My goal is to make a flight from EPSC (Szczecin) to EDDT (Tegel) in MSFS2020 in VR and in the most economic way which is possible. According to the planes manual it should use 6.8 Gallons avgas on 8500f with 65% throttle @115 knots. As im more used to L/100 Km, this should translate to 12.1 Liter for 100Km, although avgas is more costly than car gas here in europe, with round about 30cent to 50 cent more per L,  according to the data of EPSC airport (I calculated 21€ for 100km with the price at epsc @ 1.75€ per liter). Weather will be live, but daylight and I know how much wind will impact the final result, but anyway. I will use the lower airways and will taxi a little bit. I guess 10gallons will be enough for that flight, even with taxi.

So a few questions from me:

1.) Is it better to climb as fast as possible (so with 100% throttle) or already stay on 65% throttle through the climb ? In cars its more economic to drive as fast as possible to your desired km/h and then hold that, f.e. 120kmh on the autobahn, but planes use less fuel as they climb higher.

2.) Is 8500feet the economical best height for the C172S ? As I understood, the higher the plane flies, true Airspeed goes up, but the gas engines efficiency will also get worse. I guess the 8500feet which the planes manual gives for cruise speed must be the best compromise for the C172S between height and engine efficiency ?

3.) How is the relation between gas mix and throttle ? Is it more economical to fly with less throttle and higher gas mix or let the gas throttle @65% and just lessen the gas mix ? Is there any instrument on the G1000 which show´s me the engines efficiency on a particular height with the current gas mix ? I would guess that there must be always a best gas mix for an particular height (and temperature) and the rest should be done through the throttle if economy is my only goal ?

3.a) I also realized that there´s a high difference between the gas mix in MSFS2020 and in Xplane 11. In xplane I need to release the gas mix much more gentle than in MSFS2020, where it seems that I can straight go to 65% gas mix on sea level for highest rpm. Which sim is more realistic here ? 

4.) How much feet per minute and knots would be the most economical solution for the descend ?

Ok on my first attempt I had to make a emergency landing at Finow Airport (5nm distance from emergency situation), because I had took too less fuel with me (5G on each wing) and I had a near constant 17 knots wind against me.BTW this was so a lot of fun to look out for an emergency airport, although beeing on 8500 feet I had a lot of time, I guess I could have made it to the next airport in 10 nm as well.

Im currently flying my second attempt, unfortunately not with live weather as it doesnt work, so clear sky. But I have the feeling that something is off with the plane in MSFS2020. @75% Throttle the best I can get is 110 TAS with something like 8,5 G/H, according to the C172S manuals I can find in the internet it should be 124knots TAS @8500 feet ? Whatever I try with the gas mix, more fat or more lean results only in less TAS speed, 124 knots is not possible with 75% throttle it seems.

In general, MSFS has a mixture simulation that's pretty broken. Essentially, the sim requires way more leaning of the mixture than it should, since it has engine power drop off significantly faster than it should as altitude and/or temperature increase. 

As far as I'm aware, most performance charts for naturally aspirated piston singles assume a full throttle climb to altitude, since airplanes like a 172 don't exactly have a ton of spare power and it would take forever to get to altitude with a partial power climb. 

"Best altitude" depends on exactly what you're trying to do. Cessna uses 8500ft because it's the best trade-off between time to get to altitude and airspeed, but the actual best range (assuming no wind) is going to be obtained at something like 10-12,000ft, at about 45% power, which is full throttle at those altitudes. 

The percent power you're seeing in the manuals is referring to the percentage of rated power the engine puts out, which is independent of what the throttle position is. 

In general, you'd set the desired power for best range by setting the throttle for the desired RPM from the cruise charts, leaning the mixture to peak EGT, and then resetting the power back to the desired RPM.  For leaning, your primary instruments would be the EGT, RPM, and fuel flow indicators.

The actual G1000 has a "lean assist" function to help the pilot set the mixture, but since the MSFS version lacks that, you can get close by leaning for peak EGT. Keep in mind that the MSFS mixture simulation is a bit broken, so your numbers may vary from what Cessna publishes. 

As for descent, the most fuel efficient way would be an idle descent at something close to the best glide speed, but that's not terribly practical in the real world.

Edited December 31, 20205 yr by ndts

Take a look here

https://www.airplains.com/images/Installation/Air_Plains_172_Performance.pdf

 

The best GPH(gallons per hour) you get at ~4000 ft

14 minutes ago, ndts said:

In general, MSFS has a mixture simulation that's pretty broken. Essentially, the sim requires way more leaning of the mixture than it should, since it has engine power drop off significantly faster than it should as altitude and/or temperature increase. 

As far as I'm aware, most performance charts for naturally aspirated piston singles assume a full throttle climb to altitude, since airplanes like a 172 don't exactly have a ton of spare power and it would take forever to get to altitude with a partial power climb. 

"Best altitude" depends on exactly what you're trying to do. Cessna uses 8500ft because it's the best trade-off between time to get to altitude and airspeed, but the actual best range (assuming no wind) is going to be obtained at something like 10-12,000ft, at about 45% power, which is full throttle at those altitudes. 

