You should try going into Milan in high summer when it's humid AF, all pax are on board, waiting for your slot and the APU is inop... Then you really miss it on an F100 with only one door open!! That APU was worth it's weight in gold

The APU also provides bleed air to start the engines.

@PositiveRateAv

2 жыл бұрын

Which makes startup a lot easier

@suddhojitgon5929

2 жыл бұрын

Except the 787

@Rhaman68

2 жыл бұрын

@@PositiveRateAv Try “engine start possible”

@matsv201

2 жыл бұрын

@@suddhojitgon5929 also not A350

@matsv201

2 жыл бұрын

@@satunnainenkatselija4478 that is strange, becuase the bleed air system is fully removed of the A350 engines just like the 787. So it sound strange that it can use bleed air start, when there is no bleed air system

Fun fact: Concorde didn’t have an APU to save weight and space in the narrow tail. Thus first two engines were started using an air cart, the remaining two were started using engine bleed from the engines that were already running.

@DasMoose9001

2 жыл бұрын

Didn't they put one of the many fuel stowage tanks in it's place? They got rid of a few amenities to place them, I know that. Quite literally became a balancing act for them as well.

@leobakkerflightandspace6655

2 жыл бұрын

@@DasMoose9001 Affirm, the tail cone housed the aft trim tank, which was filled with fuel during supersonic flight to offset the effect of the center of lift also moving aft.

@DasMoose9001

2 жыл бұрын

@@leobakkerflightandspace6655 I figured as much, thank you very much for clarifying that with me. The Concorde is a unicorn in my generation, by the time I was interested in them AF-4590 had occured and they weren't in service anymore.

No surprise there. The B727 was designed to be self-sufficient at all the airports back in 1963 that were still only set up for piston engine planes. Unlike the first generation US jets, the B707/720 and DC-8, which required ground equipment to run A/C, start the engines and board passengers, the 727 brought its own support equipment, including airstairs. While the 707 and DC-8 were long haul jets made to serve overseas routes, the popularity of jets increased demand for jets at every commercial airport. The 727, 737 and DC-9 filled that need in medium and short haul, respectively. Back when it was only first gen jets, a common sight at a fully equipped gate was a large yellow flexible tube to bring air conditioned air from the gate to the aircraft. This would connect to the belly of the plane after engine shutdown. Ground power wasn't strictly necessary, as the flight computers that newer jets rely heavily on weren't in those old jets. Before the gas crisis and the move to hub-and-spoke, flying was a more leisurely experience. A medium haul flight would let down once or twice between terminal airports and give passengers the better part of an hour to deplane and explore the airport. Passengers would leave plastic cards on their seats saying "occupied" to let new passengers know that seat was claimed. For a kid it was ideal, breaking up a long flight and giving access to explore airports that would otherwise be unavailable. Flights were more direct, too. Today the same trip involves taking one flight to a far away hub airport, getting off the first flight and running to the other side of the airport, where a second flight is scheduled to take off only minutes after the first landed. The stress brought on by fear of missing a connecting flight makes it thoroughly unpleasant.

@CheapBastard1988

2 жыл бұрын

Actually the external airconditioning has made a comeback but usually in a mobile form. Because ground power can't operate the airconditioning systems on most airliners and the APU generates noise and pollution. The Boeing 787 which can operate the airconditioning from ground power, needs three 180KVA (KilovoltAmps AC) capable power sources connected, two at the front, one behind the left main gear. Because airport infrastructure often isn't designed for the rear connection, that connection usually requires a diesel generator which would be pointless compared to just using the APU. Therefore the mobile external airconditioning is the most efficiënt option.

@theharper1

2 жыл бұрын

The rear doors on the 727 and DC9 also made it easier to operate into airports without ground air stairs (you mentioned stairs but I thought the rear stairs were an important feature).

@StringerNews1

2 жыл бұрын

@@theharper1 the rear stairs certainly had a cool factor! And gave coach passengers an advantage. I loved that first row behind the last entry door. You got tons of legroom, were close to the rear galley, close (but not too close) to the lav, and were first off when the airstair was used. The 737 had the front airstair, but it never felt secure to me.

In order to encourage companies using a GPU instead of the APU, Innsbruck airport supplies a GPU to aircrafts for 45 min of no charge.

Probably the smartest thing Sully did that cold day in New York was immediately turn on his APU without waiting for the checklist to say to.

@donaldstanfield8862

2 жыл бұрын

What a hero, they were lucky to have him as pilot! Bravo, Sully!

The first jetliner to have an APU was the British De Havilland Trident 1C. This flew before the Boeing 727 in 1962.

@kennethreyes7859

2 жыл бұрын

From what i remember, the first few Tridents didn’t have APUs, looking at pictures of the prototype and first few aircraft might show it

@donaldstanfield8862

2 жыл бұрын

There were some amazing innovations throughout British aviation history that don't get the recognition they deserve, imho.

