@t-bonham:Good question.
AFAIK none of the current UAVs (Unmanned Aerial Vehicles in DoD-speak) are set up for quick reaction launches. At least not at the air defense scramble level of “quick”.
And yes, a lot of what’s being done with these aircraft now is aiming towards flight times measured in 10s of hours, not fractions of hours. Loitering like that can gather intel continuously until the fuel runs low. It can also wait patiently for a target to appear, the quickly get there. Which works well in the low-intensity conflicts we’ve done recently. Lots of waiting then a quick rush to attack a transient target.
@Dr. Strangelove: Cute. But not all that quick. Fireman’s poles have been used with the same idea as a fire station: vehicles on the ground floor, people sleeping above.
That would be more practical. Hadn’t heard about that.
Has any thought been put in to keeping a plane “plugged in” and kept at a semi-ready state? It’s expensive to keep the turbines spinning at all times, but with external electrical power you can at least keep the avionics booted, and perhaps the hydraulics pressurized and the like. You might also have heaters to keep certain parts warm that would have to heat up otherwise. What limits the ramp-up rate of the turbines, anyhow? Any way to speed that up if you had unlimited external power?
I’ve never heard of them keeping the engines spinning unless it was a fuel stop in Alaska. It takes less than a minute to start one. If they were parked in Alaska then the engines and cockpit and anything else that didn’t like the cold was pre-heated. I think it was the B-58 that had something like 365 vacuum tubes in its computer system.
Oddly enough, I thought that Dr. Strangelove’s like was going to be to the lion version of Voltron, with (IIRC) the pilots being zipped through dropshafts.
And drones would have an additional advantage over human-piloted craft: As mentioned before, rushing through the checklist carries an increase in the risk of missing something, but you can tolerate more risk with a drone than with a human pilot.
That’s actually what came to mind immediately, but that was the first version I found on YouTube and I thought it was funnier, so I kept it.
It’s true, and for those of us who lived through the Cuban Missile Crisis, it wasn’t anything to be flip about, either.
I remember seeing a video of a pilot and ground crew rushing up to a jet fighter; the first thing one of them did was smack a big “start” button on the front landing gear to get the turbines spinning up to speed.
Leaving everything powered up consumes useful life. In machinery that already often has single- or low two-digit MTBFs. It also creates overheating problems unless you also have a source of forced cooling air. Yes, those challenges too could be designed around at a cost in weight, price, and performance.
In my era the tradeoff was made in the direction of leaving the jet powered down. With the advent of F-22 & F-35 and vastly more computers with presumably longer boot/resume times they may in fact have already made the tradeoff the other way. It’s not a topic I’ve seen discussed in the trade press.
In airliners we generally need to provide air conditioning if we’re going to provide power. Electricity alone overheats the black boxes in just a few minutes in hot ambient conditions, and will do so eventually even on frigid days.
Starting a turbine engine involves two steps: spinning the turbomachinery up to a low RPM with some external (to the engine itself at least) power source, then lighting the fire and letting the exhaust gasses “bootstrap” the engine up to the higher idle RPM, typically also assisted by the external starter at least part of the way.
In the airliners I deal with we figure 30 seconds for the starter to spin the engine up to fire-lighting RPM, then another 10-ish seconds for it to bootstrap up to the point the starter stops helping, then another 10-ish seconds to continue bootstrapping up to the self-sufficient idle RPM. Different engine types are slower or faster than this, with fighter engines having much smaller fans with less rotational inertia bootstrapping faster.
During the bootstrap phase the engine is in a very critical condition; the fire is burning, the airflow is small so the fire is too, and there’s only so much excess energy available in the exhaust gases to accelerate the mass of machinery. All of which is operating very far off its aerodynamic optimum point which is designed for cruise (airliner) or max power (fighter). If fuel is fed in too fast during bootstrap, the fire gets too big, the backpressure increases enough to choke off the incoming airflow and acceleration quits while the fire burns a hole in the engine. That’s bad. If fuel is fed in too slow the acceleration stagnates, the temps go up, the backpressure goes up, and then the fire burns a hole in the engine. That’s also bad. Starting was one of the harder problems they had to solve back in the 1940s.
An additional issue is that a typical engine has two or three “spools”, concentrically linked layers of turbines and fans or compressors. Typically the starter motor only drives one of the spools and the other(s) begin to turn driven by the airflow created by the one driven spool. You need all of them turning at some specified minimum RPM before you light the fire. On the slower-starting models a lot of the delay is waiting for the un-driven spools to catch up to their minimum RPMs long after the driven spool has reached the max RPM the starter can do unassisted.
Armed with enough horsepower in the starter system and a way to accelerate all the spools together I suppose one could spin an engine up to normal idle RPMs, light the fire and be idling without the bootstrap phase at all.
Starter motors today come in three types: electric, compressed-air turbine, and mechanical transmission direct-driven by a miniature jet engine. The latter of course raises the question of “how do you start that one?” And for the other two you need to create the electricity or compressed air onboard or plug into a ground source thereof.
In the 1960s there was a series of engines made that used an explosive charge as a starter. Think pistol “blank” cartridge the size of a 1lb coffee can. The upside is when the cartridge fires the engine is almost instantly spun up to the fire-lighting point. The downside is it only works one-shot without ground crew replacing the cartridge, it only works on single-spool engines, and the engine gets only rapidly decaying help during bootstrap phase. That technique fell by the wayside by the 1970s.