The percent power you're seeing in the manuals is referring to the percentage of rated power the engine puts out, which is independent of what the throttle position is. 

In general, you'd set the desired power for best range by setting the throttle for the desired RPM from the cruise charts, leaning the mixture to peak EGT, and then resetting the power back to the desired RPM.  For leaning, your primary instruments would be the EGT, RPM, and fuel flow indicators.

The actual G1000 has a "lean assist" function to help the pilot set the mixture, but since the MSFS version lacks that, you can get close by leaning for peak EGT. Keep in mind that the MSFS mixture simulation is a bit broken, so your numbers may vary from what Cessna publishes. 

As for descent, the most fuel efficient way would be an idle descent at something close to the best glide speed, but that's not terribly practical in the real world.

Ok so I absolutely misunderstood "Power" with "Throttle Percentage" it seems 😅.

But then again.. f.e. the manual http://aeroatlanta.com/docs/aero-atlanta-c172sp-poh.pdf on site 4-16 writes CRUISE 1 . Power --21 00-2700 RPM (No more than 75% is recommended). 2. Elevator Trim --ADJUST. 3. Mixture --LEAN

So how do I know how much power output it is ? Or is this something a real C172S with an real G100 would show, but not in MSFS2020 ?

So if I set the RPM by the throttle like you said to f.e. 2300 which is somewhat in mid of what the manual recommends (2100 to 2700) and then change the red mix throttle, then the rpm is changing is well.

Peak EGT means to have the EGT as far to the right as possible ? I guess with a little bit of dead reckoning with the gasmix throttle ? word not allowed it seems really complicated to manage the cessna engine, compared to an car 🤣

8500 feet is too high for that length of flight.  You're spending energy going up instead of forward that you won't get back over that distance.  Most normally aspirated pistons just don't get enough of a gain from altitude to make it worth it unless you're up there for a long time, or get a good tailwind.  Since terrain isn't really an issue I'd plan for no higher than 4500'.  Also keep in mind that it's good practice to be conservative with the POH values since they're usually off a bit. You'll also want to add around 2 gallons for the climb to 4500' from sea level.

As far as leaning goes if you have an EGT gauge you lean until the temperature is at its highest (meaning leaning more drops the temperature) and then enrichen till it drops about 50 degrees. If you don't you just can do it by RPM/sound.  In fuel injected engines the fuel flow meter is also a good point of reference.

Edited December 31, 20205 yr by BrianW

9 minutes ago, Rucki said:

Ok so I absolutely misunderstood "Power" with "Throttle Percentage" it seems 😅.

But then again.. f.e. the manual http://aeroatlanta.com/docs/aero-atlanta-c172sp-poh.pdf on site 4-16 writes CRUISE 1 . Power --21 00-2700 RPM (No more than 75% is recommended). 2. Elevator Trim --ADJUST. 3. Mixture --LEAN

So how do I know how much power output it is ? Or is this something a real C172S with an real G100 would show, but not in MSFS2020 ?

So if I set the RPM by the throttle like you said to f.e. 2300 which is somewhat in mid of what the manual recommends (2100 to 2700) and then change the red mix throttle, then the rpm is changing is well.

Peak EGT means to have the EGT as far to the right as possible ? I guess with a little bit of dead reckoning with the gasmix throttle ? word not allowed it seems really complicated to manage the cessna engine, compared to an car 🤣

I mostly instruct in older models of 172. None of the have EGT, yet I managed to lean the properly over the years. I lean until engine start getting right and the back up.

I tell you more most of older  N, M, P fuel senders are very bad. You don't even get accurate fuel reading except fuel tank full or empty. Fuel gauges needles often rocks which is hard to get reading. Also left tank draw more fuel than right even with selector . So real life not the flowery ! 🙂

32 minutes ago, sd_flyer said:

Take a look here

https://www.airplains.com/images/Installation/Air_Plains_172_Performance.pdf

 

The best GPH(gallons per hour) you get at ~4000 ft

Ok I tried to set the engine up according to this table.

@4000 feet and 2130 rpm I get something like 6,3 G/H and 101 TAS
 

 

Edited December 31, 20205 yr by Rucki

3 minutes ago, Rucki said:

Ok I tried to set the engine up according to this table.

@4000 feet and 2130 rpm I get something like 6,3 G/H and 101 TAS
 

 

I'd say close enough. Since we don't how beaten MSFS default engine or can't measure cylinder compression, give or take 🙂

4 minutes ago, sd_flyer said:

I'd say close enough. Since we don't how beaten MSFS default engine or can't measure cylinder compression, give or take 🙂

But EGT is totally to the left, isn´t that too cold for an real life engine ?

32 minutes ago, Rucki said:

Ok so I absolutely misunderstood "Power" with "Throttle Percentage" it seems 😅.

