J-X4 "Whiplash" Turbo Ramjet Engine

J-X4 "Whiplash" Turbo Ramjet Engine
Jet engine by C7 Aerospace Division
Radial size		Small
Cost	(total)	2 250.00
Mass	(total)	1.800 t
Drag		0.2
Max. Temp.		2000 K
Impact Tolerance		7 m/s
Research		Hypersonic Flight
Unlock cost		18 000
Since version		0.15
Part configuration		jetEngineTurbo.cfg
Maximum thrust		130.00 kN
Isp	(max)	4000 s
Fuel consumption		0.66 /s
Intake air consumption		5.30 /s
Thrust vectoring		1 °
Electricity generated		5.0 ⚡/s
Testing Environments
On the surface		Yes
In the ocean		Yes
On the launchpad		Yes
In the atmosphere		Yes
Sub-orbital		Yes
In an orbit		No
On an escape		No
Docked		No
Test by staging		Yes
Manually testable		Yes

The J-X4 "Whiplash" Turbo Ramjet Engine is an air-breathing engine. These require liquid fuel from tanks and constant supply of intake air using air intakes inside an oxygenated atmosphere. (Note that intakes collect air and send it to jet engines regardless of where the intakes are on the craft, while fuel only flows from the same stage as the engines by default.) It is similar in appearance and function to the Pratt & Whitney J58, used on the famous SR-71 Blackbird.

Performance and usage

Visualization of the thrust multiplier curve for velocity

Visualization of the thrust multiplier curve for atmospheric pressure

The Whiplash is the fourth air breathing engine to unlock in the tech tree and marks a great step towards space-usability. As with all air-breathing engines, its thrust decreases at higher altitudes.

Contrary to pre KSP 1.2, its maximum stationary thrust is only slightly higher than that of the J-33 "Wheesley" Turbofan Engine, rated with 130 kN at sea level. Rising up to 6000 m, the thrust drops to about 75 kN, more or less staying at this performance up to a height of about 12,500 m (63 kN). From there on, thrust drops somewhat linearly until the engine shuts down at about 26000 m (4000 m higher than in KSP 1.0).

Like the other two high-speed jet engines, the Whiplash draws a huge thrust boost from high airspeeds. Up to mach 0.2 (e.g. still on the runway) it stays roughly constant. From mach 0.2 until mach 2.8, its thrust increases until reaching a peak of about 580% (~750 kN at sea level), which it maintains until mach 3.5. At speeds above that, thrust drops until reaching 0 at mach 5.5.

Since KSP 1.0, the specific impulse (I_sp) stays at a constant 4000 seconds over the full range of application. (This is the same efficiency as the J-404 "Panther" Afterburning Turbofan in wet mode but less than half that of the J-33 "Wheesley" Turbofan Engine.) However, as the thrust/height curve of this engine allows for usage in very thin air, it uses only a little more fuel per distance traveled when flying high and not too fast. Its high speed at high altitudes but low efficiency during ascent make it most effective on long range missions, where ascent takes up a smaller percentage of total flight time.

Combining the height and the speed behaviour, this engine gives remarkable thrust even at great heights as long as it moves fast enough. Practically, you need to have in mind both curves for two different reasons:

• Overpowering: from 6,000 m up to 12,500 m thrust is nearly not reduced by height. As it is speed boosted (100%+ thrust) up to mach 5, level flight at full throttle quickly leads to disintegrating.
• Underpowering: Flying very high, the engine may have enough thrust to maintain high speed (> mach 2.8) due to the speed boost, but getting slower than mach 2.8 quickly leads to a non-stoppable deceleration as the engine gets weaker.

These factors mean that the engine requires thick air to get really strong but needs thin air afterwards to maintain integrity. Carefully flying at the right ascent-path, you can easily (and quickly) reach 1100 m/s at 20,000 m (still rising fast), which is quite a useful base for continuing towards stable orbit with the same stage. A normal ascent path for a turboramjet spaceplane ends up looking something like this: climb at a 30 degree angle at full throttle until 10,000 meters, then nose down to 20 degrees or even 10 degrees ascent. The best compromise between angle of attack, rate of climb, and drag is reached somewhere in this range. Keep this attitude constant, even nosing down a little bit more, until the turboramjet flares out at 26km. If it flares out at a lower altitude, then more intakes are required. However, unless one is extremely lucky or extremely thrusty, the apoapsis at this point will not be out of the atmosphere (this, along with the need to make a circularization burn at apoapsis in vacuum, is why a rocket is still required for a turboramjet spaceplane). Immediately pitch up (being careful to avoid creating huge drag from an extreme angle of attack) and light up the rocket(s).

The exact altitude where you should drop the nose (trading the rate of ascent for acceleration) varies for each individual craft design, as does the optimal angle of attack in both the lower and upper phases of the ascent.  Some experimentation is normally required to find the optimal ascent profile for each individual design of spaceplane.

Note that currently, the only planets which this engine will work on are Kerbin and Jool's moon Laythe.

Product description

“

A highly advanced turbine engine using space-grade materials for very high performance. This new model features the latest in thrust vectoring and compression technology and is designed to operate best at higher altitudes and speeds. The advanced turbo ramjet design bleeds air around the compressor at high speed allowing a far maximum speed than regular jet engines, so engineers from C7 Aerospace assured us all those leaks are intentional. — C7 Aerospace Division

”

Trivia

• The internal part's name is turboFanEngine which is another kind of jet engine. In real life, a turbojet engine's fan pulls all the air from the intake through a combustion chamber, as opposed to a turbofan in which some of the air sucked in bypasses the chamber and is shot out of the back without being used in combustion at all. (e.g. the turbofan is a turbojet with a large fan attached to the front) The turbojet is more efficient at high speeds and in thinner atmospheres, although turbofans are much quieter and are very efficient when moving slowly. This is why turbofans are almost exclusively fitted on commercial airliners, and turbojets are more common on supersonic planes.

However, consider the bleed after the combustion chamber, it indeed does not burn all the air that come into the engine. However, those air is not actively "sucked in" to the engine, even though the accelerated engine exhaust will pull them in.

• The new engine sprite somewhat resembles a Wheesley with a afterburner of some sort attached at the back.

Changes

Appearance before 1.0.5

1.0.5

• Remodeled and retextured

1.0.3

• I_sp halved, thrust reduced

1.0

• complete overhaul of most characteristics

0.15

• Initial Release