Why aren't pulsejet cruise missiles a thing?

[Elysium]

Why aren't pulsejet cruise missiles a thing? Rockets are limited in range, as are glide bombs, both of which seem to be popular choices for low to mid-end weapons. On the other hand, turbofan-powered cruise missiles offer great range, but the engines themselves add a tremendous amount of cost to the weapon. Pulsejets are easy and cheap to manufacture, and I think they could carve out a healthy niche of inexpensive cruise missiles with decent range. So why aren't they used? Or maybe they are? Is there or has there been an attempt to build such a weapon (other than the infamous V-1)?

 

[Scott Kenny]

Today they're the farthest thing from stealthy, and I believe need unique fuel.

And honestly, microturbines in the 50-150lb thrust range are cheap (under $5k), and run on JP8.

 

[1635yankee]

Pulsejets are incredibly thirsty. I can't really comment much about their stealth characteristics, except that they are very loud, and probably more importantly, are likely to have very hot exhaust. The nature of pulsejet also means that there is likely to be high vibration levels, which would make design of the remainder of the missile more challenging.

A low-cost turbojet could probably be built with a few dozen parts[1] (single-stage centrifugal compressor[2], single stage turbine[2], shaft, foil bearings[3], fuel control based on a cheap controller, like a Raspberry Pi, single can combustor). I also suspect the price of a turbojet or turbofan for a cruise missile is much cheaper than that of the guidance system and warhead.

--------------

1: Depending on how one counts "parts."
2: Perhaps a ceramic blisk or, if cheaper, a metal disk with ceramic blades.
3: Hey, no oil!

 

[Scott Kenny]

Pulsejets are incredibly thirsty. I can't really comment much about their stealth characteristics, except that they are very loud, and probably more importantly, are likely to have very hot exhaust. The nature of pulsejet also means that there is likely to be high vibration levels, which would make design of the remainder of the missile more challenging.

A low-cost turbojet could probably be built with a few dozen parts[1] (single-stage centrifugal compressor[2], single stage turbine[2], shaft, foil bearings[3], fuel control based on a cheap controller, like a Raspberry Pi, single can combustor). I also suspect the price of a turbojet or turbofan for a cruise missile is much cheaper than that of the guidance system and warhead.

--------------

1: Depending on how one counts "parts."
2: Perhaps a ceramic blisk or, if cheaper, a metal disk with ceramic blades.
3: Hey, no oil!

I know a guy who made a demonstration purposes turbojet out of an automotive turbocharger with a combustion chamber added between compressor outlet and turbine inlet...

HS science/physics classes love it.

 

[Orionblamblam]

Pulsejets are incredibly thirsty. I can't really comment much about their stealth characteristics, except that they are very loud, and probably more importantly, are likely to have very hot exhaust.

This thing ain't sneakin' up on nobody:

View: https://www.youtube.com/watch?v=gAKekhmTRaY

 

[RanulfC]

Why aren't pulsejet cruise missiles a thing? Rockets are limited in range, as are glide bombs, both of which seem to be popular choices for low to mid-end weapons. On the other hand, turbofan-powered cruise missiles offer great range, but the engines themselves add a tremendous amount of cost to the weapon. Pulsejets are easy and cheap to manufacture, and I think they could carve out a healthy niche of inexpensive cruise missiles with decent range. So why aren't they used? Or maybe they are? Is there or has there been an attempt to build such a weapon (other than the infamous V-1)?

They don't take any special fuel but as has been noted they aint 'stealthy' at all but they were used for a while until turbojets became economic to use. More modern pulse jets can be a bit quieter (that being relative ) but it takes a very careful design and construction to accomplish and a big part of your 'draw' of a pulsejet is lower complexity and cost.

Myself I've always been partial to Messerschmitt's pulse-ram jet engine project

Randy

 

[Nik]

IMHO, pulse-jets are deprecated because too easy to build, especially the tuned 'valveless' variety...

Don't need fancy rotors, stators etc. Don't need high RPM balancing etc etc. Guidance issues solved by additional isolation of 'smarts'...

What matter they have a huge thermal profile ?? You could build a dozen or more for the engine cost of a turbojet, salvo faster than defenders can re-load with expensive SAMs meant for 'better' targets. And, if your few turbojet drones are faster, launch those in second wave for 'time on target'...

