Smooth Lady - Numbers and Disappointments

Moderator: Mike Everman

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Smooth Lady - Numbers and Disappointments

Post by larry cottrill » Thu Sep 15, 2005 3:10 pm

Last night I set up the Smooth Lady (FWE IV) vertically on the bathroom scale and ran it. I also weighed the propane cylinder before and after. Although the Lady ran well for precisely twenty minutes, results can only be described as disappointing.

I decided that I can read our scale to the nearest 1/4 pound. I put the scale in position, carefully zeroed it, and weighed the propane cylinder with regulator and delivery hose attached at 34.25 lb. I then set the cylinder aside, set the partial concrete cinder block on the scale, placed my new vise on top of the cinder block and swiveled the vise head around so the front end of the engine would hang down over the side of the block. This put the spark plug directly above the scale dial, but I decided this was OK as long as it wasn't down too close. I didn't go to extraordinary lengths to make the engine truly vertical, simply judging it by eyeball. I then carefully arranged the fuel hose around the outside of the scale and attached it to the engine. The whole assembly was just shy of 40 lb, so I tweaked the adjustment a little to make it read "exactly" 40. Note that this was without starting air hose or HV wires attached - just as it would be in normal running. Of course, I'll have photos of all this, eventually.

The engine started well and was quickly adjusted for smooth running and the HV leads and air hose detached. Now for my first glance at the scale - 41 lb - exactly one lousy pound of thrust! Naturally, I tried cranking up the propane - NO CHANGE! HOW CAN THIS BE? I went ahead and let it run out the twenty minutes I had planned, figuring that my fuel system must be so restrictive that I'd need that long just to get a meaningful reading for the fuel consumed.

After the run, moving the stuff off the scale was amusing, since the entire vise was way too hot to touch (it has a black paint job, naturally) - but even the light grey cinder block was heated through to the point where moving it was almost painful (should have brought out my work gloves). Anyway, I managed to get it moved off there, and carefully re-zeroed the scale. When I put the propane (plus attachments, as before) back on there, I recorded exactly 31 lb - 3.25 lb consumed in 20 minutes! HOW CAN THIS BE? Since the thrust was a whole pound, it didn't take long to figure out that my FSFC works out to a mere 9.75 lb/hr/lbF! WHERE IS THIS FUEL GOING? It sure isn't going into thrust!

I do know where one loss is occurring, though it can only be very slight. Early in the run, I noticed the spark plug slowly turning around! At first, I thought it was unscrewing itself from the engine dome, but then realized it was turning in the wrong direction for that. Shining the flashlight on it showed that the hexagonal shell was not moving - the porcelain was rotating inside the shell! Putting the back of my hand down close, I almost thought I could feel some pressure pulsation (though mostly what I could feel was my hand getting hot). At any rate, there has to be some leakage happening there - maybe these relatively cheap little plugs aren't quite as good as some of us think they are. Anyway, it did that for many minutes but finally stopped, all with the engine apparently running fine.

The real loss just HAS TO BE at the intake flare, doesn't it? I know Eric decided a long time ago that stopping the fuel pipe at the inner end of the flare was wasteful (even though it does give good starting, running and throttleability). I think this just about MUST be the problem, unless I'm just overlooking some other possibility I haven't heard discussed yet. The action is so odd with this particular engine: It's as if you reach a certain point where any fuel you ADD is just 100% wasted, burned out behind the intake. As before, I observed a LOT of flame behind the intake, wrapping itself around the tailpipe wall. I may try a pipe extending in to the 3/4 point as suggested months ago by Eric - this would be easy to do with my starting air / fuel pipe arrangement, by simply replacing the copper line with a longer piece.

Other observations that might be of interest:
- 3.5 inch tailpipe extension was permanently added on
- Total internal engine length = 24.5 inches
- Total engine weight = 18.8 oz
- Heating pattern: Typical FWE "all in the front end" pattern - but, this is the first time I have personally observed a slightly red-hot band maybe 1.5 inches (38mm) long, centered about 3 inches (75mm) in front of the exhaust pipe end flare
- Approx. 4 inch (100mm) tail flame, very straight, barely visible in total darkness
- Very hard pressure wave exiting omnidirectionally from intake flare
- Intake flame would not ignite a paper match head! The barely visible tail flame ignited this immediately, however!
- VERY uncomfortable, possibly harmful, temperature 1 ft (30 cm) above (i.e. 'behind') tailpipe flare
- Running sound of this engine is a strange "full bodied" sound, as if high frequency harmonics are largely suppressed - totally unlike the "Dynajet roar". But this may have something to do with the low thrust running observed in this trial.

