Abort Speed Reaction Time Considerations

[HuggyU2]

For the T-38, the takeoff Refusal Speed is computed using a 3" reaction time, during which the aircraft continues to accelerate.

In other aircraft, the speed is based on starting the abort at that speed, with no reaction time.

I'd like to know what is done in other aircraft in the military.  I'm not looking for "technique", just what is in your flight manual when it comes to the consideration that was used in creating your performance charts.  

Bombers, trainers, fighters, heavies... let me know.  Post it here or drop me a pm.  

[Runr6730]

In the KC-46 you must take the first action to reject the takeoff by V1. All field length calculations assume 1 second to recognize any malfunction and initiate the stopping action. 

[Swizzle]

Herk has a similar 'at that speed'

[HuggyU2]

BTW, for those aircraft with a tailhook... I'm talking about scenarios on a runway that doesn't have a cable.  

[Fly4five]

KC135 is based on the speed to take action as well. They talk to a "normal" reaction time of 3-4 secs in the dash 1, but that is for losing an outboard engine at rotation speed and has to do with rudder and aileron for maintaining control. Based on that, I'd assume they factored that reaction time into the numbers when calculating S1.

Sent from my SM-F926U1 using Baseops Network mobile app

[FourFans]

C-130J-30 has a 1 second reaction written in books, at least in the last -1-1  I read.  Then again I'm retiring.  In reality it's a 3 second reaction from recognition to throttle and brake actuation.  The book numbers are all way off anyway because they never updated the performance numbers for the carbon brakes, which makes all the numbers "conservative" and the actual performance during a reject is WAY better than the book number, both in the sim and the airplane.  I've heard they fixed that in block 8.1 though.  Any 8.1 dudes here that can set me straight?

Edited February 20, 2023 by FourFans130

[Danger41]

There’s no built in reaction times to TOLD to PC-12/U-28 stuff. One very unique calculation is the turn back altitude for if you lose the engine on takeoff. We used to train to that regularly prior to the Demise 25 crash at Clovis Muni. Now guys only get exposure to that in sim refresher training and updated CAP.

[FourFans]

9 minutes ago, Danger41 said:

There’s no built in reaction times to TOLD to PC-12/U-28 stuff. One very unique calculation is the turn back altitude for if you lose the engine on takeoff. We used to train to that regularly prior to the Demise 25 crash at Clovis Muni. Now guys only get exposure to that in sim refresher training and updated CAP.

I’ll be interested to hear how the training for the sky warden will address that problem.  The PC-12 is relatively clean by comparison.  Hopefully they reach out to the cropdusting community for some lessons learned so we don’t have to re-experience some avoidable crashes.

Edited February 20, 2023 by FourFans130

[Majestik Møøse]

On 2/19/2023 at 6:14 PM, Danger41 said:

There’s no built in reaction times to TOLD to PC-12/U-28 stuff. One very unique calculation is the turn back altitude for if you lose the engine on takeoff. We used to train to that regularly prior to the Demise 25 crash at Clovis Muni. Now guys only get exposure to that in sim refresher training and updated CAP.

Turn back like a 90/270?

[Danger41]

54 minutes ago, Majestik Møøse said:

Turn back like a 90/270?

Not sure if that’s the same terminology but this number is an altitude where if you lose the motor, you can feather it and turn back around to the departing runway and land in the opposite direction. It’s affected by all the usual aerodynamic suspects of density altitude, wind speed/direction, etc.

[Majestik Møøse]

When do you choose that over a high key?

[Danger41]

“That depends” of course but high key is 2000’ AGL and low key is 1000’ AGL so once above those, that’s a better bet. The turn back assumption is you totally lose the motor and don’t have the altitude to attempt a restart. If you’ve got partial power or anything, I’d keep the motor running until it was hurting more than helping. 
 

It’s also one of those things where it’ll spit out a number for turn back and the rule is if you lose it below that number, you’re supposed to land straight ahead (or at least in front of 3-9). However, if I’m taking off out of Hurlburt to the north and lose the motor, I’m turning back no matter what instead of going into 100 foot trees. Or if I’m at Cannon, I’ll turn for the crossing runway even below the altitude. Turn back is definitely more of a think about it ahead of time thing than a binary reaction for aborting takeoff.

[HerkPerfMan]

Some perspective from flight test and performance engineering on the C-130J and C-5. Both include reaction time in the decision speed (VREF) and VCEF numbers, based on flight test. So a malfunction (typically assumed to be a critical engine failure) can occur up to VREF or VCEF. Other multi-engine aircraft handle this differently.

However, flight test reaction times can be misleading since the pilot knows that a critical engine failure will occur during the takeoff run - just not when.

Another key assumption in VREF is a 3-point ground attitude. If the aircraft is rotated, then the refusal distance is invalid since the time (and distance) to lower the nose is not included.

Regarding C-130J Block 8 and carbon brakes, the only change in charted performance is maximum brake energy and cooling times. This is the primary performance benefit of carbon brakes since the flight tests showed minimal change in stopping distance.