bbchien
Touchdown! Greaser!
Did I say that? let me go re-read.
No I didn't. V2=Vyse. I thought I might have been confused. It's easy these days....
Scary VMC roll video, question for multi-pilots
- Thread starter JimNtexas
- Start date
bbchien
Touchdown! Greaser!
Dave, I'm not going to publish the grid; Henning has it right. But within usual conditions winter/summer, I fried a set of brake pads, wore rotors to below spec, and fried a set of mains getting the go/stop numbers at various temps baros and winds. Also did distance to Vyse under same, and so it's pretty obvious when it CAN be treated as an "inflight emergency". Lots of boxes of donuts delivered to PIA tracon as they're the guys with 10,000 feet.I've been raking leaves all day and trying to solve the riddle of what your method actually is. The time really passed quickly, but I never did get it!A V1 speed is the speed that matches the "go" distance with the "stop" distance under the given conditions of weight, configuration, density altitude, runway contamination, etc. It's a 'speed of indifference' with regard to engine failure, since the pilot is happy either way--go or stop. In your method, are you saying you have worked out such a speed, i.e., one that results in a balanced field? If it can be done, I'm sure you're the guy who can do it, but I'd like to know how.
Well, Vyse is too fast for a dirty airframe. As long as you're above Vxse you're in a better position climb angle-wise by being below blue line. If you've got a speed that you know will hold altitude while you clean up, then by the time you're done I bet you're pretty close to blue line without having to spend much time stressing about it. Eventually, though, what you say is true. After all, that's why they paint it bright blue isn't it?
I searched a little, but didn't see any grids. Only saw a post in 2011.
I'm afraid I just don't know what you mean, Bruce. Sorry. I'm sure there's good info there for multi pilots to consider, but if they're like me they might be scratching their heads too. You aren't saying you advocate holding the plane on the ground 'till blue line, are you? If so, I think Vyse in the P-Navajo I once flew was something like 133 MPH. Not sure it could even unstick at that speed.
Please, more info, this is good stuff to discuss.
Dave
Then I overhauled the engines.
Dead Stick
Line Up and Wait
Here you say V1 equals Vyse, so yes you did say it?? Bruce what am I missing?
dtuuri
Final Approach
Did you figure the distance to stop from different speeds or always from the same abort speed?
dtuuri
bbchien
Touchdown! Greaser!
Vyse for adjusted weight (ratio of sqaure roots).
Bruce, in addition to post 84 let me ask this question for those of us that do not understand "ratio of square roots".
Could you give us the numbers for a sample problem without assuming to much liability?
Example:Your airplane
80 gal fuel
400 pounds of passengers
6000 foot runway
density altitude of 2,000
First question: What is V1 (what speed while still on the ground) do you have to accelerate to in order to continue the T.O. assuming engine failure at this V1. (I know V1 is also that speed at which one must take first action for stopping on the runway.) I want to know what speed on the ground must you reach on the above example that you continue the T.O. on one engine. Is it possible V1 for your application is just the speed that if you exceed it you can not stop on a given runway?
Second question: what is V2 in our example? V2 being that speed one has to continue accelerating to before becoming air born on one engine.
Could you give us the numbers for a sample problem without assuming to much liability?
Example:Your airplane
80 gal fuel
400 pounds of passengers
6000 foot runway
density altitude of 2,000
First question: What is V1 (what speed while still on the ground) do you have to accelerate to in order to continue the T.O. assuming engine failure at this V1. (I know V1 is also that speed at which one must take first action for stopping on the runway.) I want to know what speed on the ground must you reach on the above example that you continue the T.O. on one engine. Is it possible V1 for your application is just the speed that if you exceed it you can not stop on a given runway?
