# How much thrust can the thrust reversers create?

Let's say for the sake of the question, the plane is an 787 Dreamliner and the engine is the General Electric GEnx-1B64 (that according to Wikipedia can produce a maximum thrust of 284 kN)

• In comparison to the "regular forward" thrust that a jet engine can generate, how much thrust can we apply to this engine in the reverse mode?
• Can we apply full power in the reverse mode?
• You're question is not clear. Full power can be applied with the buckets deployed but is your question "what is the effective thrust"? – Simon May 7 '15 at 13:06
• @Simon, now I haven't flown the B787, but I'm quite sure that the full rated N1 can not be applied with reversers deployed, more likely "full reverse thrust" is a lower N1. Gabriel, once again not sure about B787, but on most (if not all) Boeings the reverse thrust levers locks the forward thrust levers electro/mechanically from moving out of idle thrust, so you instead control N1 with the thrust reverse levers. On the B737 you usually don't see more than ~84,4% N1 with max reverse thrust, with max rated N1 usually being around ~100% (someone with better manuals might have more exact numbers) – Waked May 7 '15 at 13:41
• (I should probably add that the numbers I'm mentioning above are for the CFM56-7B27) – Waked May 7 '15 at 14:10
• @Waked plz write this in the answer. – Gabriel Brito May 8 '15 at 18:47
• @Waked although your knowledge lies with 737, your information is worth more than a comment. I support you to convert comment to proper answer. – vasin1987 May 19 '15 at 17:17

Estimations

We can at least estimate a reverse thrust case based on some numbers and some physics, a bit of a specific case of this question. The stopping distance equation:

$$d_f=\frac{v_i^2}{2a}$$

The information in Appendix B here for the 727-200 gives stopping distances for different cases. If we look at a sea level pressure altitude case with 120,000 lb gross weight, the stopping distance is 2452 feet. The correction for a reversers only case is 2.57, bringing the distance to 6302.

At a landing speed of 200 ft/s, the plane will take 11500 lb of force to stop in that distance. Each engine on the 727-200 provides 14500 lb of thrust force maximum. Considering that part of the stopping force will be provided by drag and surface friction, the reverse thrust is about 25% of the maximum forward thrust. The reversers will be more effective at higher air speeds, so the maximum will be higher than this.

Figure 39.5 here shows a graph of reverse thrust compared to forward thrust for different bypass ratios and reverse thrust types. This is a good check for a general case. The GEnx-1B64 has a bypass ratio of about 10, and reverses the fan but not the primary exhaust, which gives a ratio of 30% of maximum forward thrust.

Summary

The engine will not run at full power when in reverse mode, so accounting for this and the bypass ratio will leave you with about states that modern thrust reversers can convert up to 35% to 50% of their forward thrust into reverse thrust.