What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Musings on RV Flight Duration.....

Ironflight

Ironflight

VAF Moderator / Line Boy
Mentor
I was loafing along this afternoon, just doing a maintenance check flight after an oil change, and I pulled the power back until i was flying level at about 80 knots. The fuel flow dropped to about 2.0 gph, and since I had nearly full tanks, the "remaining duration" value on the EFIS was showing about 14 hours! Hmmmm....I got to wondering - has anybody ever gone up to see just how long that could keep an RV airborne on one tank of fuel? I'm not sure what you'd do with yourself for all that time droning along!

Think about it, you could fly off a 40 hour Phase 1 in 3 tanks of gas! (Note - This statement is for "Wow" factor only - I am of the firm belief that Phase 1 is to be used for testing purposes, and not just putting hours on the airframe......)

I've never thought about fooling around with a very long, slow flight before - interestign idea though! So what the longest duration flight you've made? Anyone stayed up ten hours!?

Paul
 
Put yourself in a situation:

VFR on top with known icing below. Nice you know you can loaf along until you fine more favorable WX or clouds to punch through.
 
Repurcussions?

This made me think of the couple of times I have flown alongside Cessna 150s going somewhere. That takes a power setting and fuel flow close to what you are talking about.

It is kind of intoxicating seeing that economy but I wasn't entirely comfortable. I was seeing temperatures completely out of the ordinary and wondering if this is very healthful for the engine.

I really don't know, but wouldn't want to do it a whole lot without some advice from people smarter than me about engines.
 
Here's some other thoughts.

80kts is 92mph, giving you 46 mpg at 2 gph.

46mpg * a full load of fuel (42 gal for an 8) is 1932 miles theoretical range.
From my local airport, you could make it anywhere within:
http://www.gpsvisualizer.com/map?lat1=&lon1=&location=ikv&radius=1932mi&format=google&radius_segments=&google_wpt_sym=circle

Note, I'm not sure which numbers your efis is most accurate about. Calculated another way:

42 gal / 14h = 3 gph. Course that's still 30mpg, for a theoretical range of 1288 miles.
Which would put you anywhere within:
http://www.gpsvisualizer.com/map?lat1=&lon1=&location=ikv&radius=1288mi&format=google&radius_segments=&google_wpt_sym=circle
 
If you did fly at 80kts level for one hour on one tank that you switched to after you established your cruse, and then switched back for landing and then fueled the cruse tank you would see that you used more like 3 to 4 gallons for that period.

It takes between 55 and 60 HP to keep a 6 or an 8 in the air at 80kts. 12# of fuel /.41=29hp........ But I might be missing something.
 
Last edited:
Longest Flight

I once did 6.6 hours in my RV6A from McKinney TKI Texas to Port Meadville Pa. GKJ when I was on my way back to France. I had a ferry tank in the fuselage 33 gals plus wing tip tanks 18 gals. Could have gone on for a bit further but that was enough fun for that flight. Once did 9.6 hours in a Turbo Arrow from Goose Bay to Reykjavik again with ferry tank. These are obviously minor hops compared with what Jon Johannson did in his RV4 as well as others who have crossed the Pacific.

Barry RV6A F-PRVM
 
I can remember from college the instructor writing on the chalk board "L/D Max = Max range for a prop airplane no wind."

Quite slow for an RV. And I too have wondered about engine heath at very low power settings.

I know the oil temp needs to be kept up but what about the CHTs down around 210?

During break-in they want the rings to have pressure on them? OK after break in? Seems like the oil gets dirty faster when running at ultra low power.
 
I was at Sun-n-Fun a few years back and met an RV-8 driver from Kansas. He had extended his wing tanks to the wing tips, virtually doubling his fuel capacity. He told me he could fly, non-stop to anywhere in the continental US. I left after asking him one more question: Why?
 
I did 4.5 flying non-stop from Austin to Indy, but my kidneys, bladder, and butt only want to fly about 3!
 
Totally Impractical, of course.....

I wasn't really thinking in terms of GOING anywhere with this musing...just thought "wouldn't be interesting to take off at sunrise and lope around the local area until the sun set...in summer!

