Turbojet engines like the one installed in the A-4 Skyhawk series typically run at about 33,000 RPM or so when firewalled – what we call “mil” power, or military rated thrust. They idle at around 61-64% of that speed on deck and a few percentage points higher in flight due to the “ram” effect of high velocity airflow – say 65-67%.
One of the curious features about turbojet engines is the non-linearity of thrust response. You get not much more than a hot breeze from idle to say 70% RPM, and just enough to taxi with between 70-80%. From 80-90% you get good, useable thrust for steady state cruise, but anytime you want to really accelerate the airplane you’re probably talking a setting of above 95% throttle. The net effect is that a disproportionate amount of thrust is generated within the relatively narrow band of 94-98% RPM (most engines are slightly “de-tuned” to ensure that they don’t overspeed, so you rarely see 100% RPM on the gauge).
Not only is the thrust response quicker in the higher RPM band, engine response times decrease as well. Unlike a piston or radial engine prop aircraft, which gives a gratifyingly immediate and proportional response to a given throttle input, spooling a J52-P6A engine from ground idle to mil could take up to 13 seconds. This is mostly a function of shaft inertia and compressor lag, but also because fuel flow increases are carefully metered at lower power settings to avoid overtemping an engine that’s not yet up to speed. While response times are slightly faster from flight idle there is still a power band on the back side of the curve that a survival-oriented pilot would avoid if he thought he might need more power in a hurry – when he was low and slow, for example. Or in the landing pattern.
Most of the time throttle response time isn’t an issue in carrier aircraft, since naval aviators are taught to fly constant angle-of-attack, power-on approaches. But sometimes it matters.
You: Why do you want to make my head hurt, Lex?
Me: Which I was just getting to the point, wasn’t I?
Besides being a sporty little crate in its own right, the TA-4J Skyhawk was the student naval aviator’s first exposure to anything like a “war bird” – although it was a training aircraft, it had many of the same characteristics as very high performance combat aircraft: Swept wing design, nimble aerodynamics, high subsonic top end and guns – actual guns! – in the wing. It was to drool.
As a single-engine airplane, the list of engine-related emergency procedures was also rather short and easy to memorize. If the only engine stopped making go-noises, you had some little time (depending on altitude) to try to get it going again, or – barring that – to go for a walk. There were also procedures for engines that, while they might have been running rough or had lost oil pressure, had not yet pooped out entirely – these were called precautionary approaches, or PAs.
One form of PA was flown from a position about a mile and a half or so abeam the intended point of landing on downwind (i.e., heading the opposite direction from the landing runway). Pattern altitude was around 2,000 feet above ground level and airspeed was whatever speed you could get out of a clean (wheels up) jet at 87-89% throttle – usually around 200 knots. Turned out that damaged A-4 engines had run for prolonged periods at that RPM without seizing, and it was a pretty much optimal ejection airspeed if you had to step out: Fast enough to trade a little speed for altitude, not so fast as to tear off important appendages in the wind blast.
Instead of the staid, power-on, exquisitely precise approach and landing that carrier pilots spend so much time practicing, the PA was an exciting, g-on, swooping turn to final that really got the heart beating – it felt more like a low-angle bombing or strafing run than a normal landing. Once safely established on final approach the pilot would throw the gear down, as well as some increment of flaps. Once the landing was assured he would retard the throttle to idle – in an actual emergency, he’d shut that baby off. Since he’d be coming in hot the pilot would have to point the nose well short of the touchdown zone and “flare” to land – another innovation for a carrier guy. Rather than on the rubber-blackened strip abeam the simulated carrier deck, anywhere on the first third of the runway was considered acceptable.
I had an early stage solo one day in training, and decided to practice my PAs – not because I needed the practice so much as that they were just fun to fly. The pattern was clear, so tower cleared me to zoom and swoop to my heart’s content. I was starting to innovate a little on my third approach – never a good idea for a student pilot with all of maybe 200 hours total time, but what did I know? – a little higher abeam, a little tighter on the runway prior to the approach turn. The combination found me turning to final carrying a whole bag o’ knots, maybe 220 indicated or so. I was also a bit high, so getting the landing gear and flaps down early seemed like a good idea. Approaching the fence I was still cooking on high heat, so I pulled the throttle to idle a bit earlier than usual and even feathered out the speed brakes.
Time came to flare and I was still going pretty fast, 165 knots maybe, rather than the target 120 kts. The excess airspeed caused me to float over the runway, delaying my touchdown. With the acceptable first third of the runway rapidly running out behind me, I finally – and somewhat ingraciously – manhandled the jet on deck. Which is when my trusty scooter – which apparently had thoughts of its own about high speed landings – bounced back into the air, 40 or 50 feet off the ground.