I work on the 727 (still) and it’s one of the loudest apus ever.

A problem with the 727 APU placement in the right wheel well was that the exhaust was also on the right side fuselage, just behind the wing. Sometimes fuel vapors would collect in there and during start up after landing, it would ignite those vapors and produce a brief flame up past the right side windows - startling the Passengers. As a Flight Attendant, we would have to be aware of this fact so that we could be ready to prevent an unnecessary evacuation that would be started by the Passengers. If you look at old photos of the 727, sometimes you can see a dark streak across the right fuselage that was caused by these flair outs.

@Greatdome99

2 жыл бұрын

The flame that you mention was only after a failed start when unburned fuel was left in the combustor. Upon a second start, that fuel would create quite a fireball roaring out of the right wing. Newer APUs have a fuel venting feature to prevent such flameups. The 727 APU could not be operated in flight.

Thank You Simple Flying For Telling What A APU Is.

In the early 80's as a new 727 flight engineer on starting the APU I would close my eyes and cover my ears as the turbine was situated under the thick part of 3 fuel tanks. They would also "torch" quite often in strong wind conditions.

@donaldstanfield8862

2 жыл бұрын

What do you mean?

@jakejacobs7584

2 жыл бұрын

@@donaldstanfield8862 it means it was like putting a bomb underneath a kerosene storage tank

@elcheapo5302

2 жыл бұрын

I used to fly a Hawker that did the same thing when the APU start nozzle was clogged. Quite a spectacle at night; it'd light up the whole ramp. We called it the "Angry Dragon".

@jakejacobs7584

2 жыл бұрын

@@elcheapo5302 Nice!

@Greatdome99

2 жыл бұрын

No. The APU was enclosed in a fireproof shroud to prevent fires. It was located inside the keel beam of the airplane in between the landing gear.

The APU on the 747 can't be started in flight, but may be used supplementally up to 15,000 feet. 😎

🤔I know APU pretty well. And this will be a fascinating technology for aviation study

Missed from the video is the fact that the APU is used to start the main engines by compressing air & delivering it to each engine’s air start. APUs can also provide hydraulic power & electrical power. The power output to size ratio is extremely impressive & they run on the same fuel as the propulsion engines. APUs however do not or cannot provide propulsion.

@thetheatreorgan168

2 жыл бұрын

i heard the exhaust force is comparable to a 7 seater light aircraft on widebodies though i could be wrong

@thetheatreorgan168

2 жыл бұрын

however too miniscule to do anything

@Greatdome99

2 жыл бұрын

@@thetheatreorgan168 No. It's only a couple of hundred pounds. The turbines are designed to extract as much power as shaft HP, not thrust.

I first became curious when I saw a dirty streak going up from the rear of the right wing on 727s back in the 70s. That led me to find out why and I learned about APUs then.

Yes, I knew but I’m an Avgeek and I love learning that stuff about aircraft… I’ve flown a Honda Jet HJ-1 with an APU however most small jets or general aviation planes don’t have them and rely upon GPU’s. However business business jets also rely heavily on APU’s

Loudest APU ever had to be on the BAC 1-11. Boarding via the rear airstairs was one hell of an experience, remember it well on Dan Air's 1-11 fleet

The only Apu I knew of was Nahasapeemapetilon... Thank you, come again!

I think anyone who is interested in aviation would know about the use of APUs. It's often a gotcha question in quizzes, ie how many engines does a 747 have - answer, 5 (although it can ferry a sixth engine under the wing). At one airshow, I saw a glider which had been fitted with a tiny jet engine. One of the commentators joked to the other (who was a 747 pilot) that the engine was smaller than the 747 APU. 😀

@donaldstanfield8862

2 жыл бұрын

With an engine, didn't it cease being a glider!?

Fun fact. The 707s that I fly were retrofitted with an APU placed in the aft cargo compartment sometime in the 1980s

Thank You for such background information.

The placement of the apu on the 727 was horrible... the noise was deafening when unloading the rear cargo bins... That was my only complaint about the 727, otherwise it was one of the most well designed products to ever come off of the Boeing assembly line.

Not sure if you can fix it but, in 0:04 it said Auxiliary Power *United* instead of Unit, guess the same mistakes happened at 2:22 for the GPU

I do remember the B727, when they rolled up to the gate it was turned on It was very noisy the exhaust was right near the window..

The biggest reason carriers use ground power units is financial. This costs on average 300 dollars an hour to use the APU. Going power units are a fraction of the cost.

@Greatdome99

2 жыл бұрын

You can't cool an airplane with a GPU except for the all-electric 787. Cooling requires huge amounts of bleed air.

I have known that the APU existed for years even though I am not a pilot.

Good to know.

