Prettiest FWE (?) - the 'Lady Anne Boleyn'

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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Graham C. Williams » Sat Aug 26, 2006 10:10 pm

James D wrote:Thanks for the kind words everyone.

I’ve attached a picture showing the heat pattern after two minutes of running, the heat has spread along the bottom of the tailpipe, the top must be cooled by the intake airflow.

I might run it again tomorrow and double check the thrust figure.


Dear James.
Could you try running the motor with the induction pipe on the side of the motor (rotated 90 degrees on its major axis) and see if the heat pattern is the same?
The other thing you might try is an injector that sprays the fuel at 90 degrees to the flow - crimp the end and make radial holes in the fuel pipe.
I just keep watching your video over and over.
Regards
Graham.
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Graham C. Williams » Sat Aug 26, 2006 11:31 pm

The Rev 3 modification with the 118mm induction pipe length offers no real improvement over the original. The model starts and runs well within 4 cycles but the thrust is about the same as the original. Don't bother with this mod.

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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Sun Aug 27, 2006 2:51 am

Graham C. Williams wrote:Larry.
What have you been doing? 2.6Lbs straight off the drawing board!!!.

Is that pretty good? It's a far cry from the Dynajet, which to me is the standard for everything. Been doing? Not much this year except working my day job and helping take care of horses (we have a new colt, 3 months old tomorrow).

And the motor's so nice and short.

I like them to give out a nice eery high-pitched squeal ;-)

We must try this beast on Methanol, could get up to 30% extra if you can get the injection correct.

That would be better, for sure. What would be a real hoot (as we rural American folk like to say) is if it turned out just by chance to be BETTER tuned for some liquid fuel than it is now, and the thrust took some really amazing jump. One might as well dream ...

My precise calculations show that to achieve the T/W ratio of the Dynajet, we would only have to reduce the engine weight to 9.79 ounces. Though bulky, that would certainly qualify as a flight engine if liquid fueling could be properly arranged. Of course, if liquid fueling really does improve thrust, if wouldn't need to be quite so "trimmed to the bone".

It's hard to imagine crash integrity in such a lightweight shell. The mounts I show in the plans would never do. Probably the best method would be to eliminate those entriely and use the Bukowsky-style "spark plug engine mount" at the front end, with just a lightweight truss strut at the rear for lateral stability. The chamber dome is such a small area that it could still be fairly thick material to spread the crash load, without weighing much. The rest of the engine (except the intake tube) is basically a stack of long cones, which would be pretty good in longitudinal compression from forward-running impact - especially if very low mass. I'll try to work out a thickness (in stainless) using Eric's calculator, abd we'll see if anything reasonable can be achieved. Jerry said the Dynajet shells were .015 inch thick material, SS Type 321, so that will give us something to compare to.

Thanks, Graham!

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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Sun Aug 27, 2006 3:05 am

James D wrote:The fuel pipe is approximately 2mm ID and terminates about 25mm from the combustion chamber, this is only the second position I tried and probably isn’t optimal, but it worked so I left it there.

Rats. I thought my guess at a fueling point would be a fairly good one. Sounds like you ended up quite a bit farther up the pipe. But, that's good information; it's one of the things we always have to deal with, it seems.

I’ve attached a picture showing the heat pattern after two minutes of running, the heat has spread along the bottom of the tailpipe, the top must be cooled by the intake airflow.

I doubt that this is the whole expalanation; it seems to me that cooling by intake air would be much more localized around the flare. OH ... wait ... maybe you're including what flows OUT of the intake (even if not visible) - that might be worth a lot more. There would be some entrained air included in that, and it certainly could provide a good deal of cooling. All right, I think I see what you're saying now. There is also some good heat sinking by the monopod engine mount and the fuel tube blade mount (is the engine mount welded onto the far side wall, or what?).

To me, the photo is just fascinating, in several respects. So little visible flame out the intake! So MUCH visible flame out the tailpipe! Having never built a "bustle" tailed or cone-tailed beast myself, I just can't get over that 56 MM WIDE column of flame coming out of the tail end! That just seems unbelievable to me.