L Cottrill

Viv
Posts: 2158
Joined: Sat Oct 04, 2003 2:35 pm
Antipspambot question: 125
Location: Normandy, France, Wales, Europe
Contact:

re: Smooth Lady - Numbers and Disappointments

Post by Viv » Thu Sep 15, 2005 4:17 pm

I had to chuckle as we have had the same thing happen with spark plugs:-) running they rotate but when cold agan they are locked in tight:-)

Had a moment! the first time it happened

Viv

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Re: re: Smooth Lady - Numbers and Disappointments

Post by larry cottrill » Thu Sep 15, 2005 5:06 pm

Viv wrote:I had to chuckle as we have had the same thing happen with spark plugs:-) running they rotate but when cold again they are locked in tight :-)

Had a moment! the first time it happened
Yes, I found it highly amusing when I realized what was going on. There must be a heck of a difference in thermal expansion between the steel and the porcelain, which you'd kind of expect, I guess. It's funny that you'd see it play out so nicely on such a small set of objects.

L Cottrill

Eric
Posts: 1859
Joined: Sat Oct 04, 2003 1:17 am
Antipspambot question: 0
Location: United States
Contact:

re: Smooth Lady - Numbers and Disappointments

Post by Eric » Thu Sep 15, 2005 6:10 pm

With the straight intake protruding into the combustion chamber, there is only so much air that the engine will want to take in. This setup is not very good at recovering energy, and is the source of the resonance dampening you noticed.

What I do, and its also fun to play around with, is pickup a box of tuning forks on ebay, and make sure it has an adjustable tuning fork too. If you find the right frequency you should get it to resonate by placing it at the intake or exhaust. You can get an idea of what is going on with the engine without ever running it.

If you have the intake protrude into the combustion chamber, you must have a very specific chamber shape, and also position the end of the intake at a key spot on the standing wave, otherwise you will only get reduced performance. Putting a spout on it is also another thing that will just mess things up. For a small engine like this the best possible thing is a intake flush with the combustion chamber wall (or CC / tailpipe transition). Both aerodynamically and acoustically it is the most efficient way.

If you position the fuel injector farther in the intake you will have slightly better fuel consumption, but at a point you will still be wasting a lot of fuel if it only wants to take in a certian quantity of air with no increase in thrust.

If you only measured the fuel consumption at exactly 1 pound thrust flow rate with no overfueling you would get a decent TSFC but only because its putting out 1/2 the thrust the combustor is capable of.

I hope you dont just get even more determined to make this layout work better. IMHO you could spend a lot of time trying to tweak the engine but never get one thats great or even good.

The original FWE design has bundles more potential, and its full potential isnt even close to being reached, even with the advanced FWE. If you took the advanced FWE principles, and designed a chinese style tailpipe with UFLOW I would be willing to bet that you could get over 3.5 lbs thrust, with excellent fuel efficiency with very little work.

Eric
Image

Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

steve
Posts: 1029
Joined: Sun Jun 06, 2004 12:29 am
Antipspambot question: 0
Location: Clinton Conneticut / Melbourne Flordia
Contact:

Re: re: Smooth Lady - Numbers and Disappointments

Post by steve » Thu Sep 15, 2005 10:33 pm

Viv wrote:I had to chuckle as we have had the same thing happen with spark plugs:-) running they rotate but when cold agan they are locked in tight:-)

Had a moment! the first time it happened

Viv
I've got a video of that happening on one of my linear fwe variants too.
Image

Eric
Posts: 1859
Joined: Sat Oct 04, 2003 1:17 am
Antipspambot question: 0
Location: United States
Contact:

re: Smooth Lady - Numbers and Disappointments

Post by Eric » Fri Sep 16, 2005 1:23 am

Here is a quick idea of what could be done with the fwe combustor. If you use a conical section thats the same as the combustion chamber things will probably be much easier to ballance and would probably keep the waveform the way you want it.

