Homebuild Cruise missiles

Planeman: that's a nifty design, nice work.

FredT, good idea.

Actually depending on what kind of operation you're using it for, it could be very useful. A civilian aircraft has certain advantages, "stealth" in a sense, in that everyone sees it but noone notices it.

I guess at this point it's good to ask who is the end user for our budget cruise missile. Small governments? Guerrilla groups fighting tyrannical regimes?

And what kinds of missions/targets are they going to be using it for?

Hi, I love the idea of the Cessna! Kinda defeats the object of this thread but I like it!

If anyone is still unconvinced about using pulsejets, see this awesome video That's two motors giving the aircraft a 230MPH top speed! To build one of these small engines you are literally talking about £50 a piece, if not cheaper.
OK, so lets strap 4 to the airframe, or just build a couple of larger ones, that's the beauty about these, scaling up is not a problem.

You're instantly reducing the budget by $15,000! Spend it on better guidance, or rocket propulsion for the final stage.

Richard Nakka is a rocket guru and another of my DIY technical heroes. He's building 4000 Newton Seconds thrust motors for pennies! We're talking earth penetrators now lol..


pulsejets....the way forward!

Cheers

Robbie

reply to post by stratsys-sws


What is the fuel economy on these pulsejets? And how long can yourun them continuously? Thrust?

If it's ok to run it for 2-3h and it doesn't take obsene amounts of juice, i'd say it's a good option.

ps. max payload for that RC model in the youtube video is probably in the 2kg class.. so hardly enough for us.

reply to post by northwolf


Hi Northwolf.

I totally agree about the engines in the video not providing enough thrust for our purposes, but just wanted to show what impressive performance a pulsejet weighing less than a kilo can provide!

In terms of economy, I would suggest a Lockwood-Hiller valveless design. The performance of a suitable engine would be in the realms of

Military max thrust (lbs) .... 300
Maximum continuous (lbs) ..... 280
Minimum idle (lbs) ........... 30
Idle to mil. max time (secs).. 0.1
Fuel/thrust (lb/lb/hr) ...... 0.85
Dry weight (lbs) ............. 30

So, an engine weighing just 30lbs can provide 300lbs of thrust!!! It uses less than one pound of fuel per pound of thrust per hour and produces half the thrust of the tomahawk engine! I'd say that's the one for the Job!

Cheers

Robbie

reply to post by Now_Then


plus... they get really upset on high up roads - the fuelling map can't cope and the inlets pre the injectors ice up... god knows what mods you'd need to do to get them to fly up where it's *really* cold!

Cool,so pulse jets' main advantage is incredible cost savings, main disadvantage is altitude/weather limitation.

Low altitude flight would require much better avionics, and put you into the AAA envelope. Also, it's damn noisey which is both good and bad.

Re pulse jets, a lot of them are "U" shaped. How well would the inlets work if they are facing backwards on a relatively fast moving aircraft (about 300km/hr)? I they'd be able to suck enough air in for good functioning, then they might aid in Radar stealth also (not that a Cheapohawk would really worry about Stealth but this would be free RCS reduction).


Some sites say that Pulse Jets are relatively inefficient (presumably relative to turbojets/fans) and looking at photos suggests the tube gets red hot during operation.

Looking at that picture there I'd say the only reason for the U shape is practicality. V-1's were pulse jet... They had no U bend.



I can see them being a lot less efficient as a proper gas turbine (jet) engine, on a pulse jet fuel is pushed in while one blade creates a combustion chamber... that one blade spins allowing the fuel to do it's business while allowing more vaporised fuel in.

Edit>> This seems to be a good pulse jet diagram, it clearly has 4 stages, a modern jet has just one, it keeps spinning as long as there is fuel.. hence reliability, stability etc.


No way that is as good as the jet we all know now - concentric shafts and 3 zones.



[edit on 12/3/2008 by Now_Then]

reply to post by Now_Then


absolutely, they obscenely innefficient unless they are going proper quick, thus cramming a lot of o2 in to get a good burn, especially compared to a turbofan. *but* they are cheap enough and simple enough to be utterly disposable.

No, the reason the one in that pic, and the one I'm suggesting are 'bent' is the actual design, the lockwood hiller VALVELESS pulsejet. It uses the resonance of the actual tubing to phase the combustion and exhaust. It's literally a tube, nothing else!
The pulsejets used on the V1 were valved, these valves fail easily and quickly and are not very reliable, certainly not for the ranges we are talking. The LH design with thrust augmentors is the way. They are far less thirsty than a traditional valved system.

I think there was some confusion with the idea of a pulsejet not working at altitude, I think that poster was talking about the bike engine, ie mapping and jetting etc. A pulsejet would be fine at any altitude discussed so far.

They do get extremely hot.....so externally mount them

Cheers

Robbie

This is today's effort, using a Hiller style pulse-jet wit augmenter.


