Hello folks,
Flying a typical light SEP type, what do people view as the minimum acceptable landing fuel on board? Of course what I mean is what are we comfortable with, what doesn't scare us?
I have always like to plan to land with at least 1hr of fuel left. That's how I view it from the LFOB perspective, but what does that mean for up-front planning? It basically means I'm putting in a 1hr contingency to cover everything, rather than going into the detail of what I need for holding, a diversion, etc. So if it is a 2hr flight, I take 3hrs of fuel and stick to that simple rule.
However, on a return trip I'm planning to make this summer (EGLM to LFBU) I am considering a stop (or a stop in each direction) at EGJA to fill up with cheap fuel. To maximise the saving, this obviously requires landing at EGJA with as little fuel remaining as possible.
W&B will not be an issue - we can brim the tanks. We are two (small people) in a TB10 with a holdall each.
My initial calculations show that with a stop in each direction we can save about £150 on relative fuel costs, and this assumes always landing with at least 1hr of fuel on board and buying some in France too. It is a shame we don't have the range to go EGJA-LFBU-EGLM with just one stop on the way out and no fuel bought in France.
How far would people push it?
I never plan below 25 liters remaining after diversion - about 45 mins at 65% in the TB10 - and I only go this low because I have a reliable fuel totaliser.
In practice, this means I plan to land with about 45 liters in the tanks (my most common planned diversion is Biggin->Southend). Flying to Alderney, I would make sure I had enough fuel left to divert to somewhere reasonably inland (fog can develop over there) and and still have 25 liters remaining.
Out of interest, what power settings and fuel flows do you use in your TB10?
I don't have a totaliser unfortunately, and I generally cruise at 23"/2300rpm. Fuel consumption analysis across our group (9 of us) shows we return slightly better than 40 litres per hour on average. I probably average less than that as I lean a fair bit more than most in the group.
Incidentally, how does a totaliser work? Does it measure fuel flow rates?
Assuming fairly constant power settings and predictable consumption at those settings, one can compute quite accurately the landing fuel on board the old-fashioned way based on the fuel at departure and the flight duration. Assuming one wants to, that is. I normally just make sure there is plenty and don't worry too much about exact numbers.
A very interesting topic...
Obviously what is smart going to a destination in the UK is not the same as going to a destination in Greece where the only airports with customs and avgas are Corfu, Athens, Samos, Sitia, Rhodos... I think.
In much of Europe, the alternates are driven by where you are willing to spend a night, though I guess that is true everywhere to some extent, especially if you have passengers.
Normally I plan to land with no less than 20USG at the destination, which is about 2hrs' economy cruise (140kt TAS, FL120). And that's true in the UK also when hacking around Class G (20USG is about 1.5hrs then).
But there is a much bigger issue here: do you actually know how much you have in the tanks? Unless you have a totaliser, and you started with an exact physical check, you don't really know. You probably know to within
I know of a bloke who flew an old TB20 from Biggin LGKB to Corfu (LGKR) nonstop, and reportedly landed with 5 USG. He was in fact extremely lucky because he could have had minus 5 USG just as easily (and ditched somewhere abeam Albania).
Incidentally, how does a totaliser work? Does it measure fuel flow rates?
Yes. You load the starting fuel on board (FOB) and it counts pulses from a little turbine transducer. It also feeds the current FOB to the GPS which, knowing the current GS and distance to run, constantly computes the Landing FOB e.g.
Some background here and here.
With a totaliser you should know the LFOB to within about 1-2%, which happens to be considerably more accurate than some airport pumps, especially ones in some places in southern Europe 
I generally cruise at 23"/2300rpm
I've recently started cruising at lower manifold pressures and higher RPM - I find my engine is much smoother there. I get about 114 KTAS on 32 liters/hour (with careful leaning). I reckon the EDM-700 with fuel totaliser that I had installed last summer saves me about £20 an hour in fuel alone. Given I've done about a hundred hours since then, it has more than paid for itself already!
Incidentally, how does a totaliser work? Does it measure fuel flow rates?
Exactly. If installed correctly (as usual, see Peter's writeup), they are accurate to 1% or better.
I know of a bloke who flew an old TB20 from Biggin LGKB to Corfu (LGKR) nonstop, and reportedly landed with 5 USG. He was in fact extremely lucky because he could have had minus 5 USG just as easily (and ditched somewhere abeam Albania).
