seattle requires a fuel stop, while 60% LOP makes it a comfortable non-stop, and the tortoise wins!
Click to expand...

The 10 compared to the 14 does need larger tanks. The 14 has 50 gal tanks and assuming a 390 so the 10 should have 75 gals with a 540? I know added flexibility and more tankage helps but still surprised why anyone wants ER tanks in the 14. LOP and 160 knots true I can be in the air 5 1/2 hrs. and still have decent reserves. Bladder and for sure my wives can't last that long.

We build want we want, I understand that very well.
 
Beauty of our machines

That's the beauty of our machines, having the choice of getting there fast reasonnably cheap or fly at slower speeds for longer and cheaper !!!
I always consider the fuel in the tanks/fuel burn as time in the air.
 
RV-8 Range

I just had an opportunity to test the range on my RV-8 yesterday while flying from Madras, OR (S33) to Torrance, CA (TOA). This flight plan was ~670 nm and I took an additional 20 mile detour at the end of the flight for ~ 690 miles total distance.

I launched out of Madras and flew a LOP climb to 13,500' (with oxygen) and encountered the forecast ~15-25 knots headwind component for 3/4 of the flight, and 5 - 12 knots headwinds for the remainder of the flight. I cruised at 2350 RPM, 6.8 - 6.9 gph (~ 10 deg. LOP) and maintained 167- 170 knots true air speed. The flight time was 4:35 and I landed with 9.6 gallons remaining of my 42 gallon capacity.

My engine is a stock lycoming IO-360A1B6, slick mags and a 74" Hartzell blended airfoil propeller.

Altitude is your friend when seeking best range.

Skylor
 
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Some guys have all the luck! I swear like 3/4 of my flying is into a headwind...

skylor said:
Altitude is your friend when seeking best range
Click to expand...

It can be an enemy when the wind is going in the wrong direction, too! I couldn't find the pic but I've got one of a 180 knot headwind in the G650. You're going 0.91 Mach but are traveling at the speed of a King Air doing like 340 knots over the ground. Had we been traveling eastbound the ground speed would have been over 700 knots.

Sometimes lower is faster. Sometimes the longer ground track will be faster (ie. flying around a high pressure system to the north instead of straight across).
 
ronrapp said:
Some guys have all the luck! I swear like 3/4 of my flying is into a headwind...



It can be an enemy when the wind is going in the wrong direction, too! I couldn't find the pic but I've got one of a 180 knot headwind in the G650. You're going 0.91 Mach but are traveling at the speed of a King Air doing like 340 knots over the ground. Had we been traveling eastbound the ground speed would have been over 700 knots.

Sometimes lower is faster. Sometimes the longer ground track will be faster (ie. flying around a high pressure system to the north instead of straight across).
Click to expand...

All true! Of course, altitude is also your friend in a single engine plane over the Sierras :)

Skylor
 
Webb said:
I’m not sure I need a gallon bag but do have a quart one available.

Litter can spill. The lining of a couple of baby diapers in the bag is superior, weighs less, more absorbent, and folds up smaller. And a folded paper towel in the bag.
Click to expand...

Great idea! I use the "Travel John" and it works great, but certainly more expensive than a diaper and a ziplock bag.
 
PilotjohnS said:
This is my dilemma. When I get down to 3 gallons on the first tank, and have 6 remaining on the second, That's still theoretically quite a bit of range left. But I get nervous below 4 gallons on each side. If I am going home, or a place with guaranteed fuel, I will run one tank down to 2 gallons and then switch over to the fuller tank for landing. But 4 gallons is 140 miles!!!
Click to expand...

Well, 8 gallons is less than one hour at 'normal cruise' for most of our fleet. So considering possible diversion (oh, airport just closed as someone landed gear up), having almost an hour in the reserve isn't dumb. Is isn't for nothing that Civil Air Patrol required us to land with higher reserves than the FAA minimums.

That said, I know what you mean. A transfer pump wouldn't be difficult to install and would let you move that last little bit of fuel from one side to the other.
 
blaplante said:
Well, 8 gallons is less than one hour at 'normal cruise' for most of our fleet. So considering possible diversion (oh, airport just closed as someone landed gear up), having almost an hour in the reserve isn't dumb. Is isn't for nothing that Civil Air Patrol required us to land with higher reserves than the FAA minimums.

That said, I know what you mean. A transfer pump wouldn't be difficult to install and would let you move that last little bit of fuel from one side to the other.
Click to expand...

With an accurate fuel totalizer, I just run one tank to within one gallon of empty, then place my hand on the selector and watch the fuel pressure. When the fuel pressure starts to waive, I switch over and the engine doesn’t miss a beat.

