Boost Pumps 

Some courage there!

I made a hybrid poster with Heather Thomas piloting an F4 Phantom 2! Sorry but I don't kiss and tell...

🤣🤣🤣

Jay-z must be your "go to" to "get er done" then

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True

Thanks! You know, I rode an airhead to Oshkosh in 2023. BMW R1200 G/S.

@@AgentJayZ ... got me

Yes. Sorry about using the word suck. It's an easy mistake, even though I try not to make it. In one of the recent Patreon vids, we go through the fuel pressure switch. It's basically there to illuminate a cockpit light indicating boost pump failure. The engine can run without boost pumps, but it's happier if it doesn't have to.

Additionally, the fuel boost pumps in the B727 and B767 were used to "dump" fuel when necessary. None of those aircraft had the ability to transfer fuel from one tank to another in flight so there were no "transfer pumps". The fuel systems were designed so that we could "cross-feed" fuel from any fuel tank to any engine when necessary for balance considerations but we typically ran "tank to engine" as the normal procedure.

Bombardier uses ejector pumps as their main boost pumps with a gear type motor driven pump as backup. Fuel is tapped from the engine driven pump to pressurize the ejector pump supply. The motor driven pump is used at startup and a backup to the ejector pumps.

"The engine driven pumps will not be able to rely upon the static air pressure at high altitude to provide enough differential pressure between the fuel tank and the engine driven pumps..." WTF? since virtually all fuel system components live at the same altitude and air pressure there is no altitude induced pressure differential. The only differential pressure that might exist is due to a difference in height between a pump and the tank from which it draws fuel. That is called "net positive suction pressure head, and yes, suction is a real engineering term used in pumping and fluid flow design. The boost pump is used to assure a positive pressure at the pump inlet. Please consider the fact that all the engines on a 727 are several feet higher than the top of any fuel tank so that should be a clear indication that atmospheric pressure is irrelevant. Another point, the tank mounted boost pumps are centrifugal pumps which like all in that family create a low pressure area at the impeller inlet while rotating, that phenomenon is is why the engineering term for that area is called the pump suction, it is the same if that pump is operated in space or at the bottom of the Marianas Trench.

Sorry for the confusion - I assumed that it was obvious that the differential pressure of which I spoke was the difference between "pump suction" (your term) and atmospheric pressure. I did not say that there was differential pressure solely due to atmospheric pressure. My point was that a fuel pump creates low pressure at it's inlet as it attempts to "draw" fuel from the tanks but then (in the absence of "boost pumps") relies on atmospheric pressure to provide the "push" to move fuel from the tank towards the pump. The most "suction" any pump can produce is 0 psi and, at sea level, atmospheric pressure is close to 14.7 psi - never a problem having enough differential pressure for fuel to flow reliably for fuel systems on the ground. At "jet" cruising altitudes however, atmospheric pressure is much lower; hence the "differential pressure" force available to "push" fuel toward the pump is lower as well.. An extreme example - a fuel pump at 0 psi inlet pressure attempting to draw fuel from a tank (at the same height) that is also at 0 psi will not be able to do so without an "in-tank boost pump" to supply the required differential pressure. There must be a difference in pressure for any flow to occur - that's how pumps work. While it's true that aircraft with engines mounted lower than the fuel tanks can usually, but not always (depending on aircraft attitude), rely on "gravity" to supply some pressure to feed the fuel pumps, even the B757 and B767 aircraft (under wing mounted engines) with which I'm familiar normally require that the in-tank fuel boost pumps be operated continuously from before start to shut down. I'm not saying the engines won't run without the boost pumps on, but the aircraft is not "legal" for dispatch if all the boost pumps in a tank are inoperative. Additionally, if even one (of several) boost pumps in a given tank are inoperative, we're required to carry huge amounts of additional "penalty" fuel in that tank to ensure the remaining boost pumps are never "un-ported". As for the "space or at the bottom of the Marianas Trench" statement - it's true that "pump suction" is the same, 0 psi in both places but the "outside" pressure is vastly different. The pressure in the depths of the Marianas Trench are in the thousands of psi, lots of differential pressure between the "outside" pressure and "pump suction". In contrast, the pressure outside a space vehicle is essentially 0 psi - the same as the "pump suction" (no differential pressure to do the "work" and therefore no fuel flow). Having been employed as a space systems engineer some years ago, my recollection is that to solve this problem, spacecraft fuel system tanks are pressurized with helium or some other inert gas. That gas pressure then provides the required differential pressure for fuel to flow (also, since they live in 0 gravity, there are additional problems related to keeping the fuel at the "pickup" location so that the pumps get only fuel, not the pressurizing gas...).

