Hi!

Simple question, but I couldn't google it at all. I would like to know typical horizontal and vertical velocity of the following aircraft during landing:

*boeing 747 or similar large airliner
*sailplane
*F-14 or similar landing on a carrier.

Thanks in advance,

Nicolas

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

For the 747, I could take 250 km/h, and assume a 3° slope, that would be 3.6 m/s vertical velocity, and 69 m/s horizontal velocity. Is that realistic? It wasn't a "solid" source .

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

In the nautical system, 140kt airspeed, 12fpm ROD, for anyone who knows more about ATC spacing rules.

__________________
2 good 2 need 4 engines

I'm going to step out on a limb and answer a technical question outside of my technical expertise. When someone corrects me that will ok with me. :-)

I believe that approach speed is computed based on the weight of the aircraft. If you are landing with a lot of fuel left then you have to be going faster. A big plane like a 747 physically can't land when full of fuel. The pilot looks at a quick reference card (or the FMS computer calculates it) and that is what determines landing speed.

Also, in high winds, I believe it is standard practice to going faster when landing and to use less flaps. That way, the wind doesn't blow you all over the place.

So bottom line, there is no one number.

As to vertical speed, I believe that an aircraft follows a glideslope which is basically like: At X kilometers from the runway you will be at Y altitude. So, it's a slope. If you are going very fast down that slope, then your vertical speed is very high.

So there is no one number for VS either.


Edit to add:::
When I say that approach speed is computed based on the weight of the aircraft, what I mean is that for each individual aircraft approach speed is calculated this way. So, there is a base approach speed for an F-4 and a table that allows you to lookup the actual approach speed given the aircraft's current weight.

There is no one number indeed, but just typical values please. I need 3 realistic but distinguished landing approaches, that's the only requirement.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Maybe this helps

B747
Tomcat (carrier approach speed = 125 kt)
No info easily available for sailplanes, but I´d guestimate a speed in the 45 kt range?

__________________
If you're careful enough, nothing bad or good will ever happen to you.

ok 125 knots. Is the approach always 3 degrees for carriers, or often more?

edit: in most cases, 3 degrees.

Hm, not a lot of difference with a 747 landing then .

Sail plane flyers, please share a typical approach!

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Your guestimate was very well: 50 kts is typical approach speed for one model of sailplane. What would be a typical approach glide slope?

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Most sailplanes control their approach with either spoilers or flaps. With the spoilers/flaps retracted, your approach angle would be very flat. Just how flat depends on the sailplane's glide ratio, typically anywhere from 20:1 to 50:1. Spoiler/flap deployment allows for a much steeper approach. Most of the sailplanes that I've seen at my local airport stay high until they're assured of making the airport then come down fairly steep, say a 6 degree angle or so. Remember, they can't do a go around, so altitude is money in the bank. That angle is just a rough eyeball estimate. I've seen steeper approaches and I've seen shallower ones.

OK I'm modelling initial approach, so I think we're closer to the natural glide slope (L/D) of the craft there, 2 -2.5 degrees. The final approach will be steep indeed, as you want to land, not skim the field . 6 degrees seems realistic then.

Does anyone have more info on initial approach of sailplanes?

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

The ASW-20 glider manual(PDF) must have the numbers you´re looking for.

__________________
If you're careful enough, nothing bad or good will ever happen to you.

they claim a 4:1, or 14°. This at 48 knots.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Me again.

I have one last question, I'd need the answer urgently but I can't find it in the literature available here. (and travelling to the aerospace library takes me 4 hours one way since I moved...)

In a standard drag calculation (D = 0.5*rho*v²*cd*S), look at the factor cd*S, drag coefficient times frontal area.

For cruise, this value is different from approach. During approach, the flaps are extended. This means the frontal area increases, as does the drag coefficient. I'd like to know by how much (typical values, say for airliners such as 757).

For frontal area, I guess that assuming a 30% increase would do. But what would you say for the drag coefficient? I'm looking for Cd/alpha curves showing both flaps extended and flaps retracted curves for airliners, but I can't find any.

