The First Flight Of The B-21 Revealed Some Interesting Details Of The New Bomber

B-21 key features
Some of the key features on the B-21’s underside (Photo by Matt Hartman annotated by author)

Here are all the interesting things we have noticed in the images of the B-21’s first flight.

At 6:51 a.m on Nov. 10, 2023, local time, the B-21 Raider made its first flight from Palmdale to Edwards Air Force Base. As time goes by more sightings of the historic flight of “Cerberus” are being published online. Most noteworthy are the high-quality images of the aircraft’s underbelly photographed by fellow plane spotters that were waiting underneath the flightpath. This has allowed for an in-depth analysis of the Raider’s lesser-known details.

B-21 also has a secondary air intake that opens for increased airflow much like the B-2 (Photo by David Swanson and Ashley Wallace annotated by author)

The sideview of the B-21 taxiing under its own power seems to confirm that the aircraft has one secondary air intake door on top of each nacelle. On the B-2, the semi recessed engines have secondary intake doors that open during take off to provide adequate airflow. While the B-2 has two doors per nacelle for its four engines, the B-21 only appears to have a total of two doors.

While it is possible that the airduct splits into two from a single opening to cater for two engine, it is more likely that the single intake door signifies that there is only one engine in each nacelle. While more evidence should be overviewed before making a sound conclusion, it seems ever so likely that the B-21 is a twin-engine bomber.

Some of the key features on the B-21’s underside (Photo by Matt Hartman annotated by author)

The B-21 seems to have two smaller bays next to the main central bay.

Having done a more in-depth analysis, some key features on the B-21’s underside can be noted.

What some initially thought to be the radar reflectors located on either end of the flying wing seems to be retractable navigation lights, similar to what can be found on the B-2. While the outboard navigation lights stay deployed in normal operating conditions, they protrude out of the wing and thus impact the total radar cross section of a stealth aircraft. Thus, it is common practice for the B-2 to retract its navigation lights when undergoing a combat sortie. The same type of retractable navigation lights is expected to be the protrusions shown on either end of the B-21’s wing.

The real radar reflectors, or Luneburg Lenses, are pictured here installed between the landing gears. As a stealth aircraft will not normally appear on radar, they tend to fly with radar reflectors on unless the need for low detection is required. Furthermore, on a prototype aircraft as this, it is rare to see one flying without radar reflectors as the true radar return tends to be a closely guarded secret.

Due to the aircraft’s low observable nature, its pitot tubes and static probes are also of a non-conventional shape. Nearly identical to the setup found on the B-2, the B-21 also utilises three sets of four air data probes located on the nose and cheek of the aircraft. While any aircraft needs a set of pitot tube and static ports to measure its airspeed, altitude, and vertical speed, they tend to stick out into the free-stream for accurate measurements. However, having a conventional pitot static tube will be detrimental to a stealth aircraft’s radar return. Thus, the B-2 utilises a set of flush mounted static ports and data correction to imitate the role of a conventional pitot tube. Due to the air data probes’ location being at an angle to the local airflow, there tends to be a few arrays of the same sensors to account for inaccuracies in measurement. In this case, the B-21 seems to have a near identical setup on its air data ports as the B-2’s.

Generally speaking, as observed on other types, the “trailing cone” is usually a nylon cable with a stabilizing cone deployed in flight, generally 1 to 1.5 times the wing span length, or about 50 metres, behind the aircraft to measure the ambient atmospheric pressure (static pressure) precisely, in the “free-stream air-flow” outside the disrupted air-flow generated by the aircraft – a key parameter for the pilots.

Figure 5 The air data probe and trailing cone are mounted on the prototype aircraft as part of flight testing and will not be present on production variants (Photo from anonymous contributor on TheDrive supplemented by Reagan K. Woolf and Space Age Control)

Much like that on the B-2, a darker shaded strip can be seen extending to the underside of the Raider’s rear end. This appears to be a thermal coating applied to the area in direct contact with the engine exhaust. Usually made from a carbon fibre reinforced polymer, thermal coatings like this ensure that the engine exhaust is cooled down to reduce IR signature. It should be noted that Very Low Observable technology (or “stealth”) not only refers to low detection from radar, but also in other spectrums of including both visible and infrared. Hence, an effort is made to reduce the B-21’s detection in those arenas through a grey paint scheme and thermal coatings.

The most intriguing detail found would be the possibility of a second set of internal weapons bays.

With the main landing gears seeming to fold forwards, the panel line between the main landing gear doors and the central weapons bays raises suspicion for another weapons bay. While the central weapons bay has two sets of doors that swing open, the secondary weapons bays appear to open up with a single door. As evident from the annotated picture, the two set of secondary weapons bays would be smaller in width and length than the main bay. It can be speculated that there will be space for self defence features such as decoys, air-launched drones, or even air-to-air missiles. It should be noted that the USAF page on the B-21’s capabilities mentions that the platform will “…accommodate manned or unmanned operations”. There is a possibility for the drone decoys to be launched from the smaller weapons bays to allow for the main weapons bay to be solely dedicated for munitions delivery. The USAF using ADM-160 Miniature Air Launched Decoy (MALD) on F-16s and B-52s, it is thought that the MALD could be integrated to the B-21 as well. Most recently AGM-160Bs were seen employed in Ukraine acting as decoys for Storm Shadow cruise missiles.

There are also chances the doors are used for something else: someone suggested they might be used for maintenance purposes, for instance to facilitate the access to the engines.

Estimated location of the B-21’s radar marked in red and blue – most likely the red squares and the possible secondary (weapons) bays (Photo by @point_mugu_skies annotated by author)

While the prototype aircraft is not expected to carry an internal radar, a rough estimate of the size and position of the radar can be deduced from the panel gaps. With the B-2 utilising two AN/APQ-181 radars below the leading edge on its cheeks, the B-21 is likely to have its radar, if any, to be in a similar position. The AN/APQ-181s on the B-2 provided 21 separate modes for terrain-following and terrain-avoidance, navigation system updates, target search, location, identification and acquisition and weapon delivery.

With the development of active electronically scanned array (AESA) technology, the radars onboard the B-21 will have s much smaller volume than the previous generation that can be found on the B-2. Therefore, it seems fairly reasonable for the B-21 to carry its own radar.

Based on the panel lines photographed, it appears that a two-radar setup like that on the B-2 will be decided, either having the antennas placed inside the blue or red boxes shown above. Although, considering the size of modern AESA radars on fighter platforms, it seems more likely that the radars will be located in the red boxes due to size constraints. One of the red panels marked above is taken up by an air data probe at the moment, but this is for sensor calibration and will only be present on the prototype aircraft. Hence, it is a reasonable assumption that the current space occupied by the air data probe mount is space for the later instalment of a low probability of intercept radar on production variants.

Finally, before you freak out about sensitive details being disclosed and things like that, please remember the flight was somewhat “announced” (i.e. several spotters knew it would happen on Nov. 10 after being cancelled on Nov. 9) and happened in plain daylight. So there was nothing to hide. Moreover, as often highlighted by Northrop Grumman, the B-21’s most important features are inside the aircraft and can’t be seen from the outside…

David Cenciotti and Stefano D’Urso contributed to this report.

About Wonwoo Choi
Wonwoo is a student journalist and contributor to The Aviationist based in London, United Kingdom. Currently studying MEng in Aeronautical Engineering with a keen interest in OSINT, plane spotting and aircraft design. He is a former Sergeant of the Republic of Korea Army, having served as an artillery Fire Direction Centre Vehicle Radio Operator.