If you are patient, that is. With the high fuel prices in Europe, I’m surprised there is almost no talk about hypermiling or economy flying.
The POH’s of most aircraft simply don’t deal with ultra long range/slow flight. It is generally agreed that for all aircraft, maximum range can be achieved by flying at best glide speed. Obviously, this is not a speed most people are comfortable to fly at – after all what’s the point of having an aircraft then? But nevertheless, it would be good to have more empirical data in this region. You never know when it could come in handy.
In the Aerostar POH there is no best glide speed published. However, the Vy at 117kts is generally considered to be the same as best glide. Unfortunately, my plane is in for engine overhauls, so I haven’t been able to check the FF’s at Vy, but a rough guess would put it around 8-12gph. With the aux 225gal tanks, this means in the region of 2300-2500nm range. That’s US trans continental, if you can stomach the time it takes. But if you can’t, a good speed that gives great range and gets you there a little faster, is the so called Carson Speed. It’s basically a speed 1.316 x Best Glide. In my case, this would be 153kts. I don’t know what my fuel burn would be there, but I’m guessing in the region of 15-17gph LOP. That gives a range of around 2000nm for my plane. Not only that, but that speed is fast enough/close enough to the economy cruise speed published in the POH, that it would probably save you time compared to flying at a higher speed and having to stop to refuel.
I still haven’t installed my aux tanks, but when I do I hope to be able to prove this by flying nonstop from LA to NY. This trip is 2150nm in a straight line, and with a little favourable easterly winds, it should be doable. Obviously, at such low power settings the cabin pressurisation won’t be able to keep up at highest altitude where the sweet winds are, so it will be a case of choosing an altitude either where it can, or stock up on oxygen. But as I come to further down in this post, fuel burn/economy is independent of altitude. In summary, great fuel economy, if you’re not pressed for time, is possible to achieve. Electronic ignition will save you up to 20% right off the bat. LOP some more, Carson or lower even more.
This Klaus Savier guy in the link below regularly manages up to 60-100mpg in his Vari-Eze. You can’t even get a Prius to those numbers. He flew from LA to Florida on 26 gallons in total – which blows my mind. That’s cheaper than any airline ticket and has much better seat-gallons-per-mileage than even a loaded 747 can achieve. Even with European fuel prices, this would probably beat any airline ticket.
Over at the Bonanza forum there’s a gentleman called Bill Compton who’s done lots of interesting experiments in this region. He talks about Vbr (Best range) and Specific Range (Nm/gal). Vbr is best glide speed. SR varies with weight of aircraft. But interestingly, Vbr and SR are independent of altitude, which I hadn’t realised. You can achieve the same fuel economy at 500ft as you can at 25000ft. He sent me a great document with his empirical data – I’ll ask if I may share it here.
Personally my backside can’t take that long in a light plane. Obviously need to check oil consumptions as well. I would prefer faster with some breaks.
If I throttle back to 40% power on the DA42-VI (~7gph total), I do around 130-133 kts at FL180, for a zero fuel range ~1350nm. (2400nm with Turtle Pac) I did experiment pulling all the way back to 35%, but the nm/gal value on the G1000 hardly changed. Also you need to pull the gear warn CB at real low power settings. FADEC sets minimum 35% power at high altitudes anyway.
Longest nonstop I did so far on fixed tanks were 1033nm over Saudi Arabia, light tailwinds, ~145ktas at 8gph. Landed with 1hr20min of fuel.
While I never considered speed that big a deal in the old days, I have to admit defeat & confess how quickly you adapt to the performance delta of a higher performance aircraft. I pretty much cruise at 180-185ktas all the time, just because it feels good. Puddling around at 130kts for hours on end just really gets on your nerves.
If I had an Aerostar I’d kick that sucker up to 230ktas at FL250, enjoy a nice lunch somewhere in Colorado (or any other number of 1000s of public airports in the US w/no landing fees & nice FBOs) & continue onwards for a nice dinner on the east coast.
Having said that, I do share your passion for long range, as it opens up to World flying, oceanic sectors, fascinating destinations etc. (which is why I bought my aircraft in the 1st place)
One advantage of low power flight – the engines get very quiet. Zero vibrations. You almost don’t even need the headset. Longest day of flying for me was 11½ hrs airborne. I was hardly fatigued at all.