I don't have access to data on the aircraft fuel system in the Sabre. It's important to watch the maneuver being performed, because inverted flight does not necessarily mean negative G. I believe the Sabre has a maximum negative G endurance of 20 seconds, mainly because the oil is only scavenged out of the bearing sumps in positive G. A swinging pickup in the oil reservoir ensures the oil supply is maintained while flying in negative G, but no oil gets returned, so the supply runs out quick. Since the engine can run inverted at all, I think there is a swinging fuel pickup at least in the main tank, into which the other tanks drain to keep it full. Negative G is avoided, but would be experienced in steady, level inverted flight. Things like barrel rolls and inside loops are positive G, all the way through.

@@AgentJayZ - Thank you.

Centrifugal compressors are simpler and cheaper to make, they are tougher and more resistant to stall. They lose efficiency after about the size needed for about a 1000 Hp engine, and they are limited in the ultimate discharge pressure they can achieve. Some exceptions at the upper end of capacity are the PT6B at almost 2000 Hp, and the PW150 at around 5,000Hp. Axial compressors are capable of much higher mass flow rate, and are able to achieve compressor ratios of up to 50:1. They are more complex, more expensive, and require more maintenance, but in the 5,000Hp to 500,000 Hp range, they work really well.

@@AgentJayZ thanks for the answer, I researched a bit and learned that they also have a relatively low rpm limit and you can't really stage them. Always great to hear different sources.

The rpm limit is determined by diameter, exactly as with axials. The limit of the number of stages is usually about 2 for centrifugals, whereas 15 or more is no difficulty with axials.

​@@AgentJayZ We/I have a solutions to the centrifugal/radial machine conundrum but it's unpatented as yet. ヅ I provided the correct answer on your '...F-35B Lift Fan Drive Question...' page. The answer is simple. The engine is not oversized because the VTOL phase power requirement is obviously not greater than the power required for forward flight which has a drag component that is not present during the VTOL phase. When I researched the lift fan system some years back, a dog clutch was mentioned in the drivetrain engagement. I don't know if that was an authoritative source so can't vouch for the veracity. With language being imprecise, that could probably mean a one way clutch, sometimes called an overspeed clutch, where metal rollers are located between two concentric rolling elements [somewhat resembling a roller bearing] that wedge themselves between these elements to act as one for power transfer/transmission. I suspect that the clutch requires frequent replacement due to the large forces present. We have patented a torque dense [i.e. compact], infinitely variable [for gradual power transfer], high speed & torque, hydrodynamic transmission/coupler [torque converter] that would significantly reduce this frequent servicing. We have also patented a simple, infinitely variable, torque dense, positive engagement, transmission which does not utilize involute/spur gears. It is called 𝔽𝕣𝕚𝕔𝕥𝕚𝕠𝕟𝕃𝕖𝕤𝕤 𝔾𝕖𝕒𝕣 © transmission and is based on our reformulation of gearing theory. In e-VTOLs the use of either allows significantly smaller motors and batteries for same performance/application. Similar benefits are derived in turbo-engine apps with smaller, lower cost, more efficient engines along with other features & benefits. FYI, in the near future, we will bring out tech which enables antigravity with propulsion apps including interstellar travel, rendering all else but museum pieces/dinosaurs. If anyone can hook me up with SpaceX or any of Musk's companies, Pratt & Whitney, etc. to improve many of their offerings, we'd each benefit greatly. ヅ BTW, I'm a triple engineer, CE, ME, AE with penchant for nanotech, quantum biology, quantum physics, astrophysics and cosmology, among other things. ヅ PS. Excellent channel. TnX. Cheers ✈✈✈ 𝕄𝕀𝕃𝔸ℕ✈✈✈