My thermojet variant project is moving towards a chinese style tailpipe, with multiple intakes. Basically the straight pipe just has to be added to the end of the flare. It would be nice to make them with smooth flowing constantly changing curves like a delaval nozzle. The chinese/escopette style tailpipe expansion reallyl has a lot of potential when made right.

Eric
Attachments
advancedfwechineseexpansion.GIF
(8.78 KiB) Downloaded 633 times
Image

Talking like a pirate does not qualify as experience, this should be common sense, as pirates have little real life experience in anything other than smelling bad, and contracting venereal diseases

Mark
Posts: 10748
Joined: Sat Oct 11, 2003 10:14 pm

re: Smooth Lady - Numbers and Disappointments

Post by Mark » Fri Sep 16, 2005 1:38 am

Presentation is Everything

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Re: re: Smooth Lady - Numbers and Disappointments

Post by larry cottrill » Fri Sep 16, 2005 3:35 am

Eric wrote:Here is a quick idea of what could be done with the fwe combustor. If you use a conical section thats the same as the combustion chamber things will probably be much easier to ballance and would probably keep the waveform the way you want it.
Eric -

That looks really good. There are two main reasons I don't try to use an expanded exhaust stack (or Graham's Type 7 exhaust design, which he has graciously basically given me to use however I want) - first, I want to prototype easily and quickly, to experiment with intake (and other front-end) variations; second, engines with a 'bustle' tail design will be hard to use in scale models of reasonable dimensions without altering the scale of the tail end unacceptably. That last probably seems absurd since I haven't done anything close to a flyable engine yet, but that's the goal. To me, the ideal would be a valveless that fits in a Dynajet space and has at least a large fraction of the Dynajet's thrust.

One thing I notice on your 'super' model is the shallow angle of the bend in the intake. This jumped out at me because I just saw a similar thing in the "original" (supposedly) Chinese plan drawing. It aims the flow right up into the front end where we want the explosion to happen. Most "Chinese" engines, though, seem to be actually built with a sharper bend, and show a 'cold spot' on the bottom of a running engine, like my prototype FWE design. There is no question in my mind now that what you show in that one detail point is vastly better design.

L Cottrill
Last edited by larry cottrill on Fri Sep 16, 2005 4:52 pm, edited 1 time in total.

ed knesl
Posts: 163
Joined: Wed Apr 13, 2005 5:27 am
Antipspambot question: 0
Location: Phoenix, Arizona

re: Smooth Lady - Numbers and Disappointments

Post by ed knesl » Fri Sep 16, 2005 4:56 am

I have built five diferent engines with chinese style tail pipe,
and all of them run very efficiently with strong steady roar
and always adequate thrust. I mix scaled first two than I went
on my own, with different designs and never failed me.

Larry, I thing scaled aircraft with pulse jet is a pipe dream because
of vibrations and extreme heat, valveless gets hotest at the front
unlike Dynajet and housing it in scaled model is imposible.
Also fueling is a serious issue still unresolved. We have to fly the C/L experimental model yet, to verify valveles engine behavior at 200 Mph.

You would be putting a vagon in front of the horse with your concern
about scaled models. We still have long ways to go !

Actually I consider chinese shape as advantageous, when fuel tank
and pumping would fit at narrow mid section where is the room to
put all necessary components.

I agree with Erik's comments.

Ed
...Nobody is right, nobody is wrong...

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Fueling Changes, Running Changes

Post by larry cottrill » Sat Sep 17, 2005 4:49 am

I fired up the Smooth Lady again tonight, briefly and without measurements, but trying something I've never tried before now: fueling at the 3/4 point in the intake tube. All I did was replace the 1/8-inch OD copper line with a longer one that reached approximately in to the 3/4 point, and used a long screwdriver to center it in the tube as accurately as I could (i.e. not very ;-). There was no pretense of precision in this process. Then I set her up in the vise for a quick test run, after dark same as the other night. Note in the following that it was a few degrees cooler tonight, probably below 70 degF. I just did this because I had never tried it, and with my fuel / air pipe gimmick it was extremely simple to rig. The only thing I feared is that starting might be harder because of possibly poorer mixing.