D'uh, given they can steer, they may zig-zag like convoy ships, so harder for AAA to hit.

Uh, would a ring-wing doubling as cowling significantly mask the hot pipe ??

( Tect affressivrly slub-efited by Duty Cat... )

 

[Elysium]

IMHO, pulse-jets are deprecated because too easy to build, especially the tuned 'valveless' variety...

Don't need fancy rotors, stators etc. Don't need high RPM balancing etc etc. Guidance issues solved by additional isolation of 'smarts'...

What matter they have a huge thermal profile ?? You could build a dozen or more for the engine cost of a turbojet, salvo faster than defenders can re-load with expensive SAMs meant for 'better' targets. And, if your few turbojet drones are faster, launch those in second wave for 'time on target'...

D'uh, given they can steer, they may zig-zag like convoy ships, so harder for AAA to hit.

Uh, would a ring-wing doubling as cowling significantly mask the hot pipe ??

( Tect affressivrly slub-efited by Duty Cat... )

I kinda agree with the point of your post - Pulsejets represent the sort of redneck engineering, that no self-respecting aerospace engineer would've considered before the Ukraine war. And aerospace companies aren't too keen on delivering weapons that can fill the niche of their high-end cruise missiles at 1/20th of the cost. But the recent war has proven that drones built out of DSLRs, scooter engines, and $200 worth of smartphone parts and hobby electronic supplies combined with cold-war surplus hand grenades or RPGs present a real and present danger to even modern systems.
All the arguments mentioned about the lack of stealth would be countered by their speed and inexpensive nature, once again creating a huge dilemma of shooting them down economically.

That being said, I'm doing armchair engineering here, and there might be perfectly legitimate reasons why this would be a silly idea.

Today they're the farthest thing from stealthy, and I believe need unique fuel.

And honestly, microturbines in the 50-150lb thrust range are cheap (under $5k), and run on JP8.

Checking on Aliexpress, for the $5k, even 50lbs is kinda ambitious, and I feel like you'd need more (the Tomahawk has 600lbs thrust ,the Storm Shadow has twice that).

Just to make my point, lets compare a Storm Shadow, to the V1, a 80+ year old design (V1 vs Storm Shadow).

V-1 flying bomb - Wikipedia

en.wikipedia.org

Storm Shadow - Wikipedia

en.wikipedia.org

Speed: 400 mph vs 700 mph
Range: 160 mi vs 310 mi
Payload: 850kg vs 450kg

Please keep in mind the Storm Shadow is air launched while the V1 isn't.
Even such lopsided comparison against my idea shows that it has potential. A modern V-1 equivalent with GPS guidance, optical target recognition, etc. (these are features available on inexpensive drones) with half the payload (due to increased accuracy), would be a dangerous weapon indeed.
Not sure if it makes sense to air-launch it, but if it does, it would probably close the performance gap even further.
Also please keep in mind, the Storm Shadow's max range is determined by the INF treaty that limits its range to 500km (310 mi).

 

[Dilandu]

Why aren't pulsejet cruise missiles a thing? Rockets are limited in range, as are glide bombs, both of which seem to be popular choices for low to mid-end weapons. On the other hand, turbofan-powered cruise missiles offer great range, but the engines themselves add a tremendous amount of cost to the weapon. Pulsejets are easy and cheap to manufacture, and I think they could carve out a healthy niche of inexpensive cruise missiles with decent range. So why aren't they used? Or maybe they are? Is there or has there been an attempt to build such a weapon (other than the infamous V-1)?

They are very fuel-inefficient. And they work satisfactory only in a limited range of velocities. Moreover, as it was mentioned above - modern turbines are quite cheap and efficient (and if you need more range, it's simpler to install a piston engine).

 

[Dilandu]

Please keep in mind the Storm Shadow is air launched while the V1 isn't.

Correction: V-1 was capable of being air-launched. Germans launched a number of them from bombers over North Sea (trying to circumvent formidable London defenses from unexpected direction).

And both American (JB-2 "Loon") and Soviet (10X) copies of V-1 were air-launched also.

 

[1635yankee]

IMHO, pulse-jets are deprecated because too easy to build, especially the tuned 'valveless' variety...