It is one thing, gentle reader, to be 40 or 50 feet off the ground after a touch-and-go landing, climbing out at full power and looking for traffic on downwind. It is another thing entirely to be hanging suspended in the air at 50 feet with the speedbrakes out and the engine at idle.
It’s quiet. Very, very quiet.
You can hear yourself squirm.
She was slowing down just fine at that point too, so much so that we were about to go below optimum angle of attack and come falling out of the sky like a turd off a tall moose. And I’d easily used up the approach end of the runway, leaving only the running off the other end portion in front of me – an academic distinction, given that I wasn’t entirely sure we wouldn’t break off important parts of the landing gear when the whole thing came clattering back to earth. And even if I wasn’t running out of prepared surface upon which to place the jet, there wasn’t altitude enough to dump the nose again for knots and still reset to a proper landing attitude.
Bit of a bind. And I’d been doing so well.
Well, there’s bad and there’s worse, and faced with no particularly good options but diminishing airspeed I rammed the throttle up against the mil stops, closing the speedbrake as I did. And sat there in the cramped and stultifying silence, waiting for the engine to spool back up from flight idle. Seconds can seem like years when the angle of attack gauge is tickling at stall, and the runway starts to fill up the windscreen. It can seem like an eternity.
A hideously. Quiet. Eternity.
But, because I’m here and not pushing sub-prime mortgage derivatives somewhere in Manhattan, you had to know that it all worked out for the best in the end. Just as I started to wonder how truly bad it was going to be, the engine caught up with my desperate need and I carefully rotated the jet to a fly-away attitude just as the main mounts kissed the runway about the midfield marker. I joined downwind set up for a normal approach to a full stop landing. Not much older, but quite a bit wiser.
I learned about flying from that.
Ooh, a sea story…
I haven’t even read past the jump yet but I’m already happy.
See, Lex, we’re easy to please, no problem at all. Just throw us the occasional
bonesea story here and there.So Lex, did you count that as 2 touch and goes, or just 1?
“Like a turd off a tall moose”…can I use that line? It’s a keeper
Some of your finest, sir, your finest indeed. Thank you.
Thank you for providing a real world example of the “closeness” of the power availible and power required curves of a jet powered aircraft at low speed.
Our flight dynamics class didn’t get into spool up time, but that must make the low speed operation much more interesting, to say the least.
Thanks Lex, great story.
“Gentle Reader” reminds me of Asimov, one of my all-time favorites. You & Mr. A. share the rare gift of being able to tell your story to ME, in a way that is most enjoyable, and not just to an “audience”. I suspect that many of your other readers would agree.
Much appreciated.
… and isn’t it funny how hard it is to supress the deep desire to push the nose over and somehow “will” her back on deck while wondering “how did I get all the way up here?” Holding AOA on an airplane that is suddenly growing a curly tail and a snout takes guts…
Thanks for the story Lex. Nice to be in your audience…
“Most of the time throttle response time is not an issue in carrier aircraft..” Too bad you never got to wave an F8 Crusader at night with a moving deck. She was so clean, boards in the belly retracted with the gear down, and speed critical, 133 to 136 kts, required the rpm to be back to 83 to 85 percent to fly an ok pass. If the intrepid aviator chased the deck, pushed over, the apc would bring the J-57 back near flight idle. This was usually followed by frantic cries of Wave Off, Wave Off, Burner and the vacating of the platform. Most of the time they missed the round down, sometimes they did not. It really was interesting to wave Crusaders.
Nice story.
Thanks. And a cool plane too.
I’m shocked, shocked I tell you, that the RDO didn’t hang a new callsign (“Dribble”) on you after that performance. Or have you been holding out on us?
Of course, this also provides new insight as to why we used to call FCLPs “bouncing”.
Bill C, after that teaser, you must tell us those stories!
Thanks for the story, Lex. I really enjoy it when you do that! Glad you were here for the telling of it.
“… turd off a tall moose.” Hmmm. Funny. Very funny.
P.s. Oh, Bill C, no necessity for revolting ramp-strike stories; just the amusing ones, in which all survived.
Just for my own curiousity, with the usable throttle being only the top 1/5th of the range, was the throttle marked in some increments so the pilot knew where he was at, throttle-wise? And did they profile the actuating lever such that the first 50% throttle was 20% of the lever movement and the remaining 50% occupied the other 70%. You know, a progressive throttle, only in reverse?