Second question: what is V2 in our example? V2 being that speed one has to continue accelerating to before becoming air born on one engine.
dtuuri
Final Approach
Now I see what you're doing, but that isn't a real V1 speed, useful as it may be for you. It's a 'max abort' speed you can use to tell if you can accelerate/stop in the runway length available. I bet you also impose limits on your takeoff weight to give a comfortable single-engine climb gradient or rate of climb. In fact, maybe you combine them in the same table? Say you wanted 200'/nm for IFR departure purposes as a minimum. You could figure the max weight for that, then use that weight for your max abort speed, er, I mean "V1"
.If that's the gist of it, I'm for it. You have a procedure you can have confidence in because of your own test data. Much better than hoping you can do as good as the manufacturer's test pilot.
dtuuri
denverpilot
Tied Down
Now I see what you're doing, but that isn't a real V1 speed, useful as it may be for you. It's a 'max abort' speed you can use to tell if you can accelerate/stop in the runway length available. I bet you also impose limits on your takeoff weight to give a comfortable single-engine climb gradient or rate of climb. In fact, maybe you combine them in the same table? Say you wanted 200'/nm for IFR departure purposes as a minimum. You could figure the max weight for that, then use that weight for your max abort speed, er, I mean "V1"
If that's the gist of it, I'm for it. You have a procedure you can have confidence in because of your own test data. Much better than hoping you can do as good as the manufacturer's test pilot.
dtuuri
From everything I've read, you nailed it. He does account for weight in his procedures. He's posted a number of times about modifying takeoff weight out if his home airport for that reason after the stupid town out apartments off the end of the runway. Best to be able to stop or out climb the building than hit it.
dtuuri, that must be it. I asked that in the post just prior to yours. If not then I want to see the numbers for the example I cited. I think I know what he is talking about now. I am not sure anybody is going to wear out a set of brakes, rotors and tires to get this data.
Also I am pretty sure that many light twins have accelerate/stop charts in the POH. Not sure about the Seneca II.
Also I am pretty sure that many light twins have accelerate/stop charts in the POH. Not sure about the Seneca II.
Fearless Tower
Touchdown! Greaser!
I believe they all have accel/stop charts. Only a handful have accel/go charts.
Fearless Tower
Touchdown! Greaser!
I don't think Doc ever claimed it was a 'real' V1 speed. As mentioned earlier in the thread, since V1 is a decision speed, Doc is using it in the context of Vyse as the point in a light twin where you would make the decision to continue.
Skylane81E
Final Approach
I don't think he ever said he was on the ground at V1 either
Whoa! Duncan. Yes he did. Dr. Bruce refers to V1 on several occasions in reference to a light twin. V1 by definition is that speed when obtained while still on the ground that T.O. can be continued if engine failure occurs.
However you must be able to accelerate to V2 in order to become air born.
V1 can also be the maximum speed in which you can stop on the available runway. This can be the acc/stop distance.
Read Bruce's post #69. He makes no distinction or insinuates that he has modified the definition of V1 or V2.
I have no argument with Dr. Bruce doing the tests to verify his abort speed in various configurations. I just feel that Dr. Bruce may be a little misleading to many on this board when stating emphatically that light twins do have both a V1 and V2 speed, just not published. I am not convinced their is any speed that it is safe to become air born with the loss of an engine in light piston twins, jmo. But, as usual I may be wrong.
If Dr. Bruce will just give us the numbers for the example I posted it will clear up a lot.
However you must be able to accelerate to V2 in order to become air born.
V1 can also be the maximum speed in which you can stop on the available runway. This can be the acc/stop distance.
Read Bruce's post #69. He makes no distinction or insinuates that he has modified the definition of V1 or V2.
I have no argument with Dr. Bruce doing the tests to verify his abort speed in various configurations. I just feel that Dr. Bruce may be a little misleading to many on this board when stating emphatically that light twins do have both a V1 and V2 speed, just not published. I am not convinced their is any speed that it is safe to become air born with the loss of an engine in light piston twins, jmo. But, as usual I may be wrong.
