Peter wrote:
45 mins is not enough for Europe. It may be OK for the US, with so many runways.
You are right, in Europe you can’t operate with 45’ of reserve to tanks dry, but not only due to the runway situation. While 45 mins is the “agreed” plan reserve you will find in any POH, in Europe that is pretty much what today is referred to as a “Final Reserve” in EASA OPS and therefore something which can NEVER EVER be used, if it is used, as per law, you’d have to file an incident report.
However, the 45 min figure is also the one all manufacturers I know use to define the calculatory range of their planes. So for the sake of comparison, that is the relevant figure.
Basically in flight planning today for GA you do need other reserves, depending on how you fly. FR is never touched, so everything else like contingency, holding, alternate is on top. For VFR many people use a fixed reserve like 45’ on top of FR, others use more complex calculations which have to fulfil a certain minimum.
However, it is highly dependent on where your destination is, what kind of reserve on top of FR you actually need.
Where I fly, there are several airfields in close proximity to my homebase, all of which would be accessible if LSZF closes or goes bad. Hence, 45 mins covers at least 3 alternates. Clearly, in other places, where the nearest alternate is 100 NM away, this calculation is very different. Also, particularly for VFR but also for IFR under certain conditions, an alternate is not actually required, in which case you need a fixed time as reserve. In any case, you are still expected to land with your final reserve intact.
For the purpose of a “challenge” like the one suggested I should have said 45 mins of AVAILABLE reserve. This implies 45 mins on top of FR, whatever that may be. That btw is also how airlines work with their range calcs.
Nowadays low fuel burn is absolutely a bragging right. The downside is that you need recent airframes (to stay away from Lycosaurs and the like) and the entry price can be quite high. In our club we are around 8L/100 on both DA20 (mogas) and DA40-TDI (Jet-A1), basically a gasoline car (with savings because of straight lines).
Other various figures I’ve compiled (economy or normal cruise settings):
Real numbers for the Elixir are likely to blow all of these examples out of the water (unfair because of 2 seats, but still).
Mooney_Driver wrote:
While 45 mins is the “agreed” plan reserve you will find in any POH, in Europe that is pretty much what today is referred to as a “Final Reserve” in EASA OPS and therefore something which can NEVER EVER be used, if it is used, as per law, you’d have to file an incident report.
I don’t know if you have to file a report (do you have a reference?), but if you expect to land with less that the final reserve fuel, you have an emergency situation. (AMC3 to NCO.OP.125(b) ). If you are a controlled flight, you must declare a fuel emergency. (NCO.OP.185(c) )
Other various figures I’ve compiled (economy or normal cruise settings)
Two seaters will surely do better in terms of both speed and fuel consumption. An RV-8 will do 9L/100 km at moderate altitude if you slow it down to 140 kts. That’s similar to a car while going twice as fast. It’ll also go 170 kts with higher fuel burn, while being strong enough for aerobatics and capable of a 1900 fpm climb. Here’s some fuel consumption data.
I remember well flying around in my dad’s Viking Dragonfly in the 1980s, burning 3 US GPH and cruising at around 120 kts. That was with an 1835 cc VW but the engine type has little to do with it for GA aircraft. It’s all about the airframe design goals.
maxbc wrote:
Nowadays low fuel burn is absolutely a bragging right.
True. You can unsettle some folks quite massively doing that.
maxbc wrote:
The downside is that you need recent airframes (to stay away from Lycosaurs and the like) and the entry price can be quite high.
Not really. There are some rather old airplanes which have quite impressive fuel figures.
Digging out tables I did for my 1965 M20 C with 180 hp O360, I find that it burns around 13 liters in long range cruise per 100 km distance flown. For something which flies at 250 km/h that is not a bad value at all. I’ve never calculated out the Mooney 201 but I could imagine it does even better, as it has the same consumption but is 20 kts faster.
A fun thing to experiment with Excel. Can be addictive.
But if you really wish to confuse those who compare cars with planes, you need to factor the ground distance reduction into the calculation. Airplanes fly much straighter than cars drive, so the difference in road distance towards air distance can be considerable. So if you start doing citypair comparisons, you end up with baffling numbers. Quite often you end up with road distance being up to 30% longer than air distance (in the mountains more) and the airplane using less fuel to cover a citypair than a car.
maxbc wrote:
Nowadays low fuel burn is absolutely a bragging right.
true
maxbc wrote:
The downside is that you need recent airframes (to stay away from Lycosaurs
here you go:
lycoming, some people say that it’s the most reliable piston engine on the market,
165kn on 29l
usually I wouldn’t fly that slow, but was low on fuel and far from home
two seater, but I can roll it upside down and the like… 
165kn on 29l
Only if screwed to the front of a very small plane 
You can unsettle some folks quite massively doing that.
Never unsettles me because I know there won’t be room for much more than a toothbrush
TB20 book values @FL80 : 17L/100
TB20 Peter’s example @FL200 : 15L/100
The book values are wrong. One can do a lot better. Why, I have no idea but suspect Socata were not doing “best economy” at peak EGT. Also they did all that c. 1980 which was a different era (the GT had to use the same POH to avoid lots of €€€€ spent on cert flights).
I get 138kt IAS at low level, at 11.7 USG/hr.
At FL100 I probably get 150kt TAS on about 10.5 USG/hr.
At FL200 the efficiency is poor because anywhere near the ceiling one is at “best power” i.e. 2575rpm, and ~150F ROP i.e. 1300F EGT. Not a useful setting other than to get above some wx.
Nice indeed ! That equates to about 9.5L/100
Agree with Silvaire, it has more to do with airframe than engines, but still newer airframes are generally more efficient. The RV-14 is no exception. Except of course for diesel, where the engine can make a massive difference (mainly applies to Diamonds). Something like the DA62 is really stunning in terms of room / speed / efficiency (especially for a twin). A baron albeit faster is around 35L/100…
maxbc wrote:
Except of course for diesel, where the engine can make a massive difference (mainly applies to Diamonds). Something like the DA62 is really stunning in terms of room / speed / efficiency (especially for a twin)
It’s not as much different as you think for small engines when compared with a gasoline piston engine, and the airframe design dominates anyway, but its a lot better than a turbine in many applications. The interest for small aero-diesels is mainly driven by fuel availability outside of the US and other places with GA infrastructure, which is fair enough but a niche market. However there is significantly broader interest in aero-diesels in the same power range as a small turbine, i.e. 400-600 HP. Since turbines also cost a lot to own, for engines slightly above the gasoline engine size range there is additional room for the expense of a diesel.
Only if screwed to the front of a very small plane
how about RV10 then?
188TAS, 16,2 USG/hr