The CT-133 is the aircraft I'm in during the formation takeoff in my video called Warbird Jets. It was an awesome experience.

@@AgentJayZ Ah lucky you, I'll have to find that vid. On my tour in Baden during the Cold War I worked mostly on the T-BIrd, just a 6 month stint line servicing on the 104. I had the pleasure of many back seat trips in the T-Bird. Never lucked in for a 104 ride though.

I would say the jettison pumps are fulfilling the role of boost pumps, wouldn't you?

@@AgentJayZ yes I would, I just wanted to highlight the fact and inform you about these airplane things that unlike the normal practice of other manufacturers of having electric boost pumps Bombardier uses this "strange" method... Ciao ;)

Thanks! You make them do a handstand?

@@AgentJayZ Should I? Ciao ;)

They are not "jettison" pumps, they are "jet pumps" or more correctly, eductor pumps. They use a high velocity stream of fuel to accelerate a larger volume of fuel. They are not "strange" but a fairly common type of pump used in many airframes. For what it's worth, some engine mounted fuel pumps use a centrifugal element at the inlet to provide boost pressure to the positive displacement section.

@18robsmith - I agree, Juan is also an A&P mechanic.

If I started a series about motorcycles, would you help out? I need questions, that I and a guest would answer based on our experiences in riding, racing, building and breaking. Jet City Moto?

Something small, like a T58, a RR Viper, a Garrett TPE 331, or an Allison 250 C-18. You need to be able to fond the overhaul manual, and a source of parts. Donor engines will save you hundreds of thousands. The used market in the aviation world is still extremely expensive, so you will need to become a detective to find the stuff you need. Check out Darren Duncan's channel where he did an amazing job on his surplus Fairchild J44. The OH manual, and the illustrated parts catalog are an absolute must. Look for those first at places like eflightmanuals.com. If you are an extremely talented technician, and have "all the tools", and think you can figure it out on your own, I wish you luck, but failure and financial loss is a certainty in my opinion. You have been advised by someone who does this for a living.

@@AgentJayZ thanks for the very informative reply! I have a home machine shop and im an engineering student so im more prepared than most. Im not gonna do this to make money, just for fun and to learn how the technology works.

P-47 thunderbolt and DH Mosquito are tied for first place, in my ranking.

This video is about boost pumps.

​@@AgentJayZYou spoke about the Challenger fuel system and the plane fueling up before it took off. I wouldn't have added pertinent information if you hadn't brought it up first.

OK, I was not trying to figure out why the crash happened. I was only trying to explain what boost pumps were. Because Juan mentioned them without saying much else about what they were.

Don't know what engine you are talking about. With a turbofan engine, thrust is mostly proportional to N1, which is the speed of the LP compressor, which is also fan speed. If you are looking to run the engine at max... right to the ragged edge, then EGT, and the speed limits of both shafts are your "redline". But as I understand it, each flight of each aircraft type, with each type of engine has a calculated optimal power setting. If you underpower, you might not make it. If you overpower, you are wasting fuel and causing more than necessary stress and wear on the engines.

Thank you for the response I was asking for a p&w jt15@@AgentJayZ

No. There is a return from the fuel control output to the pump inlet. Fuel flow is high, and generally fuel temp is about room temp, so the fuel control has no specialized cooling ability.

