Tuesday, February 25, 2014

[RANT] Speed skaters, conformity, boxes, and roof racks.

"YOUR MISSILES ARE SHOWING!"
Internal storage.

By carrying its weapons inside, the F-35 Lightning II presents a slippery shape when armed instead of carrying a bunch of dangly bits about.  Just like a speed skater's skin-tight suit.  Hanging all of these bombs, missiles and whatnot are surely going to slow down any fighter aircraft to crop-duster like speeds...  Right?

Internal weapon bays aren't the only way to reduce a weapon's drag, however.

Cue the tuba...
And the French horn...
Just look at the above fighters.  The EA-18G Growler up top is carrying 3 jamming pods, 2 big external fuel tanks, 2 AMRAAMs and two AGM-88 HARM missiles.  The Rafale below is festooned with 3 external tanks, 6 GBU-22 laser guided bombs, and 4 (2 IR, 2 RF) Mica missiles.  It is perfectly reasonable to assume that these aircraft would exhibit diminished performance compared to a "clean configuration".  All that extra weight and drag would take its toll, after all.

Slick.
Now let's look at an F-35.  With its weapons inside, the JSF certainly looks slippery.  Lets assume that the F-35 pictured above is fitted with a full internal load of air-to-air weapons, 4 AMRAAMs.  That's a considerably smaller load than the above Growler and Rafale, both outfitted with external tanks with the Growler carrying jammers as well.

Typhoon with a full load.
Now, for comparison let's take a Eurofighter Typhoon and equip it similar to the Rafale up above.  While not an exact match, this Typhoon swaps out 2 bombs for missiles, making 4 AMRAAMs, 2 IRIS-Ts, 4 guided bombs and 3 fuel tanks.

Now let's look at a Typhoon fitted similar to the F-35 pictured.
4 AMRAAMs and a Sidewinder
This Typhoon has an additional AIM-9 Sidewinder, along with an empty pylon, but you get the idea.  A Eurofighter Typhoon with 4 AMRAAMs isn't really that much bulkier than an F-35 with the same. Yes, the missiles are visible, with their fins sticking out, but the amount of extra drag created here would be minimal.  The combat radius for this configuration actually favors the Typhoon:  1,080km for the F-35, 1,389 for the Eurofighter.

Typhoon with conformal MBDA Meteors.
See how the Typhoon's AMRAAM's and Meteors are tucked into the fuselage?  Conformal weapon storage like this allows a fighter to carry weapons while adding very little in the way of increased drag or radar cross section.  It also eliminates the need for separate pylons.  This method is nothing new, conformal storage has been present in fighter jets for years.

F-15C showing off conformal AMRAAMs missiles, with Sidewinders on pylons.
F/A-18 showing off two conformal Sparrows.
Rafale with two wingtip Mica missiles and two conformal Mica missiles.  (Plus bombs, fuel tanks, and a Damocles pod)
The Typhoon, F-15, F/A-18 (both legacy and Super), and Dassault Rafale all carry conformal air-superiority missiles.  The Typhoon and F-15 have spots for 4, while the Hornet and Rafale carry 2 conformal hard points.

There's another, similar way of storing missiles without the need for complicated weapon bays or draggy pylons...

Semi-recessed Sparrow missile on a F-4 Phantom II.

Semi-recessed storage goes a step further and actually contains part of the missile inside openings in the aircraft's fuselage.  Much like conformal storage, there is a certain limit to the type of weapon that can be fitted (you can't put a AIM-9 Sidewinder in a slot made for a AMRAAM).  This is why the AIM-7 Sparrow, AIM-120 AMRAAM, and MBDA Meteor all look so similar, so they can be mounted on the same conformal or semi-recessed station.

RAF F-4 with 4 semi-recessed Sparrows, Sidewinders, and a gun pod.  Notice how the fuel tanks and gun pod add the most bulk.
Like conformal missile storage, semi-recessed missiles are nothing new.  They can be seen on the F-4, F-14, and even venerable "century series" interceptors like the F-101 Voodoo.

