Airbus Lover
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Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 1:22 pm

Can an aircraft rotate and climb at a low rate of RoD before reaching Vr? or even a little short of V1? I assume if it can then the plane should not be on MTOW or somewhere near that right?

I remember a Delta B737-300 did that I think it was at DFW to avoid an aicraft which entered the runway and the near collision was around 10 feet apart or sort...

TIA
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 5:48 pm

If you try and rotate before VR then chances are the airplane will still climb. Depends on how much before VR you rotate- let's say VR is 125kts and you rotate at say 122 kts instead then the plane will climb but it's climb will be shallower i believe? There was an accident at LGA involving a US Air F-28 where the captain rotated about 5 kts below VR and the plane failed to become airborne and crashed into Flushing Bay(although ice contamination also played a part).
 
JoakimE
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 6:10 pm

Positive rate: This one?
http://www.airsafe.com/events/models/fokker.htm
17.
22 March 1992; USAir F28-4000; New York, NY: The aircraft crashed just after takeoff due to icing on the aircraft's wings. The aircraft was departing from La Guardia airport under in snowy conditions. Three of the four crew members and 24 of the 47 passengers were killed.
That one?
 
erasmus
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 6:35 pm

Hi,
Take a look at Getting Caught Between V1 And VR?

It gives some more info about Vmu (minimum unstick speed).

Regards,
Erasmus
 
Airbus Lover
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 7:37 pm

I started a new post because I think this is not so much relevant to the other post. I got the idea of this after seeing the other post...

What is mean is say V1 = 140kts, Vr = 145kts and the aicraft say 75% of MTOW rotates at 115kts? if they pilot makes steep climb then the aicraft will stall but what if a vertical speed of 200ft/min is kept?
 
Guest

RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 11:24 pm

As I've thought about the question, it's hit me as being comparable (more or less) to the classic "softfield" takeoff scenario from our initial flight training days. There the goal was to get the weight off of the wheels as soon as possible; i.e., get it flying as soon as possible. This is a maneuver that we all have practiced in our single-engine training airplanes. When we stepped up to multi's we were taught never to go there because of the obvious dangers of being airborne at a speed below Vmca in the event of an engine failure - especially at low altitude.

Just for grins, I went into the Gulfstream 200 flight manual to see what I could come up with. It must be understood that this information is for a Gulfstream G200 and may not be directly comparable to any other make and model of turbine-powered airplane. It may not be too far off though, it has a high wing loading and uses leading edge devices (slats and Krueger flaps) similar to those used by larger airline category aircraft.

In the "normal" takeoff configuration (Slats and Kruegers deployed, trailing edge flaps up) for a max gross weight takeoff, the G200 has a Vmcg of 108 knots and a Vmca of 122 knots. I went to the abnormal procedures checklist and calculated the "emergency return" Vref for the airplane at max gross takeoff weight with the flaps & slats restricted to the takeoff configuration - 178 knots. By definition, Vref is 1.3 times the stalling speed; so in this particular example, the stalling speed would be approximately 137 knots.

Calculating V1 and VR for the G200 for a max weight, sea level, standard conditions, no wind, etc. takeoff, the numbers were 149 and 152 knots respectively.

Would the Gulfstream fly if it was rotated at V1? Yes, since its speed would be approximately 12 knots higher than the stall speed for that particular configuration. You could maybe get it into the air as slow as 137 knots (stall speed) but it would depend on what happened with the tail - you might be dragging it on the ground. Directional control in the event of an engine loss probably wouldn't be an issue either since the Vmca is 122 knots.

Jetguy
 
IMissPiedmont
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sat Jun 15, 2002 11:43 pm

Consider a Twin Otter on a 12000 foot runway on a standard day. V1 is almost as high as Vne. So yes, certain aircraft on certain runways, under certain conditions do take off before V1 on a regular basis. In fact in many cases V1 is greater than V2 even for the big boys.
The day you stop learning is the day you should die.
 
Rick767
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 12:19 am

V1 cannot be greater than Vr.

From JAR-OPS "Take-off Speed Requirements" 25.107:

"V1:

a) may not be less than Vef plus.....

b) must not exceed Vr

c) must not exceed Vmbe

d) must not be less than Vmcg"

On longer runways with the 757/767 V1 is often equal to Vr, but cannot be above it (doesn't make sense). With shorter runways V1 is less than Vr.
I used to love the smell of Jet-A in the morning...
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 1:39 am

Steve,
I think you're confusing some things here. The "Twotter" is a light (under 12,500 lb aircraft) aircraft. It is not certified to the same rules or criteria as the large (12,500 lb +) turbine-powered aircraft that, I assume, we've been talking about.

Part 23 airplanes have no guarantees when it comes to takeoff performance as large turbojet-powered aircraft have. Although some manufacturers publish accelerate/stop and accelerate/go for their light aircraft, these charts really don't pertain to the discussion. (The charts for the large aircraft provide for a certain minimum level of performance, the charts for light aircraft only provide for the aircraft to become airborne.)

When flying light aircraft you have the option of delaying your decision to fly right up until you rotate. (In certain instances, even afterwards - for example, leaving the gear down on a light retractable until there is no more usable runway in front of you.) Although you might assume that in this case "V1" = Vr, this is an entirely different thing - you're trying to compare apples and oranges. Light aircraft have no published V1 speeds. When a pilot of a light aircraft "decides" to fly is not calculated from data.

Jetguy
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 10:08 am

Yeah JoakimE that's the accident i was talking about. I read about it in Air Disaster vol. 3.
 