Terrifying
I do actually plan to do that flight one day, but while it is definitely technically feasible, with legal IFR reserves, if LGKR did not clear me to land (which has happened to others, who got PPR by phone and the person then went off shift) I would end up at one of 3 airports where it would cost me € 4 figures to get back out (avgas shipped in drums).
Obviously one would do it from Lydd and with lots of tailwind 
BTW one can get significant errors due to fuel loss when parked in a hot place with full tanks, and also (less so) due to evaporation. In this thread I posted a graph of the errors I have seen.
Thanks folks.
Obviously the mission I'm talking about is on a somewhat smaller scale from what you tend to fly Peter. But I suppose the same principles apply.
I could of course just go EGLM to LFBU non-stop, filling up at the destination for the return trip.
What got me thinking was the trip I did to Alderney on the bank holiday. I wanted to save as much on fuel as possible (the group reimbuses at EGLM prices regardless of the price paid, so the pilot can win/lose depending on destination). I told myself that, for that trip, I was happy to land in Alderney with 30mins (20 litres) LFOB, so with the flight being 1.3hrs I planned to take only 1.8hrs (72 litres). In the end I chickened out when I was on the pumps at EGLM and gave myself 100 litres. I had visions of my instructor wagging a finger at me saying "the only time you have too much fuel is when you're on fire". But then at Alderney, when it only took 140 litres to brim the tanks, I cursed my over-caution.
Unfortunately I don't have the luxury of a totaliser. I can only really measure my own consumption with a brim-to-brim test (the dipsticks aren't really accurate enough) and I suspect the next opportunity for that will be the France trip. I suspect that I probably beat our group average by a bit, since I lean more than most.
jwoolard - what altitude is that 114 KTAS at? I might give lower manifold pressure and higher RPM a go, see what sort of speed and smoothness I get. 23/23 gives me about 105-108 KIAS.
Do I bother to stop for cheap fuel on the way to Angouleme, or is it not worth the time? I suppose it depends on how much fuel costs at Angouleme, and how much time/hassle the stop takes. Alderney is pretty quiet, and (based on my experience last week) if I had all my paperwork in order I might be able to be taking off again 20-30 mins after landing.
It depends a lot where you are flying. In general, I plan on having 1hr+ on landing at the very minimum. That said, it's a very different proposition flying somewhere with an airfield (and Avgas available) every few miles from flying over some desert and/or mountains, e.g. parts of the western US or southern Africa where any unforecast headwind can really ruin your day.
I certainly wouldn't cut it too fine going to any island - learned about that some years ago when on approach to Jersey, the tower guy came on and calmly informed 'all stations, airport is closed'. Turned out they had a commuter a/c (Aurigny??) with an unsafe gear indication and were preparing for a gear-up landing. Turned out to be a false alarm, the airport re-opened and we landed, but still... btw, we did have enough fuel on board for a diversion, it was just one of these occasions where you think 'I learned about flying from this".
This is not a simple question. The answer will vary a great deal depending on power settings and, most importantly, how the tanks are arranged. I have 4 tanks, all 30usg each, high level (FL100) cruise power needs 12.5gph, low level cruise 14gph and holding speed 8gph. Of great interest is where the fuel is e.g. 14usg spread over 4 tanks is next to useless, however all in one tank is fine (it'll give me 1.45hr at holding speed).
A lot depends how comfortable you are with running tanks dry. You don't have to wait until the power cuts, the fuel flow meter will start to fluctuate shortly before the engine cuts - you then switch tanks and turn on the aux pump. Running tanks dry in level flight at altitude will give you much more useable fuel. The TB10 has 2 wing tanks? You can get down to 45 mins at low level cruise power (VFR) before you need to panic - just so long as all that fuel is in one tank.
Do I bother to stop for cheap fuel on the way to Angouleme
It would be fairly unusual for an approach, landing and a takeoff and climb to be worth doing, to get cheaper fuel.
Also the duty drawback when leaving the UK (with full tanks) is worth close to the saving one gets filling up on the Channel Islands, and it's much safer.
The TB10 has 2 wing tanks?
Yes, but you get a LOW FUEL warning light come on, at 7.9 USG in that tank (may be a different figure in some airframe serials). I have in the past continued to burn about 50% of that amount i.e. a further 4 USG, but that's as far as I have ever gone...
