from the wiki

The Rockwell XFV-12 was a research project for combining supersonic speed with Vertical Take-Off and Landing, From wikipedia:

The XFV-12 used a thrust augmented wing concept... in which exhaust would be directed through spaces in a wing opened up like venetian blinds to increase available lift, somewhat like Lockheed's unsuccessful XV-4 Hummingbird.

So I've seen a little bit about the "Rockwell XFV-12 Fighter" plane and "Jetoptera's Bladeless Propulsion System" for a while and I found these types of aircraft and propulsion systems quite intriguing.

However, I couldn't find many aircraft that use this type of propulsion system. Even less information comparing to conventional planes.

How efficient is this type of propulsion compared to conventional systems?

  • 3
    $\begingroup$ "Thrust augmentation" is generally understood as temporary extra-thrust by using an afterburner or another method. XFV-12 used a thrust augmented wing" which is a wing using venetian blinds to redirect engine gases vertically for VTOL. It's not the same. $\endgroup$
    – mins
    Dec 14 '21 at 17:19
  • 8
    $\begingroup$ This question essentially requires a reader to watch multiple YouTube videos in order to know what's being asked; that's rather time-consuming, and the credibility of videos on YouTube runs the spectrum from extremely credible to not-at-all. I don't think it makes for a good question to ask for commentary on such videos, especially given how little info is apparently out there on the subject generally (i.e. the OP's 2nd paragraph). Add to that the comment above by @mins, this comes off as a very low-quality question. DV'd accordingly. $\endgroup$
    – Ralph J
    Dec 14 '21 at 18:05
  • $\begingroup$ OP means thrust vectoring. Have edited the title and voted to keep open. $\endgroup$
    – Koyovis
    Dec 15 '21 at 1:50
  • 3
    $\begingroup$ Does this answer your question? Why is Russian super-maneuverable thrust vectoring more prevalent than American? $\endgroup$
    – Ralph J
    Dec 15 '21 at 2:28
  • $\begingroup$ @RalphJ That’s a question with some great answers, it focuses more on supermanoeverability though. The Harrier, and the engineering difficulties that failed the XVF-12, were not mentioned, $\endgroup$
    – Koyovis
    Dec 15 '21 at 3:36

What is shown in first video is thrust vectoring, the second video seems to be of no practical aeronautical engineering value at all. Thrust vectoring has two major applications:

1. Vertical take-off

From the Harrier wikiImage source including license, cropped photo

Redirecting thrust vertically, for vertical take-off and/or landing. Like the subsonic Harrier does, with four nozzles that can rotate over a range of 98°.

  • Advantage: tiny runways required, enabling building much smaller and affordable aircraft carriers.
  • Disadvantage: Four nozzles required, splitting the exhaust from a single engine. Difficult engineering problems as demonstrated by the XFV-12, and piloting problems by having to keep the nose into the wind at vertical take-off. The STOVL F-35B Lightning II uses a separate shaft driven lift fan.enter image description here Image source and credits

2. Post Stall Technology.

PST is for manoeuvring during combat, as discussed in this question mentioned in a comment by @RalphJ. Supermanoeverability like in the Pugachev Cobra manoeuvre demonstrated by the Su-27 at the 1989 Paris Air Show. An innovative feature at the time, with two camps polarising on the issue at the time according to AIAA paper 91-3194 and expressing the advantage/disadvantage:

enter image description here Image source

  • Pro:

"The key to success in combat with all-aspect missiles is to shoot first. Supermaneuverability allows a pilot to gain a shot opportunity earlier than with conventional maneuverability.

  • Against:

"Because of the high energy bleed rate, I believe the manoeuvre has no tactical value. It is just an airshow stunt".

Pugachev Cobra - on Youtube

How efficient is this type of propulsion compared to conventional systems?

Thrust vectoring for VTOL implies re-directing the exhaust flow over 90°, and distributing it over at least three support points. And this redirection is associated with considerable losses as experienced in the XFV-12 program, plus stability problems.

  • The XVF-12 could not produce enough thrust for VTOL and had stability issues. From this link, commentary from people involved in the design:

Just a couple of comments from someone who was involved in the original concept, proposal, and early development of the XFV-12A. The basic problem was with the canard configuration. In order to have the CG in the correct place to maintain positive longitudinal static stability in conventional flight, AND to balance the wing and canard lift forces in hover, the canard augmentors had to produce proportionally quite a bit more lift in much smaller surfaces and ducting than the wing augmentors. In order to do this, the AUGMENTATION RATIO, or the ratio of the augmentor lift force to the lift force of the basic airflow without entrained air, had to be much larger for the canards than for the wings. Couple this with the losses in the canard ducting due to the much longer duct runs, smaller ducts, turns, etc., and that balance was not achievable with any practical useful load.

  • The drawing below from the wiki shows the arrangement of the four nozzles of the Harrier, the two front ones driven by the bypass fan and the rear ones by the hot exhaust. From the wiki:

The Harrier has been described by pilots as "unforgiving".[61] The aircraft is capable of both forward flight (where it behaves in the manner of a typical fixed-wing aircraft above its stall speed), as well as VTOL and STOL manoeuvres (where the traditional lift and control surfaces are useless) requiring skills and technical knowledge usually associated with helicopters. Most services demand great aptitude and extensive training for Harrier pilots, as well as experience in piloting both types of aircraft. Trainee pilots are often drawn from highly experienced and skilled helicopter pilots.[N 8][12]

enter image description here

  • 3
    $\begingroup$ It would be interesting to see what else was on display at the 1089 Paris Air Show. :D (some typos are so good, they're not worth correcting!!) $\endgroup$
    – FreeMan
    Dec 15 '21 at 16:09
  • 3
    $\begingroup$ @FreeMan There were stones flying, and a people brought their trained albatrosses. 😳 $\endgroup$
    – Koyovis
    Dec 15 '21 at 18:59

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