It says the exact same thing I have already posted but from another textbook. I would steer clear of most internet sites. There is quite a bit of flaky information on most of them.we need a reliable source of information.
John Denker's site is one of the better ones on the net.
http://www.av8n.com/how/#contents
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http://www.allstar.fiu.edu/aero/airflylvl3.htmAnother common phenomenon that is misunderstood is that of ground effect. That is the increased efficiency of a wing when flying within a wing length of the ground. A low-wing airplane will experience a reduction in drag by 50% just before it touches down. There is a great deal of confusion about ground effect. Many pilots (and the FAA VFR Exam-O-Gram No. 47) mistakenly believe that ground effect is the result of air being compressed between the wing and the ground.
To understand ground effect it is necessary to have an understanding of upwash. For the pressures involved in low speed flight, air is considered to be non-compressible. When the air is accelerated over the top of the wing and down, it must be replaced. So some air must shift around the wing (below and forward, and then up) to compensate, similar to the flow of water around a canoe paddle when rowing. This is the cause of upwash.
As stated earlier, upwash is accelerating air in the wrong direction for lift. Thus a greater amount of downwash is necessary to compensate for the upwash as well as to provide the necessary lift. Thus more work is done and more power required. Near the ground the upwash is reduced because the ground inhibits the circulation of the air under the wing. So less downwash is necessary to provide the lift. The angle of attack is reduced and so is the induced power, making the wing more efficient.
Earlier, we estimated that a Cessna 172 flying at 110 knots must divert about 2.5 ton/sec to provide lift. In our calculations we neglected the upwash. From the magnitude of ground effect, it is clear that the amount of air diverted is probably more like 5 ton/sec.
GE is more like the effect of a tailwind than any silly notion of "more lift" being created.
If you held a constant angle of attack and airspeed additional lift is never created. The wing can generate more energy and that energy is what changes the rate of descent.
If you held a constant rate of descent, then the energy is what changes the velocity. Lift force remains constant.
The only thing that changes lift force is another force. Dynamic pressure is the same in GE as it is out of GE.
This goes back to my questions to M_Gunz:
http://forums.ubi.com/eve/foru...111012558#3111012558Let's talk about our lift force picture in a climb or descent compared to level flight. This is key to understanding ground effect.
Do we require more lift force in a climb or less left force compared to level flight?
How about a descent? Does our wing need to generate more lift force to descend compared to level flight or less?
Answer these questions correctly and the lack of understanding in the following quote becomes obvious:
Thanks for that, Kettenhunde. Very useful.
I've done a bit more experimenting, and confirmed that in the sort of situation I described - holding a constant pitch angle of +6 degrees at 50% or so throttle, the Ju-88 tends to follow the terrain hight, rather than sea level altitude, though obviously it will only climb relatively slowly, so this will be of little use in mountain avoidance! I'd hope to gather some data for a graph demonstrating this, but my AP threw one of its periodic hissy fits and cut out at the critical moment.
I'll probably have another go at this later, and will report back...
I think the answer to that has to provisionally at least to be no - it seems to model the drag reduction due to ground effect, and the change in CL, but these are evident at much greater heights above ground than I'd expect. From my measurements, at highish AoA (no way to determine the angle actually modelled, since I don't know the angle of incidence relative to the aircraft datum) there is strong evidence for ground effect at 70m, with an aircraft with a 20m wingspan. I'd almost suggest that there was a misplaced decimal point involved, though there may be more to it than that. Perhaps Team Daedalos can be asked to look into this for a later patch, but for now at least I've shown that IL-2 can model it, and that its presence can be verified. I should probably do some testing with other aircraft types, to see if that throws any further light on what is going on. Meanwhile, I've learned a little more about aerodynamics......if your game exhibits the correct effects
That should read convert and not generate. That is how gliders work, btw.The wing can generate more energy and that energy is what changes the rate of descent.
Will your game airplane hold altitude out of ground effect at those settings?I've done a bit more experimenting, and confirmed that in the sort of situation I described - holding a constant pitch angle of +6 degrees at 50% or so throttle, the Ju-88 tends to follow the terrain hight, rather than sea level altitude, though obviously it will only climb relatively slowly, so this will be of little use in mountain avoidance! I'd hope to gather some data for a graph demonstrating this, but my AP threw one of its periodic hissy fits and cut out at the critical moment
A good question. If it does, then something is clearly wrong, though I'd have thought I'd have noticed it if it did. As a said in my last post, the effect seems to occur at a greater height off the ground than I'd expect, but I haven't as yet tested enough to see how much it varies - I'll look into this. It may not be that easy to actually measure though, because as the aircraft moves further out of ground effect, the changed flight characteristics diminish, and finding the 'level flight' altitude for a given throttle setting becomes harder (and less meaningful in any real world context too - I'm effectively testing with a constant-mass aircraft - no fuel burn - which is a little unrealistic).Will your game airplane hold altitude out of ground effect at those settings?
Originally posted by Kettenhunde:
<BLOCKQUOTE class="ip-ubbcode-quote"><div class="ip-ubbcode-quote-title">quote:</div><div class="ip-ubbcode-quote-content">M_Gunz says:
If you increase power to a plane in flight, it will climb.
Exactly!
Let's talk about our lift force picture in a climb or descent compared to level flight. This is key to understanding ground effect.
Do we require more lift force in a climb or less left force compared to level flight? </div></BLOCKQUOTE>
Actually it is less lift in a -steady- climb of descent when the vectors are shown, but more drag. The rise of the
plane is a matter of power, not lift at all as long as it is steady. Nose up tilts the lift vector back, it is thrust that
raises the plane and lift actually decreases as the path no longer crosses gravity at 90 degrees ++ in a steady climb or
descent ++. However it did take me seeing diagrams and a few re-reads to understand that and I don't show them here. For
one, I don't know where those sites are now that I went to back before 2000.
What most people do is add power then keep pushing the nose down to gain speed but if you don't then you just climb.
You're not going faster. You're not getting more lift. ** The climb is about power alone. **
Throttle controls height, pitch controls speed as long as you stay on the front side of the power curve. Back side of the
power curve.. uh-uh.
Very good again, also a good confirmation that your testing setup works, a 2m variance is good. Thanks for posting these. This confirms both drag and lift change.Originally posted by AndyJWest:
50.0% throttle, level flight at 69m, groundspeed 240 Km/h, indicated airspeed 230 Km/h
47.3% throttle, level flight at 20m, groundspeed 233 Km/h, indicated airspeed 224 Km/h
44.0% throttle, level flight at 3m, groundspeed 222 Km/h, indicated airspeed 213 Km/h
Groundspeed is from 'wonder woman view' instrument, IAS is from DeviceLink.
Regarding the difference between ground speed and indicated air speed, the indicated air speed is off. On our so called "standard atmosphere" map, I'm using a cubic correction formula to get a good relation between indicated and total air speed over altitude. At sea level, my factor is 1.04. It is my impression that the IAS isn't even the one determining the flight physics, if you test the cl/AoA relation you can get the programmed number fairly accurately if you use TAS for EAS at sea level, but IAS is off.
Your findings with w&t off contradict mine, that's something that should be looked into.
Interesting info on the terrain!
I don't consider the w&t effect the ground effect because it goes up that high. That's why I recommended you to switch it off early on. But then you might be right that it is supposed to be it, or part of it, but just goes up too high. It's also not depending on wingspan.
Thanks for taking the time to do this testing!