What are those hatches on the engines of a B-2 that are open during takeoff?

Question

I just watched this drool-inducing video of Northrop Grumman B-2 Spirit, And noticed that there are a couple of hatches near each engine, which were open:

I initially thought they were open for some sort of maintenance. But the video features a takeoff roll of the bomber (around 5:00 minute mark), and I again noticed that the hatches were open during the roll. However, they were retracted immediately after the aircraft left the ground (around 5:25 mark):

This makes me wonder if these hatches serve some special purpose. What are they, and why are they open during the takeoff roll?

Edit: Please don't say you don't see an aircraft, because the landing gear doors are down and radar signature is immense due to that. :)

Once I toured AMARC. They had displays of most of their aircraft with signs plainly identifying them. This one sign said "Stealth bomber". It appeared to be an empty spot. — Harper - Reinstate Monica, Jun 04 '18 at 15:42
The refueling door rotating to close at the end is pretty neat - I didn't know it did that. — CrossRoads, Sep 02 '18 at 15:15

Peter Kämpf · Accepted Answer · 2018-06-02T20:35:15.700

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These are secondary intake doors which allow more air to reach the engines. They are opened by the engine control computer when the main intakes are not providing enough air for the power setting of the engine. In order to minimize radar cross section, the engines of the B-2 are buried in the wings and the intake needs to be curved. Also, and for the same reason, the intake lips need to be sharp-edged. Both factors increase the drag of the intake flow and reduce the mass flow of air to the engines. Like on other low-RCS aircraft, secondary intake openings are needed to increase this mass flow.

In automatic mode they will close when the aircraft accelerates above Mach 0.4. Below 43F, they remain closed for taxi and are only opened for take-off. A take-off with closed doors is possible according to this thread, but needs a reduced power setting to 80% for the engines below 50 kt speed.

edited Jun 02 '18 at 20:35

answered Jun 02 '18 at 20:21

Peter Kämpf

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Sounds like a similar function to "derumble doors", the suck-in panels on normal jet aircraft. – John K Jun 02 '18 at 22:13
On the F-117 they're also present, but they open inwards, above and behind the grill inlet. – Jun 02 '18 at 23:58
@JohnK Right, and that is why I linked to the JT3D-related answer in the first link. – Peter Kämpf Jun 03 '18 at 07:41
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Did the 727, Tu-154, L1011 and other S-duct aircraft have anything similar? – Harper - Reinstate Monica Jun 04 '18 at 15:45
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@Harper: No, but they have a much more favorable geometry: Round (almost in case of the 154) and with well rounded intake lips. – Peter Kämpf Jun 04 '18 at 20:59

Pilothead · Answer 2 · 2018-06-03T01:00:23.913

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Doors for secondary air intakes. Buried engines need additional air during takeoff and low speed flight.

edited Jun 03 '18 at 01:00

answered Jun 02 '18 at 20:37

Pilothead

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What are those hatches on the engines of a B-2 that are open during takeoff?

2 Answers2