Landing deceleration - help me with product design

[OrryFace]

Hi clever chaps,
No, I'm not a driver but I have had a long career in encouraging freight to self load (otherwise known as passenger marketing).

I need some help with understanding the physics of take-off and landing in order to develop a component switch which would use either an accelerometer or air pressure sensor to automatically detect the status of the aircraft.

So my questions are -
a) is there an absolute minimum acceleration below which a commercial aircraft cannot physically take-off...and an absolute minimum deceleration once the wheels hit the tarmac ?

b) likewise with cabin air pressure. Or are these modern aircraft so sophisticated that some can land and take-off with inperceptible air pressure change?

thanks,

OF

[error_401]

Hmm - I'll give it a try not too sure what the aim of the questions is.

The status of the aircraft is actually important and monitored by "several" other means or switches. These also influence e.g. the cabin pressurization in order to equalize the cabin pressure upon landing etc.

coming back to the exact questions:
a) is there an absolute minimum acceleration below which a commercial aircraft cannot physically take-off...and an absolute minimum deceleration once the wheels hit the tarmac ?

theoretically NO - you could do with sub threshold accelerations (not perceivable by humans) given the runway is long enough.

No joke: Basically you need to accelerate to take-off speed within the distance available taking into account some limitations such as to be able to stop before runway end or take off safely when e.g. loosing an engine. Maybe a minimum acceleration could be determined but you would still not know if it is flying or not ;)




b) likewise with cabin air pressure. Or are these modern aircraft so sophisticated that some can land and take-off with imperceptible air pressure change.


Hmm - some might. Others not. Again all depends on the flight and equipment. To determine a flight status IMHO not a good way as the cabin pressure needs to do some special things exactly during take-off and landing.

Hope my 5 cents help clarify.

[barstow]

You're confusing the issue talking about acceleration. The minimum acceleration required is a function of the aircraft's V2, and runway length.

On landing, the minimum deceleration is also a function of groundspeed at touchdown and remaining runway length.

Perception of air pressure differential is a widely variable individual difference, generally influenced by the equalisation abilities of the inner ear.

All in all it's a confusing question, since it's not clear exactly what you are trying to acheive. :confused:

[Tinstaafl]

What do you need to determine? What is it that needs be activated and under what conditions? There may well be other sensors already installed on the aircraft.

If you want your device to remain independent of the aircraft's systems why not use a GPS sensor to determine speed? Set a reasonable speed that will be a bit below the minimum rotate & landing speeds of whatever range of aircraft types you're considering. Single chip GPS receivers are easy to get & not hugely expensive.

[Mad (Flt) Scientist]

I need some help with understanding the physics of take-off and landing in order to develop a component switch which would use either an accelerometer or air pressure sensor to automatically detect the status of the aircraft.

What "status"?

In-Air/On-Ground?

Configured for takeoff? Taking Off? Completed Takeoff? About to Land? Landing? Landed?

There are already various aircraft systems which use various of these conditions - config warnings, EGPWS, Ground Spoilers, and so on.

If you tell us what exactly you want, it may be there's already a clever bit of logic on the plane doing it for you.

[dkaarma]

I need some help with understanding the physics of take-off and landing in order to develop a component switch which would use either an accelerometer or air pressure sensor to automatically detect the status of the aircraft.

So you want to make a self contained portable device that tells a passenger when the plane takes off and lands?

[OrryFace]

Ok, to be more clear, I am looking at a personal electronic device that would automatically switch itself into 'flightsafe mode' (for example switching off the GSM signal on a mobile phone) if the passenger forgot to do so. Therefore it has to be clever enough to realise the aircraft is taking off, and then switch back to normal mode once it senses the deceleration of landing.
From what I've read so far, the vagaries of different aircraft and approaches would mean there would not be a foolproof way of doing this based on either pressure or acceleration.

[All-Ex]

I don't think it will work with measuring acceleration:
What if that device is used in a car accelerating quickly to 120+ knots - no problem at night on german autobahns (at least for porsche drivers) ;)

Customers wouldn't want their phone switched OFF then... Same with braking, cars can do that a lot better than planes.

