FWE From Outer Space - Revised Lady Guinevere
Posted: Thu Sep 14, 2006 2:14 pm
This has not been the Year Of Valveless Pulsejets at our house; it has been the Year Of Animal Husbandry. However, a few days ago I was able to pick up for a little while where I left off back in February with the Lady Guinevere. I had marked up the sheet steel for the cones and the oddball intake back then, and the sheets had been lying around in the basement gathering a thin film of rust ever since. But, Saturday morning I grabbed the sheets, hauled them out to the garage along with my air shear, and in about half an hour had the cut pieces ready to form. A later trip out to my cone-forming tool in the horse barn (i.e. freezeless water hydrant) got the cones basically in shape ready to weld. Astoundingly, less than a half hour's work with the bench vise and a large (3/8-inch) twist drill got the intake shell formed (except for flaring) in good shape; I couldn't believe how well that went, considering I had never shaped anything like it before. It took longer to carefully hammer the inlet flare than it did to basically form the piece.
Unfortunately, after forming the cones, I naturally decided to change the design to bring this pipe more in line with the apparent success of the much smaller Lady Anne Boleyn engine (recently built and run by James D of the UK). I say 'unfortunately' because I don't want to re-design any of the cones I made, and I naturally want to keep the 32-inch overall length so as to still have a contender for the proposed "32 inch Chinese" engine cookoff. Graham and M at least will recognize that this imposes a set of constraints that aren't necessarily conducive to creative design: an engine whose front and rear sections are already "cut in stone", with only the middle piece to play with. In the case of this particular engine, the middle section is particularly short, as well. But, I decided to blunder on ahead, anyway.
What I came up with is shown in approximately scale form in the drawing, below. The dome, chamber cone and the two rear cones are the same as on the original drawing. However, all cylindrical parts are eliminated. The very short cylindrical section in the 'dilutor/augmentor' tail section was dropped (even though clearly shown in the famous SNECMA drawing) in order to allow lengthening the center section of the engine as much as possible. The center cylinder is replaced with an enlarged mockup of the Anne Boleyn 'mid-cone / choke cone' combination (which again is based on Graham's Type 07 tailpipe mid-section). The tail end of the choke cone extends slightly (5mm) past the front end of the 'dilutor/augmentor' intake cone, as in the SNECMA drawing. This engine reminds me of some kind of shoulder weapon from the 1930s Buck Rogers books.
It is impossible for UFLOW1D to correctly model the 'gap' in the middle of the pipe (by this I mean the extra intake at the 2/3 point), and also impossible to model the 5mm 'overlap' in the two sections at this location. Of course, I'm not about to let mere details like this stop me: In the model, I shoved the intake rearward a few mm (shortening the tail cone by the same small amount) so that the mid-cone and choke would be unaltered. (The choke and intake are designed so that they are "parallel" segments of identical cones, giving a constant 12 or 13 mm "width" to the intake gap all around.) Then, the opening is simply replaced with a very flat conical wall. This unsavoury detail is admittedly a totally artificial device, and will not be elaborated upon further; it is not good, but is the best I could do under the circumstances. The idea is to make the basic acoustics right (at least approximately); the flows will just have to take care of themselves. The extremely low temperatures in the tail cone are wild guesses, based on the supposition that in real life, the augmentor section will suck in vast quantities of outdoor air.
It is also impossible for UFLOW1D to tell us what the effect will be of the emerging pressure waves from the front intake and dilutor/augmentor intake making their (relatively slow) cool air traverse between the two locations. (Working out this detail will be left as an exercise for the reader ;-)
Anyway, here it is. All I need now is another little sheet of steel to make the extra cones from (I'd have needed it for cylinders, anyway). Time is still hard to come by, so I have no idea how soon this will get finished up and test run. I may publish a few construction photos later. How the model runs is basically shown in the graphs below, which can be compared to the ones I published for the Lady Anne; keep in mind, however, that there is a big size difference in the two engines.
All comments welcome here.
L Cottrill
Unfortunately, after forming the cones, I naturally decided to change the design to bring this pipe more in line with the apparent success of the much smaller Lady Anne Boleyn engine (recently built and run by James D of the UK). I say 'unfortunately' because I don't want to re-design any of the cones I made, and I naturally want to keep the 32-inch overall length so as to still have a contender for the proposed "32 inch Chinese" engine cookoff. Graham and M at least will recognize that this imposes a set of constraints that aren't necessarily conducive to creative design: an engine whose front and rear sections are already "cut in stone", with only the middle piece to play with. In the case of this particular engine, the middle section is particularly short, as well. But, I decided to blunder on ahead, anyway.
What I came up with is shown in approximately scale form in the drawing, below. The dome, chamber cone and the two rear cones are the same as on the original drawing. However, all cylindrical parts are eliminated. The very short cylindrical section in the 'dilutor/augmentor' tail section was dropped (even though clearly shown in the famous SNECMA drawing) in order to allow lengthening the center section of the engine as much as possible. The center cylinder is replaced with an enlarged mockup of the Anne Boleyn 'mid-cone / choke cone' combination (which again is based on Graham's Type 07 tailpipe mid-section). The tail end of the choke cone extends slightly (5mm) past the front end of the 'dilutor/augmentor' intake cone, as in the SNECMA drawing. This engine reminds me of some kind of shoulder weapon from the 1930s Buck Rogers books.
It is impossible for UFLOW1D to correctly model the 'gap' in the middle of the pipe (by this I mean the extra intake at the 2/3 point), and also impossible to model the 5mm 'overlap' in the two sections at this location. Of course, I'm not about to let mere details like this stop me: In the model, I shoved the intake rearward a few mm (shortening the tail cone by the same small amount) so that the mid-cone and choke would be unaltered. (The choke and intake are designed so that they are "parallel" segments of identical cones, giving a constant 12 or 13 mm "width" to the intake gap all around.) Then, the opening is simply replaced with a very flat conical wall. This unsavoury detail is admittedly a totally artificial device, and will not be elaborated upon further; it is not good, but is the best I could do under the circumstances. The idea is to make the basic acoustics right (at least approximately); the flows will just have to take care of themselves. The extremely low temperatures in the tail cone are wild guesses, based on the supposition that in real life, the augmentor section will suck in vast quantities of outdoor air.
It is also impossible for UFLOW1D to tell us what the effect will be of the emerging pressure waves from the front intake and dilutor/augmentor intake making their (relatively slow) cool air traverse between the two locations. (Working out this detail will be left as an exercise for the reader ;-)
Anyway, here it is. All I need now is another little sheet of steel to make the extra cones from (I'd have needed it for cylinders, anyway). Time is still hard to come by, so I have no idea how soon this will get finished up and test run. I may publish a few construction photos later. How the model runs is basically shown in the graphs below, which can be compared to the ones I published for the Lady Anne; keep in mind, however, that there is a big size difference in the two engines.
All comments welcome here.
L Cottrill