Looking at a photo of the A model
refueling from a KC10 using a boom
and a receptacle above and behind the
cockpit is what I expected


But does the A model also have a probe ?
If not, what is the long fairing above the left side of the forward fuselage that looks like
it encloses a retractable probe ?

Max Q wrote:

Looking at a photo of the A model
refueling from a KC10 using a boom
and a receptacle above and behind the
cockpit is what I expected


But does the A model also have a probe ?
If not, what is the long fairing above the left side of the forward fuselage that looks like
it encloses a retractable probe ?

The A model does not have a probe although the space for a probe has been reserved and if a current or future customer, such as Canada who currently only have drogue refuelling, wants to use a probe they can. There is some engineering work and certifications for the A that would have to occur but unlikely to be too substantial.

The long fairing down the left hand side of the aircraft is the 25mm GAU-22 cannon.

Ozair wrote:

Max Q wrote:

Looking at a photo of the A model
refueling from a KC10 using a boom
and a receptacle above and behind the
cockpit is what I expected


But does the A model also have a probe ?
If not, what is the long fairing above the left side of the forward fuselage that looks like
it encloses a retractable probe ?

The A model does not have a probe although the space for a probe has been reserved and if a current or future customer, such as Canada who currently only have drogue refuelling, wants to use a probe they can. There is some engineering work and certifications for the A that would have to occur but unlikely to be too substantial.

The long fairing down the left hand side of the aircraft is the 25mm GAU-22 cannon.

Ok, thanks for that


I’m surprised the cannon installation
is not more integrated, especially on a stealth aircraft

Max Q wrote:

Ok, thanks for that


I’m surprised the cannon installation
is not more integrated, especially on a stealth aircraft

Not sure I can do anything about your surprise Max other than say smarter people than I designed it and it has met all the objectives for its RCS so clearly they are doing something right.

Ozair wrote:

Max Q wrote:

Ok, thanks for that


I’m surprised the cannon installation
is not more integrated, especially on a stealth aircraft

Not sure I can do anything about your surprise Max other than say smarter people than I designed it and it has met all the objectives for its RCS so clearly they are doing something right.

When you can do something about my surprise let me know..

Essentially, that design was chosen for it because the USAF wanted to retain an "internal" gun, where the USN and the USMC didn't deem it needed. Since the name of the game for the F-35 is commonality between the variants, the designers chose the fairing approach as the best balance of cost, design difference, and RCS. While the fairing does indeed marginally increase the RCS of the A model, it makes up for it by being MUCH smaller than the RCS of having to carry the gun in an external pod like the B and C do. It's also nice in that, it's easier to remove for repair or replacement, and, it allows all the systems "under" it to be similar between the variants. They balance the drag from that fairing with the cooling air scoop over the oppose side of the fuselage.

I'm personally not enamored with gau-22 itself. I believe that it is not the best choice for the task, and the aircraft would have been better served by the Mauser BK-27 (currently used in the Eurofighter Typhoon). The BK-27 has several advantages over the GAU-22 in that, it consumes less electrical power (important in an electrical constrained platform like the F-35), is physically smaller by volume (important for reducing the size of the fairing and the RCS hit), is marginally lighter (ALWAYS important for aircraft), can get more projectile mass down range in the first one half and one second time-frames from firing (The GAU-22 requires time to spin up to full RPM), if the size of the gun compartment were maintained, then there would be additional space for extra ammo, which is VERY constrained in the A model. Also, the BK-27 fires a projectile with better armor piercing characteristics than the 25mm projectile in the GAU-22. While this isn't the most important item for A2A engagements, since the F-35 is designed primarily to be a ground attack aircraft, it will be used in the anti armor role. THERE, it is quite important. However, the differences in practice are not so dramatic, and the GAU-22 is not a horrible selection. Though, I do often wonder what the true utility is for a gun to be carried at all if it will only have 170 rounds of ammo, which represents under 2 seconds of sustained fire. They could have stuck with the existing 20mm vulcan that's in use in their current aircraft and actually been able to carry a much greater ammo load. However, these aircraft are not intended to be WVR knife fighters and are instead meant for penetrating ground attacks while maintaining the ability for self defense in the process, and in that sense, it makes more sense.