It sorta 'looks' like a cruise missile but that's not really the logic behind the layout - I wanted to put the fuel tank(s) much closer to the longitudinal centre of gravity. Also the payload (still a Mk81 250lb type stripped of tail).

Most of the avionics would be in the nose far away from the hot engine. The fuel pump and other stuff would be in the rear fuselage central compartment. The small compartment behind the payload would be fuel also.

I have no idea about specs on this one except it's quite large. The fuselage is moulded fibre-glass or similar plastic, the wings are wood with a consistent cord and profile for cheap production.

I'd recommend a carbon fiber or a carbon/foam/carbon composite over fiberglass for weight savings.

High stress areas could be easily reinforced with Kevlar fabric for extra shear strength.

I'd definetely mold the wings out of foam-filled carbon: cheap, lighter than wood, easily mass-produced, and far more rigid than wood.

The fins on our rockets were built this way; they weighed just ounces, and were flight-tested to about mach 2

reply to post by planeman




use these engines:



might just do the job


[edit on 14/3/08 by Harlequin]

reply to post by Harlequin


Hi,

Yeah thats two Lockwood/Hiller pulsejets strapped together, producing some serious thrust. No augmentors on there though. The white haired guy is Bruce Simpson......legend! :-)
The do get extremely hot, but not as hot as you may think from watching that video. Most video cameras are very sensitive to infra-red, hence them working at night with an infra-red light, therefore the hot sections appear to glow much brighter than they do in real life.
Bruce usually uses LPG as his fuel, which I think is what's being used here. Basically it's self pressurising, if we use av gas or Jet then we'll need to pressurise the fuel system, or pump it.

Cheers

Rob

[edit on 14-3-2008 by stratsys-sws]

reply to post by stratsys-sws


absolutely... i meant the bike engine wouldn't work at altitude. sorry!

sometimes i forget this board doesn't put replies to posts below the post they relate to! so comments appear at random places!

Guidance thoughts, several options:

GPS - the obvious one for general navigation. Best to add a terminal-phase guidance as well. Uses satellite signals to triangulate to calculate location.

Ground beacons - works similarly to GPS but beacons are hills etc. Has some strengths over GPS except that as we are designing a US/US-ally system GPS is already in place. Less global reach obviously, and easier yo jam.

Beam riding. Proven in WWII by Luftwaffe and RAF, several methods available. Basically you transmit two (or more) narrow beams directly over the target. The missile follows the beams and needs some way of knowing when it's got to the correct distance (i.e. over the target), this is normally via another set of beams crossing the first. Has limitations on number of targets (one per beam) and missiles necessarily fly a very straight path etc. Can be blocked, maybe even distorted.

Cellphone triangulation. Dependant on cellphone network, but basically you buy phones from the enemy country, then adapt them to feed a triangulation method - "ghetto GPS". Could be foiled by enemy simply turning off mobile phone network.

Optical recognition software. I favour this for terminal phase but conceptually could be used all the way. Proven technology used in several missiles, and now I think much cheaper because it's essentially one or more cameras and some software - no need for bespoke kit and hardwired coding as there was years ago.

As if we don't have a hard enough time dealing with the terrorist. Now we teach them how to make rockets on the discovery channel. This is what we call OPSEC. Not that he is but the OP could very well be a terrorist in Gaza or Iraq for all we know.

Ok, the pulse jet desing got me thinking:

Here is my solution to the valve problem. Dual plate valve, one drilled plate is fixed to the tube, one is revolving with either airflow turning it or an electrical motor.

This design has four pulses/revolution cycle. So turning the plate at 1000rpm would give it 4000 pulses/min operating cycle.

It also has three sparkplugs for increased reliability of ignition. and three point injection (just holes in my design.)

Red plate is fixed, blue turns. Valve is closed at this position.



Valve open,




Exploded view of the pulsejet engine,




Valveplate designs are just illustrations, one would need to calculate the optimum positions and diameters for both airflow and fuel-air mixation.

[edit on 16-3-2008 by northwolf]

Interesting valve design, but that's got a fair bit of drag from the flat face. As well, we'd have to figure how much air would need to be let in, but I like that idea.

You may want to shape the intake like you would see on a MiG-21 or Su-7, but aside from that I think your idea has merit as long as enough air gets in at the right time for the pulses.

I'd just suggest using model remote control plane engines. I would expect a proper turboprop or jetengine to be far more fuel efficiant, and quieter, than a pulse jet.

wrenturbines.co.uk...

I think the easiest would be a Wren turbine or turboprop mounted on a remote control plane. Add moderately large hobby rocket engines to it for a short takeoff from a guide rail pointing straight up. For guidance just put a POS computer sending GPS messages to the servos. Wouldn't be more than a few thousand dollars.

Put cameras on the bottom and it would make a fantastic surveillance UAV.

[edit on 17/3/2008 by C0bzz]