F-15 Vref

[SpoilerFault]

Hi, I have a question for any Eagle pilots out there. What would be an average Vref for the F-15? It came up in conversation at work and I was looking for a ballpark speed. Thanks.

 

[Pantherpilot]

Approach and Landing

Instrument holding airspeed is a 250 KCAS, and we can hold off a TACAN fix or a notional INS waypoint. Penetration airspeed is 300 KCAS and, depending on the descent gradient, is accomplished with nearly idle power and 10° nose low. Approaching the Final Approach Fix, we again reduce airspeed below the landing gear white arc (even though there are no round dials where a white arc is marked, you get the idea) and simultaneously drop the gear and flaps.

Once configured with the gear and flaps down, the Eagle is a little more sluggish to control inputs, but still vastly superior in maneuverability to your average Cessna 172 or 182. Approach and landing is flown referencing an angle of attack, rather than a particular airspeed. In an airplane that can vary as much as 40,000 pounds in landing weights, approach and landing speeds can be anything from 155 KCAS all the way up to the 190s. The "perfect" speed for approach and final correlates to 20-22 "cockpit units" of AOA. You can compute a "backup" airspeed for final approach by starting with 155 KCAS and adding two knots for every thousand pounds of fuel or ordnance on board the jet.

Flying a straight-in final with or without instruments is very simple. All you have to do is place the velocity vector in the HUD over the top of the runway threshold and maintain approach airspeed to fly down final. If you make sure that, when the velocity vector is on the end of the runway, it is sitting 3 degrees low in the HUD pitch ladder, you’ve just given yourself a 3° glide path all the way down to the runway!

Of course, the preferred way to arrive at an airport in the F-15 is not via the Localizer straight-in (for wimps!), but via the overhead break (Man style!). Generally initial is flown at 1,495’ and 300 KCAS. Once over the approach end runway numbers, I roll into 80° of bank and perform a 3-4G level turn while pulling the throttles back to idle. Once I’ve rolled out on downwind, I’m below 250 KCAS, so I drop the gear and flaps and continue to decelerate for the final turn. Prior to the perch point, I confirm my landing configuration by saying, "4 green, good pressures, brakes off, antiskid on, lights on" (translation: gear and flaps down, all three hydraulic systems are showing good pressure, the holding brake is off, the antiskid braking switch is activated, and my landing light is on).

The "perch point" is where most pilots would turn base in a normal box pattern. In the Eagle, though, instead of a squared-off base and final leg, I fly a constant-rate descending turn to final. To do this I dip the nose 8-10° low, roll into 60° of bank, and maintain about 190 KCAS. Something that might make the hair stand up on the back of your average civilian pilot’s neck while flying the final turn is how much the airplane buffets. This is normal, and is just another one of those great sensory cues that the pilot can use to evaluate his speed and bank in the turn. If there are "mice dancing on the wings," you’re okay. If the elephants have come out to play on your wings, you’re about to stall in the final turn - bad news. If I’ve judged my pattern spacing and pattern winds correctly, the descending 180° turn should spit me out on a 1 NM final at 300 feet AGL and my computed final approach airspeed. From there, the approach and landing picture is the same as described above for a straight-in…you just looked a lot cooler getting to that point!

Once the airplane is over the runway over-run, you shift the velocity vector to the departure end of the runway and softly flare. The landing picture in the F-15 is very different than any other aircraft I’ve ever flown due to the nose-high attitude in the flare and the length of the landing gear. In fact, in the landing attitude, the cockpit is almost 30 feet off the ground! With the main gear tires on the pavement, the preferred method of slowing the Eagle down is the aero brake. This is where we both save wear and tear on the wheel brakes and take advantage of the Eagle’s huge wing area to slow down. To aero brake, simply hold the nose 10°-12° nose high until 90 knots, increasing aft stick until it is all the way back to the seat pan. Once at 90 knots, briefly neutralize the aft stick to get the nose lowering, then haul it back to soften the impact on the nose strut. With the nose gear on the ground, you can honk on the toe brakes as hard as you want and watch the antiskid braking work wonders. After exiting the active runway, I safe up my ejection seat, turn the radar to standby, and turn off other power-hungry avionics like the LANTIRN pods.