LightningZ71 wrote:

Essentially, that design was chosen for it because the USAF wanted to retain an "internal" gun, where the USN and the USMC didn't deem it needed. Since the name of the game for the F-35 is commonality between the variants, the designers chose the fairing approach as the best balance of cost, design difference, and RCS. While the fairing does indeed marginally increase the RCS of the A model, it makes up for it by being MUCH smaller than the RCS of having to carry the gun in an external pod like the B and C do. It's also nice in that, it's easier to remove for repair or replacement, and, it allows all the systems "under" it to be similar between the variants. They balance the drag from that fairing with the cooling air scoop over the oppose side of the fuselage.

I'm personally not enamored with gau-22 itself. I believe that it is not the best choice for the task, and the aircraft would have been better served by the Mauser BK-27 (currently used in the Eurofighter Typhoon). The BK-27 has several advantages over the GAU-22 in that, it consumes less electrical power (important in an electrical constrained platform like the F-35), is physically smaller by volume (important for reducing the size of the fairing and the RCS hit), is marginally lighter (ALWAYS important for aircraft), can get more projectile mass down range in the first one half and one second time-frames from firing (The GAU-22 requires time to spin up to full RPM), if the size of the gun compartment were maintained, then there would be additional space for extra ammo, which is VERY constrained in the A model. Also, the BK-27 fires a projectile with better armor piercing characteristics than the 25mm projectile in the GAU-22. While this isn't the most important item for A2A engagements, since the F-35 is designed primarily to be a ground attack aircraft, it will be used in the anti armor role. THERE, it is quite important. However, the differences in practice are not so dramatic, and the GAU-22 is not a horrible selection. Though, I do often wonder what the true utility is for a gun to be carried at all if it will only have 170 rounds of ammo, which represents under 2 seconds of sustained fire. They could have stuck with the existing 20mm vulcan that's in use in their current aircraft and actually been able to carry a much greater ammo load. However, these aircraft are not intended to be WVR knife fighters and are instead meant for penetrating ground attacks while maintaining the ability for self defense in the process, and in that sense, it makes more sense.

Thanks for that really detailed reply Lightz
very interesting


I still find this sort of ‘slap it on’ installation odd when comparing to the integrated, built in cannons on the F14/15/16 and 18
especially when considering the billions spent on development

LightningZ71 wrote:

Essentially, that design was chosen for it because the USAF wanted to retain an "internal" gun, where the USN and the USMC didn't deem it needed. Since the name of the game for the F-35 is commonality between the variants, the designers chose the fairing approach as the best balance of cost, design difference, and RCS. While the fairing does indeed marginally increase the RCS of the A model, it makes up for it by being MUCH smaller than the RCS of having to carry the gun in an external pod like the B and C do. It's also nice in that, it's easier to remove for repair or replacement, and, it allows all the systems "under" it to be similar between the variants. They balance the drag from that fairing with the cooling air scoop over the oppose side of the fuselage.

What is your source for the fairing increasing the RCS of the A model? I haven’t seen this stated anywhere and again as already indicated the aircraft is meeting the RCS design spec.

LightningZ71 wrote:

I'm personally not enamored with gau-22 itself. I believe that it is not the best choice for the task, and the aircraft would have been better served by the Mauser BK-27 (currently used in the Eurofighter Typhoon).

I think the GAU-22 is an excellent compromise between the heavier calibre 27 and 30mm and the 20mm M61. The BK-27 was contested against the GAU-22 during the first few years of the program with the GAU-22 winning the selection.

