FAR 25 Performance

[citdrver]

Hey folks,

Anyone have a good resource to get all the info on FAR Part 25 performance criteria, especially all that segements and stuff for the take off. I know Part 25 is availble online, but I dont enjoy reading regs. I am looking for a website, book, carving on a wall, or anything else that explains in good detail the performance criteria, especially for second segment climb. There really isnt much info on the subject in any of the materials I have here at home. Flight Safety material has a brief overview and the FAR/AIM doesnt mention it (or so I think, may have missed it?).

Thanks,



Citdrver

 

[up frnt]

There is a book called FLYING JETS by Linda D. Pendleton that has a good discription of Part 25 performance. I believe it is Chapter 8. Part 25 basically makes flying safer because of all the performance requirements the aircraft has to meet.

 

[100LL... Again!]

Warning - the following post contains no references to Delta, Comair, PFT, the RJDC, Freedom, or airline management. I.e. BORING!
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To answer your question-

There is no real easy way - you might try that book that was mentioned.

Also, I have heard of a book by a European pilot called "From Takeoff to Landing.' If you find it, let me know - I haven't tried yet.

Some knowledge of the Terps is helpful. Specifically, what gradients are, how they are used to compute takeoff performance, but here is what I got off the top of my head:

Correct me if I got this stuff wrong.

Segt1- Liftoff to gear retraction, assumed to be 35' over the end of the runway.

Segt2- Initial Climb at V2. This segt is complete at 400 abv the runway, or the acceleration altitude. Most are 400'. Obsacles can dictate higher. Roanoke, Aspen, etc.

Segt3- Level off and accelerate to flap retraction speed. Retract flaps.

Segt4- Climb to 1500' abv rwy elev. at whatever speed the manual dictates. V-whatever, varies among aircraft.


Vef- The speed at which the engine is assumed to fail. (Basically V1 minus pilot reaction time.)

V1- The speed above which a takeoff will be performed regardless of engine failure. Depending on weight, can also be the max speed from which an accelerate-stop can be accomplished (on the runway).
At low weights, there are a range of possible V1 speeds, limited on the upper end by stopping ability. Limited on the lower end by one engine acceleeration ability.

Example: Take a 727 at a light weight. If v1 is too high, an abort would take you off the pavement even if done before V1. If V1 was (for sake of argument) 10 knots, the airplane might not be able to accelerate to Vr before running out of runway.

As you get heavier, the spread between the upper and lower limit converge. (KINDA like Vy and Vx do).


Vr- The speed at which a normal rate of rotation will produce V2 at 35' abv the runway. (not necessarily the runwway end.)

Vmu- Min unstick speed figures, in but can't remember how off the top of my head.

V2- takeoff safety speed. A VERY ROUGH analogy would be Vx. This speed is designed to get you over the obstacles. It is limited by (among other things) Vmca and Vs.

I think the factors are 1.1 Vmca and 1.2 Vs.
Therefore an airplane with tail mounted engines would probably have V2 limited by Vs, since there is little assymetric thrust. Wing mounted engines could go either way. If lots of power is available and the weight is low, 1.2 Vs might be lower than 1.1 Vmca.
If the weight is high, 1.2 Vs will probably be more limiting than 1.1 Vmca.

Vs is stall speed for the takeoff configuration being used.
Vmca is what you think it is. Air minimum control speed.

There are several (depending on aircraft) V-designators for the speed at which the flap retraction BEGINS, as well as the fourth-segment climb speed. Check the manual.


Vmcg- Ground minimum control speed. This is the speed ABOVE which, when an engine is lost, control of the aircraft can be maintained on the ground USING ONLY AERODYNAMIC CONTROLS. No nosewheel steering. "Control" means being able to keep it within 30' of the centerline after an engine failure. Yee-Ha!

Again, off the top of my head, I can't remember if this speed is associated with V1 (my bet) or Vr/V2.



Climb gradients (not rates) are associated with 2, 3, or 4 engine aircraft, and affect how much performance is requied for each engine out condition.

Also, be careful, some gradients are published as percent slope, some as feet per nautical mile. NOT interchangeable - math required.

I worked out the formulas if you want them, along with some common gradients and slopes.


'scuse me now, I'm going to go try to get a life...




Oh yeah, read part 25 (also the perf. parts of 121) a couple times. It ain't that bad. Really.

 

[cheater1239]

100LL...Again!, wrote:
>"V2- takeoff safety speed. A VERY ROUGH analogy would be Vx."


a different viewpoint regarding V2 is that it is a speed that allows the aircraft to be maneuvered, at 15 degrees bank, rather than considering it to be like Vx...just a viewpoint

your "top of the head" info is great, and expansive
regards, 1239

 

[NJA Capt]

Correct me if I got this stuff wrong.

Segt1- Liftoff to gear retraction, assumed to be 35' over the end of the runway.

True: 35' dry/15' wet = reference "0"
1st seg ends at end of gear retraction

Segt2- Initial Climb at V2. This segt is complete at 400 abv the runway, or the acceleration altitude. Most are 400'.

End of 2nd segment depends on type. Citation 560XL and 750 (X) are certified (V2) to 1500' instead of 400'.

V2- takeoff safety speed. A VERY ROUGH analogy would be Vx. This speed is designed to get you over the obstacles.

I would vote VXSE, since V2 is the reference for a single engine climb.

Thanks for prompting some research. It's good to knock the dust off every now and then.

 

[citdrver]

Thnaks for the info guys,

There has been a lot of dust on this subject for me and many things I just didnt know. I know in the past I avoided much of this stuff because it seemed confusing and a bit daunting. But now that it is the season for people wanting to fly to places with big rocks around them, I feel much better reviewing many of these requirements.

I found a very good explanation of many of these concepts (with proper refernces) that I had all along in the form of an E-Mail from one of my FSI instructors that I had saved from the NBAA Air Mail board. If anyone wants it, PM me.

Fly Safe and remeber 2.4%.....or wait 1.6 net??........Whatever keep it at V2!!!!!!!!!!!!!!!