Tag Info

58

Even if we ignore the salaries of everyone involved; engineers, sales people, management, Q/A teams, manufacturing teams, more sales people, and then a few spare engineers... I don't understand. If it's just designing a jet engine, then raw materials cannot possibly be a major factor even if it's something like titanium or composites. While the raw ...

52

No, the helicopters are standard production versions. The Eurocopter AS350 is a common model used for these operations. In 2005, Didier Delsalle landed a Eurocopter AS350 B3 on the summit of Mt. Everest at 29,029 feet (8848m) (twice). The only changes he made to the standard version were removing a few things like extra seats to reduce the weight, and of ...

45

Now that's an interesting phenomenon! I do not believe that this is a case of an illusion of any sort, or the engine dilating. What the video probably shows, is the engine slightly turning towards the window as takeoff thrust is being applied. Engine mounts are not 100% rigid, this can easily be observed on pretty much any passenger flight if you can see ...

34

Jet engines are some of the most complex machines ever created. They have to be as light, efficient, safe, and reliable as possible. There's a reason that most new airliners recently have been affected by delays from engine manufacturers. This is a hard balance to engineer when on a schedule and budget. Jet engines could certainly be cheaper to develop and ...

25

The most (kinetic) energy is in the fan and turbine blades and disc. The engine is enclosed in a containment chamber whose purpose it is to protect the rest of the airplane from shrapnel in case of a fan disc or fan blade failure. Here's a video of a test where a fan blade failure is simulated: As you can see, the fan blade ...

22

Turboprops are actually turbine engines. They can produce bleed air just like turbine engines (e.g. turbofan). The bleed air can be used directly to pressurize the cabin, or it can drive another turbo compressor to pressurize fresh air from the outside: Modern aircraft with supercharged piston engines simply use bleed air from a) the main engine's ...

19

A turboprop plane can be pressurized in the same way a turbofan plane can: via bleed air from the compressor stage of the turbine engine. A turboprop and turbofan are not that different actually. You have a turbine engine core that powers the big fan at the front or the big propeller via a gearbox (although the turbofan still gets some of its thrust from the ...

19

the centrifugal clutch will only disengage after its rotating speed falls to the disengagement point. The over-running clutch disengages the engine from the rotor at the very instant that the engine's rpm falls below that of the rotor. In this way, the rotor is never wasting kinetic energy by trying to turn over a dead engine and the vehicle stands a better ...

15

They do not have drastically lower rates of failure than comparable piston engines. Their manifest unreliability in automotive applications is one reason they failed so badly in the marketplace. My college materials science TA owned one and had it rebuilt four times. His record for the shortest distance before failure on a zero-timed Mazda rotary engine was ...

15

if you decrease the duct cross-section, you must apply work to accelerate the flow through the smaller duct. this means the fan driving the duct has to work harder (it must absorb more shaft horsepower) against that constriction in the flow and you derive no benefit- unless you mount the fan on a more powerful engine, in which case you are burning more fuel ...

14

The main place engine manufacturers will focus on minimizing damage is with the large fan at the front of a turbofan engine. FAA Advisory Circular 33-5 discusses the regulations that cover this. The manufacturer must show that the worst case blade rotating at the highest RPM can successfully be contained. Only 15 seconds after the event is the operator ...

14

Last I checked, most scientists and engineers do not make millionaire salaries. I think it's more around 100 to 250k tops. Even if you had 100 of them working for 10 years on it, that would be 250M, or a quarter of a billion dollars. The salaries in aerospace average less than 100k, it ain't IT, but they're not the issue. You can develop a basic ...

12

The answers are all very good in that they detail potential costs, but let me give a different angle for looking at these types of questions. In a highly competitive environment, companies will throw as much money at a problem as it is worth for them to have it solved. In economic speak: "marginal cost equals marginal gain". When designing a new engine, one ...

11

The NK-12 engine uses a differential epicyclic (planetary) gearbox. Unlike the typical planetary gearboxes where one of the gears is fixed, here all three parts are moving: the turbine drives the sun, the planet pinion drives the front propeller, and the ring drives the rear propeller. The gear ratios are the same between the front and rear, but the torque ...