I really need to build one of these ... (maybe I could scale it up to a 32-incher for the "Chinese Competition" ;-)

Thanks again, James!

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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby milisavljevic » Sun Aug 27, 2006 5:20 am

Larry, James, and Graham -- Congratulations!

I calculate the fundamental frequency as 317.7 Hz, averaged from the fundamental and first eight harmonics.
The fundamental group frequencies are by far and away the strongest part of this motor's acoustic signature.

She's SHORT and SWEET!!

Best regards,
M.
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Eric » Sun Aug 27, 2006 8:12 am

.015 stainless is a total bitch to weld. If you have good straight edges its possible to run a nice weld, but when you go to weld cones together things get shot to hell pretty fast.

I have only made a few really successful engines from .015 sofar, the 4.5 lb chinese designs are coming in at .875 lbs. Without doing any math would estimate that this engine would come in around .65 lbs.

From what I have tried with the normal adv FWE, I can back up the potential for 30% thrust increase from using methanol over propane.

As long as the engine isnt run in direct light turning it at an angle will not really change the heat distribution, or how you see the distribution. The intake flow really cools things down a lot.

If you turn it completely upside down the side oposite of the intake may glow a little brighter, probably not noticeably, but the distribution along the length should be the same.

Eric
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby James D » Sun Aug 27, 2006 4:27 pm

Larry wrote: Rats. I thought my guess at a fueling point would be a fairly good one. Sounds like you ended up quite a bit farther up the pipe. But, that's good information; it's one of the things we always have to deal with, it seems.

I put the fuel pipe as far down the intake as I could without having to bend it, the only other position I tried was just inside the intake flare. Your fuelling point may well prove to be better. I might try some different fuel injectors and positions later this week.
Larry wrote: I doubt that this is the whole expalanation; it seems to me that cooling by intake air would be much more localized around the flare. OH ... wait ... maybe you're including what flows OUT of the intake (even if not visible) - that might be worth a lot more. There would be some entrained air included in that, and it certainly could provide a good deal of cooling. All right, I think I see what you're saying now. There is also some good heat sinking by the monopod engine mount and the fuel tube blade mount (is the engine mount welded onto the far side wall, or what?).

Yes, I did mean the intake out-flow; it must make a huge difference because the top of the pipe still ‘blue’. The engine mount is welded on the centreline and it is a lot thicker material than the fuel pipe mount, which is also on the centreline.
Larry with reference to the flame ejection from the tailpipe, the video was filmed in quite low light, Outside on a bright day I doubt it would be visible at all.

Thanks
James D
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Graham C. Williams » Sun Aug 27, 2006 4:57 pm

I finally got round to looking at Mikes suggestions. After a few very quick tests I'm running a standard model but with the 42mm dia. point in the tailpipe moved to the left 6mm. The cone to the left of this point is now 110mm long and the cone on the right 32mm long. Early tests show a trend towards increased combustion chamber pressure. The as built model ran with a CC peak pressure in the 1.65 to 1.7bar region. This mod after a very short run indicates that it may run in the 1.8 to 1.85 bar region. Of interest is the pressure build at the 42mm dia. point, with this mod I'm showing a pressure build above that in the CC at a little over 1.9bar. The timing of this secondary pressure build is a little after the CC peak pressure and when the tailpipe is full of cold air.
I’m doing a full 10-cycle run now - it takes about an hour to do the 2600 odd iterations.
'Till then
regards
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Mike Everman » Sun Aug 27, 2006 6:00 pm

ooooh, I wait with baited breath. Sounds encouraging!
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Sun Aug 27, 2006 8:50 pm

Yes, that's wonderful. No matter what you do, it seems like there's always something, somehwere that can be improved. I really like that pressure building up there, as it will go forward to help re-pressurization. The trick is making sure the timing's right.