Once I leave the active runway, the flight’s not over. There are still postflight tests of avionics to be accomplished, an update to the inertial navigation system to be accomplished, and finally I will download the flight data to the same Data Transfer Module that I brought to the jet. The DTM download accomplishes two things; one, the airplane assesses it’s own maintenance issues and puts that information on the DTM, and two, the central computer has kept track of the parameters of every gun and missile shot that I’ve taken, as well as every bomb I’ve dropped. After the flight, maintenance doesn’t have to fuss with talking with pilots to assess the maintenance condition of the airplane - they just read the DTM codes. As for the weapons parameters, they are infinitely valuable for use in postflight debriefings of the day’s missions.

 

[SIG600]

As was mentioned, fighters don't calculate landing speeds based on weight. We just fly angle of attack. Your average airliner is doing the same thing when calculating Vref, it's just more complicated.

 

[SpoilerFault]

Thanks for the info guys. Since the downturn in the airlines, I took a gig as a DoD civilian working on the C-17 but recently transfered to the F-15. Almost everyday we have jets going out on post PDM functional flights and I was curious about the landing speed because I'm so use to heavies. I always enjoy seeing the F-15 fly and my hat is off to you guys who operate them.

 

[Fox-Tree]

Good grief - the guy asks a simple question and he gets the history of the world.

The real answer is 138 + 2 knots per 1000 pounds of weapons and/or gas. I don't know who the goof is that wrote the stuff Pantherpilot cut/pasted into his answer but some of his info is wrong.

SIG,
Flying AOA isn't as critical to us as it is to our Navy bros. We actually are/were taught to calculate an approach speed to have as a backup or cross-check of the AOA gauge.

 

[Mud Eagle]

The real answer is 138 + 2 knots per 1000 pounds of weapons and/or gas. I don't know who the goof is that wrote the stuff Pantherpilot cut/pasted into his answer but some of his info is wrong.

What is wrong about it?

The paragraph quoted is for an F-15E, not a C model...which does NOT use 138 as the base airspeed.

 

[SIG600]

SIG,
Flying AOA isn't as critical to us as it is to our Navy bros. We actually are/were taught to calculate an approach speed to have as a backup or cross-check of the AOA gauge.

We were too, but it's used as a cross check to make sure the AOA indexers are accurate.

 

[Pantherpilot]

Fox-Tree,
The info I posted was from an article by Randy Haskin, here is his profile:

Name: Randy Haskin Company: US Air Force Position: AIRCRAFT COMMANDER Current Aircraft: F-15E
http://www.pilotmentornetwork.com/mentors.php?mtor_id=35

Also here is a link to the article in full text:

http://www.f-15estrikeeagle.com/articles/story_eagledriver/eagledriver.htm

I figured the F-15E Strike Eagle would be a good aircraft to represent the Eagle since it is considered an all around F-15 capable of strike and ground. There are too many models to list approach info for all: F-15: A-D,J, DJ,N,F,H,I, K,S,SG,SE,S/MTD,ACTIVE,IFCS,MANX,ERIS, and NACA TB 0001-0015 (TESTBED).

Glad too see even on FI we check references.

 

[Colonel Savage]

What is wrong about it?

The paragraph quoted is for an F-15E, not a C model...which does NOT use 138 as the base airspeed.

Base speed for the F-105 was 200 knots plus 1 knot for every 1000lbs of fuel/ordinance.

 

[CFI2766]

Base speed for the F-105 was 200 knots plus 1 knot for every 1000lbs of fuel/ordinance.

You are showing your age there...

I recently saw some pics of some neat ones at Lackland, however...