Cessna Skyhawk Max Range

[Dean Talbot]

Just a quick question for the more experienced of you out there.

I've been flying this sim for around 4yrs and have spent a great deal of that time on the stock Skyhawk. MS put the max range at 638 miles, and yet I've just finished a 702 miles journey (Socotra, Yemen to Muscat, Oman).

I didn't expect to make it on 1 hop and so routed over 3 airfields in case I had to fill up, but I've done journeys of 550m plus before, and was hoping I'd be able to make it in 1 hop. In order to give myself the best shot, I got as high as I reasonably could (13,000ft - apparently ceiling is 14k, but by 13,000 you're leaned to 25/75% fuel/air mix).

By the time I landed I was well into the yellow, but not quite into the red (I had 16% left). That probably puts my range at around 750 to 800m.

I know this sim is supposed to be realistic, but is this just an error, or is the "max range" in the vehicle specs calculated at a given lower altitude, or is the "max range" conservatively pitched well below its actual range?

Cheers

Dean

[ReggieF5421]

Your higher altitude extended your range. I assume you used bottled O2 - becaue a flight that long at 13K would definitely impair your mental capacity. Also, leaning the engine down that much helps extend the range, but would likely cut a little time off your TBO.

The Cessna web site list the Current C-172 model range is 640 nm - with a 45 minute reserve @ 12,000 ft @ 45% power and a payload of no more than about 550 lbs.

Ranges are listed rather conservative by the manufacturers, and always include an efficient cruise speed, altitude and a reserve. It is normal in the real world for efficient, conservative pilots to be able to get quite a lot more range out of a new aircraft than the listed number. And to get quite a bit less range out of older aircraft where the engine is not as efficient.

I assume you are refering to natical miles and not statue miles with your numbers since GCM puts the distance between those airports at 701 nm.

[mrzippy]

Another possibility, if using at least a snapshot of real world weather, a nice tailwind at 13,000 could really help extend that range.

[mallcott]

Taking that engine to 13,000 did not do anything to help the range. A normally-aspirated engine will be at its' most efficient between 6,500 and about 8,000 feet. So the answer had to be the tailwind.

As for range, that's dependent on many factors including weight, aircraft cleanliness, how far lean of peak you are prepared to go, the weather, the prop pitch (fixed pitch prop, cruise or climb?) even how you fly it. The stated range is just an average. Without knowing and repeating precisely the conditions under which the claimed range is achieved you have no way of verifying the range against an arbitrary figure, nor do MS state whether the range claimed included or excluded standard reserves of 45 minutes.

[Dean Talbot]

Thanks for the responses and I'll respond to them in order.

@ Reggie - conservative - that certainly makes sense and helps explain things. Re: miles, yes nautical miles, although I took the reading straight from MS - 702nm was the distance it gave me from airbase to airbase. In fact, the distance read 703nm from the point where the nav changed over from waypoint 1 to OOMS (this is actually the second half of a journey from Aden to Muscat, via Socotra, with a refuel at Socotra).

@ Mr Zippy - I only ever fly with real life weather, and funnily enough someone (who regularly flies in that part of the world - really flies, not simulation) mentioned to me the day before the flight, that the area is known for tailwinds (he didn't say in which direction).

@ Mallcott - I hear what you say, but it would seem logical to my admittedly technically primitive mind, that flying to an altitude where you reduce the fuel feed to 25% should extend the range? That's one of the reasons I decided to try it in a Cessna, as opposed to something larger. You mention how far lean of peak - I have no aviation experience, only 12 years in various simulators, and so am not entirely sure what that means, however, if it helps you understand how the flight was flown please see the following:

Leaning: my leaning followed the RPM (as I always do). As I ascended I periodically adjusted the leaning to maximise RPM.

Fixed pitch prop: the Cessna Skyhawk is a fixed pitch prop, isn't it? I've flown the Baron and King Air and understand the advantages of a variable pitch prop, but although I try not to get too far into the technical side of things, my understanding is that the Skyhawk is fixed pitch - correct me if I'm wrong.