[OrryFace]

Don't worry about the Porshce, this actual device will only be used when travelling:)

[Parahelio]

Hello



I don’t like the idea of pax or cargo having electronic devises that determine when a plane is airborne or to be able to count the number of stopovers / takeoffs before :mad:

[bfisk]

Furthermore, mobile phones shall be switched off/in flight mode from the time the doors are closed to the time they are open. Ie sensing the takeoff roll might be a tad late...

[deltahotel]

Base it on GPS. Pick a speed to switch off that's so fast you must be airborne, switch on again so slow you must have landed or crashed. eg 150 and 60, but other speed ranges would do nicely.

[welliewanger]

Detecting lateral speed could be misleading for the device. As other posters have said, many cars will accelerate / decelerate faster than an aircraft.

1. A threshold speed could be used. Cars sold in Europe are limited to 155mph (unless a geek has plugged his laptop into it and tweaked things) Therefore if the device detected a speed higher than this (either by gsm or gps) it could switch off.

2. Alternatively the system could detect a sustained rate of climb. Even a 152 can climb at 500 ft / min whereas there are very few roads which would facilitate this. GPS could detect this with sufficient accuracy (yes, gps can detect altitude. Not accurate enough to fly by, but enough for this). If the climb continued for more than a minute (i.e. takeoff), the device would turn off.

3. The two systems above could be combined with a database of airport locations, so it could only be triggered when the device is at (or near) an airport. This would eliminate spurious activations of flight mode.

Hope that helps.

[boink105]

how would the cellphone be placed? turbulence could turn it on and off with each bounce. insert punchline here:}

[OrryFace]

WW,
Helpful, but there is a problem with basing the device on GPS. If passenger is sitting in middle row there is unlikely to be any signal detection.
That's why I have concentrated on acceleration or pressure, both attributes that do not require line of sight.
Those little sensor devices in vending machines and fruit machines that detect vibration and shut off if someone kicks or rocks the thing are probably best for the job.
OF

[welliewanger]

Orry, I appreciate your conundrum.
Unfortunately, the devices used in vending machines are generally tilt/mercury switches, which aren't versatile enough for this application.
Mercury switch - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Mercury_switch)
Small, low powered accelerometers could be used (cheap versions of what's in an IRS), although I'm not sure of their availability, size, price or power consumption.

Thinking out of the box, how about something that detects transceiver squawk.
Transponder (aviation) - Wikipedia, the free encyclopedia (http://en.wikipedia.org/wiki/Squawk_code)
Very few aircraft don't carry these devices. They're pretty much mandatory in anything used commercially. Aircraft only squawk "mode A" or "mode C" when airborne, so the device could work like this:
- Can I detect a squawk (am I near an aircraft)
- Can I detect the same squawk a minute later (am I near the same aircraft, or is this a different one and I'm therefore just parked near a runway)
- How strong is the signal (is it the same aircraft, but it's just flying around above my house)

[80sman]

If the device is only going to be used while travelling? I'm guessing this is only while travelling aboard aircraft, then why not use noise detection, background noise above certain 'x' Db and 'x' frequency range = the engines are running.

Seem's the simplist way to me.

[dkz]

Will your device make a nice "ticking" sound ? I see a lot of guys eager to help without asking the kind of device needed, if i get a new id with a nice arabic name, would you help me build a device that only activates upon takeoff ?

[Capt Pit Bull]

Accelerometers are a no hoper. As is any gps based method given the signal reception issue. tbh I really can't think of any foolproof passive method.

Best from a technological point of view would be an active system. e.g., off the top of my head, maybe a low power inhibition signal in the cabin, or a 'turn off' signal in the airbridge, coupled with a 'turn on' signal during offloading. But even then you'd have to give the device a manual override, for emergencies or company mobiles or just to make sure a device didn't end up disabled by accident. So people would override it anyway. So you might as well not bother (because you'd need worldwide cooperation by airports and carriers).

[Checkboard]

Forget acceleration, forget speed etc. You want a pressure sensor to detect a rate of climb of around 400 feet per minute or more to detect the "take-off", and an absolute pressure around 1500 to 2000 feet above sea level, and a zero rate of descent, with say a twenty minute timer after those configurations for the landing. It would be better, in fact, not to bother detecting the landing - but to make this an "auto off - manual on" device as the cabin pressure on descent can level off quite some time before the actual landing in pressurised aircraft (depending on holding etc.)