Don't need fancy rotors, stators etc. Don't need high RPM balancing etc etc. Guidance issues solved by additional isolation of 'smarts'...

What matter they have a huge thermal profile ?? You could build a dozen or more for the engine cost of a turbojet, salvo faster than defenders can re-load with expensive SAMs meant for 'better' targets. And, if your few turbojet drones are faster, launch those in second wave for 'time on target'...

D'uh, given they can steer, they may zig-zag like convoy ships, so harder for AAA to hit.

Uh, would a ring-wing doubling as cowling significantly mask the hot pipe ??

( Tect affressivrly slub-efited by Duty Cat... )

I think you're simultaneously pessimistic about disposable turbojet costs and wildly optimistic about guidance system costs. The development and purchase costs of a guidance system capable of zigzagging would be very high. Pulsejets are also very inefficient, which would drive up the size and cost of a missile with medium or long range. At short range, the pulsejet gets to compete with solid fuel rockets which, while not stealthy have no moving parts and don't require booster for ground launch

 

[Byeman]

,salvo faster than defenders can re-load with expensive SAMs meant for 'better' targets.

D'uh, given they can steer, they may zig-zag like convoy ships, so harder for AAA to hit.

There is nothing special about them that makes them easier to salvo or steer like anything else

 

[Elysium]

I think we've seen in Ukraine just how cheaply the guidance systems can be built out of commercial or high volume military components. The entire Shahed drone is supposed to cost just $20k.
As for the efficiency of pulsejets, forgive me, but can you give concrete data on this matter?
I looked at a random hobbyist turbojet on Aliexpress, and it seems to have 120N of thrust with 0.35kg fuel consumption/min (or 175kg/kN/hr).

Comparatively, again, according to Wikipedia, the V1 carried around 600kg of fuel, and had 3kN of thrust, with a flight time of about 25 minutes (based on max range), which gives it about 480 kg/kN/hr), so about 2.7 times less efficient. Although I believe this to be an overestimation, since I calculated flight time as range/max velocity, and assumed a constant fuel consumption.
This is obviously totally wrong, since most of the energy is spent in climb/acceleration.

 

[OliverSedlacek]

I've no experience of military electronics but I've pondered what I could achieve as an experienced electronics engineer in the Ukranian conflict. I believe I could make a cruise missile guidance system electronics for less than $500 from commercial computer boards. The military wouldn't look twice at it because it wouldn't match their accuracy expectations but guerilla groups have quite different viewpoints.

 

[overscan (PaulMM)]

120N = 12.2kg
0.35kg/min = 21kg/hour

SFC = 1.72kg/kg/hr

That's about the same as an EJ200 with afterburner on. So not very efficient.

I've seen figures for the Williams F112 as low as 0.25.

For long range cheap drones/missiles, its hard to argue with piston engines for efficiency.

 

[red admiral]

We seem to be mixing up a few things

For a high end cruise missile like Tomahawk or JASSM etc then the propulsion costs are less than c. 10% of the unit cost. A cheaper propulsion system doesn't really change the cost regardless of the negatives of a pulse jet e.g. range

Some really cheap "cruise missiles" / one way attack drones now exist. These are not really comparable to the above e.g. generally much smaller total size and warhead size. Some of these are fitted with piston engines (slow, long range) and some with very low cost turbojets (>5k unit cost) (faster, shorter range). Some companies are trying to develop pulse jets for these currently (slightly cheaper, much shorter range).

Range is important for cruise missiles and a pulse jet one will be significantly larger to fit in all the extra fuel, which then complicates logistics e.g. fewer per launcher so more difficult to do attacks in mass. There's bunch of trade offs.

 

[sferrin]

This thing ain't sneakin' up on nobody:

View: https://www.youtube.com/watch?v=gAKekhmTRaY

Back in 1985-ish I was in the aero lab at Utah State University when someone fired a pulsejet up in the lab. I was on the other side of the lab area (think warehouse interior). It was so loud I was screaming at my instructor as loud as I could and he just laughed because we could barely hear ourselves yelling.

 

[kqcke for you]

I've seen figures for the Williams F112 as low as 0.25.

I even heard as low as 0.15 for F112.

 

[1635yankee]

I even heard as low as 0.15 for F112.

What units are being used?

