We heard about the X-33 space plane, there was the X… was it X-37 crew return vehicle? Now the X-43 hypersonic plane is going to be tested. Does this go back to the Bell X-1, the plane which broke the sound barrier? Is there a list somewhere of all of the X designations?
Here’s a starting point: Experimental Research Aircraft X-Series.
It doesn’t seem to list all of the experimental aircraft which have ever been designated the X-n, and I’m not sure that there is in fact a single series of sequentially numbered “X-planes”. I believe that planes are sometimes designated by year, not sequential number (I think the B-52 was so designated because it was introduced in 1952, not because it was necessarily the 52nd model of American bomber), and sometimes they start over (e.g., the B-1 and B-2 bombers). I’m sure there have been similar continuity gaps in experimental aircraft.
I’m not sure if they have all of the X-planes, but these two site seem to have fairly comprehensive lists.
the History of the X Series of Aircraft
X-Planes Experimental Aircraft
I have an excellent book about the X-planes (called “The X-Planes”, fancy that), although it only covers up to the X-31. If you’re looking for something specific about any of the planes, I’ll be happy to look it up for you. It’s almost bound to be in there.
X- was simply the U.S. Air Force prefix for an experimental airplane. (In 1963, all the armed forces began to use a single numbering scheme that was based more closely on the USAF series than the U.S. Navy designations.)
X-1 was the first designed-as-experimental plane commissioned by the USAF after they separated from the U.S. Army and devised their numbering schema.
The X-33 is the 33d plane proposed for design as an experimental craft.
I came across a book a few weeks ago which may be “The X-Planes” that RobotArm mentioned, or something similar anyway. I browsed through it and was surprised to discover that many of the X- designated aircraft weren’t airplanes but experimental missiles.
I did not know that.
The order is the order in which the aircraft were proposed, not when they were actually built or first flown, which causes some confusion in the ordering. There’s also a few (such as the “space plane”, the X-30) which were never built at all. Nowadays, they’re mostly small, cheap, unmanned “technology demonstrators” to establish the value of various technologies for production planes.
I remember this one aircraft which had “reversed” wings (the tips pointed forward). Which designation did it have? Must’ve been some X-3…, iirc.
That would be the X-29.
Yes, indeed!
Thank you. Great plane, imho. Such a pity they apparently abandoned the design.
This USAF Museum page says the Boeing B-52 was initially ordered in 1949 as the XB-52. As someone mentioned above, the designations for new aircraft start out with an X in front until they’re past the testing stage. Elsewhere on that site it says the B-52 was first conceived in 1946. While it first flew in 1952, it was first delivered to the Air Force in 1955. The list at American Bomber Designations shows an unbroken sequence in designations, with the Martin XB-51 preceding it and the Convair XB-53 following it.
FWIW, the X-43A was destroyed today when the Pegasus rocket it was riding on malfunctioned.
It’s also important to remember that there are three sets of X designations out there. The traditional one (starting with the X-1 flown by Chuck Yeager) and including my personal favorite the X-15, X-29, etc is used by NASA. The Air Force uses the X designation along with the aircraft type designation for prototypes of possible production craft (such as the above mentioned XB-52 which BTW was the 52nd contracted for bomber, coming shortly after the B-50 variant of the Boeing B-29). The traditional next step from this prototype is the Y designation for pre-production, then the producion models. The Air Force also uses X for proof of concept and some experimental craft such as the current Boeing X-32 and Lockheed Martin X-35 which will prove the proof of concept for the multi use JSF fighter to be known as F-24.
This is a very good site that expains designations and the systems that were used.