The technology is small, easily packaged (many watches and phones already have barometric sensors), and if you want a separate device you can look at parachute automatic deployment safety sensors,

About CYPRES (http://www.cypres-usa.com/faltblau.htm)

http://www.cypres-usa.com/cntrl05a.gif

[BryceM]

Yes, an air pressure sensor's the way to do it at low cost and with reasonable reliability. You won't be able to guarantee that it turns off as the a/c leaves the tarmac, though (could be some minutes delay) or when it lands (all sorts of reasons why there might not be significant pressure changes at that point). You'll need to detect the descent from cruise and assume that the plane has landed (say) an hour after that.

Obviously, GPS won't work for anything inside the cabin. Accelerometers could be used to assist the pressure sensor to give a better estimate of the current status (air or ground). But it would get reasonably complicated quite quickly if you wanted to be sure of turning your device on/off within seconds of takeoff/landing.

The accelerations during takeoff and landing are extremely variable, and it would be very difficult to design something based only on an accelerometer.

Turning things on (ie after landing?) is usually less of an issue than remembering to turn them off, isn't it? I mean, the user can turn it on, if he's using the device.

Takeoff will generally be easier to detect reliably than landing (always get a gain in altitude of several hundred feet, which the very cheap barometers in e.g. Polar heart rate monitors will detect very repeatably).

[mathy]

Am I being silly here? What is the air pressure inside the cabin of a typical pressurised passenger transport flying at a Pressure Altitude of 35,000ft.

Please select your answer from the options below:

a) It's 35000ft you plonker, you just said so!
b) Oh no it isn't because you don't know barometric altitude!
c) Are we talking Airbus or Boeing here because it all depends!
d) Would it be about 5000ft perhaps? I mean roughly.
e) This could never happen in a TriStar
f) This could never happen in a B777
g) Couldn't happen in an Airbus they can't accelerate, far less climb.
h) Can't happen in a B787, they can't even take-off.
i) It all depends on Mach No because it just does.
j) None of the above.

I think you want something that detects an acceleration of about 7 ft/sec/sec for about 45 secs then the rumble stops; the pressure moves towards about 5000ft then stabilises provided they've remembered to click a few switches up front; it can detect a few "ding-dong" chimes inside the next 20 mins; then detect the sound of 150 seat belts unclicking etc. And then it turns the phone off.

Sorry. I must be missing something vital here. Acceleration, pressure, flying. Oh no...., it's a wind up. Well done!

[Wizofoz]

mathy,

The typical cabin altitude of a jet in cruise is 8000', not 5000'.

This and other things in your post indicate you don't know what you're talking about, so perhaps accusing others of a wind-up might be a case of fighting above your weight....

Furthermore, mobile phones shall be switched off/in flight mode from the time the doors are closed to the time they are open. Ie sensing the takeoff roll might be a tad late...

Not under everyones Regs. Under ours it's push-back till the on board system is switched on, then TOD till touch-down. Not everyone has the same rules.

[mathy]

None of the above?

I must be in a wicked mood today.

[NSEU]

The typical cabin altitude of a jet in cruise is 8000', not 5000'.


How would this device handle atypical aircraft? (e.g. 787, with a cabin altitude of 6000')

Having all electronic devices switched off for takeoff and landing kind of limits the design/creation of a product designed to continuously monitor the environment and automatically switch off another electronic device.

Having a device to switch off a mobile phone in a Porsche travelling at 155mph down an autobahn wouldn't be a bad thing, either :ok:

Rgds.
NSEU

[flash2002]

Useless piece of equipment if you ask me.
And btw the phone needs to be OFF for takeoff and landing, and maybe used in flightsafe mode in other flightphases!
So how is your device going to get powered if it needs to be OFF.

Some airlines have modified their aircraft so phones can be used, in that case there is no need to use flightsafe mode.

Hope your device won't make a ticking sound!!!!:}

[Capt Pit Bull]

btw forget about detecting cabin altitude as well. Some pressurisation controllers, for shorter / lower sectors, may not even leave sea level.