If Dr. Bruce will just give us the numbers for the example I posted it will clear up a lot.
dtuuri
Final Approach
I'm not familiar with the Seneca, but I bet there are accelerate/stop charts. They won't show distance to accelerate to an adjusted Vyse though, they'll show only to Vmc or, perhaps, some other speed deemed capable of continuing the takeoff, such as the 105 MPH given by Cessna for the 310 I mentioned up thread.
The lesson to be taken from all this, IMO, is to have a standard procedure that gives predictable performance the pilot can rely on and achieve. Being your own test pilot is one way, but not the only way. I'm fairly comfortable using AFM data in my recipe for dealing with takeoff engine failure, but I use the data differently than originally intended by the manufacturer (add ME takeoff distance to landing distance + fudge factor). Even there, it's a general model that needs to be tweaked for the particular model plane and data available. If the speed at the 50' barrier isn't close to one that's known to allow acceleration while cleaning up, more fudge or some other procedure is in order. It's more art than science, but it's better than crossing fingers.
dtuuri
poadeleted20
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Then you should read the accident report on the Continental DC-10 at LAX a long time back. If they had continued the takeoff after the center engine disintegrated right as they were passing V1, they would have pre-enacted the UA 232 accident but probably with no survivors at all instead of only the two fatalities they actually sustained.
poadeleted20
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Agreed. Good research.
Dtuuri, my question was not did Dr. Bruce have information that is valuable to him, it was his use of V1 and V2. The 105 mph you mentioned for the 310 is not V2. It is a speed that if you can obtain the plane may be able to stay in the air.
V1 is very specific, a speed in which it is considered to be safer to continue than try to stop with engine loss.
V2 is also very specific, that speed which when obtained allows you to safely become air born. It is a matter of specific definitions given by the FAA.
Is there any light twin that if an engine is lost on the T.O. roll you can continue the T.O.? That is all I asked of Dr. Bruce, what is that speed?
I think what we have is a slight modification of V1 and V2 for a point Dr. Bruce was making. The point is well taken once I understood what he is talking about, namely acc/stop performance.
V1 is very specific, a speed in which it is considered to be safer to continue than try to stop with engine loss.
V2 is also very specific, that speed which when obtained allows you to safely become air born. It is a matter of specific definitions given by the FAA.
Is there any light twin that if an engine is lost on the T.O. roll you can continue the T.O.? That is all I asked of Dr. Bruce, what is that speed?
I think what we have is a slight modification of V1 and V2 for a point Dr. Bruce was making. The point is well taken once I understood what he is talking about, namely acc/stop performance.
dtuuri
Final Approach
Had a lesser pilot used the term V1, I might not have got confused. :wink2:
dtuuri
dtuuri
Final Approach
For 2-engine turbojets, Vr (rotation speed) allows you to become airborne and attain V2 by 35' AGL (not "while on the ground". I don't remember if V2 is like you say for large recips.
The 105 MPH for the C-310, as I remember, was the basis for accelerate/stop and the minimum accelerate/go speed, therefore it was on the takeoff roll. I'm not at home, but when I get back there I'll check an old owner's manual to see for sure.
Btw, here's an interesting paper on the MU-2 gear retraction debate:
EDIT: This too, see pgs 132 & 134:
dtuuri
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Fearless Tower
Touchdown! Greaser!
There was also an accident back in the 70s that involved a rejected takeoff after V1 involving a TWA 707 and DAL DC-9.
The DC-9 had just landed and in clearing the runway gone off the pavement and got stuck in the mud but reported they were clear of the active. The 707 was subsequently cleared for T/O and as they passed the stuck DC-9, the exhaust caused a compressor stall in the nr 4 engine. Due to the violent noise and shudder, the FO who was PF rejected the takeoff after V1. Overran the runway and there were a couple fatalities. In the final report the NTSB agreed with the actions of the flight crew to reject the takeoff after V1.