What a difference! The first thing I noticed was that the 'sputtering' range of operation at too-lean fuel flow is vastly narrower. Hence, starting was even easier than before! Then, as soon as good lean running was obtained, the combustion chamber IMMEDIATELY ramped up to bright orange heat, with what must have been a mere trickle of fuel compared to the other night. I still didn't get up to rich extinction, but didn't really work at it much - I was more interested in the low end because it seemed so different. Tonight I noticed that when I lean it out not quite to cutoff, it enters a slightly rough 'purring' mode that will sustain it indefinitely (apparently) just above lean cutoff. This sound seemed more like the 'deep' or 'throaty' sound that I was hearing last night through basically the whole run! The sound at higher fuel levels seemed sharper and 'hotter' sounding than what I heard in my long test. One thing I realize now that I should have done was to go back to driving the fuel needle valve at 10-14 PSIG as I do with my other engines - in this configuration, 20 PSI is excessive and requires a really delicate touch on the valve at the low end.

Interesting, I think. Certainly makes me want to set up measurements one more time.

L Cottrill

hagent
Posts: 413
Joined: Sun Feb 06, 2005 9:01 pm
Antipspambot question: 0
Location: Simi Valley CA

re: Smooth Lady - Numbers and Disappointments

Post by hagent » Sat Sep 17, 2005 5:31 am

That's great to hear Larry,

I can't wait to see the thrust results.

Did you have as much flame coming out of the intake?
Hagen Tannberg

hinote
Posts: 1241
Joined: Sat Oct 04, 2003 1:54 am
Antipspambot question: 0
Location: Central California

Re: Fueling Changes, Running Changes

Post by hinote » Sat Sep 17, 2005 6:23 am

Larry Cottrill wrote:I fired up the Smooth Lady again tonight, briefly and without measurements, but trying something I've never tried before now: fueling at the 3/4 point in the intake tube.
Larry:

Would you care to draw-up a pictorial of the possible pressure/velocity nodes, and how they may affect the fueling in the intake of your engine?

It might promote some discussion.

Bill H.
Acoustic Propulsion Concepts

".......some day soon we'll be flying airplanes powered by pulsejets."

Bruno Ogorelec
Posts: 3542
Joined: Sat Oct 04, 2003 7:31 am
Antipspambot question: 0
Location: Zagreb, Croatia

Re: Fueling Changes, Running Changes

Post by Bruno Ogorelec » Sat Sep 17, 2005 9:15 am

hinote wrote:[Would you care to draw-up a pictorial of the possible pressure/velocity nodes, and how they may affect the fueling in the intake of your engine?

It might promote some discussion.
Yes! Yes!

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Re: re: Smooth Lady - Numbers and Disappointments

Post by larry cottrill » Sat Sep 17, 2005 9:12 pm

hagent wrote:That's great to hear Larry,

I can't wait to see the thrust results.

Did you have as much flame coming out of the intake?
Sorry I didn't mention that. There seemed to be a bit less (or was it just wishful thinking?), but still wrapping around the tailpipe at the end. What was interesting, though, is that there was definitely a much more prominent tail flame - and the red hot zone towards the end of the pipe was much hotter (more visible). Incidentally, this was a run with the engine set up horizontal in my usual manner, not vertical as when I was attempting to measure.

L Cottrill

larry cottrill
Posts: 4140
Joined: Sun Oct 05, 2003 1:17 am
Antipspambot question: 0
Location: Mingo, Iowa USA
Contact:

Re: Fueling Changes, Running Changes

Post by larry cottrill » Sat Sep 17, 2005 9:17 pm

Bruno Ogorelec wrote:
hinote wrote:[Would you care to draw-up a pictorial of the possible pressure/velocity nodes, and how they may affect the fueling in the intake of your engine?

It might promote some discussion.
Yes! Yes!
Bill & Bruno -

Well, I have no idea where all the "possible" nodes might be. The best I could do is try to get an accurate measurement of where everything ended up in relation to the front edge of the chamber and draw that up to scale with dimensions. That would be far more precise than my guesses as to what's acting like a node or antinode and what isn't! My acoustic knowledge is no better than elementary.

L Cottrill

Post Reply