My hypothesis about pressure waves and nozzles is that a nozzle does (at least) four different things to a pressure wave that we might be able to use:
a. Divides the wave into passed and reflected components - of course, there is conservation of energy, so the sum of the areas under these curves equals the area under the original wave curve
b. Lengthens (as in "stretches") the passed and reflected waves over time
c. Smooths high-frequency "ripple" (as in harmonics) out into the lower-frequency "envelope" (i.e. the nozzle acts as a "filter choke" or "low-pass filter") !!!
d. Because of a and b: In effect, causes a fairly long period of "stagnation" (perhaps I'm mis-using the term) where pressure remains elevated in the nozzle zone

The effects of these hypothetical properties are what led me to design the original FWE chamber as nothing but a long nozzle with an end dome. I think the combination of these is what leads directly to the extreme concentration of heat in the chamber evident in all the FWE engines.

Any differing / more educated opinions on this?

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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Mon Aug 28, 2006 12:44 am

milisavljevic wrote:Larry, James, and Graham -- Congratulations!

I calculate the fundamental frequency as 317.7 Hz, averaged from the fundamental and first eight harmonics.
The fundamental group frequencies are by far and away the strongest part of this motor's acoustic signature.

She's SHORT and SWEET!!

Best regards,
M.

milisavljevic -

Thank you, sir! Would it be a simple matter for you to give us your famous 'Acoustic Temperature' value for this pipe? That would be interesting, since you have mentioned this value for several other examples.

The high frequency evident in the run really surprised me, the short length notwithstanding, because I imagined that the average gas temps would be on the low side due to the (presumed) good breathing of the tail-end cone. Of course, I end up being surprised by a lot of things ...

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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Eric » Mon Aug 28, 2006 6:01 am

Would it be possible for you to run it with a piece of flashing under the intake so that it doesnt cool the pipe and we can get a good idea of the temperature gradient across the engine?

Some of you might remember the peculiar heating pattern on one of my linear FWE's, I'll have to take a look and see if there is any possible relationship between the heating pattern positions and the design features on this new engine.

I cant quite tell from the pics, but the intake might be able to be flared more. The intake flare is probably one of the most important things for full power development.

How does the sound compare to your first FWE? Both are absolutely beautiful work.

Eric
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby milisavljevic » Mon Aug 28, 2006 12:50 pm

Hello Larry --

Larry Cottrill wrote:Would it be a simple matter for you to give us your famous 'Acoustic Temperature' value for this pipe?

I gave you one better wrt. acoustic temperature - I put Lady Anne through her paces in the pulsejet model.

As you asked for it, the acoustic temperature is a rather anemic 319,5 °K. This is not surprising if you were
to consider this motor in the same context as your previous offerings; the combustor section that you have
adopted for the FWE-series motors is apparently unable to support higher values of OAT. Sorry about that!

Setting acoustic temperature aside, you may be interested to read about this motor's other characteristics:
Note: I used Larry's drawings as a baseline for modeling, and substituted James' changes where available.

Code: Select all
Thrust and temperature data is referenced to ICAO standard day, sea-level at 15 °C

Physical length   547,0 mm      : interior length
Acoustic length   563,8 mm      : std. correction
Fundamental (OF1) 317,7 Hz      : reported before
Temperature (OAT) 319,5 °K      : see note for N1

S1 (step ratio)     4,04:1      : relatively large, < 3 typical for smaller motors
S2 (forward bias) > 2,50:1      : overexpanded; optimum exit diameter 49,5-50,5 mm

N1 (lockup ratio)   6,00:1      : acoustic temperature synchronised for lockup
E2 (gate ratio)     3,02:2      : exact integer ratio, e.g., 3:2, is preferred
E3 (tail ratio)   ~ 8,5         : relatively(!) short, but motor runs out well

Thrust division    30:70        : relative contributions (%) inlet and exhaust

Maximum thrust   1280 g         : NOC method (rigid combustor model) S2 = 2,45
Minimum thrust  < 150 g         : may require a precison fuel injection system
SFC at maximum  < 1,8 kg/kgf/hr : range 1,6-1,8, for equivalence ratio 1,2-1,3