Other factors - aircraft cleanliness - with the Skyhawk there isn't much choice, as other than the flaps there is nothing to retract. Weather was whatever the weather was like in the Arabian Sea at the time (real life weather) - bright with high clouds - and I flew the entire flight on autopilot (alt/nav hold). The climb was also on auto, and climb to cruise altitude took 93nm (ie: up a few 1000; build up speed; up another few 1000 etc). Fuel = 100% from Socotra and payload=default. Finally, it was VFR, and was a straight line from Socotra to Muscat.

Reserve - good point; MS don't explain whether the reserve is included, but at 702nm, I was just over half way through the yellow section on the fuel indicator. As I said above, after I'd switched off, I checked the fuel load, and it was at 16%. Working back, that should put the range at 814nm.

[Dean Talbot]

It's definitely altitude and leaning.

My longest journey in the Cessna is 794m - Samarkande (Uzbekistan) to Atyrau (Kazakhstan), direct. Again I flew at 13,000ft which gave me a 25/75% fuel air mix. Here is the map plate for this flight;



Last weekend, I flew Peshawar to Karachi (Pakistan). It wasn't a direct flight and roughly followed the path of the Indus, but it was 602m. I hadn't intended testing the range, but that's what happened - because it was low country, I flew at 5,000ft dropping down to 2,000ft. Range hadn't occured to me as an issue. In fact my route took me over Hyderabad, and I contemplated popping down to refuel, but thought I had enough fuel to make the distance, and so didn't.

However, around 40m from Karachi, it became clear I was shortly going to be on fumes, so I climbed to 7,000ft, which proved to be just enough altitude, as I ran out of fuel 6.5 miles from the runway (just enough height and distance to manage a flameout landing).

I think this shows that in the Cessna, at least in MSFSX, altitude very definitely makes a significant difference to your range. Whether that's true in real life is another matter.

[mallcott]

Not sure where you get this notion of the 25/75 fuel air mix. An engine runs at the stoichiometric ratio

Read here
http://en.wikipedia.org/wiki/Air%E2%80%93fuel_ratio

You have a tiny range of adjustment either side of the basic stoich of 14.7:1 but can never reach a 1:4 ratioas the engine will not run.

the reason the altitude makes the difference is because of the tailwind component, NOT the impact of the leaning through reduction in air density. Therefore if there had been a 20-knot tailwind at 7,500 AGL and a 10-knot headwind at 13k, your flight would have been more efficient lower down.

Higher does not mean more efficient - there are many factors at play.

[Dean Talbot]

Thanks for this. As I said, I am not talking about real life.

The "75/25" simply refers to the graduations on the Saitek throttle quadrant. If tailwinds are the reason, in the simulation, then I can buy that, but it's difficult to accept that that is the reason, in the simulation, when you get the same results in the same general geographical area, both east and westbound. I am traveling around the world, and therefore am doing multiple flights in the same localities, some in the Cessna, some not. Those in the Cessna I am typically traveling in every direction, albeit with a general eastbound course, and I am consistently seeing better fuel economy at altitude.

Now if this is not reflective of real life, that's fine. I wouldn't know as I am not a pilot. But that is what is happening in my experience of flying MSFSX.

[pwafer]

Hi Dean,

I tried for max range - NZKT to YLHI, Kaitaia on New Zealand North Island to Lord Howe Island off the coast of Australia. Flight plan distance was 750nm. I used As2012 real weather. I calculate I was doing 105 KTAS at 10000 feet but flight time was 7hrs 45mins, so I had a slight headwind. I landed on fumes, 2lbs left in the tanks when I shut down.

Philip

[Dean Talbot]

Hi Phillip

2lbs! That's really pushing it! LOL Nice one. That's very much my experience. The higher I go, the more I seem to be able to stretch the fuel out, even in a headwind.