Lockheed Wants Fewer F-35 Tests

[Tracy White]

Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.

[Werner]

I am no engineer; I will have to plead ignorance, but these problems sound like their very bread and butter. These things do not spring fully formed from the forehead of Zeus, but are the result of asking the very questions we are discussing here. What we lack is the impetus of danger to make the impossible, possible. Indeed, the zero risk path has proven itself to build unworthy aircraft in the past, and perhaps now with the F-35.

I believe the argument against low intakes is that they may ingest steam and warm air from the catapult track; with the CV 21's electric catapult this would not be an issue. Presumably, a British carrier's ski lift or catapult could avoid this issue.

[Guest]

Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.

One might gather from a simple census of the intake design choice made by modern fighter designers that square intake has strengths that far outweigh the issue raised above.

In reality, a fighter's intake is never a load carrying structural member. So resistence against stress concentration would have only a modest impact on its weight. The design of intake on a supersonic aircraft is largely dictated by the fact that jet engines can not operate unless the air it is sucking in hits its compressor face at subsonic speeds. This applies even to engines in highly supersonic aircrafts. What square intake allows one to do is to set up multiple intake shock ramps to reduce supersonic intake air to subsonic velocities before it hit the fan and compressor faces of the engine. This allows turbojet and turbofan engines to function efficiently at Mach 2+. While in theory this can also be done with a central shock cone in a round or semi-circular intake as was done in the SR-71, Mig-21, Mirage III, V and 2000, the shock cone in a round intake can not disappear while the shock ramps in a square intake can retract completely. Consequently a square intake with ramps is adaptable to efficient engine operation over a wider range of speeds than with a Mig-21 like round intake with a central shock cone. Fighters with round engine intakes and no shock cone, such as F-16, can not efficiently slow the supersonic intake air to sonic speeds before it hits engine face. Consequently they are limited mostly to below Mach 1.8.

[Seasick]

Tracy White wrote:
Additionally, the Typhoon's square intakes will focus the stresses on the corners whereas the ovoid structures on the Vought birds spread it out.



One might gather from a simple census of the intake design choice made by modern fighter designers that square intake has strengths that far outweigh the issue raised above.

In reality, a fighter's intake is never a load carrying structural member. So resistence against stress concentration would have only a modest impact on its weight. The design of intake on a supersonic aircraft is largely dictated by the fact that jet engines can not operate unless the air it is sucking in hits its compressor face at subsonic speeds. This applies even to engines in highly supersonic aircrafts. What square intake allows one to do is to set up multiple intake shock ramps to reduce supersonic intake air to subsonic velocities before it hit the fan and compressor faces of the engine. This allows turbojet and turbofan engines to function efficiently at Mach 2+. While in theory this can also be done with a central shock cone in a round or semi-circular intake as was done in the SR-71, Mig-21, Mirage III, V and 2000, the shock cone in a round intake can not disappear while the shock ramps in a square intake can retract completely. Consequently a square intake with ramps is adaptable to efficient engine operation over a wider range of speeds than with a Mig-21 like round intake with a central shock cone. Fighters with round engine intakes and no shock cone, such as F-16, can not efficiently slow the supersonic intake air to sonic speeds before it hits engine face. Consequently they are limited mostly to below Mach 1.8.

The square intake is good for a fighter jet, but the square intakes on the Typhoon diminish further its ability to be adapted to carrier operations.

Before the F/A-18 was adapted to carrier operations it was the YF-17 Cobra. The Cobra was much lighter and easily capable of mach 2.

[bb-56]

Colored pencils are hard wax, an insulator

[Pieter]

Strange. Most published sources give a maximum speed of mach 1.95.

Tracy White wrote:


Before the F/A-18 was adapted to carrier operations it was the YF-17 Cobra. The Cobra was much lighter and easily capable of mach 2.

[Tracy White]

Just to clarify, I didn't write that top speed; Seasick did and stripped out the quote tags.