Not all diesel engines return large quantities of fuel or use it for injector cooling. Practically all have a return line to collect leak off fuel (all plunger pumps leak) and return it to the system but that might only amount to an occasional drip. It all depends on the engine design. Turbine engine aircraft often use fuel as an oil coolant so heat is added, not removed. "Room temperature" for an airliner cruising at high altitude may be 60 or 70 degrees below zero and wing tanks rapidly cool in the airflow. Take a look at the bottom (sometimes top) of the wings of an aircraft that has just arrived at the gate after a transcontinental flight and you will almost certainly see frost in the shape of the remaining fuel level. This doesn't apply to SR-71s of course, they had exactly the opposite issue.

Higher safety margins, lower allowed tolerences, better QC, redundant systems, R&D. It's why turbine engines specifically for aircraft (vs. internal combustion engines, or even industrial gas turbines) cost so much.

Well, the only time(s) I've had an engine cut out on me when driving was when I was very sloppy over maintenance.

I've had an ignition coil fail on a new vehicle, stopping it in the street. Once running, a jet no longer needs its ignition system. But, yes. Design differences. Jets and piston engines are different in almost every way possible.

@@AgentJayZ -- Well, I "conveniently" forgot to mention that most of the time car engines are at a glorified idle. But I've going up some long "20 minute" grades at times. An aircraft engin operates at 50 to 75% most of the time.

@@AgentJayZ Thank you, and thank you to all who responded

Boost pumps ensure a reliable source of fuel for the fuel pumps. Fuel pumps are not necessary at all when the engine is not "running".

@@AgentJayZ thank you

It all depends on the airframe manufacturer and becomes part of the Pilot's Operating Handbook or aircraft operations manual. Some say that auxiliary or boost pumps must be on for takeoff and landing then selected off at some point, some are selected on before takeoff and turn off automatically so they remain in a standby condition unless fuel pressure to the engine driven pump decreases. There are any number of combinations and procedures, all of which are dictated by the airframe manufacturer as part of the certification process.

@@oldtugs bell jet Ranger Alison 250 turbo shaft Has two of them

A small number of twin engined helicopters were built as the Twin Ranger model. Not very many.

Well, you are lucky. those idiots have threatened me.

@@AgentJayZ Sorry to hear that

@@AgentJayZ - Threaten you? Seriously? What a bunch of morons. These are the idiots who believe jet engines don't use fuel, right?

@@wickedcabinboy Of course it's them. The number of conspiracy lunatics drives me crazy and they are generally not nice people.

Thanks. "the condition of the center being over the ball"? Gibberish. The center of what?

So the offensive team (the ones that start with the ball) has 4 attempts to gain Ten yards distance towards their goal line. Normally when they talk about gameplay you’ll hear the number of down which the offensive team is playing, and the distance they have yet to traverse before they can restart the count of “downs”. Now it can be a number greater than ten if the player with the ball runs away from the starting line as well IE “1st and 15”. I only played football because my friend did, otherwise could not care less about the sport.

Much better. Thanks!

When I describe fuel pumps as gear driven, I mean they are attached to the engine, and driven from a gearbox literally attached to the main shaft of the engine via a radial drive shaft. Boost pumps are in the fuel tanks, and electrically driven. They are nowhere near the engine.

@@AgentJayZ Sorry, I meant to say gear type, not gear drive.

Also, yep generally in port fuel injected cars, you're exactly right, the fuel pump in the tank is the only pump. On cars with direct injection (diesels and newer gasoline cars) there's a second high pressure pump mechanically driven off the enine to provide the >1000 psi required for the injectors

I don't listen to her music, but I am impressed with her humanity.

@@AgentJayZ LOL. And her humility. She's practically a monk.

Get schwifty.

I will look into it again, but so far the automatic subtitles are garbage. So inaccurate that they are not useful, and just annoy me. A lot of what I do is to straighten out misunderstandings about how these machines work. The subtitles only add to that misunderstanding. Why would I think audio translations are any better?