# What is the GE90-115b turbine power output in horsepower?

The GE90-115b is rated at 513 kN maximum thrust and is often said to have 110,000 shaft horsepower, but I have yet to find any document or specification that backs the claim on horsepower figure.

A comparable engine, the Trent XWB-97 rated at 430 kN and puts out 50,000 shp according to the Rolls-Royce website.

The vast difference in horsepower 50,000 shp vs 110000 shp and not all that huge difference in thrust 430 kN vs 513 kN makes me suspicious if the GE90 actually puts out 110,000 or if this has become a "thing" for the GE90 without being correct. Or, perhaps shaft horsepower and turbine horsepower is not the same?

Does the GE90-115b actually output 110,000 shp?

• According to the GE website for the GE90-110/115 the engines ran at 127,000lb-thrust at "triple redline conditions" for 60 hours. So what you may be seeing is the difference between "maximum thrust" and "rated thrust". The GE90-110/115 puts out around 74-94,000lb-thrust. Feb 17, 2020 at 16:35
• @RonBeyer so the GE90 is rated at 115,000lb maximum and 94,000 continuous if I understood you correctly? The XWB-97 is rated at 430 kN maximum and 370 kN continuous. But, if we compare maximum numbers and not continuous, that means we're looking at XWB97 with 430 kN vs GE90 with 513, (although 569 kN was achieved once) - but thats only ≈ 80-130 kN difference, compared to the massive 60,000 shaft horsepower difference if we are to believe the articles.
– Erik
Feb 17, 2020 at 17:44
• Talking about jet engines in HP really doesn't make much sense, but media likes to do it. Power is forcedistance/time or ForceSpeed. So at 0 speed, you get 0 power. At takeoff speed and full thrust you get around 55,000 HP for GE90-115B, while your thrust actually decreases the faster you go. The actual fan shaft will transfer around 30,000 HP from the LP turbine to the Fan, internal to the engine. Feb 19, 2020 at 3:07
• Comments have been moved to chat; please do not continue the discussion here. Before posting a comment below this one, please review the purposes of comments. Comments that do not request clarification or suggest improvements usually belong as an answer, on Aviation Meta, or in Aviation Chat. Comments continuing discussion may be removed.
– Ralph J
Mar 4 at 14:21

According to the GE website, they used a GE90-115B as a power generation unit, called the LM9000. GE cited 65,000 horsepower, which seems to scale rather reasonably when compared to the RR Trent XWB.

• +1, however, I don't think that power generators like LM9000 would operate at full power. I believe that they would operate at power settings below max continuous, so maybe GE90's actual power is much more than 65k HP. Jan 26 at 7:12

#### TLDR

The number given for the Trent engine is only for a specific engine component and is not representative for the total output of that engine. The 110000 hp for GE90 is plausible.

It is not as natural to compare shaft horsepower for turbofans as it is for piston or turboprop engines, where it is canonical to measure the shaft power delivered to the propeller.

### The Trent engine

Looking at the source cited for the Trent engine in the question, the 50000 horsepower figure is "Horsepower generated by 68 high pressure turbine blades". I think that means 50000hp is extracted by the HP turbine. This does not contribute directly to thrust, as most of that power would be used by the compressor. The Trent is actually a three spool engine, I cannot tell if this figure includes the IP turbine or not, but the same goes for the IP as the HP turbine, most of the power extracted is used by the compressor. The fan, which does most of the propulsion, is powered by the low pressure turbine. Similarly, the high pressure turbine would not contribute directly to the output of a derived turboshaft.

### Power of GE90

That leaves the question of what is actually meant by 110000 hp. This could be the shaft power being transferred by both the spools combined, the power delivered to the fan, or the work done in propelling the airplane, i.e. thrust*speed at some chosen conditions.