Very inacurate. APU's swept in for flying boats, which had flights of several days, and stays on the water. APU's powered tube radios, cockpit and cabin lighting, fans, ventilation, plumbing, bilge pumps, vacuum cleaners, cabin appliances, and backed up landing gear. Each radial had a big generator and one more ran off a quality Advanced Power Unit air cooled gasoline engine. The APU also took strain off the small batteries for starting motors.

@donaldstanfield8862

2 жыл бұрын

I wondered about that, they landed in some pretty remote areas, so would need to be self-contained, thank you!

@willarddevoe5893

2 жыл бұрын

@@donaldstanfield8862 just some minor rewriting.

@ruthgroh7574

2 жыл бұрын

In the mid 1950s the USAF Grumman Albatross amphibian (Sa16) had an APU in a separate compartment in the rear fusillage which we used to start engines both on the land and on the water. George Groh(former USAF navigator)

@Chris_at_Home

2 жыл бұрын

I used to go on detachments with P-3 crews to some places where support was limited. One time we were flying out of Bogota and the APU didn’t have enough power to start our engines as the airport was at 8600 feet above sea level. A 2nd P-3 that did start used its prop wash to assist to get that first engine going.

@Greatdome99

2 жыл бұрын

I saw a diesel APU in Howard Hughes Flying Goose. Located just behind the flight deck.

auxiliary power unit also provides backup

2:24 Ground Power United?

Talk more about how APUs relate to redundancy and etops!

@Greatdome99

2 жыл бұрын

180 minute ETOPS requires twin-engine airplanes to fly with one engine inoperative for 180 minutes (some now 240 minutes). In case of an engine failure, the APU is fired up to provide electrical power since it has essentially the same generator as the engines. The APU doesn't directly power hydraulics, but can via the Electrically Driven Hydraulic Pump. It doesn't have the pneumatic power to restart engines at altitude--that's accomplished below 20,000 feet via "windmilling" the engine.

How does the APU get its air? Does it bleed air from the engines? I didn't see an air inlet.

@Greatdome99

2 жыл бұрын

It takes in air from a dedicated inlet located on the upper fuselage which closes when not in use (that's why you don't see it). Some of the air goes to the combustor, the rest to a shaft-driven "load compressor" which sends air to the airplane's pneumatic system (ECS packs, engine starters).

Ground power united?

Is there a reason why some planes like 767, 777, 787, and A350 have APUs that vary in sound pitch while other planes like 737, 747, A330, and 757 have APUs that make a steady sound pitch?

@ndirangugichuki6260

5 ай бұрын

I think it's the amount of power they produce and the design of the exhaust that contributes to different sounding APU's, I could be wrong, never thought about that before.

The Boeing 727 jetliner was the first aircraft to be outfitted with an APU

Ground Power United?

👍👍👍

At the more modern airports don't they use ground power wired connections?

And when the APU is an operative be prepared for an air start

HS 121 Trident ?.

That’s partially new for me, I knew about it, but not with all those details

"Thank you, come again" - Boeing 727

the APU sounds like a vacuum cleaner

I think that airlines used to instruct their pilots to keep one of the planes engines running in order to provide power to the airplane before APUs became standard.

i also know there is an aircraft equipped with 5 APUs ... (cough cough you know who)

@Kalvinjj

2 жыл бұрын

Wasn't it 1 APU and 4 hair dryers?

Fully aware…

🤔

i think i read once that an apu on a 737 technically increases its glide distance/time by like 13%, assuming both engines die

@davec8921

2 жыл бұрын

How would it do that? It produces electricity and compressed air, not thrust.

@vevenaneathna

2 жыл бұрын

@@davec8921 its exhaust is pointed backwards.... and while it might not be optomized to throw it backwards with as much momentum as possible like a regular jet engine, it both lightens the plain and has some mass velocity in the opposite direction. might also have to do with keeping systems online that optimize glide ratio in newer models

@harrysharp2648

2 жыл бұрын

@@davec8921 During our Delta Airlines B737 training, we were told the APU generated 37 pounds of thrust...insignificant for powered flight but good for trivia questions.

First comment

I bet a banana wont fit

Auxiliary Power United? Ground Power United? Don't you people have editors? One mistake is carelessness, two are incompetence. How can we be certain the information in your video is correct if you can't even get the name of the topic correct? Just terrible.

@aarondynamics1311

2 жыл бұрын

Calm down. Humans make mistakes, how do you not know this?

Why mention about an Indian man name APU???? He design the plane?

@tightcamper

2 жыл бұрын

Apu was a character in The Simpsons!

@truthful3777

2 жыл бұрын

@@tightcamper Thanks for reminding...I was thinking where in the world I hear this man's name.

@farrellhinkley8940

2 жыл бұрын

@@truthful3777 m.p

@v12ts.gaming

2 жыл бұрын

@@tightcamper that's the joke, bud 🤦🏾‍♂️