 

[RanulfC]

What units are being used?

kg per hour fuel use I think.

Randy

 

[edwest4]

I kinda agree with the point of your post - Pulsejets represent the sort of redneck engineering, that no self-respecting aerospace engineer would've considered before the Ukraine war. And aerospace companies aren't too keen on delivering weapons that can fill the niche of their high-end cruise missiles at 1/20th of the cost. But the recent war has proven that drones built out of DSLRs, scooter engines, and $200 worth of smartphone parts and hobby electronic supplies combined with cold-war surplus hand grenades or RPGs present a real and present danger to even modern systems.
All the arguments mentioned about the lack of stealth would be countered by their speed and inexpensive nature, once again creating a huge dilemma of shooting them down economically.

That being said, I'm doing armchair engineering here, and there might be perfectly legitimate reasons why this would be a silly idea.


Checking on Aliexpress, for the $5k, even 50lbs is kinda ambitious, and I feel like you'd need more (the Tomahawk has 600lbs thrust ,the Storm Shadow has twice that).

Just to make my point, lets compare a Storm Shadow, to the V1, a 80+ year old design (V1 vs Storm Shadow).

V-1 flying bomb - Wikipedia

en.wikipedia.org

Storm Shadow - Wikipedia

en.wikipedia.org

Speed: 400 mph vs 700 mph
Range: 160 mi vs 310 mi
Payload: 850kg vs 450kg

Please keep in mind the Storm Shadow is air launched while the V1 isn't.
Even such lopsided comparison against my idea shows that it has potential. A modern V-1 equivalent with GPS guidance, optical target recognition, etc. (these are features available on inexpensive drones) with half the payload (due to increased accuracy), would be a dangerous weapon indeed.
Not sure if it makes sense to air-launch it, but if it does, it would probably close the performance gap even further.
Also please keep in mind, the Storm Shadow's max range is determined by the INF treaty that limits its range to 500km (310 mi).

The V-1 was also launched by air. It was underslung the wing on an He-111 bomber. Just like the Americans would later launch the X-15.

 

[publiusr]

I don’t know that terrorists even thought to use them…

 

[Nicknick]

All the drawbacks have allready been mantioned, but there is still one job a puplse jet could do quite well and that is overwhelming defence systems by pure numbers. They are cheap to build when they lack a complex guiding system and powerfull warhead, so starting hundrets of pulse jet driven drones could help to enable more valuable drones to get through the air defence.

 

[Orionblamblam]

All the drawbacks have allready been mantioned, but there is still one job a puplse jet could do quite well and that is overwhelming defence systems by pure numbers. They are cheap to build when they lack a complex guiding system and powerfull warhead, so starting hundrets of pulse jet driven drones could help to enable more valuable drones to get through the air defence.

It's unclear that that's true. A cheap pulsejet drone would have longer range than an equivalent cheap solid rocket missile... but without a fairly complex control system, those drones are going to be all over the place at long range. One virtue of being relatively short ranged is that rocket missiles can saturate a target such as a city.

 

[paralay]

БПЛА-мишень E95М.

БПЛА-мишень E95М. :: БПЛА-мишень E95М. Разработчик: Эникс Страна: Россия Первый полет: 2006 г. Комплекс Е95 предназначен для обеспечения боевой подготовки войск и отработки

xn--80aafy5bs.xn--p1ai

https://nauchkor.ru/uploads/documents/60469f48ccefde000149db34.pdf

fuel consumption 0.456 - 0.477 kg/Newton * hour

 

[Orionblamblam]

БПЛА-мишень E95М.

БПЛА-мишень E95М. :: БПЛА-мишень E95М. Разработчик: Эникс Страна: Россия Первый полет: 2006 г. Комплекс Е95 предназначен для обеспечения боевой подготовки войск и отработки

xn--80aafy5bs.xn--p1ai

That'd make a strange target, especially for IR guided systems. It seems like it'd stand out a *lot* for its size, making it extra bright, and too easy to target.

 

[Scott Kenny]

All the drawbacks have allready been mantioned, but there is still one job a puplse jet could do quite well and that is overwhelming defence systems by pure numbers. They are cheap to build when they lack a complex guiding system and powerfull warhead, so starting hundrets of pulse jet driven drones could help to enable more valuable drones to get through the air defence.

