HANDS-OFF LANDING

[mgh 89]

Two points:1 - Of course is was the autopilot raising the nose and reducing the rate of descent. My posts were aimed at finding out why it did it. I believe is the way FS deals with the offset of the glide slope transmitter. Is the circled item in the picture FS's representation of this transmitter? I can assure you that in FS 2004 the stock C172 does bounce under the following conditions because I've replicated it several times to be sure:Autopilot approach mode engagedno windfull flap1900 rpm350-400 ft/min rate of descent68kt IAS Disengage the autopilot at 100ft above the runway. The rate of descent falls at about 25 ft to about 200 ft/min at touch down. Tyre squeal is heard, the aircraft bounces to between 2.5 and 3.5 ft above the runway, then touches down with a another squeal about 5 sec later. The height is easy to check because height of the stock C172 at Gatwick is 200 ft.http://forums.avsim.net/user_files/109591.jpg

[Guest enave]

I do that all the time. It's my dream to one day have flight sim so automated that, after I leave for work in the morning:The computer will turn itself on and boot up. It will load flight sim and create a flight.The aircraft will start up and taxi to the runway.It will request clearance and take off.It will fly to the destination airport and line up on the runway.It will land and taxi to parking.Flight sim will exit and the computer will turn itself off.That's my dream. That's what I want to see in fs10 or I'm not going to buy it.

[Guest av84fun]

<>With genuine respect, the only thing that you can assure anyone of is how the 172 reacts on your rig.On mine, and on every one I have ever had...at least 6 in my simming career...the behavior of the 172 and most other aircraft is as I described, not as you have described.Possibly, the good folks at RealAir (whose add-ons I have bragged about incessently) will chime in there because they have an IMPROVED add-on for the 172.If they say that their model behaves like you describe the default 172 and not as I describe it, then I will purchase that add-on to add to my other RA models....but they won't say so because it doesn't behave as your suggest is the case on your rig.And FYI, I too have REPEATEDLY tested the default 172 and numerous other aircraft and FEW bounce AT ALL and FEWER STILL float in ground effect to any realistic degree, when attempts to land at excessive airspeeds are conducted...at least no float anywhere near ITRW.I just flew the 172 AGAIN as follows:70 kts400 fpm ALL THE WAY TO TOUCHDOWN1850 rpmflaps 20Result?Chirp and stick...NO BOUNCE...confirmed by pausing the sim a couple seconds after the chirp and cycling to a side on spot plane view and both the nose tire and mains were ON the runway and when unpausing the sim, they STAYED on the runway. ZERO bounce.Then I did exactly the same thing with the SUPER GREAT RealAir SF260 and not suprisingly given their state-of-the-art modeling...I DID get bounce...once...to an altitude of about ONE FOOT...and DID float...maybe 75 feet.The only difference in the approach stats is that I flew at 80 kts and landing flaps as is normal.CONGRATULATIONS to RealAir for even ATTEMPTING to model the real world...most aircraft are not modeled for realistic landing at all...such as the default 172...in MY experience.I have no explanation for why your experience in the default 172 is so different from my. I wouldn't think than flight models would be very computer-specific but apparantly they are.But you might want to try one more time and be SURE that you maintain 400fpm all the way to runway impact (I intentionally avoided the word "landing"). I did notice that within about 100 ft agl, the default 172's rate of descent did start to diminish. Possibly that was FS9's attempt to SUGGEST ground effect...only it doesn't occur anywhere near that altitude.But just try using forward pressure to make sure that you IMPACT at 400 fpm HANDS OFF. By the way, your bounce experience of 2.5-3.5 feet after impact at 200 fpm would be WAY not as much as you would get ITRW. 200 fpm is 3.3 feet PER SECOND so you would descend from the height of the top of a pro basketball player's head to the runway in this much time.ONE THOUSAND ONE, ONE THOUSAND TWO.....And would therefore SLAM onto the runway and bounce very nearly back to 6+ feet...assuming you didn't just collapse the nose gear and/or wheelbarrow into the weeds.A good landing is accomplished at maybe 6.6 INCHES per second...not feet!As I stated before, I have no doubts that you experience what you experience...just as I have no doubts about my experiences.Regards,Jim

[Guest av84fun]

