Coming out: bought an Arrow!

@Mateusz look for an app that is called “AircraftPower” from James Petty. It has all the relevant engine data installed. And then play around to see, for example, which combinations of MP, RPM results in which power, including OAT, density altitude and so on.

Maybe similar to this: ROP – oxygen controls power: %power = (MP/27) * (RPM/2700), HP = %power * 200, LOP – fuel controls power, HP = 14.85 * FF, %power = HP/200

I do similar maths, it works beautifully…I think the formulas in EDM are based on MP & RPM alone (not on EGT/FF unless RPM drops when you are too lean)

The AFM/POH does the same mistake, it show % power vs MP×RPM in both best power and best economy cruises, that is not true when fuel flow = 1gph or 100gph at 29"/27

In reality few people fly “by power”.

At low level, you set 23" 2300 rpm (or whatever the engine is happy at) and peak EGT/LOP. The engine power is probably about 65% but you don’t care.

At higher levels you are air limited (flying with wide open throttle) so the rpm is set for 2300 or so again (unless you need to approach the ceiling; then you need max RPM for best power) and you just move the mixture. Set peak EGT/LOP for cruise, or enrich for ~1330F for max power.

Climbs are done with all 3 forward, and leaning the mixture gradually for a fixed EGT on a chosen cylinder. Usually this is about 1300-1350F and you just maintain that until top of climb.

It’s really simple.

In all cases, you accept whatever speed you get. You can’t control the wind, either Then all that matters is the calculated LFOB, and the ETA versus destination closing time.

This is the correct way to manage the engine, and is also why the performance models in say the Autorouter tend to be way off

Peter wrote:

In reality few people fly “by power”.

In aircraft with accurate fuel flow meters (and preferably totalisers), I agree. In other aircraft, setting a precise power is the only way of having some knowledge of the fuel flow.

In aircraft with accurate fuel flow meters (and preferably totalisers), I agree. In other aircraft, setting a precise power is the only way of having some knowledge of the fuel flow.

Sure, but people without fuel totalisers almost never fly anywhere

Well, nowadays. I know a guy who flew a stock-spec TB20 EGKB-LGKR, about 1150nm, landing with what turned out to be 6 gallons. Probably 30 years ago.

Also, to set “precise power” you are trusting old instruments rather a lot.

I am quite certain I don’t have GAMI injectors. The seller didn’t mention them. Of course they could have not known :D, but on top of that, replacement of injectors is not mentioned in any work report. And I’ve gone through everything I got with the plane.

They are standard Lyco injectors, but selected for fuel flow and marked. Rarely, they have been enlarged (hence the STC). Well worth getting.

Peter wrote:

Sure, but people without fuel totalisers almost never fly anywhere

I know I’m an exception…

Also, to set “precise power” you are trusting old instruments rather a lot.

You can cross-check with the ASI. Also, you learn pretty quickly if the rpm indicator over/underreads significantly.

By “anywhere” I obviously meant doing flights which are significant relative to the range of the aircraft.

That isn’t possible to do safely unless one has a totaliser. Even if the aircraft is a known quantity (it rarely is) you have the wind making a very big difference (because GA TAS is slow relative to wind) and the wind varies all the time, the winds aloft forecasts are often fiction, and to deal with this classically (by using the old style plog with times for waypoints, and calculating how far ahead or behind you are on the ETA at each waypoint) will do your head in, and that kind of stuff takes out most of the fun of flying.

Peter wrote:

By “anywhere” I obviously meant doing flights which are significant relative to the range of the aircraft.

Depending on what you mean by “significant”, that’s what I do.

Peter wrote:

By “anywhere” I obviously meant doing flights which are significant relative to the range of the aircraft.

The question is always what kind of fuel policy you use, particularly in terms of what reserves you plan. “Significant to the range of the aircraft” can mean various things. The main thing is obviously not to get into situations, where you dig into final reserves or similar.

Range is very often a pure advertizing term. Why? Because the range given in the POH’s are practically never reachable as they include nothing (if even) but 45 mins final reserve, which should never be touched.

So in practice, you need a lot more fuel reserves: Alternate, Contingency and whatever else you determine to get the peace of mind you wish.

In the end, this truncates the range of any airplane significantly. Assuming an average of 10 GPH consumption and 150 KTAS cruise:
- 45 mins final reserve = 7.5USG final reserve, for planning “unusable fuel”
- Alternate: With our planes anything between 45’ and 90’. So between 7.5 and 15 USG
- Contingency: 10% of trip fuel or 30 mins holding, whichever is higher: 5.USG.
Plus whatever else comes to mind.

So looking at this, between 20 and 25 USG are gone for reserve fuel even before you start. That is 300-375 NM off zero fuel range, 200-260NM off POH range.

With a fuel capacity of 50 USG, that truncates the range to about 2.5 – 3 hours instead of 4.25 hours which are the base of range calculations in the POH. So of the 630 NM POH range, some 350-400 NM remain.

85 USG you are down to 60 USG which corresponds to very roughly 5.5 to 6 hours flight time. That is 825-900NM down from 1150 in the POH.

Peter wrote:

to deal with this classically (by using the old style plog with times for waypoints, and calculating how far ahead or behind you are on the ETA at each waypoint) will do your head in, and that kind of stuff takes out most of the fun of flying.

Really? For me that IS the interesting part. PLOG’s are imho still something I would never ever leave the ground with unless I stay in the circuit and keeping a fuel track record is about the essence of situational awareness. Cases like the Air Transat A330 show that brutally, where a hyper-modern airliner runs out of fuel due to the loss of situational awareness.

From what I see looking at how most people operate their airplanes, far too many are blissfully unaware of what their airplanes really can do and how to set up professionally for flying airplanes to their max efficiency and range available. It is not enough to fly “by ear” but the only way to really being able to achieve POH figures is to keep at them very carefully and more over to keep to the fuel schedule your flight planner has used to calculate your PLOG.

While this should be obvious, it rarely happens. Most flight planners use fixed percentage of power fuel flow, so i.e. 65% as the probably most common. However, 65% power is hardly an absolute value, you can achieve it with various RPM and MP settings to achieve the 65% fuel flow, but the way its done has impact on TAS. So unless you know for sure which power setting exactly was used in the PLOG by the flight planner, you won’t achieve the result the plan gives you. And way too many pilots will then blame the differences on “inaccurate wind forecasts” and similar excuses.

Performance imho is the crown jewel of flight planning and is very often not taken anywhere serious enough in our GA world to enable us to really fly to the limits of our planes. I would think that knowing exactly what figures to see and maintaining the awareness of whether what you see is what corresponds to the basis of your planning is far more important than any gadgets, however practical they can be. Having said that, a fuel flow instrument with verified performance and a totalizer are certainly the most valuable tools in this game.