Flight distance/time discrepancy?

Discussions surrounding the software that lets pilots connect to PilotEdge and the actual simulators
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Pieces
Posts: 342
Joined: Fri Jul 13, 2012 8:25 pm
Location: Ely, IA (KCID)

Flight distance/time discrepancy?

Post by Pieces »

I just got down from the East Coast flyin (KVNY to L65). I was flying my trusty Archer N2877B and took off just after a Bravo (N201EP). Here are the two flight tracks from PEaware: As you would expect, the Bravo was significantly faster than my Archer. The odd thing is, I passed him (about 1500 ft above) and landed about 10 minutes prior. Unless I am missing something, it seems there is a discrepancy between how fast I was going and how soon I got to L65. Our flight paths did not differ significantly, and he was flying faster than me most of the time. I'm not sure how it is possible for me to arrive first.

I use FSX on a Windows 7 machine. The sim was lagging pretty badly, probably because my REX settings have changed and I was getting into the clouds. That may have something to do with it. I was also higher and had a 15 knot tail wind but PEaware reports ground speed so I don't thing that made the difference.

Any ideas what is going on here?
Reece Heinlein, PPL - IR, KMZZ
PilotEdge I-11
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kullery
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Re: Flight distance/time discrepancy?

Post by kullery »

I am just guessing but take a look at this link (http://www.x-plane.com/?article=the-sim ... me-is-slow). If N201NP was running at a low frame rate, they could in fact be passed by a "slower" plane. I assume that the PE data is recorded based on what they are being told......they don't independently calculate ground speed. So they are being told that the Bravo was flying at 150-160kts and the pilot might think he was but compared to "real time" he might have only been flying 110-120.

I see this effect if I fly more complicated aircraft (I fly using a relatively "weak" laptop) or spend too much time looking at detailed scenery. The frame rate slows down and the flight takes longer then it logically should. I have a Beech Staggerwing that I would love to fly more but it kills the frame rate and takes forever to get anywhere.
Ken Ullery - PPL-SEL, 1G5
Pieces
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Re: Flight distance/time discrepancy?

Post by Pieces »

That makes sense, though my sim was running quite slowly as well. Maybe FSX has a way to correct for a slower simulation rate?

FSX reported 1.4 hours in its internal logbook for that flight, and PEaware has 1.35 hours. I did take me about 3 minutes to connect to PE, so they are reporting the same amount of real time.

Some off the cuff calculations: Assuming Jeff is running Xplane and the time expansion is linear below 20 fps, he would have to be running about 13 fps to have his ~38 minute flight take the 58 minutes reported to PEaware. Seems reasonable.
Reece Heinlein, PPL - IR, KMZZ
PilotEdge I-11
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Jeff N
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Re: Flight distance/time discrepancy?

Post by Jeff N »

I never thought about frame rates effecting time in the sim. Could've been the case; I was running lower FPS than usual due to having a few applications still open when I launched X Plane. I was rushed in general - late start, trying to plan a flight under the lowish ceilings without busting KBUR's surface Charlie, hand flying a tempermental Mooney while flipping back and forth from XPlane and Sky Vector... Not my best flight ever.
Tim Krajcar
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Re: Flight distance/time discrepancy?

Post by Tim Krajcar »

Hi guys,

I'm pretty sure you're correct about PE just taking the ground speed reported from the sim. Frame rate can absolutely influence that, as well as pausing the sim, etc.

One cool thing I noticed about X-Plane 10, vs 9 anyway, is that there is both an 'actual frame rate' and a 'simulator frame rate'. It appears that the flight modeling has been fully decoupled from the visual system, which allows for the actual sim to keep chugging along at 19 Hz (not really "frames" per second since it's not drawing frames!) even if the visuals lag further. Seems like a great idea and I'm guessing if everybody had been on XP10 you wouldn't have seen the issue :)
Tim Krajcar
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kullery
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Location: Medina, OH

Re: Flight distance/time discrepancy?

Post by kullery »

I'm guessing if everybody had been on XP10 you wouldn't have seen the issue
Hey Tim,

Not sure I agree with that conclusion about X-plane 10. I think it is MORE likely to occur with X-plane 10.

I am running X-plane beta 10.20b11 (32-bit). I just ran a test flying a Beech Staggerwing. I can never get this plane above 20fps and for most of this test I was getting 12-15fps. I ran a 10 nm route as determined by a measured course on Foreflight. I timed the 10 NM leg at 4 min 29 seconds in real time. That works out to a groundspeed of 133kts. During the entire run, both indicated airspeed and indicated ground speed on Foreflight were 205kts (I assume this is what would have been reported in PE).

I believe that by decoupling the flight modeling from the visual system, when resources get low, X-plane is favoring keeping the flight dynamics accurate, even at the expense of flying in real time. So if my crappy laptop were to race Keith's new system in identical complex aircraft in a heavy scenery area, he would arrive well ahead of me, but PE would show us both traveling at the same speed......I would just take longer to get there!!!

This messes up any chance for doing good ded reckoning if the frame rate is below 20fps. It would be nice if the onboard clock would correspondingly slow down but it doesn't (I checked).

It's enough to make Einstein rethink his theory of relativity :)
Ken Ullery - PPL-SEL, 1G5
Ryan B
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Re: Flight distance/time discrepancy?

Post by Ryan B »

It's possible the Mooney paused his sim at some point...
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Jeff N
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Re: Flight distance/time discrepancy?

Post by Jeff N »

Nope, I didn't pause - it was definitely due to low frame rate. I've since turned down my rendering settings in X-Plane and notice that the duration of my flights actually match my flight plans now.

Amazing.

I guess I just kept turning the settings up gradually, one by one, and didn't realize HOW slow things had gotten. Kinda like the frog in boiling water thing...
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