FWE with increased Throttle Range?

[larry cottrill]

Intake is slightly angled. Difficult to slice it just right.

Not that easy to "weld all around", either ;-)

Nice work, though.

L Cottrill

[PyroJoe]

Thanks,
Have been welding these last few from the inside before installing the front plate. Not the sharp transition that I often use. I guess with an intake this open, it is less of an issue.
Joe

[larry cottrill]

Cool. I've thought of doing that, but have never tried it because of the very limited area in which to work.

L Cottrill

[PyroJoe]

Happy new years!

I noticed during a night run last eve the intake is filled with flame. More so than a linear of the same volume.

This I suppose is due to approx. 25% or so of the rear CC not acting as a true CC. If this is the case I have lost CC volume. This afternoon welded 5/8" extra CC onto the front of the CC. This appears to have improved it. Will check it again tonight.
Joe

[PyroJoe]

Checked the volumes this morning. found the estimated 5/8" wasn't enough. should have been nearly 1". Posted new CC dims and the difference as seen on a linear chamber.

The initial volume was based on CC alone, the new chamber volume is based on the linear CC PLUS transition cone volume.

Joe

[PyroJoe]

Wrong! ha. Started this one up and the extra volume remained empty up front. The CC was glowing all over except at the front. Looks as if these type of FWEs are akin to half linears. Strange stuff.

[PyroJoe]

Well, if a half linear is closer to the correct volume. My last two attempts had extra volume. Should be able to re-calculate and achieve nearly a dead on corrected volume.
Joe

[PyroJoe]

The new volume runs, but with little to no throttle range. The engine is running much stonger though. The sound has increased considerably and the chamber feels much more filled.
20% is the difference in volume between the CC with throttle range and and the half linear CC. May try a volume at the halfway point.
Joe

[PyroJoe]

Out of propane and welding rod at the moment. Here is a linear Midway engine, similar in volume to the FWE engine. Looks pretty close to Mikes pocket jet. I would urge this type engine not be built with a tailpipe smaller than 1.5" ID.(if fueled with propane)
Joe

[PyroJoe]

The midway linear is a little tricky to start. Injector placed at about the mid point of the intake. When it is about to catch, slowly pull the injector out and increase the throttle. It will either lock in or flame out. When hot, it has considerable throttle range while locked in. Throttled so far down the chamber nearly had no red glow, just a hint of red in the middle of the CC. Strange it would stay locked in that far down.

Had to throttle up smoothly or she would flame out, another touchy tank valve. ha
The injector could be inserted far into the intake. Doesn't do well out at the flare.

Increasing the throttle would cause the CC to glow farther towards the tail. The front 3" ID section would glow in the middle first then the glow would spread both forward and backward into the cone and also up to the front plate. The front plate would then start to glow.

The engine sounded strongest with the injector near or almost into the CC, the pressure high from the bottle. The tank soon started frosting, but she stayed locked in for extended time at low level as the tank pressure tapered down to nill, and flame out.

Not much middle throttle, no fast jarring sounds, just a fast sequence of pop-pop-pops then she locks, or doesn't. Only a few times did she throttle up into a lock in.

Joe

[GRIM]

Well done Joe ,
I know you have put a lot of work into these engines to get to this point,

so that will start up with no sparks and no air right ? what were your final dimensions ?

great stuff

G

[PyroJoe]

Hi G,
How have you been? Bet that summer heat is in full swing down there.
50s and 60s Far. here,,, cold for my taste.

All these engines have been no air starters with bic lighter ignition. This one being tricky with injector position.

Current dims (subject to change) are:
tail is 1.52"ID x 30"L. Intake is 1.22"ID x 4.87" long. The CC is 2.9"ID x 3" long. The cone is 3" large ID, 1.52" small ID, 4.2 in long (the cone has a angle so the engine can be cleanly folded, more to come).

She would probably start easier if the CC was closer to 3.0" ID, maybe even 3.04"ID.
The 30" tail maybe a little long also, since the CC cone is longer (1.25" longer than a typical draft cylinder CC).

The intake may be long also, but she runs out of the gate, inspite of hasty, approx. constructs with material on hand.

I am curious if Mikes pocket engine had throttle range. He did post two seperate thrust levels, a 1 pound run and a 3 pound run, if memory serves.

Was a little disappointed the engine glow starts at the larger portion of CC and grows towards the ends. Was hopeing the entire CC would slowly increase glow at the same time. Still great fun. Locked in throttle range is insane. The most I have seen in a PJ. Probably overshot the target, with this one being tricky to start.

Joe

[Mike Everman]

Hey Joe,
Yeah, very good throttleability, but the small one was definitely not a no air start candidate. The scale up was the easiest starter of them all.
i've got a new scale up I want to start up soon, but have "injector selection block". I didn't do my usual headplate injector scheme on this one, and was going to use a stinger. Are you still doing the three lobed stinger?

[PyroJoe]

Yes, using the same three point for all these engines. Here are some photos, apologies for the quality.
The fabrication is easy, crush a little more than 3/8" length of 1/4" ID copper line in the drill chuck to about the same diameter as a straight pin, insert the straight pin deep and carefully crush around the needle with needle nose pliers.
When done, slightly file a small back angle on each lobe. Try to file as close to 3/8" length for the final crushed length of the injector. clean burs with exacto or utility knife.

Tested this engine hard folded. She still runs great, maybe even easier to start. 30 inches in length.

Joe

[larry cottrill]

Joe -

First of all, great work! I really like the folded one.

Now, something I'd like you to try sometime: It has occurred to me that one of the problems with the typical FWE geometry is that there is a "dead spot" out in front of the intake transition that is mostly untouched by vortexing during the intake phase; and, possibly another corresponding spot down in the lower front (just because the gust can only go so far before it's dissipated in vortexing, etc.). So, try this, preferably using an FWE cone (the original long, gentle slope) with a Lady Anne style intake and transition 'fairing':

Right in front of the transition, cut off the front of the cone and replace it with a cylindrical wall (length same as cone segment removed) similar to what you've done recently. Then, smash the front edge of the cylinder down from the top and bottom fairly radically so the front of the chamber is strongly "duckbilled". I would say, roughly, squash the top and bottom together to half the circular diameter. Finally, weld on a quasi-elliptical front plate or "dome" to match the squashed oval shape. So, you should end up with a flattened area centered on the intake CL (and opposite), with slightly bulged "cheeks" on each side. This will reduce the chamber volume somewhat, so it won't tune quite the same as the original FWE chamber, of course.

I'd just like to see that tried, and see what can be observed from the heating of that kind of front end. What do you think?

- L Cottrill