I once had a hillclimber with a powerband like that. Suzuki GT380 powerplant, 380cc worth of two-stroke triple. Below 4000rpm it couldn’t pull first gear. From 4000-5000 it sputtered and thought about maybe running right, sounded like a badly-tuned chain saw. 5000rpm saw it start to run properly, and from 5500rpm until the 8000rpm redline everything happened in about a second and with a whoosh of power. Too light on the clutch and you’d fall off the hill or float the points. Too heavy and you’d bog it down or flip it over, at which point the svelt, nimble hillclimber turned into a 300lbs hammer with which to pound the rider into the ground like a tent peg. Which it would do in a heartbeat.
Some days, when the formerly-broken bones aren’t aching and my vision isn’t blurry, I miss that bike.
– Max
Low and slow with no power and half way down the paved part…not good Lex! Not that I’VE never bent landing gear struts…
So, today with your experience, if you encounter the same situation is the solution the same as what you did then?
Justthisguy,
If Lex gives the ok I can relate one really funny F8 story that has it all, ramp strikes, barricades, ejection seats that don’t work, and nobody dies.
Go for it, Bill. By the way, did you ever know a Gerry Arbiter? Light attack guy, flew in ‘nam, force paddles at AIRPAC. My first CO. When I was first becoming an LSO, he mentioned to me that he’d seen 8 ramp strikes in his career – mostly F-8′s off 27-Charlies. Privately, I thought to myself, “Maybe if you’d waved them off a little earlier, skipper…”
Phil – what I learned is that some approaches aren’t salvageable. I’d have 1) stuck to the published profile or, 2) taken it around much earlier, when I was too fast on final approach.
Max, the throttle was linear on the A-4 it was the response that was non-linear. Pretty austere fuel control system in that jet.
While waving FCLPs in a T-2 squadron, on CQ-1 so instructors were with the studs, our intrepid Skipper was flying in the pattern and had a low oil light on the stbd engine. So he takes the plane from the student and declares he’ll be full stop on this pass.
For some reason, he decided to shut down the starboard engine while on short final, and flying a decent pass. Too bad he grabbed the flap handle instead. Up go the flaps, away goes the lift. So he goes from a niggling ball high and just PLUMMETS to landing short of the runway, in the paved region with all the yellow paint. Us LSOs are all standing there WTF-ing each other, but figuring his goal was to land anyway, so no need to wave him off. He’s the Skipper…he knows what he’s doing (not (always)).
The overrun was below the runway, so we couldn’t see his landing gear as he came toward us. There was a bit of a ramp where the overrun meets the runway proper, and our Skipper’s T-2 hit that and vaulted into the air, soaring past us at about 20-25′ AGL, engines at idle, looking like hurdler taking a leaping, 200′ long bound. It was beautiful. He 3-pointed the landing and taxied home.
Captain, I know you’ve heard it a million times before, but you have a gift that is truly precious.
I read this story this morning with great delight, and chuckled all day over the term ‘prepared surface’. You made my day a very happy one.
Thank you for taking the time, and making the effort, to share your earned wisdom with us.
Best regards, Peter W.
Great story to start the day (at least mine).
I agree…some approaches will not result in safe landings. For those that have never piloted, it’s all in the approach. “a whole bag o’ knots, maybe 220 indicated or so. I was also a bit high” = a missed approach.
Thanks for the story, you’re so good at it!
First paid gig, flew right seat in a Piper Navajo on approach. Flap lever was all the way down…when the red line said they were there, what did I do? Popped the lever back up. Hey, they were down…won’t they stay there? Tends to make the tail drop, kinda like Britney…
Not my finest moment.
Justthisguy.
In late 63 or early 64, off the coast of Japan I found myself assisting the cag LSO one dark but not stormy night. the F4′s came in first no sweat but then came the f’ing 8′s. Ed Lighter was cag paddles and he was good, really good. He got them all but one, Checkertail 105, Lcdr Goosey driving. Not his real name but you get the idea. He was too fast, flat and long bolters. On his third pass he decided to go for it and dipped his nose in close. F-8′s really dropped when you did that and all Easy Ed could do was hit the wave off lights just before the pride of the Crusader kingdom bounced 105 off the back side of the mighty Midway. Midway won, and 105 went screaming down the angle sans main landing gear. The hook missed everything and we all watched him go off the angle and out of sight. All waited to hear the silence of engine stop as water vice air filled the intake. No silence for what seemed a long time and then out off the starboard quarter was the sight of Goosey’s F8, in burner, climbing at a 45 degree angle. Like a homesick angel was Lighter’s exact comment. Seems as tho our boy’s stricken bird did a 90 deg roll to stbd as he left the angle, and he pulled the alternate handle. The one between your legs. It came out in his hands with no result. Good thing or he would have had a short ride into the side of CVA 41. He then pulled the stick, hard, and proceeded to pull just in front of the bow, below flight level. If at first you don’t succeed yada yada He pulled the primary curtain, same result as before, so he did the only thing left, level the wings, pull hard and light the burner.
