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According to my research, a pulsejet's thrust grows as the airspeed increases. Most pulsejets require no moving parts which makes it easier to manufacture them. They are also very lightweight which can have some great effects on aircraft.

They are very slow at zero airspeed but very fast at high airspeeds. Therefore you could simply have a normal jet engine to power the take off and then switch after take off to the pulsejets.

Here is an example where I've labelled a DC-10 of what a pulsejet with jet engine plane could look like:

enter image description here

The plane would taxi onto the runway using the jet engine as power, it'd then line up on the runway. It'd then power its jet engine and take off. Shortly after take off it would switch to the pulse engines and optionally turn the jet engine off.

So why don't planes use pulsejets? Surely they would allow planes to go faster and in turn allow them to reach destinations quicker. Also the pulsejets are easier and cheaper to produce than jet engines and there lighter than jet engines.

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    $\begingroup$ There are quite a few drawbacks listed in the Wikipedia-Article you linked to, which should answer your question. $\endgroup$
    – user12485
    Commented Dec 29, 2015 at 16:06
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    $\begingroup$ "They are very slow at zero airspeed but very fast at high airspeeds" I guess that is true for everything that moves. $\endgroup$
    – Peter Kämpf
    Commented Dec 29, 2015 at 16:50
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    $\begingroup$ @PeterKämpf I meant that the produce more thrust at high airspeeds than zero airspeed. $\endgroup$
    – Hyden
    Commented Dec 30, 2015 at 12:35
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    $\begingroup$ @Hyden: I understand that, but I just couldn't resist ;-) $\endgroup$
    – Peter Kämpf
    Commented Dec 30, 2015 at 13:39
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    $\begingroup$ Would it not make more sense, if you wanted to use a pulsejet with all its drawbacks, to reverse the engine configuration? 2 conventional engines, and 1 pulse? That way, plenty of power would be available for takeoff/landing, and low-power cruise would be covered, too. Also, with a failure, there would always be at least 1 conventional engine for landing. $\endgroup$
    – Jeffiekins
    Commented Dec 30, 2015 at 16:48

3 Answers 3

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2 reasons really:

  1. Airplanes need most of their thrust right when their airspeed is low. (to get more airspeed at takeoff and go-around).

  2. The maximum airspeed in cruise is not dictated by how much thrust the engines can throw out. Instead it's dictated by the aerodynamic forces on the airframe. They cruise right below the speed of sound where the rules of aerodynamics change drastically. Going too fast would rip an airplane apart.

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    $\begingroup$ I'd add another: noise and vibrations. Pulse jets, or the more promising pulse detonation engine (PDE) are not exactly renowned for their quietness. $\endgroup$
    – Sanchises
    Commented Dec 29, 2015 at 15:47
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In your proposed design an engine failure at low speed would result in essentially no thrust. So, additionally you would need to carry a second gas turbine engine for redundancy. Then, during cruise you would be carrying around these two extra engines that are not being used, so they are just dead weight. Overall, airliner engine selection is driven largely by fuel efficiency. Wikipedia reports that pulse jets have poor specific fuel consumption.
Also, pulse jets tend to be very loud, which can be a noise problem.

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    $\begingroup$ Activate the jet engine or leave it on? Ignoring the fact that an airplane shouldn't really be flying at low speed at any point except take-off and landing at which points it will be using the jet engine. Unless of course the plane is doing loop-de-loops. $\endgroup$
    – Hyden
    Commented Dec 30, 2015 at 12:37
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    $\begingroup$ @Hyden What Adam is saying is that if the turbine engine failed, you would have nearly no thrust during takeoff, which is exactly the time when it's most critical to have as much thrust as possible. You'd have to have at least 2 turbine engines in case one of them failed during or shortly after takeoff and the remaining engine(s) would have to be large enough to have enough thrust to complete the takeoff and climb out in the event of such a failure. This is already a legal requirement for transport category aircraft. $\endgroup$
    – reirab
    Commented Dec 30, 2015 at 20:50
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    $\begingroup$ Also, not very long term stable, especially the valved type - the V1 engine was probably too worn to reuse even if it wasn't used in a way that INTENDED burning and ripping it to shreds upon reaching destination.... $\endgroup$
    – rackandboneman
    Commented Apr 27, 2018 at 23:10
  • $\begingroup$ @Hyden no thrust at TO/approach = crash = crash into city = mass death $\endgroup$
    – Abdullah is not an Amalekite
    Commented Sep 12, 2020 at 6:59
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There are multiple reasons for pulsejets not being used in aircraft (or manned aircraft generally).

  • They are quite loud. In fact most of the pulsejet aircraft are (in)famous for their noise. One of the reasons for the US Army to reject the pulsejet powered XH-26 was the unacceptable noise.

XH-26

"XH-26 Jet Jeep in flight" by San Diego Air & Space Museum Archives - http://www.flickr.com/photos/sdasmarchives/4561399305/in/photostream/. Licensed under Public Domain via Commons.

  • The intermittent (combustion) operation means that vibration is a serious problem. For aircraft engines this causes serious problem; especially for commercial airlines, such vibration levels would be unacceptable.

  • Though pulsejets can be operated in low (and even zero) airspeeds, it uses the dynamic pressure of air for compression. Hence the engine will be producing little thrust in the most critical phases of operation (takeoff and climb).

  • Pulsejets' combustion chamber operates at high temperature and requires heat resistant materials. Air cooling can improve this, but will complicate the engine.

  • There are other things here- having a dead engine (assuming that the turbofan is turned off at some point) simply increases drag and weight penalty.

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