Landing gear extension time

[Echo38]

This manual here:

 

http://www.scribd.com/doc/34811808/North-American-P-51-Mustang-Pilot-Training-Manual

 

... says (on page 17) that lowering the gear should take 10 to 15 seconds. But I'm continually noticing that in DCS, it takes much less. I just timed it with a stopwatch at 4 seconds. What's the reason for the discrepancy?

Edited May 20, 2015 by Echo38

[Random]

Found a video on youtube of a P51 having its gear tested at duxford

 

[YOUTUBE]jtVQRCA0[/YOUTUBE]

 

Obviously there's no slipstream loads on the gear so it's probably slower when in the air but still it's a start! Need to find some of the gear coming down in flight now! But the problem there is you won't be able to tell when the process is started by the pilot. Just how long it takes for the actual gear to deply.

[Ala13_ManOWar]

It's plenty of videos on the subject out there. Every of them gear retracts in quite different times.

 

9 seconds fold, 6 seconds unfold,

 

18 seconds fold,

 

6 seconds fold,

 

 

Anyway, that's all ground testing. Looks like that external hydraulic pressure used to test makes a difference.

 

S!

 

Edit: don't know why youtube vids doesn't work for me now, but you can get them directly there.

Edited May 23, 2015 by Ala13_ManOWar

[Echo38]

Is it possible that the gear retraction/extension system has been modernized in some of the replicas, with the result that they raise & lower more quickly?

[Ala13_ManOWar]

Don't know, but looks like Duxford Ferocious Frankie, very quick, is just using a high hydraulic pressure machine, more than other videos. The thing is, how much different is internal hydraulic pressure? If internal pressure is higher can be even faster, or if lower time should be longer. I guess system itself haven't major changes, don't think so. Anyway, Duxford Ferocious is an original P-51 I think.

 

S!

[Echo38]

Anyway, Duxford Ferocious is an original P-51 I think.

 

Even "original" airplanes tend to be heavily restored and/or modernized. I don't think any of the ones flying are entirely in their original condition. I dunno about this one in particular, but bear the previous in mind.

 

Four seconds still seems awfully far out of the margin. Perhaps whoever wrote that bit in the manual was being sloppy & guessing, the USAAF manuals do contain examples of this. But the sim could also be in error; it happens.

[NineLine]

I'll see if I can look into this over the weekend.

[Art-J]

Just out of curiosity, I've just tested both extraction and retraction in flight with both max and min RPM settings, to get different hydraulic pressures and see if they would affect the operation in any way. That didn't seem to be that case (not that it bothers me all that much).

 

Extraction is much faster indeed, but I can't comment how correct/incorrect that might be.

[NineLine]

I imagine its an animation from 3D Studio, not sure if the speed could be controlled by different pressures, but I can ask that too.

[msalama]

but I can ask that too.

Please do! Kinda nitty-gritty, all this, but good to see the wherefores (if any) still. Salud!

[NineLine]

Yup, I would be interested to know if the FM can control the speed of the gear, you almost think it could/should... so worth asking.

[msalama]

Please report back if/when you get an answer.

[Echo38]

Kinda nitty-gritty, all this

 

With the kind of approaches & landings I do, the time to deploy the gear is important, because I have a narrow window for deploying them (compared to standard low approaches under power), and thus, the longer the deployment time, the greater the difficulty in getting it right. If it's currently wrong by as much as 50% (not yet determined), then it's making my dead-stick approaches significantly easier than they should be--by making it half as difficult to make my airspeed/time window as it would be IRL.

 

I suppose if one only does normal, at-power approaches, then this might seem like a nit-picky issue, but the apparent error is large in factor and has a very noticeable effect on my touch & goes. At any rate, a 50% error (if it exists) in a high-fidelity sim must be corrected, regardless of how little some notice it; acceptable margin of error for a high-fi sim of this sort is generally regarded to be ~10%.

Edited May 23, 2015 by Echo38

[NineLine]

I did this little comparison vid to show the difference, warning I grabbed the first real video I could so dont know if its perfectly accurate or not.

 

 

[msalama]

Huh? Not much difference there it seems.

[Echo38]

50% more isn't a big difference? If we were talking about airspeed instead of gear time, that'd be the difference between 300 MPH and 200 MPH. Granted, we're talking about gear time, and so the difference (in that video) was about two seconds--which, I'll concede, isn't that terribly much--however, that 6-second example was the most optimistic RL example that's been given in this thread so far. If the quickest RL example we could find is still 150% of the time in the sim, that supports my suspicion that the sim is in error.

 

Then, too, it's been noted within this thread that it's possible that these videos are showing extensions which are occurring more quickly than they'd be in the air, because of differences in conditions (such as slipstream, external hydraulic assistance, modernized hydraulics, etc.). Using an outlier (e.g. the fastest) in a sample set, for your reference point, isn't an accurate way of doing things.

 

So, in our "best case scenario," our sim P-51 is still dropping its gear in ~66% of the time that { the fastest RL example we found } is, and ~27–40% of the time that a RL manual suggested it should be. Something doesn't add up. That's a big margin of error in any case--looking at it in the most optimistic way, the margin of error is still twice the normally accepted margins for flight sims. Am I missing anything?

Edited May 24, 2015 by Echo38

[msalama]

the difference (in that video) was about two seconds

 

That's what I meant. Still, if it's wrong it should be fixed, so I'm not disagreeing with you one bit here mind ;)

[NineLine]

It really looks like a simple error in the animation timing. I will talk to Yo-Yo and see if or where they got the source of their animation from, perhaps I am missing something.

[NineLine]

Has anyone found any in flight extension vids? I found this, but very hard to see the travel, but extension seems quite fast here?

 

At about 4m 26s

3flutD3d1UQ?t=4m26s

 

This one has the gear going up:

http://www.dailymail.co.uk/news/article-3027209/Incredible-vertigo-inducing-video-shows-flight-70-year-old-WWII-P-51-Mustang-fighter-jet-painstakingly-pieced-200-parts.html

 

More

 

Some glimpses in here, but not full shots of full travel.

 

More raising...

 

Edited May 25, 2015 by NineLine

[Ala13_ManOWar]

More raising...

I was looking some vids in my phone from that year at Duxford, no need now :lol: .

 

Just a guess but, may be external hydraulic power units are all weaker than internal one? All inflight P-51 you can see raising gear out there are quite fast compared to ground test shots and may be that's the animation time DCS used.

 

S!

[NineLine]

In discussion with Yo-Yo, he assumed that external systems would be the same or less than onboard systems as not to risk any damage, which makes sense to me.

[Echo38]

Curiouser and curiouser, cried Alice. Six seconds seems to be standard, then, in modern restored P-51Ds, at least, judging by this collection of videos. Quite a bit slower than the ~3.9 seconds we have right now in the sim, but much faster than the "10 to 15 seconds" of the manual.

 

Why, then, did that manual give such a large figure? Was the USAAF pilot guessing based on feel & memory, or did the example he flew, perhaps, have weaker hydraulics? Do modern restorations/replicas have stronger hydraulics than wartime examples?

[NineLine]

Are you basing your timing from the lights in the cockpit? The 4 seconds?

[Ala13_ManOWar]

Are you basing your timing from the lights in the cockpit? The 4 seconds?

Going further, how are we all measuring times? I posted times based on legs movement, but if we count also main doors full movement time it's even more, but also main doors time are quite different from vid to vid.

 

S!

[Echo38]

I hit the stopwatch start at the same time as I hit the gear key on my keyboard, and I stopped the stopwatch as soon as the light was green and the noises stopped. You make a good point--I should do external camera instead of relying on the lights & sounds.