It would be interesting to try it for a little while and see where you actually had to run to keep the engine happy - I suspect it would be closer to L/D max than slow flight, and that would probably be 3.0 gph or so. Still a long time in the air on standard tanks...
 
Endurance

Paul,
I spent 4+48 in the Doll Oshkosh WI to Northwest Regional TX with 1+20 remaining at that cruise setting last August.
 
ronschreck said:
I was at Sun-n-Fun a few years back and met an RV-8 driver from Kansas. He had extended his wing tanks to the wing tips, virtually doubling his fuel capacity. He told me he could fly, non-stop to anywhere in the continental US. I left after asking him one more question: Why?
Click to expand...

I saw that RV-8 at LOE a few months ago... and while quite impressed with it, I also wondered "why?" myself. I'll admit that an extra 9 gallons (HWA ER tanks) would be nice to have, but 75-80 gallons? Ouch, that hurts to think about that kind of endurance. I'd have to bring along a jumbo sized pee bottle...

My long range "record" was 853nm from Thermal, CA to Junction, TX; took roughly 4+45, had 6 gallons remaining and my butt and bladder were ready for a break. Then again, if I'd had those 9 gallon ER tanks and another piddle pack, winds permitting I could have made Palm Springs to Houston non-stop... tempting.
 
Just because you have fuel for 6 hours plus reserve does not mean you are always going to fly for that time. I found having the wing tip tanks which give an extra 2 hours useful when I fly to places that don't have fuel or have expensive fuel. I can fly back home without having to fill up or divert to a field that has fuel.

I am afraid we have somewhat deviated from the original question on this thread.

Barry
 
I also wondered "why?" myself. I'll admit that an extra 9 gallons (HWA ER tanks) would be nice to have, but 75-80 gallons
Click to expand...

I understand that we are experimental. I just don't think it is that wise to stick that much gas out there. That is a long way from intended design.
 
About 40 hp at best range (L/D) speed

QUOTE=gasman;288864]If you did fly at 80kts level for one hour on one tank that you switched to after you established your cruse, and then switched back for landing and then fueled the cruse tank you would see that you used more like 3 to 4 gallons for that period.

It takes between 55 and 60 HP to keep a 6 or an 8 in the air at 80kts. 12# of fuel /.41=29hp........ But I might be missing something.[/QUOTE]

In round numbers, something close to 40 hp at best range speed.

So that is something like 2.7 - 2.9 gal/hr.

Just imagine how much further you could go with an aspect ratio 6.3 tapered wing! :) Power required drops to about 35 hp.
 
Endurance

Years ago (late 70's), a fellow USAF OV-10 pilot in our squadron had been looking over our performance charts and decided to max endure on a xcountry. He went to max endurance at high altitude and by the time he arrived back at home station, the command post and squadron had a SAR going trying to find the 'overdue' OV-10. Needless to say, he met some interesting people and his career was no longer a happy one! He is now with the FAA!
 
About the lowest fuel consumption I have been able to do maintaining level flight is 3.5 or so, and that is around 100 knots or something like that. I know Pete's 9A will maintain level flight down in the 3 or just below gph range. I will try to get a fuel burn chart developed the next time I fly (probably not today, -23F at my house this morning!). When I make this chart, I will make sure I am at "optimal" economy settings, usually just LOP.

BTW, my airplane will overheat eventually flying level at 80 knots in the summer. The power required is high relative to the cooling air. I'm guessing I need around 4 gph at that speed. The charts will be interesting.

Paul, does your fuel flow meter see pulsed flow? I wonder if that could be fooling it a little. 2 gph does not seem possible. My burn at idle is around 1.3 IIRC.
 
AlexPeterson said:
Paul, does your fuel flow meter see pulsed flow? I wonder if that could be fooling it a little. 2 gph does not seem possible. My burn at idle is around 1.3 IIRC.
Click to expand...

Yes, it does - I don't really think the 2.0 gph is a valid number...but even at 3.0 gph, with 42 gallons of fuel on board, we're talking an amazing 14 hours....OK, allow a couple gallons for initial climb, let's say 13 hours! (That's still sun up to sundown....)

Paul
 
What will also be interesting is how the RV-12 responds to endurance challenges. The Rotax 912S can sip gas better than any engine I have seen, and keep you in the air.
 
You must log in or register to reply here.
Back
Top