F-14
The F-101 Voodoo carried its Falcon missiles semi-recessed in a rotating pallet with extending launch rails.  A novel, if complicated, method.
These older designs kept their missiles tucked away for purposes of speed.  The less drag, the faster the aircraft could go.  This was very important to interceptors like the F-101.  Others, like the F-106 Delta Dagger and the F-105 Thunderchief fighter bomber, kept their missiles tucked away in weapon bays.

F-106 with open missile bay.

Of course, when it comes to stealth, internal carriage is practically a must.  The radar evading shape of a stealth aircraft must be maintained.  Since shape is such an important factor in an aircraft's "stealthiness", one cannot simply design a stealthy missile and attach it to a stealthy fighter.

An F-22 says "AHHHH!"  
 A weapon bay is, basically, a box.  That box holds the missiles inside the aircraft until it's time to fire, at which point a door opens, the missile is positioned outside the box either on a rail or by gravity, the missile fires, then the door closes

Weapon bays are great for keeping an aircraft stealthy and sleek.  They do have a few trade-offs however.  For one, there is the added complexity of opening doors, trapeze systems, and the like.  There is also the limitation of size.  Any weapon going into that bay needs to conform to a certain size.  For example:  While the Typhoon, Rafale, and Gripen will all have the ability to carry the MBDA Meteor missile, the F-35 will need to wait for a "clipped wing" version.

There is also the fact that, no matter what payload the aircraft is carrying, it needs to carry this weapon bay "box".  The very shape of the aircraft is dictated by this box.

Imagine shopping for a vehicle.  You're an outdoorsy type, so you want a vehicle capable of carrying your bicycle, camping gear, and other stuff.  Your first impulse is to get something with lots of cargo space, like a minivan, a pickup truck, or a big SUV.  While they all do a good job carrying what you need to bring on a weekend getaway, none of them get particularly good gas mileage, and driving them to work during the week will be a pain.  Certain items, like kayaks, still don't fit, and bringing home the Christmas tree every year results in your upholstery getting covered in sap and pine needles.

This...
Or...  You could buy something a little simpler...  But add a roof rack.

Or this?
The roof rack adds a little extra drag, but not much.  It give you flexibility, however.  Got a couple of bikes?  No problem.  A kayak?  No problem.  Bringing home a Christmas tree?  No problem.  Just need some extra cargo room?  Just add a cargo box, no problem.

And for those days when you just need to commute to work, maybe pick up a few groceries?  You simply leave the roof rack off.

I don't know about you, but I'll take simplicity and flexibility over big, boxy, and complicated.


3 comments:

  1. Well written Doug, your comparison of the 'clean' Typhoon vs the F-35 really opened my eyes. I know Swiss F-18s have a lower drag pylon for their wings, which also improves performance. This could be a potential fit for RCAF Supers if they choose to go this way, or maybe even Gripens.......

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  2. Isn't a Block iii Super Hornet with CWPs just a Subaru with a cargo box on the roof. Simple and effective.

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  3. Interesting post. I agree, the two pictures of F-35 and Typhoon with roughly the same payload are a very good illustration. In my opinion, internally-loaded aircrafts are in fact difficult to compare with externally-loaded aircrafts. Both configurations have separate sets of strengths and weaknesses.
    Aircraft with internal weapon bays offers :
    - possibility to be stealthier, but external loading remains possible
    - no impact on drag of internal ordnance
    - permanent drag and mass penalty -> hence bigger engine need -> higher fuel consumption -> reduced range + highest acquisition and life cycle costs
    - probably higher maintenance costs and more reliability issues : all these moving parts!
    - new weapons integration limited by internal weapon bays size.
    ...

    Hence, there are many difficulties to compare this two types of aircraft : fuel fraction must be seen differently, influence of weapons load on performance is different (add drag + mass when external, only mass when internal), aircraft with external weapons remains more open to future evolution, etc.

    And a little precision. MICA in rear fuselage hardpoints on Rafale aren't conformal :

    As you can see, there is a little pylon. Drag addition remains low, but that's not a "true" conformal point like on Typhoon.

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