How do STOVL and V/STOL aircraft differ?

Question

Wikipedia's page for STOVL begins with

A short take-off and vertical landing aircraft (STOVL aircraft) is a fixed-wing aircraft that is able to take off from a short runway (or take off vertically if it does not have a heavy payload) and land vertically (i.e. with no runway).

while V/STOL is

A vertical and/or short take-off and landing (V/STOL) aircraft is an airplane able to take-off or land vertically or on short runways. Vertical takeoff and landing (VTOL) aircraft are a subset of V/STOL craft that do not require runways at all. Generally, a V/STOL aircraft needs to be able to hover.

On both pages, it is stated that the respective type should not be confused with the opposite one.

Essentially, it says STOVL is not the same as V/STOL and vice versa.

However I have trouble understanding where the differences lie between them.

I was about to clear it up on my mind when I thought STOVL definitely requires some (short) distance for the aircraft to clear before taking-off, while V/STOL aircraft are simply able to start hovering in order to take off. But apparently, it's possible for STOVL aircraft to do so if they don't have heavy payload.

What am I missing here? Both are supposed to be able to land vertically so I suppose there's either a difference on the take-off or if not, there are differences on the wing structure/geometry of each type of aircraft.

Answer 1

To put it simply, it's about the ability to take of vertically at any mass:

V/STOL aircraft can take off fully loaded (max. operational weight).

STOVL aircraft does not have sufficient engine thrust to take off vertically at any weight, and at higher T/O weights it must have some lift from wings to assist the T/O. It may be able take off vertically at less than max. T/O weight.

Answer 2

The distinction between STOVL and V/STOL is largely a matter of naming. As it stands, no one has operationally deployed a fixed-wing aircraft that can land vertically, but cannot take off vertically. All modern aircraft referred to as STOVL or V/STOL are, in technical terms, VTOL (as well as STOL) capable aircraft.

Designating them V/STOL was a matter of emphasizing that they can combine the higher useful load advantage of STOL operation with the flexibility of VTOL operation. The term "STOVL" is a further attempt to distance away from the notion of VTOL as low-performance. In the F-35B's case the justification is that a conventional takeoff ramp is still required for practical operations, but a simpler and more compact vertical recovery can be used. Actual operational practice may dictate outright STOL operation to be preferable.

In short: As used presently, these terms do not carry an inherent technical meanings. It's just practice, and in some cases can even be thought of as public relations choices.

Answer 3

V/STOL and STOVL are as much operational modes as types of aircraft.

In V/STOL, the aircraft is envisaged as sometimes taking off and/or landing vertically and sometimes using a short runway, adapting its mode of operation to the job in hand. Some hybrid and compound rotorcraft can operate in STOL mode as well as VTOL.

In STOVL, the aircraft is envisaged as taking off from a short runway, either because it is heavily loaded or it is based there, and at the end of its flight landing vertically, again either because its fuel load is now so light that it can hover, or the destination demands vertical descent. The UK Sea Harrier fleet typically operated in STOVL mode, taking off up a ski-jump and landing vertically.

Some aircraft are optimised for the one mode or the other and described accordingly, others are designed for both modes and the choice of description is a marketing or editorial one.

Weirder non-standard variants are sometimes cooked up for specialist modes or sub-modes such as VTOSL or VTOCL (conventional landing) for a vertical-launch point-defence interceptor, or STOV/SL which speaks for itself. Thankfully, none has stuck.

Answer 4

You’re right. V/STOL and STOVL are one in the same.

It would probably be better to consider the term STOVL more of a mission profile than an aircraft capability.

All powered lift aircraft eg Harrier, F-35B, etc. are capable of vertical takeoff and landing within certain weight limits. They are not capable of vertical flight outside this.

The directed lift system on these aircraft do allow lift to be augmented by vectored thrust, allowing for short takeoffs and landings this way at greater weights.

The upshot of which is that, for certain operations, it makes more sense to a jet like that to execute a short takeoff when heavily loaded ie fuel + weapons load, fly a mission, thence, once fuel and stores are significantly depleted below max hover weight, then make a vertical landing. The profile works well for ops from small helicopter carriers or unpaved, short airstrips where CTOL operations just aren’t possible.

Now a STOVL or V/STOL capable aircraft should not be confused from a pure VTOL aircraft eg MACAIR DCX, SpaceX Falcon 9 Booster, DJI Mavic, etc., which cannot accomplish short field takeoffs and landings. Even a helicopter would be considered a V/STOL aircraft as it is common for some ops to do short field takeoffs and landings when operating at density altitudes above the maximum hovering altitude for a given takeoff weight.