Pulse Jet Petal Valves

I am encouraging a friend to resurrect his model pulsejet. The snag is that I have been volunteered to make new petal valves. I understand that the originals were made from "blue spring steel, not anealed, about .006 ins thick". I have seen references to high carbon spring steel C1095 but there may be others.

Can anyone confirm or have a recommendation? Also any suggestions for a supplier of suitable flat sheet. I was thinking of a 12 x12 in sheet to make 4 off and trying electrochemical etching as per a previous thread. I believe the originals were made with individual petals spot welded to a centre. I don't think any will last very long!

My local supplier of fasteners, tools, and practically everything else stocks standard shim steel in various thicknesses and IIRC 12" square sheets. I have bought a couple of sheets and it's pretty springy. I see that MSC Direct have it in 0.005" though the minimum quantity might be a bit large. So should be easy to get from the engineering suppliers. RDG have feeler gauge stock 1/2" wide in various thicknesses. Google is your friend.

Shim stock may be springy, but in my experience if you bend it too far it snaps. To bend shim properly it needs to be annealed. While a petal valve may not bend very far the fatigue life may well be limited.

Andrew

I'm no expert on pulse-jets - just interested. I read an article recently on replacing the petal valve assembly with a Tesla one-way flow system in one of these motors. There's quite a bit of stuff on the Toob and online about the operation, and it has no moving or flexible parts - may be difficult to make though!

Original "Brauner" was quoted as using spring steel 0.15mm (0.006" thick and quoted about 30 starts from this material. There is a U-Tube posting describing electro chemical etching for that engine and uses shim steel. Operation tends to be flexing rather than bending but the frequency of oscillation is the killer.

Regards Ian.

You can buy the valves ready made that will fit the Dynajet and it’s clones. Hobbyking made a copy of the dynajet it runs very well with a little work. Mine has performed well in a control line speed model 120 + mph.

The people with extensive running experience of these items were members of the Ghost Squadron , perhaps the RCME forums would be the place try.

Thanks.

Yes, I saw the YouTube video which was what prompted me to consider electrochemical etching. Shim steel shouldn't be difficult to get hold of but to be honest I'm not sure what "Shim steel" actually is and wondered if there would be something better. From what I hear, a life of 30 starts would be quite an achievement! Looking forward to trying though.

Follow this link Petal valve etching Very simple process using salt water and 12 volt battery charger.

https://www.youtube.com/watch?v=jEnNMTMZadw

Back in 1979, I bought a new DT175 MX Yamaha trail bike. It was a two stroke single cylinder with a reed valve just downstream of the carburettor. The reeds were similar to the ones described, made from some sort of spring steel with curved backing plates to limit the bend in the reeds to give them a long life. There were tuning kits which replaced the steel reeds with thin fibreglass plates exactly like printed circuit boards only about 1/32" thick. They worked very well and may have even have increased the bikes performance. I later bought a set for my PE 250 X Suzuki enduro bike which combined piston port with direct crankcase induction via a reed valve. This is not a material which you would normally think of as a replacement for steel reeds, but it worked.

The best ones are water jet cut from spring steel stock. The petal thickness depends a bit on the fuel being used as well, so some have 0.006 inch, 0.007 inch and 0.008 inch thick spring steel petals made. The hobby king petals work quite well for the standard or the sport jet class to 150mph or so. To go faster requires testing with other material thicknesses and keeping records of the  day temps and humidity. 

Laser cut ones are not as fast as the waterjet cut ones . It maybe due to the very small heat distortion from the cutting of the petals from the laser.

Neil

Edited By Neil Lickfold on 11/12/2021 00:36:11

Lot of stuff here, but the site hasn't been updated for a long time - the guy seems to have produced some impressive motors - some of it has been televised.

Link