How much weight does a thrust reverser add?

Question

How much weight does a thrust reverser add to an engine?

Let's take the CFM Leap 1B as an example, which powers the new version of the Boeing 737. This engine can produce up to 130 kN of thrust for takeoff, and has a dry weight of 2.78 tons. I could not find how much weight is the thrust reverser system. Closest thing I found was this FlightGlobal article which at least talks about it, but doesn't give numbers.

One purpose of this question is to compare it to old-school drag chute system. I will open a separate question on that.

Answer 1

For the LEAP-1B example, the weight you found is a dry weight that does not include the reverse system per the type certificate. Such weights are very hard to come by, even from the respective system manufacturer. However, statistical data can help.

According to NASA, the reverse system of a GE90 class engine can weigh upwards of 30% of the nacelle weight.

[Studies] conducted by General Electric Aircraft Engines indicate that the thrust reverser system accounts for more than 30 percent of the nacelle weight (not including engine) for an engine having a fan diameter in excess of 100 inches. This could be as much as 1500 lb [680 kg] for a GE 90 class engine.

As for the nacelle, an older NASA paper says the weight is in direct relation to its surface area constructed from simple cylinders.

[For the nacelle, the surface] area is used to correlate weight, and, rather than introduce the complexity of the actual nonaxisymmetric shape of the nacelle, simple cylinders are assumed, using the fan diameter, the turbine diameter, and the lengths from the previous section.

[And] a unit weight of 17.1 t o 19.6 kg/m2 appears reasonable.

From the same paper, here are some examples for the weight of the reverse systems of different engines:

Since the CF6 days manufacturers were able to reduce the weight of the nacelle and its components due to the "extensive use of composite materials."

Answer 2

The detailed weight of the components of the Leap 1B are elusive to find at the moment. There is statistical data available in pre-design books, such as Synthesis of Sub-Sonic Airplane Design by E. Torenbeek. Chapter 6.6.1 deals with thrust reversers, and mentions that the weight is considerable: between 15 and 20% of the bare engine weight, with the higher region being for high bypass engines like the Leap 1B.

Wikipedia lists the weight of the 1B as 2,780 kg. If we take the mid region of percentage due to improved technology since the book was written, the resulting guesstimate for the weight of the 1B thrust reverser is 0.18 * 2780 = around 500 kg. Plausible if we consider the complexity of the system.

The book also mentions an alternative means of thrust reversal for turbofans, the same one as used for turboprops: fan pitch adjustment, developed by the Dowty Rotol company early enough to be mentioned by the book. This mechanism weighs about half of that of the thrust reverser, amounting to about 250 kg, and has of course the advantage of being able to optimise blade pitch during cruise and take-off. Rolls Royce has announced plans for adjustable fan pitch for the next generation engines.

Answer 3

It obviously depends on the engine and airframe involved. For example, in case of Hawker 700, the aircraft with thrust reversers,

... has 248 pounds less useful load than a Hawker without reversers.

As the Honeywell TFE731 used in the Hawker weighs around 734 lb, this works out to about 17% of the engine dry weight. The thrust reversers seem to be classified as a structural component.

In case of present generation high-bypass turbofans, this value will be on the higher side due to various other factors like acoustic liners for meeting noise requirements (which the TFE31 doesn't). So, 15-20% appears to be extra weight due to the thrust reversers.