For the Original poster, Vans advertises 590 Statute miles (513 nautical miles) range for my RV-4 (0-360 180 hp). My longest flight to date was KVGT to KITR, 4:20, 640nm or 736sm, landed with 5 gallons reserve, or about 45 minutes.This was achieved by going to 17,500 feet, backed the throttle off just to close the enrichment valve and perhaps induce some throttle blade turbulence, and lean to peak egt, right before it got rough. It cost 5 gallons to get to altitude (20 minutes), then burned 6gph in cruise at 164 KTAS, then 1000fpm descent, backing off the power only as necessary to keep from overspeeding. I burn that first 5 gallons from one wing, then switch over to the other wind and empty it. Then I know exactly what’s remaining in the first tank (full minus 5). The RV-4 only has 32 gallon tanks, I would bet a RV-9 with its 38 gallon tanks could do vans published numbers if you use their power settings and lean properly.
 
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Taltruda said:
... then 1000fpm descent, backing off the power only as necessary to keep from overspeeding. ...
Click to expand...

This gets into the descent phase. From 15500 at 500 fpm, that is a 30 minute descent. I went down with the power backed off at 500 fpm and the same forward speed. I think this helped save a lot of fuel as opposed to running near VNE with the same fuel burn. By backing off the throttle, I figured I saved 2 gallons.

But maybe the best descent is to buzz in at 15500, then idle the engine and do a descent using no fuel burn? sounds kind of scary.
 
PilotjohnS said:
This gets into the descent phase. From 15500 at 500 fpm, that is a 30 minute descent. I went down with the power backed off at 500 fpm and the same forward speed. I think this helped save a lot of fuel as opposed to running near VNE with the same fuel burn. By backing off the throttle, I figured I saved 2 gallons.

But maybe the best descent is to buzz in at 15500, then idle the engine and do a descent using no fuel burn? sounds kind of scary.
Click to expand...

Flight idle descents are great for jets but not for props. You lose energy from the drag associated with a windmilling prop. I pull the prop to about 1700rpm and use just enough manifold to retain cruise TAS in an 800fpm descent. This keeps the engine warm and avoids the prop driving the engine. LOP results in 4-4.5GPH all the way down.

Aerodynamics for Naval Aviators has some good info factors related to efficiency.
 
Descent planning

I don't see very much in the way of data driven descent profiles.

If I'm in a hurry, I will have cruised at 75% or so and descend at near VNE. That descent should be delayed as long as practical for the better TAS at the higher altitudes (assuming no wind).

Personally, I'm seldom in a big hurry and cruise at 60% power. I just maintain the cruise IAS in the descent. I'ts a compormise above Carson speed and well above max range.

An idle descent may not be efficient depending on your propeller and airspeed. The propeller may provide aerodynamic braking. A zero thrust setting might be most efficient, but that setting would probably require testing to establish.

Plenty of room for discussion here.
 
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Reserve fuel can vary depending upon where one is flying.

Am I going to a big airport with multiple runways? 45 minutes is probably adequate, and that gives me 15 minutes to accept ATC delays before it's time to get nervous. If an airliner can land without diversion fuel (no-alternate IFR), then it's probably okay for me too.

Destination is a small, single runway airport with nothing else nearby? I'm going to want enough fuel to make it to another airport, and that could mean 90 minutes in reserve fuel.
 
ChiefPilot said:
Aerodynamics for Naval Aviators has some good info factors related to efficiency.
Click to expand...

Brad, is your method based on the above? Do you have a minimum MP you use for engine health in descent?

The "how to manage the descent profile" question has been top of mind for me for some time. I've been intending to start a stand-alone thread on the topic..
 
Kyle Boatright said:
Brad, is your method based on the above? Do you have a minimum MP you use for engine health in descent?

The "how to manage the descent profile" question has been top of mind for me for some time. I've been intending to start a stand-alone thread on the topic..
Click to expand...


Not so much based on it, but informed by it. The "Range Performance" section of chapter two has a lot of info which I used to design some flight tests; specifically to find specific range factors at various power settings and speeds. That helped with developing power settings for various speeds at various distances and altitudes, and also with the corresponding descent profile.

It's not exact, of course - it'd be different for every weight, temperature, and altitude combination. Instead it's a guideline by which I can look at what power setting is required (fuel flow since I fly lean of peak) for a given density altitude and get a predictable performance in either cruise or descent.

I don't have a minimum MP to look for in descent per sé, but rather one which maintains cruise TAS and keeps the cylinders from dropping temp too much. In practice it's about 16"-18" from the low flight levels and increases on the way down.

I can share more data but don't have it handy since I'm on a trip and away from all the spreadsheets etc. at home.
 
Rv-9 Max Range

Set speed for 120 mph, up around 10k-12k feet, lean of peak, run one tank empty, check back with results. I’m thinking about 800- 1000 miles range all things considered.
 
VANDawg said:
Now do the calculation for your bladder. LOL
Click to expand...

BINGO. I want to get out at 3.0 hrs and stretch my legs and empty my bladder, as I love my coffee. Forget those ER tanks. After 4-5 hrs my rear-end is howling. I've done 7+ in the "work" aircraft and that is a butt-numbing experience even with a standup lav.
 
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