My understanding is that there are two times when you reject a Takeoff after V1: flight control issue or the airplane is on fire.
dtuuri, I think this is true if you have already rotated then lose an engine. You must be able to accelerate to V2 by some pre determined altitude. BTW, I am not type rated so I very well may not be understanding this.
Let me quote from the electronic code for federal regulations chap 14:
"V1 is the maximum speed at which a pilot must first take action to stop the airplane within the acc/stop distance. (this is Bruce's use of V1) V1 is also the minimum speed in the T.O. following a failure of the critical engine at which the pilot can continue the T.O. AND reach the required height above the runway surface and within the required distance."
And here is the rub "V2 is the safety T.O. speed" from the same source.
It seems to insinuate that if you are on the ground but at or above V1 you have to accelerate to V2 to go air born. However if you have rotated then you must reach V2 with in a certain height above the surface and a certain distance to be able to continue. Generally light piston twins do not have enough power to accelerate after engine loss.
This has been interesting even though I will never need to know this.
On the MU2 that is exactly my point. The SFAR teaches the 50 to 100 foot method. Sucking the gear up immediately puts you in a critical situation 5-10 seconds later. You want enough air under you to be able to settle a little during the last half of the cycle. Also as a side note you leave the flaps in take off position. The MU2 just requires a different methodology than many turboprops thus the SFAR. I appreciate your input.
Let me quote from the electronic code for federal regulations chap 14:
"V1 is the maximum speed at which a pilot must first take action to stop the airplane within the acc/stop distance. (this is Bruce's use of V1) V1 is also the minimum speed in the T.O. following a failure of the critical engine at which the pilot can continue the T.O. AND reach the required height above the runway surface and within the required distance."
And here is the rub "V2 is the safety T.O. speed" from the same source.
It seems to insinuate that if you are on the ground but at or above V1 you have to accelerate to V2 to go air born. However if you have rotated then you must reach V2 with in a certain height above the surface and a certain distance to be able to continue. Generally light piston twins do not have enough power to accelerate after engine loss.
This has been interesting even though I will never need to know this.
On the MU2 that is exactly my point. The SFAR teaches the 50 to 100 foot method. Sucking the gear up immediately puts you in a critical situation 5-10 seconds later. You want enough air under you to be able to settle a little during the last half of the cycle. Also as a side note you leave the flaps in take off position. The MU2 just requires a different methodology than many turboprops thus the SFAR. I appreciate your input.
dtuuri
Final Approach
No, the pertinent reg is here:
§25.111 Takeoff path.
(a) The takeoff path extends from a standing start to a point in the takeoff at which the airplane is 1,500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In addition—
(1) The takeoff path must be based on the procedures prescribed in §25.101(f);
(2) The airplane must be accelerated on the ground to VEF, at which point the critical engine must be made inoperative and remain inoperative for the rest of the takeoff; and
(3) After reaching VEF, the airplane must be accelerated to V2.
(b) During the acceleration to speed V2, the nose gear may be raised off the ground at a speed not less than VR. However, landing gear retraction may not be begun until the airplane is airborne.
(c) During the takeoff path determination in accordance with paragraphs (a) and (b) of this section—
(1) The slope of the airborne part of the takeoff path must be positive at each point;
(2) The airplane must reach V2 before it is 35 feet above the takeoff surface and must continue at a speed as close as practical to, but not less than V2, until it is 400 feet above the takeoff surface;
...
Vr is chosen so as to render V2 at 35' AGL--they're married, so to speak.(a) The takeoff path extends from a standing start to a point in the takeoff at which the airplane is 1,500 feet above the takeoff surface, or at which the transition from the takeoff to the en route configuration is completed and VFTO is reached, whichever point is higher. In addition—
(1) The takeoff path must be based on the procedures prescribed in §25.101(f);
(2) The airplane must be accelerated on the ground to VEF, at which point the critical engine must be made inoperative and remain inoperative for the rest of the takeoff; and
(3) After reaching VEF, the airplane must be accelerated to V2.