At 117 kts you’re doing the same as a Piper Archer or C172 on about the same fuel. You could add fuel stops for backside relief, but what is the point of purchasing a pressurized twin capable of 200+ kts if you’re planning on hanging out at Cherokee speeds?
IIRC, a couple ex Austrian Airways captains ferried a DA42 across the atlantic in one go (or one stop? can’t remember), using LRC (45-50% power). Speeds probably close to what you’re mentioning and 10 hrs on a wooden bench. Ouch!
I wonder why Carson speed is so uniformly related to Vbg.
Surely, the variation in engine efficiency versus power must come into it.
With no engine, Vbg is the best range speed in still air (well, obviously 
)
It seems obvious that if the engine efficiency dropped by half at/above the power required to reach say 1.2 Vbg, the Carson speed could never be greater than 1.2 Vbg. So there must be an engine efficiency assumption in there. If you extend the axes in this diagram until the power output reaches zero, and look where the best power line intercepts it, you see there is a lot of fuel flow there, and this represents stuff like the pumping losses. So engine efficiency will improve with power (subject to being still able to operate stochiometric i.e. around peak EGT) and this must be factored into the Carson formula. I am just suprised one could say 1.316 because that is an accuracy of better than 0.1%. Are engines that consistent?
The best-MPG speed will be slightly above Vbg (if the engine efficiency was constant over power – that may be just about true for a 3 phase brushless electric motor, driven from an electronic inverter – it would be at Vbg) and well below the Carson speed, but that speed, which is probably about 110kt for a TB20 (Vbg=95kt) is far to booooring to fly at
With the high fuel prices in Europe, I’m surprised there is almost no talk about hypermiling or economy flying.
There is in some circles (you are welcome to start an LOP thread here 
) but it is only the pilots who populate the internet based pilot communities who know about this stuff. These are mainly the American ones which were originally in Usenet (rec.aviation.*) and later moved to web forums as Usenet died out.
I also can’t understand why for example the PPL training business almost wholly refuses to do mixture leaning – with fuel prices totally dominating the operating costs in Europe.
a couple ex Austrian Airways captains ferried a DA42 across the atlantic in one go (or one stop? can’t remember), using LRC (45-50% power).
I recall reading adverts for the DA42 when it first came out, claiming a 2200nm range with extended tanks. Much later, I was shocked that the actual figure was closer to half of that. They also claimed 210kt TAS. 2200nm would get you from Ireland to the US east coast.
Yes, there was some discrepancy in the promised figures and real world figures. I also recall that Diamond blamed Thielert for providing tuned engines for the performance testing without them knowing about it. Politicians, anyone?
We fly to get there and I agree with you Hodja – it’s insidious how quick you get used to speed. Now, screaming along at 190-200kts in economy cruise even seems slow. But for me personally, as long as I’m alone and can pee in a bottle, I don’t mind long flight times. I can even get up and stretch if I have to, although it is a bit contortionist. In my experience, any fuel stop is at least 1hr, so you can slow down pretty considerably and still get there ahead of that lost hr.
Didn’t Diamond fly their Oshkosh demonstrator back across the Atlantic without a ferry tank? Think they did St Johns to Porto in Portugal in one go. That’s got to be at least 1800nm. Seem to recall they had a 40% power setting.
Interestingly, Max Conrad, the hyper ultra long ranger only drank and didn’t eat during his long solo trips. We’ve all read about his Casablanca to Los Angeles non-stop flight, but he actually broke his own record later by flying his Twin Comanche from Cape Town to St Petersburg, FL. 6600nm over water alone, for a total of almost 8000nm. I wonder what the size of mr Conrad’s pee bottle was?
Finally, installing electronic ignition will add roughly 20% to your fuel economy according to that guy Klaus Savier. He owns Light Speed Engineering. FAA and EASA have not allowed it to be certified to replace both magnetos yet, but they do allow it to replace one. I think it’s just a matter of time before they do. When both are replaced, savings of up to 30% in fuel consumption can be expected. Quite a big improvement.
I am very sceptical about such claims. If you, on a conventional setup:
the difference will be very small.
Apparently it’s the possibility of advanced timing up high that gives the electronic ignition such a dramatic improvement.
This Klaus Savier guy in the link below regularly manages up to 60-100mpg in his Vari-Eze. You can’t even get a Prius to those numbers.
Yeah but the Prius carries 4-5 people plus the trunk.
It’s worth compaing the Vari-Eze with someone in their motorcycle.