PS:<<1 - Of course is was the autopilot raising the nose and reducing the rate of descent. My posts were aimed at finding out why it did it. I believe is the way FS deals with the offset of the glide slope transmitter. Is the circled item in the picture FS's representation of this transmitter?>>Your reference to the glideslope offset issue came after your first few posts which only asked for opinions on why the aircraft leveled off when you inadvertently forgot to disengage the a/p.I just explained it was because the a/p was chasing the glidespope indicator bar as it rose above neutral...which was correct.You are, of course correct that the gs transmitter cannot be placed on the runway but the point is that there is no need to do so and the gs tower's "offset" has nothing to do with the issue as I will explain below. The offset is irrelevant because the signal is not pencil thin like a laser beam but rather is composed of two UHF signals...one broadcast at 90 hz and the other at 150 hz. If your receiver is getting equal amounts of those two signals, then you are on the glideslope. If you are receiving more 90 hz than 150 hz, then the needle will be below neutral which, of course, means you are too high and vice versa. That is why a coupled approach will track the glideslope downward even if you are not yet established on the localizer.Due to certification issues, the height of the tower causes the two signals to cease being equal at roughly the MAP....rougly 200 ft. agl(for Cat I at least) So, one way to determine that you are inside the MAP...although quite a dangerous one...is an inability to keep the needle from rising.One "old salt" instructor of mine gave me this "live or die" formula for deciding when to flare in zero/zero conditions.A descent rate of 400 fpm = 6.6 feet per second. Therfore, at that rate, you would descend the 200 ft. from the MAP in 15 seconds. So, once the MAP is crossed you A)Count off 13 seconds:( Flare outC)Pray out loud!I hope this helps.Regars,Jim

[Rottenlungs 0]

AbsolutelyI was amazed at how the Pa-38 had the ability to just 'stop flying' when it was slow enough. Whilst dual I discovered what the tiedown ring on the tail is really for - the last ditch attempt by my instructor to soften the impact of my appalling landing managed to scrape the tail. There was no perceivable ground-effect to speak of, and that was a low-wing where the effect should be more pronounced (apparently).CheersLungs

[mgh 89]

JimI have flown and reflown the approach and I still get the bounce I am reporting. The rate of descent begins to reduce at about 20-25 ft, falling to 200 ft/min at touchdown: the tyres squeal, the aircraft bounces to between 2.5 and 3.5 ft (it varies); the VSI shows a small positive indication followed by a negative one: there is another type squeal and the aircraft final settles on the runway.As far as the height of the bounce is concerened, I never claimed it was was realistic - I'm just reporting what I found.I'm using a standard Dell 2350 (2Mz Celeron, 512Mb ram and Intel Integrated Graphics) so its very low end. Your explanation about the glide slope transmitter is correct for the real world but probably irrelevant. I was attempting to explain the effect in FS, not the real world. I'd be surprised if FS models it with two frequencies. I suspect it's modelled based on distance and glide slope angle.

[Guest av84fun]

<>I didn't say that you claimed it was realistic. I just assumed you were searching for knowledge and have been trying to provide it to you.<>Actually, you started by asking for explanations not providing them and then you attempted to explain the effect ITRW (the tower offset theory) which was incorrect.<>Of course not. I am sure that FS doesn't broadcast UHF signals nor do our computers have UHF receivers.<>That would be correct...so when you fly below a given altitude/distance coordinate, the glideslope bar rises and the a/p chases it, which is why the airplane attempts to level off which was you question in the first place.Just as a reminder, this was your first post. "was making an ILS approach to 08R at Gatwick (EGKK) in the stock C172 with the autopilot engaged and approach selected. I forgot to switch the autopilot off (distracted by the cat!) and the aircraft flared out and made a perfect landing - practically zero vertical speed at touch down.I flew it a few more times and noticed that just before touchdown the glide slope needle rose almost to the top just before the signal was lost. That must have been enough to cause a near perfect flare out.I guess this effect must be very dependent on aircraft type and the location if the ILS?"The opposite of your comment in your last post you earlier wrote:"The glide slope transmitter is modelled as being offset from the centre of the runway to reflect real-life: you can't have a transmitter sitting on the touchdown area for obvious reasons. This means that the distance from the aircraft to the glide slope transmitter can never be zero - its minimum value is the offset.""So, you did suggest that FS modeled the glideslope in relation to its offset from the runway which is neither correct in FS9 nor real life.I'm not trying to beat up on you here. You asked for information and I have tried to provide it.Again, I have no idea why your 172 bounces with a 200 fpm descent rate when mine does not with a 400 fpm rate but so be it.But let me assure you that ITRW, if you dropped it on from 3 feet, after your first bounce, you would get to choose which of SEVERAL subsequent "landings" you liked the best.Regards,Jim

[mgh 89]

JimI'm only concerned with how FS works. Yes I did suggest that FS modelled its glide slope in relation to its offset because the transmitter is offset - I checked Gatwick using AFCAD. This offset can account for the reason the FS ILS thinks the aircraft is dropping beneath the glide slope as I proposed in an earlier post. If that isn't the reason, could you tell me what is?