But then again.. f.e. the manual http://aeroatlanta.com/docs/aero-atlanta-c172sp-poh.pdf on site 4-16 writes CRUISE 1 . Power --21 00-2700 RPM (No more than 75% is recommended). 2. Elevator Trim --ADJUST. 3. Mixture --LEAN

So how do I know how much power output it is ? Or is this something a real C172S with an real G100 would show, but not in MSFS2020 ?

So if I set the RPM by the throttle like you said to f.e. 2300 which is somewhat in mid of what the manual recommends (2100 to 2700) and then change the red mix throttle, then the rpm is changing is well.

Peak EGT means to have the EGT as far to the right as possible ? I guess with a little bit of dead reckoning with the gasmix throttle ? word not allowed it seems really complicated to manage the cessna engine, compared to an car 🤣

You get the power output from the performance charts, which are pages 5-19 and 5-20 in the POH you linked, so there's no instrument that directly tells you what your power setting is. As an example, if you're flying at 8500ft on an ISA standard day, 75% power would be somewhere around 2700RPM and you'd burn around 10GPH at that setting. 

Since the same RPM setting corresponds to different power outputs at different altitudes (2500RPM is about 73% power at 2000ft, but only 57% at 10,000ft) and temperatures, there's no real way outside of the charts to figure out the exact power setting. 

Peak EGT is pretty much what it sounds like. You'd find it by setting the throttle to the desired RPM, then leaning the mixture until the EGT number reaches a peak (the exact value changes depending on altitude and temperature) and starts to drop off, then enrich it slightly to get back to that peak value. 

The POH you linked to also refers to "recommended lean mixture", which Cessna defines as 50 degrees rich of peak EGT (so you'd find the peak EGT, and then enrich the mixture until it drops 50 degrees from that point), but if you set the "best economy" mixture (peak EGT) that gets you about a 4% increase in range for about a 3kt drop in cruise speed.

Edited December 31, 20205 yr by ndts

You should bear in mind too that when sources talk about 'the most economical operation of an aeroplane', they don't always mean for the flight you are doing at that time. For example, if you look at most airliner operations, you will find that they tend to fly the airliner at a fairly high throttle setting for the climb to expedite it, but this isn't purely because it is getting them up to cruise quicker for a reduced fuel burn, although that is part of it, it's also the fact that if you use higher throttle settings for less time because your climb is fast, that will invariably put less overall wear on the engine than using a slightly lesser power setting for the climb (which is still a fairly high power setting) but for an extended period of time.

It's the same story with reduced power take offs, sometimes called flex temperature take offs. Most people know that the theory behind these is simply ramming the throttle to the firewall in the hopes of getting the most power, only works on a 'standard day' at sea level (i.e. 29.92.1013Mb pressure), whereas in warmer temperatures when the air is less dense, applying full throttle in an engine without any fancy fuel management systems will mean there is too much fuel and not enough air going into the engine, so it can't handle it efficiently, wasting fuel and also reducing the amount of power the engine can put out to accelerate the aeroplane up to flying speed.

But it wasn't the fact that not doing flex temperature reduced thrust take offs uses more fuel and a bit more runway which made airlines adopt 'flex' take offs, it was the fact that the first airline to do this regularly was Laker Airways when they used the BAC 1-11 and it resulted in considerably less wear on their Rolls Royce Spey engines. Initially Laker developed this technique as a policy in order to save fuel, but it was fairly soon discovered that their 1-11's Spey engines engines experienced far less wear and tear than those with other airlines which were not doing flex temp take offs, meaning their time between overhauls was greater than it was with other airlines and thus Laker's engines were more reliable as well as being a bit cheaper to maintain. This was the real saving they made on costs. It's also slightly more cost effective on tire use too, since with a shorter take off run, there is less wear on the tires.

Another consideration is center of gravity. If you are nose heavy it takes more fuel to fly the plane at the same speed compared to being tail heavy. Because lift is coming from the wings which are forward. It takes more power (i.e. more fuel) to overcome gravity with more lift at the wing, if the front end weighs more.

Ok, so in the end the trip from EPSC to EDDT (85NM) took me 8,14 Gallons of avgas (started with 10G in each wing and 1 person 190LB, no baggage, clear sky standard weather).But in the first half of the flight I flew up to 8500 which I learned today wasn´t very clever for such an short trip.In somewhat the second of the trip I flew with 2130 RPM @4000feet, EGT absolutely to the left (whatever I tried, EGT didnt moved anymore) and fflow @ something like 6.3. I guess this is the absence of an economical flight 🤣 but well, in the end I just put on Take me Home from John Denver and enjoyed the incredible beautiful landscape in VR. Flying from country like regions into EDDT (Tegel Airport Berlin, now closed) had something special. At least we can still do it in flightsims.

Edited December 31, 20205 yr by Rucki

38 minutes ago, Fielder said:

Another consideration is center of gravity. If you are nose heavy it takes more fuel to fly the plane at the same speed compared to being tail heavy. Because lift is coming from the wings which are forward. It takes more power (i.e. more fuel) to overcome gravity with more lift at the wing, if the front end weighs more.

I was indeed more nose heavy (pretty much at the limit).