LightningZ71 wrote:

The BK-27 has several advantages over the GAU-22 in that, it consumes less electrical power (important in an electrical constrained platform like the F-35), is physically smaller by volume (important for reducing the size of the fairing and the RCS hit), is marginally lighter (ALWAYS important for aircraft), can get more projectile mass down range in the first one half and one second time-frames from firing (The GAU-22 requires time to spin up to full RPM), if the size of the gun compartment were maintained, then there would be additional space for extra ammo, which is VERY constrained in the A model.

Electrical power is not an issue at all. There is no electrical constraint in the F-35…

The size difference is marginal and the weight difference for 4kg…

Let’s compare all the cannons found in current fighter aircraft today.

F-35A, 25mm GAU-22/A with 180 rounds.
3300 RPM / 55 RPS rate of fire, 223 gram projectile weight for 12.3 kg/s throw weight, 3.27 seconds firing time of ammunition and 40.1 kg of total projectile weight.

F/A-18E/F, 20mm M61A1 with 412 rounds.
6000 RPM / 100 RPS rate of fire, 102 gram projectile weight for 10.2 kg/s throw weight, 4.12 seconds firing time of ammunition and 42.0 kg total projectile weight.

Typhoon, 27mm BK 27 with 150 rounds.
1800 RPM / 30 RPS rate of fire, 260 gram projectile weight for 7.8 kg/s throw weight, 5.00 seconds firing time of ammunition and 39.0 kg total projectile weight.

Gripen, 27mm BK 27 with 120 rounds.
1800 RPM / 30 RPS rate of fire, 260 gram projectile weight for 7.8 kg/s throw weight, 4.00 seconds firing time of ammunition and 31.2 kg total projectile weight.

Rafale, 30mm GIAT 30 with 125 rounds.
2500 RPM / 42 RPS rate of fire, 275 gram projectile weight for 11.6 kg/s throw weight, 2.98 seconds firing time of ammunition and 34.4 kg total projectile weight.

Su-35, 30mm GSh-30-1 with 150 rounds.
1800 RPM / 30 RPS rate of fire, 390 gram projectile weight for 11.7 kg/s throw weight, 5.00 seconds firing time of ammunition and 58.5 kg total projectile weight.

https://www.ar15.com/forums/general/F-3 ... #i74212670

The aircraft could have been modified to carry more ammunition if it was required. As you can see with other airframes the number of rounds is comparable, as is the firing time. The difference is the F-35A has selectable firing modes, it can configure a burst of specific shell number, so nine 20 round A2A shots or three longer 60 round A2G shots.

LightningZ71 wrote:

Also, the BK-27 fires a projectile with better armor piercing characteristics than the 25mm projectile in the GAU-22. While this isn't the most important item for A2A engagements, since the F-35 is designed primarily to be a ground attack aircraft, it will be used in the anti armor role. THERE, it is quite important.

That depends on the projectile used. The Norwegian APEX ammunition that has been developed for the GAU-22 is a phenomenal round which has exceptional impressive anti amour while also being a dual purpose round. The BK-27 has a similar round but I haven’t seen testing results on it.

LightningZ71 wrote:

However, the differences in practice are not so dramatic, and the GAU-22 is not a horrible selection. Though, I do often wonder what the true utility is for a gun to be carried at all if it will only have 170 rounds of ammo, which represents under 2 seconds of sustained fire.

All the aircraft above carry smaller loads of ammunition compared to previous generations and similar loads comparatively to each other.

LightningZ71 wrote:

They could have stuck with the existing 20mm vulcan that's in use in their current aircraft and actually been able to carry a much greater ammo load. However, these aircraft are not intended to be WVR knife fighters and are instead meant for penetrating ground attacks while maintaining the ability for self defense in the process, and in that sense, it makes more sense.

As you can see from above the increased load of 20mm in the F-18E does not provide a significant increase in firing time while it has less ballistic properties in both A2G and A2A engagements.

Given the calibre size of the F-35 compared to the other aircraft I’m not sure how you can claim the gun is a poor decision for A2A. The F-35 was designed to exceed F-16 WVR capability and aim for F-18A/C ability. It has done so and hence is the same as and likely, with its additional sensor suite, better at WVR combat than its competitors.