I would argue the most natural thing is to measure the work done on the air mass propelled by the engine, i.e. the kinetic energy of the air leaving a static engine over one second, for a static engine at full thrust at STP. Now we can attempt an estimate of this for the GE90-115. For this we need to know the mass flow rate and exit velocity. According to this the specific thrust for a kg of air is 278 N*s(=m/s) in those conditions for an earlier less powerful GE90 variant. Assuming GE90-115 has the same exit velocities, at 513 kN that would give a mass flow of 513000/278=1845 kg/s. Then the power is 2782 * 1845/2 W, which is approximately 71.3 MW, or 95600 hp. The exit velocities of the air leaving the core nozzle and bypass nozzle are actually different, which means the above is a slight underestimate. Given that and the fact that our exit velocity is from a speculative source assessing a different GE90 variant, this is not too far off the 110000 figure.

• I guess "shaft horsepower" suddenly becomes "natural" when you turn the GE 90 into a generator? We can actually determine "shaft horsepower" in Newton meters/second as the exact same number as compressor drag × radius/second + fan drag × radius/second. But, thanks for showing that work is being done by moving air even if the engine is stationary. Mar 4 at 6:28
• @ Aditya Sharma I am linking to a source using this same mass flow number, 1350 kg/s. This is the mass flow of an earlier GE90 variant delivering 388kN takeoff thrust, but the question explicitly mentioned the GE90-115b. I don't have a better source so I scaled the mass flow up proportional with the thrust increase. Mar 4 at 14:13
• @ÖgmundurEiriksson very interesting information, thanks for sharing :-) Mar 4 at 21:14

I think the numbers (93.7khp) are accurate (https://www.geaviation.com/commercial/engines/ge90-engine).

I recall numbers from CFM56 (smaller engine) being something like 10khp for the fan and 20khp for the core so like 2/3 for the core and 1/3 for the fan (can't find where i saw that, but it was definitly shaft power).

On the Trents it is said 50 khp from "high power turbine blades", so i'm guessing it might be the hp core shaft power which is probably like the CFM, something like 2/3 of total engine power which would put it at 75 khp and GE90 core power around 62.5khp which matches the number given (65 khp) for the LM9000 (core technology similar to that of the GE90).

I think that horse power of GE90 is about 97.000 hp (65.000 kW = 88.000 hp). I have a book about the Concorde which at cruise has a certain air resistance. I calculated that the engine had to produce 90.000 hp to maintain that speed. Efficiency of the Olympus engines at cruise was 40%, a high value for a turbo jet (no fan). Many turbojet/fan engines are used to drive a propeller. In these cases we measure the power in kW (or hp). GE's engines often exist also as stationary engines to drive a generator or a pump. Then power are measured in kW. One may think that these engines take out less power because the shall work months continually (but I do not know).

– Community Bot
Mar 2 at 1:01
• @KETILLJACOBSEN please show your Concorde calculations starting with "air resistance". Mar 2 at 13:47

A "Rosetta Stone" of high subsonic Thrust Specific Fuel consumption and Power Specific Fuel consumption can be found by reviewing data for the Progress D 27 turbo prop engine: 11g/(kNewton second) and 0.14 kg/(HP hour)

Working through some math:

11 g/(kN second) × 1 kg/1000 g × 3600 seconds/hour × 1 kN/1000 N x 1 N/.225 lb force we have 0.176 kg/(lb force hour).

Comparing this to 0.140 kg/(Hp hour) for a turboprop shows (sadly) that the "3 pounds thrust per horsepower" efficiency enjoyed by props$$^1$$ at less than Mach 0.5 declines to less than 1 pound of thrust per HP$$^2$$.

But, comparing apples to apples, the SFC of the Jumo 004 is:

143 kg/(kN hour) × 1000 g/kg × 1 hour/3600 seconds) = 40 g/(kN second)

The LEAP engine that powers the 737, and the GE 90 of the 777, use around 15 g/(kN second) in cruise.

Efficiency is why "old time" Horsepower is rarely applied to jet engine thrust. Although the D-27 SFC of 11 g/(kN second) is less than the LEAP, it is only had at a lower speed (450 knots vs 520 knots).

$$^1$$ the 1600 lb propeller driven Helios flew to over 90,000 feet with 28 Horsepower. It's indicated airspeed was around 22 knots (300+ True airspeed)!

$$^2$$ see Ron Beyer comment under the question.