10

Mostly because there is no need to strongly accelerate the flow. In fact, thrust engine is given with the formula below: $$F_N \approx \dot{m} \cdot \left(V_{out} - V_{in} \right)$$ Which means, there are two ways to produce the same thrust: strongly accelerate few air massflow or speed up a little bit a big amount of gas. Turbofans use the second strategy,...

9

A jet engine may not contain a severe explosion (for whatever reason) but there are various mandated things that are put in place to help protect the airframe. The engines are generally mounted such that they shear off cleanly and away from the airframe. There are a few AC's like this one and this one that discuss how to deal with and comply with various ...

9

As another answer points out, the main problem is poor reliability. In a conventional piston engine, the sliding contact of the piston against the cylinder wall is mostly against relatively cool metal and is constantly lubricated by oil from underneath. The contact is often maintained tightly by piston rings, which have a natural outward spring. In the ...

8

Adding to other excellent answers, I'd like to focus on the nature of the research. The work involved in developing and exploring ideas that aren't just capable of resolving via computer models, are huge. As other answers note, jet engines develop at the leading edge of theory and new ideas,as well as pushing existing ones. Concrete typical example #1 ...

8

A performance increase after a compressor wash is expected to happen, but it does not return to the original performance as there are more degradation mechanisms at play. This answer explains that organic build-up causes a change in airfoil shape causing the recoverable performance degradation. Another source may be deposition of salts and dissolved ...

8

I was a P-3 Flight Engineer and the Allison T-56 engines had engine driven compressor's mounted on the propeller gearboxes on the inboard engines that allowed for a 30'000 ft. Ceiling.

7

Short answer This space is part of the inter-turbine duct (ITD), a duct which is required to maintain a satisfactory flow continuity between HPT and LPT rotating at different speeds (in the ratio of 1:3) and having different diameters. The duct is made of the gap and the larger (in the axis direction) LPT stage 1 vanes. Note this duct is a diffuser as the ...

7

The simple answer is that the pressure ratio across fan is generally small, in order to maximize the propulsive efficiency, as outlined in @Asced's answer. If you have a flow that has high total pressure (compared to inlet total pressure), then you have the real-estate to accelerate it further isentropically until the nozzle pressure reaches the ambient ...

7

Lubrication. The low wear of piston engines is due to an oil film between piston rings and liner, so both never get into immediate contact. This perfectly thin oil film left on the liner bore by the oil control ring will flash off if temperatures exceed 180° - 200°C, and the piston rings will scuff. This need for lubrication is the weak link which makes ...

6

Cowlings can be designed to contain fan failures but if the core comes apart you have some pretty high velocity shrapnel coming out that nothing short of quarter inch armour plate will stop. The main design feature you typically see to mitigate burst risk is the placement of cable runs and hydraulic runs, where there are redundant runs, spaced apart in the ...

6

They do. It's just not by very much. Typical high bypass engine like a GE90 might narrow down the exit area by a few percent. Small enough that you probably don't even notice it when looking at it. But the air can feel it.

6

All three engines you show are for fighter jets flying at supersonic speeds. These engines need a low bypass ratio: Why do military turbofan engines use a low bypass ratio? To achieve more thrust at lower bypass ratios, the bypass air needs to be accelerated more, which requires more than one fan stage because axial compressors can only add a limited ...

5

The compressor blades accumulate a coating of organic material from the atmosphere on the blades, which in the later stages, where the temperatures get above the material's flash point, may be mostly carbon from cooked organic material like pollen and bugs (the same sort of blackened accumulated crud you'll see on the butterfly of a late stage compressor ...

5

In addition to the other answers: Jet engines are not only complex, they operate on the edge of what's physically possible. For example, modern jet engines run at internal temperatures that can be higher than the melting point of the metals used. When you design a new jet engine, in order for it to be successful in the market, it has to be better than ...

5

It's not unique to the LEAP. You can find similar grills on the CFM56-5 and Trent 700, for example. That grill is the PCE's (precooler heat exchanger) air outlet. Compressed (hot) air is taken from the engines (before combustion) for pressurization and air conditioning. This air has to pass through a PCE (cooled by air from the fan) before heading to the ...

Only top voted, non community-wiki answers of a minimum length are eligible