IMissPiedmont
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 12:52 pm

OK. I admit I took a bit of liberty here. The point I was trying, futile it seems, to make is that V1 is the speed at which an pilot either takes off or aborts.
I fully realize that V can never legally exceed VR but, hypothetically, given enough runway, as in my examples, an aircraft can safely get all wheels off the ground and back down with plenty of room to stop.

Sorry for not explaining better.  Smile/happy/getting dizzy
The day you stop learning is the day you should die.
 
Guest

RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 1:35 pm

Steve,
Don't feel bad. 99% of professional pilots, myself included, don't fully understand this topic. We know it well enough to function in day-to-day operations, but misconceptions abound. For example, if I were to ask most pilots to define V1 I would expect the majority to answer that it was the takeoff decision speed. Wrong answer.

Thanks to the miracle of "cut & paste", I've inserted the definition of V1 as contained in Part 1 of the FARs (OK, I know that they are now known as 14 CFR...):

V1 means the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance. V1 also means the minimum speed in the takeoff, following a failure of the critical engine at VEF, at which the pilot can continue the takeoff and achieve the required height above the takeoff surface within the takeoff distance.

Here's the reference so you can check it out yourself. http://ecfr.access.gpo.gov/otcgi/cfr/otfilter.cgi?DB=3&query=14000000001®ion=BIBSRT&action=view&SUBSET=SUBSET&FROM=1&SIZE=10&ITEM=1#Sec.%201.2
Scroll down to Section 1.2

The point is that if V1 is the maximum speed in the takeoff at which the pilot must take the first action (e.g., apply brakes, reduce thrust, deploy speed brakes) to stop the airplane within the accelerate-stop distance, then the decision to abort or continue the takeoff must be made at some point prior to reaching V1 in order to allow for pilot reaction time.

Jetguy
 
Airbus Lover
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Sun Jun 16, 2002 10:21 pm

Then how did an aircraft rotate at around 115-125kts.. i mean a B737-300? with 50% of the MGTOW?
 
IMissPiedmont
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Mon Jun 17, 2002 2:26 am

Aargh. I forgot all about the second part of V. OK. I guess I should have read the FARs to double check myself. Of course with my luck they've changed substantially my last copy is from 2000. Thanks for the clarification.

Good thing I'm not an active pilot.
The day you stop learning is the day you should die.
 
Rick767
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Mon Jun 17, 2002 2:47 am

The JAA are more simple about this! V1 definition:

"V1 - Takeoff decision speed"  Big grin

The actual calculation however, in terms of Accelerate-Stop distance (JAR 25.109), is that the aircraft may:

"...continue acceleration for 2 seconds after V1 is reached with all engines operating (and) come to a full stop from the point reached at the end of that acceleration assuming that the pilot does not apply any means of retarding the aeroplane until that point is reached."

So under JAR a two second gap is permitted on reaching V1 before the pilot does anything, to allow for the decision to be made. The continued acceleration of the aircraft from that point is also allowed for, with both engines operating, for 2 seconds (a long time in aviation).

It seems the FAA won't let you do this. Or should I say if you used the FAA calculations then waited 2 seconds before you did anything you'd end up off the end.

There is a different calcuation for ADSA in an engine failure situation, but it's pretty long and complicated so I won't post it. The above scenario assumes all engines operating throughout.
I used to love the smell of Jet-A in the morning...
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Mon Jun 17, 2002 3:29 am

It wasn't all that long ago that the FAA changed their definition of V1, prior to that, it was the takeoff decision speed. From what I understand, it was done to, just as you said, keep you from going off the end. (This was a real, in some cases, inevitable possibility if the crew aborted at or very near to V1 on a short runway.) US operators need to know what "delay" is built into their charts. The G200 (which was certified about 3 years ago) has, as I remember, 7 or 8 seconds built in. This should be plenty of time. A Lear 35 (which was certified sometime during the late Jurassic), for example, had only about 3 - which probably wasn't enough. At my last Lear recurrent, the folks at FlightSafety were suggesting that the crews start calling V1 about 5 knots early.

There are several differences between what the FAA considers adequate and what the aviation authorities in other countries feel is necessary when it comes to aircraft certification - both in the equipment that must be installed on the aircraft and the charts and data that is included in the AFM, etc. and even in some cases, operational techniques. For example, our V1 charts assume a dry runway. If it's wet or has ice and/or snow on it we're still good to go, but it's up to us to decide how much if any "fudge factor" we want to add. I've seen the Canadian charts for our airplane, they list the correction factors. There are also some differences on operational techniques, for example, to comply with the Canadian performance charts, a Lear 35 pilot would technically have to taxi into position, hold the brakes, set takeoff power and let it stabilise for 30 to 45 seconds prior to releasing the brakes. Yeah, right. There is no way anyone here (or for that matter, in Canada) is going to do that. I guess the point I'm trying to make it this stuff is not as simple or straight forward as it might seem.

Jetguy
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Tue Jun 18, 2002 1:17 am

It's important to keep in mind that there's no guarantee you will be able to lift off at V1. To be guaranteed liftoff success you need to rotate at Vr (sometimes Vr is same as V1, then you rotate at V1  Smile/happy/getting dizzy).

Vmu (minimum unstick speed) is used to determine Vr and V2, it has nothing to do with V1.

Airbus Lover keeps asking ...what about at lighter weight... V1 is calculated based on weight so it doesn't matter what weight you are at, if you exceed V1, there's a really good chance you will run out of runway if you abort.

Regards,
Nut
 
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RE: Can An Aircraft Take Off Before V1 Or Vr?

Thu Jun 20, 2002 10:47 pm

oh nails on the head Md11nut! thanks very much.. now i fully understand,.

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