V2 and the 4 segment climb

[Bandit_Driver]

It amazes me that people live around Air Force Bases or Air Stations, especially off the extended runway centerlines. There's a reason these places started life out on the middle of nowhere. When I had my engine failure on takeoff in the Hog, I couldnt get rid of my munitions for this very reason and had to struggle to keep the jet airborne. Although if the jet is going to crash anyway, it might not make a difference.........only geographically.

I know. When I was working line at a joint use airport people would call and complain to us all the time about the noise of engine runs and hogs coming and going. It was funny because they were calling the FBO to complain about the guard ops sometimes. It was always fun when the F-15's and F-18's would drop in on their x/c's and then do full burner takeoffs. We usually didn't engage too many of the complainers but I was able to shut up one of the regular complainers by asking him when he moved in. I then told him well, the airport has been here a few of decades longer than you have, so what's your point again. He never called back again.

 

[MikeD]

I know. When I was working line at a joint use airport people would call and complain to us all the time about the noise of engine runs and hogs coming and going. It was funny because they were calling the FBO to complain about the guard ops sometimes. It was always fun when the F-15's and F-18's would drop in on their x/c's and then do full burner takeoffs. We usually didn't engage too many of the complainers but I was able to shut up one of the regular complainers by asking him when he moved in. I then told him well, the airport has been here a few of decades longer than you have, so what's your point again. He never called back again.

Agree. MCAS Yuma in AZ used to be out in the boonies on the east end of town. Everyone moved out that way around the airport and it wasn't some 6 years ago that a Harrier loaded with 4 live Mk82 500lb bombs crashed on landing into a neighborhood. Two homes in the neighborhood burned down since fire crews couldnt approach the wreckage with the live bombs there. Luckily, it was a USN/USMC aircraft and the bombs didn't have a chance to explode in the fire.......had it been a USAF plane, four exploding Mk82s could've leveled the entire neighborhood.

Here's the story:

http://www.kold.com/global/story.asp?S=3481135

 

[Bandit_Driver]

Ok I'll bite. Why would USN/USMC bombs not go off and USAF ones would?

Another question would what if had been a nuke? I believe the Nukes can't go off unless armed but how well would they tolerate a fire that hot? Would the package end up getting exposed?

 

[MikeD]

Ok I'll bite. Why would USN/USMC bombs not go off and USAF ones would?

Another question would what if had been a nuke? I believe the Nukes can't go off unless armed but how well would they tolerate a fire that hot? Would the package end up getting exposed?

Though the bombs are the same between the services, ie- Mk-82 500 pounder, etc, there are subtle differences.

In the two pics below, you see the same bombs. The yellow striping indicates they're lives, as opposed to blue indicating inerts. The USAF bombs have a single yellow stripe and the normal, smooth bomb casing. The USN bombs, however, have two yellow stripes and the rough coating surrounding the bomb. The rough coating is for fire safety so the bombs take longer to "cook off" in a fire onboard ship. This was added following the fires aboard the USS Forrestal in 1967, where unprotected bombs detonated causing much additional damage along with the original flight deck fire.

 

[Bandit_Driver]

Ahh makes complete sense, I was waiting here some inter service ribbing. I saw a special on the Forrrestal accident and actual footage from it. That was a bad bad accident and let to a lot of changes. The question then remains why don't they do it across all the services then? I know a ship is more vulnerable than a base may be but there is still a fire potential on a base correct?

how bad is the drag penalty for navy vs airforce bombs.

 

[MikeD]

Ahh makes complete sense, I was waiting here some inter service ribbing. I saw a special on the Forrrestal accident and actual footage from it. That was a bad bad accident and let to a lot of changes. The question then remains why don't they do it across all the services then? I know a ship is more vulnerable than a base may be but there is still a fire potential on a base correct?

how bad is the drag penalty for navy vs airforce bombs.

Hehe, no interservice rivalry this time. AF just doesnt feel the need for the cost expenditure, for if an aircraft catches fire on the flightline, there's lots of real estate to escape to; unlike the ship where you're forced to fight the fire.

 

[ovrtake92]

One thing I didnt see mentioned in regards to the advantages of keeping your excess speed if an engine fails after you accelerate past V2 is the fact that V2 is below L/D max. The closer you are to L/D max the higher your excess thrust available and therefore better climb gradient. If a sim instructor got on me for a few extra knots past V2 I would remind him of this principal of aerodynamics. Food for thought. Carry on.

