Maximizing Vertical Lift: VTOL Engine Designs in Fighter Jets

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Discussion Overview

The discussion revolves around the fuel consumption of the Harrier aircraft, particularly during vertical takeoff and hovering, as well as the implications of different takeoff methods such as the use of ski jumps. Participants explore various aspects of VTOL engine performance, fuel efficiency, and operational limitations.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant inquires about the fuel consumption of the Harrier during vertical takeoff, noting difficulty in finding information.
  • Another participant humorously suggests that the fuel consumption is "a lot," prompting further discussion on the actual mechanics of thrust redirection.
  • Some participants propose that the fuel consumption during vertical takeoff may be less than that of other military jets due to the non-afterburning nature of the Pegasus engine.
  • A participant suggests that the Harrier's fuel consumption must be calculated based on achieving over 97% of maximum thrust for takeoff.
  • There is a discussion about the Harrier's ability to hover and the limitations imposed by fuel availability and engine temperature, with some participants asserting it can hover longer than initially suggested.
  • One participant mentions that the Harrier carries about 1000 gallons of fuel and questions the plausibility of a consumption rate of 1 gallon per second.
  • Another participant clarifies that water is injected into the exhaust to cool it and increase jet density, rather than directly cooling the engine, and discusses the implications for hovering and takeoff under different conditions.
  • There are claims about the advantages of ski jumps for takeoff, including potential fuel savings and the ability to lift heavier payloads.
  • Some participants express uncertainty about the efficiency of hovering compared to rolling takeoffs, with one suggesting that hovering may be less efficient due to the nature of thrust generation.
  • There is a mention of the historical context of the Harrier's design and operational practices, including the use of ski jumps versus catapults.

Areas of Agreement / Disagreement

Participants express a range of views on fuel consumption during different flight modes, with no consensus reached on specific figures or the efficiency of hovering compared to rolling takeoffs. The discussion remains unresolved regarding the exact mechanics and implications of fuel usage in various scenarios.

Contextual Notes

Participants note that fuel consumption rates may depend on multiple factors, including aircraft weight, external conditions, and operational parameters, which are not fully resolved in the discussion.

  • #31
The Harrier has less structural fuel capacity than mentioned in the forum but outboard tanks fix flight time problems as mission requirements demand. The engines are intercooled turbofans which means that air is not a problem. An internal sealed coolant system takes care of that and shuts off at preset vertical speed and altitude.
 
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  • #32
mgb_phys said:
In another Physics link - in 1983 a harrier got lost on an exercise and ended up landing on a Spanish container ship near Teneriffe. The big flat crate it landed on was carrying the base plate for one of the British Telescopes on La Palma. There is a photo of the landing in the tea room there.
It's funny how one remembers things from a while back. I knew I had heard this before when I saw this picture:

8233591f6329d56e25.jpg


A good thread here:
http://rus-military.livejournal.com/51607.html
 
Last edited by a moderator:
  • #33
mgb_phys said:
A couple of conventional jet fighters can steer the output nozzles of their jet engines a few degrees to provide a little more maneuverability.

The F-22 has one of the most unique designs like this. There is also that "other" VTOL plane the US has been playing with for years. It has a single main engine where the output can twist 90* so it faces down twards the ground it out behind the plane. It also has the 2nd fan in the middle of the Fuelsalage (sp) to balance the vertical lift. I wish I could remember a name so I could post a picture.
 

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