He was really rattled (no sh_t, who wouldn’t be) and he got to 15,000 feet before Lighter got him out of burner and level. Now began the greatest psych job I’ve ever witnessed as Lighter talked a terrified pilot down to take the barricade. You could hardly understand him due to his teeth chattering. Samples of the conversation..” No Jim, you can’t stay up there. You have no gas”
“You can’t eject, remember the curtain is on the cockpit floor”
“Get the GD bird down now or you are going to die, in about 10 minutes, and we are all going to watch”
It took two passes but Lighter literally talked him every second to a barricade arrestment. Colorful to the end, he went into burner as the aircraft stopped and it took three screams from the LSO to get him to shut down. The quacks told us that three hours later, with 10 shooters of booze in him, his eyes were the size of silver dollars and he wouldn’t stop talking. I told you waving F-8′s were interesting.
Lex,
In defense of your skipper about not waving F-8′s off sooner. I had one hit the deck on me 11 seconds after initation of wave off lights and verbally. The last time I saw him he was below flight deck level and coming hard. As I hit the net he hit the ramp in a full stall, in burner, and nose high. The bird cartwheeled through the mirror assembly, took it right off the side of the ship. We lost the pilot and two deck crew due to flying debris.
GD it B.C. that’s one helluva story! Told better’n Grampa Pettibone coulda!
Lex, I got a down in the A-4 on a dual fam check of some sort for being “underpowered on approach”, (non PA) but your use of the boards adds a distinct variable. Boards? You musta had a flashback to the Buckeye.
What’s that other thing called “the region of reversed command” or some such? Where you actually continue down despite all that power.
How do you remember all this stuff? Have you a bootleg copy of A-4J NATOPS about da house?
Gotta wonder about that huge diameter JSF engine. I know it ain’t a turbo-jet and all and I’m sure it has all them sw doodads to keep a pilot from screwing up, but surely it must have the same sorta characteristics a little.
b2
Great story Lex. You tooo Bill C.
13 from idle to mil? Wow, that’s slow. The last check we’d do for full power TF30-P414 (F-14 a/c) engine tests was a “Throttle Response Check”. Reset the clock, slam the throttle from idle to full Zone 5 AB, and start the clock when the throttle hit the Z5 detent. 6 to 9 seconds later it would be in full Zone 5 burner. Burner light-off and staging to Z5 was a kick in the pants
Just out of curiosity, what was the response time in the F-18?
PIMF. That should be “You too Bill C.”
Dang, Bill C. Thanks! (I reckon, it made me pucker a bit, so maybe I’ll have better intonation when farting, now)
Bill C. – what is ‘the rest of the story’… why did the seat fail? Did he skip the ‘showed and stowed’ preparation and leave the pins in? Or was it a faulty seat (mmmm – what would that do for the aircrew thoughts at T/O … got a chute strapped on do I have a way to shell out and use it). Putting together you and our modest host here for an evening of stories would be quite an event! You could sell tickets ….
Thinking about it some more…
Theoretically, it might have been possible for the guy to close the throttle, point the aiplane up high until IAS was a nice gentle 50 knots or so, open the canopy, and just jump. However, after doing one really bad mistake and seeing two systems failures, maybe the poor guy was not willing to do something like that. Am glad he got talked down from that.
Did he get over it?
P.s. I think that the F8U which John Glenn used to break the transcontinental speed record, back when I was a kid, got used up by that Viet-Nam thing and now rests on the bottom of the South China Sea.
And this is why you don’t make an approach in a jet like you do a prop, and vice-versa.
JTG-
That’s correct. On 16 July 1957, in “Project Bullet,” John Glenn flew BuNo. 144608, an F8U-1P, to a new transcontinental speed record – Los Angeles to New York in 3 hours, 23 minutes, an average of 725mph. The aircraft was later remanufactured into an RF-8G. Assigned to VFP-63, it was lost in a landing accident aboard ORISKANY while operating in the South China Sea on 13 December 1972. The pilot ejected.
I always learned more from crap … read as “stupid stuff” … done on a solo that no instructor EVER saw. Makes you wonder how we ever survived.
Love reading about this stuff, also love collecting carrier footage, home video’s and mishaps mainly.
Say hello at jkaposi@hotmail.com if you have footage to share.