 

[C150J]

One thing I didnt see mentioned in regards to the advantages of keeping your excess speed if an engine fails after you accelerate past V2 is the fact that V2 is below L/D max. The closer you are to L/D max the higher your excess thrust available and therefore better climb gradient. If a sim instructor got on me for a few extra knots past V2 I would remind him of this principal of aerodynamics. Food for thought. Carry on.

I certainly hope no one would get on you for a few extra knots, but the principal you mentioned doesn't work very well when you haven't cleared an obstacle during your first segment. Hot day, short field, heavy airplane - speed won't help you. 121.189 only promises you 35' of clearance in the takeoff path. Combine that with the first segment's minimal required gradient ("positive" for two-engine jets) and the "carrying extra speed" argument doesn't fly. This is all in design and theory of course... If I see a guy trying to maintain V2 through the takeoff path during a single engine event, great. It's when I see someone climbing out on two engines at V2+30 (our profile is V2+10 for a normal takeoff) that raises an eyebrow: he/she is so far from V2 during the first segment that they won't be able to hop an obstacle in the event of a failure.

 

[Hacker15e]

I would have figured that someone who has gone through some initial jet training for any jet type would understand the importance of gaining ALTITUDE rather than DISTANCE / AIRSPEED at a low altitude with only one motor.

Be careful with phrases like "any jet type". I have thousands of hours in high performance multiengine jets, and I'd never even heard of a "segment climb" until I got a civil type rating in a turboprop. There are other multiengine jets out there that don't use the paradigm you're talking about.

In a jet fighter, airspeed is king first, then altitude. In an engine failure on takeoff with the takeoff continued, my immediate action items reference lowering the nose and accelerating to what we call "SETOS" (Single Engine Takeoff Speed -- which guarantees a climb of 100 fpm out of ground effect). SETOS is generally close to the speed at which the airplane gets airborne after rotation, and is similar to V2. After getting to SETOS, I rotate, clean up, then climb only as required to avoid obstacles while I accelerate to my safe single engine airspeed (which is L/D max, essentially, and depends on the gross weight of the jet. Somewhere between 240 and 280 knots generally).

In both the T-38 and the F-15E, speed is life. "V2+50" (even though we don't use V speeds in the USAF fighter/trainer biz) is a perfectly happy place to be after an engine failure. If I could get V2+100 before I actually climbed to any significant altitude that would be perfect, too.

So, the lesson here is that "the profile" isn't the same for every aircraft, nor are even the paradigms in which that profile is designed.

 

[C150J]

So, the lesson here is that "the profile" isn't the same for every aircraft, nor are even the paradigms in which that profile is designed.

Absolutely. That being said, I think the reason you guys might not use V2 is the fact that its vague definition revolves around screen height, climb gradients, and sometimes part 25 requirements. Do your manuals actually say "V2+50" or is it a specific speed? Just curious.

 

[Hacker15e]

Do your manuals actually say "V2+50" or is it a specific speed? Just curious.

In the T-38 actually says "safe single engine airspeed", which is L/D max adjusted for fuel weight. In the F-15E, it was about the same speed but not called the same thing.

I just used the "V2+50" term because that's what was being thrown around in the other posts.

 

[ovrtake92]

I certainly hope no one would get on you for a few extra knots, but the principal you mentioned doesn't work very well when you haven't cleared an obstacle during your first segment. Hot day, short field, heavy airplane - speed won't help you. 121.189 only promises you 35' of clearance in the takeoff path. Combine that with the first segment's minimal required gradient ("positive" for two-engine jets) and the "carrying extra speed" argument doesn't fly. This is all in design and theory of course... If I see a guy trying to maintain V2 through the takeoff path during a single engine event, great. It's when I see someone climbing out on two engines at V2+30 (our profile is V2+10 for a normal takeoff) that raises an eyebrow: he/she is so far from V2 during the first segment that they won't be able to hop an obstacle in the event of a failure.

You are correct on all of this as 1st segment is defined by being at V2 at 35 feet with one engine. However I took the argument to be that one loses an engine some time after the first segment when you are above V2. In this case 2nd segment is the only issue and keeping your speed at whatever speed the engine fails would be beneficial to your 2nd segment climb gradient as long as you are at or below L/D Max which most jets dont publish anyway so kind of a moot point. Its really all academics but its fun to nerd out sometimes

 

[Bandit_Driver]

Hacker, I would wager a guess the fighter world is different in regards to engine failures because the aerodynamics on those jets. Just look how thin and short the wings are on fighters compared to the transports. I would bet if you talk to the tanker guys they probably fly those similar to the way we fly the transports.