With the terrible fuel efficiency of a pulse jet, you might as well use a solid rocket for short range saturation/distraction. Solid rockets are relatively easier to administer, which makes them cheaper to operate.

Even a cheap guidance system is a significant % of the total costs, I'd bet that the guidance system of a Shaheed is $10k, fully half the cost of the drone!

 

[Nicknick]

To irritate a defence system, the drones have to be very precise, I would even say, it might be helpful to deviate from the real targets to confuse the system even more. Despite that, I think that even target systems are no longer extremely expensive any more, GPS navigation is quite common for standard drones.

BTW: the range of a solid rockets is by far shorter than that of a solid rocket!

 

[Scott Kenny]

To irritate a defence system, the drones have to be very precise, I would even say, it might be helpful to deviate from the real targets to confuse the system even more. Despite that, I think that even target systems are no longer extremely expensive any more, GPS navigation is quite common for standard drones.

BTW: the range of a solid rockets is by far shorter than that of a solid rocket!

Typo?

Solid rockets are easily getting 150km as artillery types. MLRS types. Okay, ballistic flight isn't the same as aerodynamic flight when you're talking ranges, especially at low altitude. Solid rockets at low altitude would be for a fast missile, Mach 2.7ish, that gives minimal time for the defenses to respond.

But a pulse jet is also short ranged due to fuel consumption, and as I said a small turbofan is cheap. If you don't need speed, you can install a piston engine (or baby wankel) and that's even cheaper. It's the guidance systems that make a missile expensive.

 

[overscan (PaulMM)]

kg per hour fuel use I think.

Randy

SFC is the mass of fuel burned by an engine in one hour divided by the thrust that the engine produces.

The units of this efficiency factor are mass per time divided by force.

SFC is the same whether you measure mass and thrust in lbs or kgs, though in metric system it could (should) be quoted in kilograms per hour per N thrust (where 1kgp =9.8N) , in jet engines often the thrust is measured in kgp so the ratio becomes directly comparable to the ratio using imperial measurements.

 

[Nicknick]

The V1 allready had a range of 350 km, which is significant more than 150 km. Air breathing is reducing the amount of chemicals you have to carry very significantly. How do you compare the efficiency of a rocket with a pulse jet? Its not an easy thing to do...Do you take regard the oxidizer as fuel or not?

I like to promote piston engines for all sorts of applications, but pulse jets are much cheaper to built than piston engines or jet engines. The V1 pulse jet was built out of ordinary steel, not even austhenitic steel and you don't need any precission in any part. The valves (out of spring steel) was the only part in a V1 which requires at least some quality in manufacturing.

 

[Thos9]

Where can we see details of Messerschmitt's pulse-ram jet engine project?

 

[Scott Kenny]

The V1 allready had a range of 350 km, which is significant more than 150 km.

The V1 was also a very large missile, some 2100kg/4500lbs and 8.3m/27ft long! Only 1800lbs of that was boom, too.

Air breathing is reducing the amount of chemicals you have to carry very significantly. How do you compare the efficiency of a rocket with a pulse jet? Its not an easy thing to do...Do you take regard the oxidizer as fuel or not?

Generally not. So you compare range and weight of the total package.

I like to promote piston engines for all sorts of applications, but pulse jets are much cheaper to built than piston engines or jet engines. The V1 pulse jet was built out of ordinary steel, not even austhenitic steel and you don't need any precission in any part. The valves (out of spring steel) was the only part in a V1 which requires at least some quality in manufacturing.

It's also a physically large/long item, which does not lend itself to most missile launch setups.

Seriously, when not even the Shaheed suicide drones are powered by pulse jets, that's a hint that there's something fundamentally wrong with the concept.

 

[publiusr]

That'd make a strange target, especially for IR guided systems. It seems like it'd stand out a *lot* for its size, making it extra bright, and too easy to target.

Might a proximity release allow the pulse jet to be shed to draw off fire..the body glides to a laser pointer spot…r/c controls

 

[Nicknick]

The propulsion net power is the driving force (thrust) multiplied with the speed. Since the thrust of a rocket is independent from the speed, it comes clear, that the net propulsion power of a rocket is linear to the speed which makes them only suitable for very high speeds. Powering a sub sonic drone is solid rockets which have a very short burn time is therefore completley unsuitable.