The reason behind this question is that I want to be sure that assuming cd*S at approach is tenfold the cruise value, is indeed a very extreme estimate, certain to be too large.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

Flaps serve two purposes as discussed here. They increase lift and increase drag. How much they do so varies with the type of flap (plain, split, slotted, Fowler). On airliners, the flaps are highly effective at increasing the lift coefficient (often to greater than 3). Airliners often use a type of complex split or Fowler flap design where they extend aft quite a bit (increasing both the lift coefficient and the wing area) before turning down. Many airliners also use leading edge slats to further increase lift at higher angles of attack.

When the flap is partially extended, the primary effect is to increase lift, allowing the plane to fly more slowly. The last 10 degrees or so of deployment is mainly downwards - increasing drag - which allows the plane to make a reasonable approach without picking up speed. Without the increased drag, it'd be difficult to fly a standard 3 degree approach without picking up speed. This would require the plane to fly a much flatter approach (say 1 degree) which would present terrain and obstacle clearance issues.

This link provides some good performance estimation formulas and explaination of aerodynamics. Books like "Theory of Wing Sections" can provide specific lift and drag curves for different airfoils. Good luck.

I've found values of 25% increase in drag at 10° flap deflection.

So if we take twice the area (huge) and twice the drag, that's still only a factor 4, and I've taken a factor 10. So that is certainly more than you'll ever encounter on an airliner. And that was the purpose of that factor 10. (I wanted to show that gusts in the direction of flight have little influence on forward airspeed of airliners during approach)

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

I wanted to show that gusts in the direction of flight have little influence on forward airspeed of airliners during approach

If I'm reading this correctly, you're investigating the effects of wind sheer on an airliner. Wind sheer is a sudden change in wind velocity. This can and does have a big influence on an aircraft's performance and has lead to several accidents. Suppose you're flying into a 10 knot headwind (takeoffs and landings are normally done into the prevailing wind to the extent possible) and the wind suddenly changes direction and/or speed. Suppose, for example, the wind speed suddenly drops to zero. Your plane doesn't instantly accelerate so the immediate effect is that your airspeed just dropped. So will you. If you know wind sheer is present, you make your approach at a higher airspeed to give you a safety margin.

I've encountered wind sheer many times while flying my plane. It makes for some pretty tense moments, especially when it catches you by surprise.

Oh yes, don't get me wrong, it certainly has major influences on the aircraft. What I needed to show was that forward gusts have very little influence on forward ground speed. the reason is the large inertia of the plane and the small drag coefficient.

Of course for lift and hence vertical velocity, the influence is far larger.

You agree with me that c_d * S will never change a factor 10 between cruise and flaps out config for airliners?

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.

If you're landing into the wind (as is desired) and the wind shifts to suddenly give you a tailwind, the plane's inertia will prevent the plane from suddenly speeding up. The result is a loss of airspeed leading to a loss of lift - leading to a high descent rate. If the pilot wasn't prepared for it and has insufficient altitude to recover, crunching sounds ensue.

Ground speed isn't the issue - airspeed is. The worst thing that can happen is to run out of airspeed, altitude, and ideas all at the same time.

There's also the matter of the landing technique. Airliners and sailplanes perform a flair maneuver just before touchdown to reduce the vertical velocity as much as possible. In the case of the carrier landing, the airplane is literally flown onto the deck with no attempt at a flair whatsoever; the F-14's glide slope intersects with the carrier deck at an acute angle.

This is the major difference between Air Force and Naval Aviation aircraft - Navy aircraft have a more robust design to withstand the force of repeated impacts with the flight deck, while the Air Force fighters perform a normal landing flair to reduce the impact and therefore can be build with a more lightweight construction.

__________________
"Any technology, no matter how primitive, is magic to those who don't understand it." - Florence Ambrose

I know what I'm calculating isn't the main issue, but the whole point of my calculations is showing that it isn't an issue: forward ground speed will not change all that much.

__________________
To the regular visitor of internet bulletin boards it is clear that it's an excellent idea your parents get to choose your real name.