(b) During the acceleration to speed V2, the nose gear may be raised off the ground at a speed not less than VR. However, landing gear retraction may not be begun until the airplane is airborne.
(c) During the takeoff path determination in accordance with paragraphs (a) and (b) of this section—
(1) The slope of the airborne part of the takeoff path must be positive at each point;
(2) The airplane must reach V2 before it is 35 feet above the takeoff surface and must continue at a speed as close as practical to, but not less than V2, until it is 400 feet above the takeoff surface;
...
dtuuri
Fearless Tower
Touchdown! Greaser!
Maybe that's why Vr/V1/V2 are all the same speed in the DC-3......no nose gear.
poadeleted20
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Another concern with computed V1 is that it's for a perfectly functional undamaged aircraft other than sudden, complete loss of power in one engine. Throw in damage like loss of hydraulics due to uncontained engine failure (the UA 232 syndrome), blown tires, loss of braking power, adjacent engine damage, structural damage affecting aerodynamics (see AA 191), etc., and advertised guarantees of V1 (being able to fly if above it and stop on the runway if below it) go out the window. You may find your best option in some of those situations is to abort from above V1 even if it means running off the runway. Likewise, you may go off the runway despite making the decision to stop from below V1. My thinking is that it's probably better to go off the far end at 30 or even 60 knots than to get airborne and find you can't control or climb the plane, so my default choice if I hear a great loud bang while still on the ground even above V1 is to abort unless I'm sure the plane will fly.
dtuuri
Final Approach
Not got it just yet... You don't need V2 before retraction, a positive rate will do. That is what SFAR 108 is telling MU-2 pilots as well, if I'm not mistaken. The pages I referenced before don't require delaying gear retraction with a loss of an engine as far as I saw.
dtuuri
On the MU2, I have not been to the school but have spent several hours in the MU2 with a friend. I am pretty sure you are suppose to get a certain distance AGL because the MU2 will settle during the last 5 seconds of gear retraction on one engine. If you raise the gear at say 10 feet and at the same time lose an engine it will settle back down and not give a good result. Need to have a cushion to allow for that settling.
I guess the definition of V2 (safety take off speed) is confusing me, not hard to do.
I have done some more reading. Now I think I got it. V1 we agree on. If engine failure after reaching V1 take off continues.
Vr is calculated to allow take off with one engine out. V2 is that speed you must obtain by the 35 foot screen height. V2 allows for required climb gradient. Once V2 is reached you continue the initial climb phase at V2 or as prescribed by mfg's POH for said aircraft. Gear retract at positive rate. Am I closer?
I guess the definition of V2 (safety take off speed) is confusing me, not hard to do.
I have done some more reading. Now I think I got it. V1 we agree on. If engine failure after reaching V1 take off continues.
Vr is calculated to allow take off with one engine out. V2 is that speed you must obtain by the 35 foot screen height. V2 allows for required climb gradient. Once V2 is reached you continue the initial climb phase at V2 or as prescribed by mfg's POH for said aircraft. Gear retract at positive rate. Am I closer?
dtuuri
Final Approach
More likely Vr wasn't invented yet.
See pg 42: That leaves V1 and V2, so I figure all that aerodynamic drag from those round engines makes the stopping distance rather short enabling the takeoff to reach V2 before running out of stopping distance.
dtuuri
dtuuri
Final Approach
You might like this, especially the part about balanced field length:
http://www.faa.gov/other_visit/aviation_industry/airline_operators/training/media/takeoff_safety.pdf
From my experience, V2 simply happens--when you follow procedures. You don't have to "make it happen". Pretty much the same way with Vyse in a light twin, IMO. I'd rather concentrate on methodically doing the memory items while holding a proper attitude (level in a twin) and heading, then take a look at where I am on airspeed. Then adjust to milk out a climb. YMMV.
dtuuri
RotorAndWing
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Rotor&Wing
Uh, aborting for blown tires or loss of braking is a major mistake. With a blown tire you no longer have anything to grip the runway, thus no stopping. With loss of braking power......well, that goes without saying, you ain't stopping.