All in all we’re only dealing with spinning up a few hundred to a couple thousand pounds of machinery to anywhere from a few hundred to a couple thousand RPMs. The challenge isn’t mechanical; it’s just fitting that much horsepower into a starter system small enough and light enough to carry around for the rest of the mission. It’s all just tradeoffs.
As I said in my first post in the thread, I’m not thinking this is the area across the total kill chain where we can cost-effectively shave a few seconds. Solid-fueled SAMs are the zero-time-to-launch interceptors the OP is looking for.
I have nothing to add to this topic but I like the phrase “firewall the go stick” so much I’ve already used it twice at work to my colleagues’ bewilderment.
Could you tell me what it means, just in case someone asks?
Understood, but I figure there’s a range of lifetimes depending on the component. The turbomachinery itself–yeah, you don’t want that spinning constantly. But solid-state electronics should have a long useful life if you keep it cool.
Why not external electric? I guess what I’m imagining is a plane in a specialized hangar. Being a fixed installation, it can provide effectively unlimited cooling, electrical, and mechanical needs. A big electric motor could drive whatever power input shaft the aircraft was capable of supporting. Maybe just drive it with a long shaft going into the rear of the engine–designed right, it could drive the two or three spools simultaneously and independently.
Neat. Sounds like an extension of the Coffman cartridge.
No disagreement there… but it’s fun to think about how you would do it if you really had to.
The firewall is the plane that separates the passenger compartment from the mechanical stuff in front of it (in both cars and aircraft). The go-stick is the throttle, and increases as it’s pushed forward. To “firewall the go-stick” means to push the throttle as far forward as possible–i.e., to the maximum (also see post 16).
nm
Fighter radars used to have 10-15 hour MTBFs. All solid state. Everything was bleeding edge. And designed for performance, weight, and volume first. Reliability past the duration of a couple missions was about #17 on the engineer’s priority list. Most stuff ran stupid-hot relying on convective / radiative cooling only; no spare space for forced air ducting.
Yeah, given a dedicated alert facility there’s not much reason not to plug a shaft in for mechanical power, plus electricity and cooling air. We do part of that in the airline business; most jetbridges contain power cords and fully cooled air hoses that plug right into the jet. Driving a couple hundred HP (WAG) through a flex-shaft into a big-ass female splined fitting in the belly shouldn’t be that hard. That much HP would be enough to whip the engine up to RPM pronto. Don’t stand too close just in case something pops loose though.
Great movie.
Here’s a paper on the development of the cartridge http://arc.aiaa.org/doi/abs/10.2514/6.1967-1508. Here’s one in use: https://www.youtube.com/watch?v=g9fkmqPHTDE. After the bang you can hear the whine of turbine combustion start almost instantly. Then there’s 15ish seconds while the pitch and RPM are bootstrapping up. Then the whine stops changing and they’re at idle.
Yup.
Dr S, I don’t think I ever saw the movie but I remember the tension over the “Coffman cartridges” (? right ?) from the book. It was the first thing I thought of when LSLGuy mentioned cartridge starters.
My brother flew B52s for SAC out of Loring AFB circa 1966. I visited him there that summer. I recall guarded mentions of flight crews manning the “ready shack” for a week at a time. I think they kept six aircraft at the ready at all times. He wouldn’t tell me how quickly they could launch beyond saying the “official time” was 8 minutes. When pressed he admitted it was “Less. … … … … … … uhh … … … … … Much less.” He refused to talk about potential missions or the weapons they carried except that they were nuclear and each aircraft carried “more than” a couple. I remember being simultaneously awed and horrified at the thought of my proximity to so much hellish awfulness. I also went bass fishing a couple of times with his tail gunner. I was amazed that a plane capable of delivering nuclear weapons half way around the world and carrying one crew member in charge of “Electronic Warfare” also had a guy whose job was to sit in the back with a machine gun.
Thanks - makes perfect sense.
I endlessly amuse myself at Banksiawoman’s expense by slamming myself back into the passenger seat when she changes gears, so this will make me even more annoying.
No one’s mentioned the “alert five”?
A fighter is kept on the flight deck, with the pilot/crew aboard, hooked up to a catapult. All that is needed is to spin up the engines, turn the carrier into the wind, and let fly.
You say that like turning an aircraft carrier is a quick operation.
Back in the day, there was another kind of external start Aerospace Ground Equipment. This was used in SR-71 operations. Because SR-71s get all the cool weird toys.
The AG-330 start cart has a pair of GM 454 cu in. V-8 engines and an upward-projecting driveshaft that engages a start drive pad in the underside of one of the SR’s J-58 engines. Mate it up, start the V-8s, engage the transmission, and throttle up to 3-4 k RPM. When the engine catches, reverse the sequence and bring the cart around to the other J-58.
Obviously, this is not “ready in 5 seconds” or even “ready in 5 minutes”. It’s just cool, that’s all, Because SR-71. 
I was going to mention the SR-71’s start cart as well. I have this sneaking feeling that half the reason they built the start cart was because they could. Someone at Lockheed really loved the idea and so wanted to build one.
The other part of the startup was triethyl-borane which was needed to light the engine and the after burner. Plane carried enough to start the afterburner some reasonable number of times. It always bothered me that both SR-71 and A12 could only light the afterburner a fixed number of times in a mission.