I would assume the T-38 doesn't have too much problem single in regards to yaw. What is Vmc for the F-15 and are you below it on approach? I've been told the F-14's were really bad and an engine failure on approach would be an automatic ejection because you were below Vmc and would be able to recover the plane below a certain altitude.

 

[MikeD]

Hacker, I would wager a guess the fighter world is different in regards to engine failures because the aerodynamics on those jets. Just look how thin and short the wings are on fighters compared to the transports. I would bet if you talk to the tanker guys they probably fly those similar to the way we fly the transports.

They are. The C-141/C-17/C-5/KC-10/KC-135 guys, et al, all fly just like airliners. Same same. Which makes complete sense.

I would assume the T-38 doesn't have too much problem single in regards to yaw. What is Vmc for the F-15 and are you below it on approach? I've been told the F-14's were really bad and an engine failure on approach would be an automatic ejection because you were below Vmc and would be able to recover the plane below a certain altitude.

-38 is centerline thrust and pretty much flies like it single-engine....not much in the way of yaw noticable. A-10 is classified as centerline thrust, but has some significant yaw when single engine. My unit in Korea 12 years ago, we lost one on an S/E approach following a precautionary shutdown when the pilot got slow, added power to correct and ran out of rudder. As for the F-14, it just depends where you're at when the failure occurs and if you catch it in time. But so far as the FAA is concerned, the F-14 is a normal multiengine, not a centerline thrust bird. As is the A-37 Dragonfly. All other US fighter/trainer jets, they consider centerline thrust.

 

[Hacker15e]

Hacker, I would wager a guess the fighter world is different in regards to engine failures because the aerodynamics on those jets.

I agree, that's probably the reason.

I was really just making the statement to show that surreal1221's comment that, "someone who has gone through some initial jet training for any jet type would understand the importance of gaining ALTITUDE rather than DISTANCE / AIRSPEED at a low altitude with only one motor" isn't correct for any of the "jet types" that I have considerable time in.

What is Vmc for the F-15 and are you below it on approach? I've been told the F-14's were really bad and an engine failure on approach would be an automatic ejection because you were below Vmc and would be able to recover the plane below a certain altitude.

Remember that the only factor the FAA used in determining which aircraft have a Center Thrust restriction is if there's a manufacturer's published Vmc. It has nothing to do with how much yaw is generated, how far apart the engines are, or how tough the airplane is to muscle around when it's single engine.

The Eagle is on the "Center Thrust" list in AC 61-89E, so it does not have a published Vmc. That fact, however, doesn't mean that the airplane doesn't have significant yaw when single engine.

What the F-15E does have (in the bigger engine models only) -- and what keeps it from having a published Vmc -- is an electronic module called the ATDPS (Automatic Thrust Departure Prevention System) that limits afterburner on the good engine should the other one fail.

I'd say that the rudder force required to keep a loaded F-15E going the right direction with one engine failed is very similar to what I've seen in other "normal" twins that I've flown. The difference, I suppose, is that there's not a point above stall speed where you run out of rudder before you run out of control, hence no published Vmc.

 

[Bandit_Driver]

Thanks Mike and Hacker

 

[Sp33dB1rd]

All good points. But what is a VMC climb?

Confused me too

You can climb in VMC (good weather), or you can climb at Vmc (minimum control speed).

pretty sure you won't be climbing very much at Vmc unless you're in a F-15.

 

[Hacker15e]

pretty sure you won't be climbing very much at Vmc unless you're in a F-15.

Haven't you been following the thread? There is no Vmc in an F-15!

 

[Sp33dB1rd]

Haven't you been following the thread? There is no Vmc in an F-15!

gawsh...im bad at it...its literally my frist day on a web forum.

 

[Bandit_Driver]

Haven't you been following the thread? There is no Vmc in an F-15!

I still think it is BS that they (FAA) consider planes such as the A-10, F-15 Centerline Thrust...The T-38 I get but not planes with the engines that far apart.

On a more comical note what is the STS classified as? centerline thrust, glider,