Maximum thrust   1410 g         : NOC method (rigid combustor model) S2 = 2,50
SFC at maximum  < 1,8 kg/kgf/hr : range 1,6-1,8, for equivalence ratio 1,2-1,3

Ultimate thrust  2050 g         : NOC method (rigid combustor model) S2 = 2,50
SFC at ultimate < 1,4 kg/kgf/hr : equivalence ratio < 1,3; combustor saturated*

Observed thrust  1200 g         : NOC method (rigid combustor model) S2 = 2,50**
SFC at observed < 2,2 kg/kgf/hr : range 2,0-2,2, for equivalence ratio 1,2-1,3
SFC at observed < 1,8 kg/kgf/hr : stoichiometric equivalence ratio ~ 0,95-1,05

*ultimate thrust assumes combustor is 100% saturated; may require special hardware
**observed thrust model incorporates visual evidence from James' latest photograph


Best regards,
M.
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for ye merchants who do the prop'r t'ing only if
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an' threat'nd wit' forfeiture of all ye precious loot
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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Mon Aug 28, 2006 1:40 pm

milisavljevic wrote:Hello Larry --

Larry Cottrill wrote:Would it be a simple matter for you to give us your famous 'Acoustic Temperature' value for this pipe?

I gave you one better wrt. acoustic temperature - I put Lady Anne through her paces in the pulsejet model.

Thanks very much! Above and beyond the call ...

As you asked for it, the acoustic temperature is a rather anemic 319,5 °K. This is not surprising if you were
to consider this motor in the same context as your previous offerings; the combustor section that you have
adopted for the FWE-series motors is apparently unable to support higher values of OAT. Sorry about that!

It is perhaps not such a good thing to have an engine with all the heat development up front. That, of course, was the most obvious "surprise" when the first FWE was run. The tailpipe stays relatively cool and slow. This, of course, is the key to the short physical lengths that can be achieved.

Setting acoustic temperature aside, you may be interested to read about this motor's other characteristics ...

Probably the biggest disappointment to me is the (at this point, theoretical) SFC. It seems to sort of emerge as a truism that low acoustic temp means "gas hog". For the average sport jet U-control flyer (i.e. my audience of choice), I don't think this means much; a heavier fuel load basically just means a longer takeoff run. Other classes of users might feel differently.

Once we have some engines with really decent SFC, it would be fun to have jet-powered "endurance" contests. Doesn't look like any FWE will be a contender in such events, though.

Thanks, very much, M!

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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby milisavljevic » Mon Aug 28, 2006 2:36 pm

Hello Larry --

Larry Cottrill wrote:Probably the biggest disappointment to me is the (at this point, theoretical) SFC.

What are you talking about? People are becoming spoiled for ultra-low TSFC in pulsejets!
The figures that I listed were determined at maximum thrust, and in any event, they are
far below the Dynajet (your standard of excellence ;-) Did you notice the TSFC calculated
at ultimate thrust? Did you notice that this thrust level exceeds the Dynajet by some 6%?

"Spare the Jet-A, spoil the pulsejet enthusiast." (^_^)

milisavljevic wrote:Yes, the tailpipe is overexpanded, and the relative lengths of intake and tailpipe are not in
optimum proportions to one another, and the intake needs to be relocated back a little bit;
so what? Go forth, and design a FWE VIII MkII! And ditch a few pesky Roman numerals!

You are CLOSER now to realising your oft-stated pulsejet goals than you have ever been!

Larry Cottrill wrote:Once we have some engines with really decent SFC, it would be fun to have jet-powered "endurance" contests.
Doesn't look like any FWE will be a contender in such events, though.

Did you write that last sentence, Larry? It does not sound like you! This is a sweet motor!

She just needs a little more work... You would not want life to be too easy, would you? ;-)

Cheers!
M.
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