[Guest av84fun]

<Well, I already have but in the spirit of these forums to help others with their questions, I will do so again...briefly...while referring you to my earlier posts.The offset has nothing at all to do with the signal that the aircraft's radios receive.The gs tower broadcasts radio signals in the UHF frequency band...just like your favorite radio stations broadcast their radio signals...albeit on different frequencies.Just as your car radio doesn't care where the radio station's antenna is (except for line of sight issues)neither do the aircraft's radio receivers care where the gs tower is placed.As you noted, it is only offset from the runway to hold insurance costs down...not for any reason related to the glideslope's functionality.As long as the aircraft's radio receivers are in range of the signals...and the aircraft does not have to be very near to the localizer course to be in range of the glideslope signal...then the needle will react up or down in relation to the proportional strength of the 90kz and 150ks signals being broadcast from the gs tower.As far as I can recall AND I MAY BE INCORRECT ON THIS POINT...I do not believe that the gs signals are broadcast out 360 degrees like a music radio station...but only outward "LOOKING AT" the ILS approach course. In other words, I don't think you can receive the fs signals from the OPPOSITE side of the ILS approach course...but you can get those signals in a WIDE arc while on the proper side of the approach course.Hope this clears it up for you.Regards,Jim

[mgh 89]

JimYou seem to be incapable of distinguishing between FS and real life. I took care in my posts to refer to FS ILS.Although you said in a previous post "Of course not. I am sure that FS doesn't broadcast UHF signals nor do our computers have UHF receivers", you have gone back to your explanation about the way FS ILS works on the real life radio signals.I moved the Gatwick ILS transmitter onto the runway and flew the same flight onto the runway with approach mode engaged in the autopilot. The glide slope needle DROPPED to the lower limit before disengaging whereas with the transmiter offset it ROSE to the upper limit.I think this proves beyond doubt the the offset does have an effect on FS.I'm always prepared to engage in rational discussion but this is my last reply.

[Guest av84fun]

THE IMPUDENCE OF YOUR JUST PROVES THAT NO GOOD DEED GOES UNPUNISHED.With respect to the differences between simming and real life YOU are the one who merged those two matters when you wrote:"The glide slope transmitter is modelled as being offset from the centre of the runway to reflect real-life: you can't have a transmitter sitting on the touchdown area for obvious reasons. This means that the distance from the aircraft to the glide slope transmitter can never be zero - its minimum value is the offset."OBVIOUSLY you didn't understand the dynamics of glidesplope functionality ITRW and I was just trying to help you understand that. Most simmers are QUITE interested in increaseing their knowledge of RW aviation subject.I would also remind you that A) there were two lines of discussion in this thread...gs modeling and ground effect and :( there were several other posters other than you to whom my posts were, in part, directed.FINALLY, in spite of your swipe about my being so delusional as to be unable to distinguish between simming and reality, try to brush up on your reading comprehension skills and you will see that I SPECIFICALLY commented on gs behavior in BOTH worlds. See below.____________________________________________________________________ Actually, you started by asking for explanations not providing them and then you attempted to explain the effect ITRW (the tower offset theory) which was incorrect.<>Of course not. I am sure that FS doesn't broadcast UHF signals nor do our computers have UHF receivers.<>That would be correct...so when you fly below a given altitude/distance coordinate, the glideslope bar rises and the a/p chases it, which is why the airplane attempts to level off which was you question in the first place.____________________________________________________________________With respect to exactly how FS models the glideslope, I am not a computer programmer and didn't pretend to be. So I have no clue what code is involved in simulating the glideslope.Of course, the tower is modeled to be off the runway as is the case in real life...for obvious reasons. But you didn't inquire about FS9's code in your initial post, you just asked why the gs bar rose when you neared the ruwway when you wrote:<ONE, aircraft TYPE has ZERO to do with glideslope behavior in the sim or ITRW and B)the "ILS" isn't located ANYWHERE since it is not a physical object. TWO, the "ILS" is a SYSTEM comprised of localizer and glidslope devices as well as outer and middle marker devices etc.I will join you in ending my contributions to this thread.Regards,Jim