The V1 weighted 2160 kg (fully loaded), but it was tanked with "only" 570 L Gazoline (<450 kg) fuel, thats about 20 % of the take off weight, try that with a rocket...

The shaheed are long range stealthy drones (at least for the defence systems at the beginning at the war), those were not extremly cheap.

 

[Nik]

May I point out that terrorists are not rational ?? Beyond wonky philosophy, they rank terror far above actual 'military' damage...

Currently demonstrated by eg repeated Rus targeting of civilians in Ukraine ?

IIRC, back in the 'Irish Troubles', trucking big 'fertiliser' bombs etc into Central London was an IRA priority due to the 'boom' factor.
Yet, one innocent civilian truck accidentally catching fire beneath a busy motorway junction bridge grid-locked everything for dozen miles around, closed that bridge pending survey and repair, closed junction due bridge-out, closed motorway at junction due unsafe bridge and a roadway compromised to foundations etc etc etc...
After seeing this, IRA could have easily, repeatedly closed multiple routes to/from London. Nah, they'd rather go for the 'boom' factor.
Logic analogous to Victorian anarchists who burrowed, aided by electric lights, from cellar under busy road, then set their explosives with a traditional slow-burning fuse which completely missed their intended target...

My point ? Deploying a Rocket or modern Cruise Missile carries a certain frisson, akin to hearing PBI's hapless cry of 'ITSA TANK !!'

Also, per US experience during Gulf Wars, when many cruise missiles took same, predictable routes between same way-points, became vulnerable to ground fire, a soupçon of variation is beneficial. Even a few dog-legs mean a lot of possible recipients must 'honour the threat'. And, as vectors shift, variously diverging and converging, local 'Command & Control' develops work-load issues.
Call it the 'WTF Factor' ?
A 'time on target' attack, with umpteen clunky pulse-jets, variously guided, leading and/or accompanied by more precise whatsits, would represent a bad problem for defence. At the very least, each steam-punkish el-cheapo pulse-jet may require an expensive, supply-limited 'SA' to down...

Sorry, text a tad terse as aggressively sub-edited by Duty Cat... Who's now sprawled across my right arm and wired track-ball.

 

[Scott Kenny]

The propulsion net power is the driving force (thrust) multiplied with the speed. Since the thrust of a rocket is independent from the speed, it comes clear, that the net propulsion power of a rocket is linear to the speed which makes them only suitable for very high speeds. Powering a sub sonic drone is solid rockets which have a very short burn time is therefore completley unsuitable.

The V1 weighted 2160 kg (fully loaded), but it was tanked with "only" 570 L Gazoline (<450 kg) fuel, thats about 20 % of the take off weight, try that with a rocket...

Flip side is that solid rockets are cheap and easy to store for long periods.

Plus you really need a couple of solid rockets to get that pulse jet up to working speed from a ground launch, or else you're stuck using some absurdly long catapult that is blatantly obvious to whatever sensors you care to point in that direction. Also, single catapults greatly limit your launch rate, which throws the idea of cheap drones/missiles to be decoys for expensive missiles into question.

The shaheed are long range stealthy drones (at least for the defence systems at the beginning at the war), those were not extremly cheap.

Reports are that Shaheeds cost about $20k each. They're super cheap by modern weapon standards.

 

[RanulfC]

Information on the Messerschmitt pulse-ramjet is pretty hard to find. I first heard of it through an online book on the history of pulsejet development, (found on pulsejetdotcom website) and managed to find a couple of more pictures (apparently flight tested to some degree) and at one point a couple of pages in German, (which I neither speak or read, which is why my wife cusses at me in for that reason ) but not much else.

Randy

 

[Desertfox]

If you want a super cheap jet engine, just go with a ram-jet, even more simple than a pulsejet and doesn't have the vibration issues that kills pulsejets.

 

[Scott Kenny]

If you want a super cheap jet engine, just go with a ram-jet, even more simple than a pulsejet and doesn't have the vibration issues that kills pulsejets.

Because in theory a pulse-ramjet can start at much lower speeds? The Germans are pretty notorious for sticking with a project that has theoretical advantages, even when it has massive practical disadvantages.

But yes, just using a solid rocket booster to get the ramjet up to startup speeds is better.