Airbus says in the FCOM a blown tire(s) within -20knots of V1 is a go item. Boeing is also similar.
Rejecting after V1 is a bad idea and both Airbus and Boeing disagree with your assertion. When you hear that loud bang how much time do you have to begin to evaluate your situation? You're much better off getting airborne and work the problem out that attempt a high speed abort and crash.
Boeing and Airbus have written extensively on this subject and the FAA has contributed as well.
Basically anything above a 100 knots I'm going unless I know the aircraft won't fly.
And to be fair, I assume you are talking transport category aircraft.
From the Airbus A319/320/321 FCTM
FACTORS AFFECTING RTO
Experience has shown that a rejected takeoff can be hazardous, even if correct procedures are
followed. Some factors that can detract from a successful rejected takeoff are as follows:
• Tire damage
• Brakes worn or not working correctly
• Error in gross weight determination
• Incorrect performance calculations
• Incorrect runway line-up technique
• Initial brake temperature
• Delay in initiating the stopping procedure
• Runway friction coefficient lower than expected
Thorough pre-flight preparation and a conscientious exterior inspection can eliminate the effect of
some of these factors.
During the taxi-out, a review of the takeoff briefing is required. During this briefing, the crew should
confirm that the computed takeoff data reflects the actual takeoff conditions e.g. wind and runway
condition. Any changes to the planned conditions require the crew to re-calculate the takeoff
data. In this case, the crew should not be pressurised into accepting a takeoff clearance before
being fully ready. Similarly, the crew should not accept an intersection takeoff until the takeoff
performance has been checked.
The line-up technique is very important. The pilot should use the over steer technique to minimize
field length loss and consequently, to maximize the acceleration-stop distance available.
DECISION MAKING
A rejected takeoff is a potentially hazardous manoeuvre and the time for decision-making is
limited. To minimize the risk of inappropriate decisions to reject a takeoff, many warnings and cautions are inhibited between 80 kt and 1 500 ft. Therefore, any warnings received during this
period must be considered as significant.
To assist in the decision making process, the takeoff is divided into low and high speeds regimes,
with 100 kt being chosen as the dividing line. The speed of 100 kt is not critical but was chosen in
order to help the Captain make the decision and to avoid unnecessary stops from high speed:
• Below 100 kt, the Captain will seriously consider discontinuing the takeoff if any ECAM
warning/caution is activated.
• Above 100 kt, and approaching V1, the Captain should be "go-minded" and only reject the
takeoff in the event of a major failure, sudden loss of thrust, any indication that the aircraft will
not fly safely, any red ECAM warning, or any amber ECAM caution listed below:
• F/CTL SIDESTICK FAULT
• ENG FAIL
• ENG REVERSER FAULT
• ENG REVERSE UNLOCK
If a tire fails within 20 kt of V1, unless debris from the tire has caused noticeable engine
parameter fluctuations, it is better to get airborne, reduce the fuel load and land with a full
runway length available.
The decision to reject the takeoff is the responsibility of the Captain and must be made prior to V1
speed:
• If a malfunction occurs before V1, for which the Captain does not intend to reject the takeoff, he
will announce his intention by calling "GO".
• If a decision is made to reject the takeoff, the Captain calls "STOP". This call both confirms the
decision to reject the takeoff and also states that the Captain now has control. It is the only time
that hand-over of control is not accompanied by the phrase "I have control".
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Fearless Tower
Touchdown! Greaser!
No kidding. That is exactly what killed the Lear 60 crew in Columbia, SC in 2008.
Skylane81E
Final Approach
Question is, how many light twins will even stay on the pavement, much less finish accelerating to take off speed with a flat?
Now loss of braking on take off, well how the hell am I supposed to know about it:wink2:
Light twins and transport category planes are rather different beasts however.