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

Moderator: Mike Everman

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

Postby Eric » Mon Aug 28, 2006 4:18 pm

Those numbers are pretty good, and the AMA speed contests do allow the use of augmenters.

One thing though that very few people seem to realize, or ever talk about on the forum is that the Bailey Fast Jet, and the Jet Bill Tuned Jets produce about 7.5 lbs thrust compared to the dynajets 4.5.

It would have to run in the unlimited speed class though, unless a new valveless class is formed, in the unlimited it would not be only competing against the stock dynajets though. The sport class is for the stock dynajets and bailey jets only.

An endurance contest would be fun, would it be at max thrust? I estimate on ultra low throttle the TP-180-18 could run for about 300 hours on a tank of propane :D
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Graham C. Williams » Mon Aug 28, 2006 5:20 pm

Dear Mike.
Apologies for the delay. Had some work to do.
I had to run the model twice to check I'd not made a mistake. I'll try and post the Temporal plot for you.
Basically the motor started with no problems (Methanol and Propane). After an initial 4 cycles the pressure reached a peak, after that every other combustion was at full power but the combustion between was at some lower level. The shock (or strong compression wave) returning from the tail was strong then weak.
I'll get a screen grab.
Regards
Graham.

Dear M.
Why do you have 2 maximum thrust values? I guess it's connected to the S2 value but what is S2 (Forward Bias)? Does the second maximum value assume perfect expansion at the tailpipe? A reduction in the tailpipe diameter will change the tuning of the motor - do we then have to assume that other sizes need changing to bring the motor back into tune and are these effects taken into account?
The ultimate Thrust value is interesting but what does it assume to get this value?

Sorry about all the questions (I’m not having a go), I'm not sure I fully understand the results of your analysis and would like to.

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

Postby milisavljevic » Mon Aug 28, 2006 10:16 pm

Hello Graham --

Graham C. Williams wrote:Why do you have 2 maximum thrust values?

My remarks in the analysis section could benefit from more clarification - but I did not want to write a book! ;-)

The models for the 1280 and 1410 g maximum thrust ratings differ only in the maximum allowable S2 ratio.
This ratio, also called forward pressure bias, is formed by comparing peak dynamic pressures across both
individual inlet and exit planes, and assumes a self-aspirating duct; the upper and lower limits of this value
determine maximum and minimum developed thrust, respectively. A classical, self-aspirating pulse duct is
constrained to operate within the upper and lower limits. The actual values of these limits are not fixed, as
deficiencies in duct design, construction and fuel delivery can act to narrow the range of proper operations.

Data from literally dozens of historical and contemporary pulse ducts suggest that S2 (max) = 2,5:1. With
allowances for (unquantified) deficiencies (as mentioned above), the practical ceiling for S2 (max) is 2,45:1.

In both cases, the tailpipe was modeled 'as is' (ID = 56 mm). You are correct in your assessment that any
change in the exit diameter will affect duct tuning; however, this duct is not properly tuned at present - as
evidenced by the values determined for OAT, N1 and E2. This is in part driven by the combustor shape, as
one of Larry's design goals for the FWE-series motors was to suppress upper harmonics, aka HF ringing.*
The spectrogram taken from Jame's video demonstrates that Larry has been very successful in this regard.

Of course, there are some of us who have a completely different perspective on the value of harmonics! ;-)

Graham C. Williams wrote:The ultimate Thrust value is interesting but what does it assume to get this value?

Wrt. the term 'ultimate thrust, it is clear from James' video (and corroborated by the model) that this motor
is making efficient use of the available combustor volume - more so than in previous FWE releases. With
this observation comes the possibility of completely saturating the combustor and attaining the theoretical
maximum thrust (Cronje score = 100%). This is why I encourage Larry to keep revising this particular FWE!

One note: James' interpretation of the intake design is best; Larry's smooth transition into the combustor
is contraindicated by the model. I strongly encourage Larry to revise his plan to reflect James' intake style!

Please do not take anything written here as criticism of your efforts; the same applies to Larry and James!

Hope this helps!
M.

*Larry's term, not mine! ;-)
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for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

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

Postby larry cottrill » Tue Aug 29, 2006 2:45 am

M & Graham -

I am usually in trouble when pretending to be a theoretician ;-)

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

Postby milisavljevic » Tue Aug 29, 2006 3:33 am

Larry --

Larry Cottrill wrote:I am usually in trouble when pretending to be a theoretician ;-)

milisavljevic wrote:I am usually theorising when pretending I want to stay out of trouble! ;-)

Evil M.
no safe haven for merchant scum


for ye merchants who do the prop'r t'ing only if
ye be haul'd-up on charges b'fore ye ship-mates
an' threat'nd wit' forfeiture of all ye precious loot
hear this - so-called stand-up guys YE BE NOT

avast!
Cap'n M.
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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Tue Aug 29, 2006 4:50 pm

milisavljevic wrote: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%?

Well, no. Part of it is that I'm just not used to seeing forces in grams. However, there does seem to be something of an "apples and oranges" problem to this. The advertised (and often verified) DJ thrust of 4.25 lb is almost certainly not the best it could do (even on ordinary gasoline) - it is almost certainly a compromise between max thrust and reasonable SFC. The thrust figure you're talking about sounds like we're pushing everything to the limit, probably not the way we would really want to run as a practical flight engine.

This sounds kind of cynical, but practically speaking, it's never enough that it just "works really well". It has to work well enough, in several different senses, that the perceived benefits to the user clearly outshine the competition.

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!

Do you feel that these effects (particularly the overexpansion) are too subtle for UFLOW to show clearly, or am I just not seeing the details of behavior that show this? Would this show as a moment of sub-atmopspheric pressure at the tail end, for example?

NOT having the tail end oversized is important. The 'straight pipe' FWE is obviously far suboptimal, but it fits just about anywhere a Dynajet will go! Of course, one possible way around the problem would be to go ahead and market a skinny-tailed low-thrust "scale" FWE and a horn-tailed "performance" FWE. From a marketing standpoint, that would not be unthinkable, though it complicates manufacturing, inventory, etc.

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

Chicago and the rising moon are both to the east, but I'm a heck of a lot closer to one than I am to the other ;-)

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? ;-)

If I did, I guess I'd be all mired up in something else. As it is, I'm enjoying seeing guys having fun building and running my junk - at the same time, I figure that right now I'm already world famous (to about 300 people)!

READ THIS FANTASTIC CLAIM: I would be willing to bet that if it were somehow measurable world-wide, the Fun-to-Effort Ratio would be higher for the Short Lady than for any other homebuilt jet ever designed. Won't get me in the Guinness Book of World Records, but it's a comforting thought (or arguably, delusion), just the same ;-)

L Cottrill
Last edited by larry cottrill on Tue Aug 29, 2006 5:02 pm, edited 1 time in total.
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Re: re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Tue Aug 29, 2006 4:59 pm

milisavljevic wrote:One note: James' interpretation of the intake design is best; Larry's smooth transition into the combustor
is contraindicated by the model. I strongly encourage Larry to revise his plan to reflect James' intake style!

Well, I am not in love with the curved pipe - it just represented an easy way to build (in mild steel) for this particular size engine. Building a bent intake is the least of my worries (as if I ever built anything any more). Could you clarify, though, why you feel strongly about this? Is it just that he gets a little more length in the pipe, a better angle going in, or is there some benefit to having the 'sharp' elbow, or what?

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

Postby hinote » Tue Aug 29, 2006 5:17 pm

Larry Cottrill wrote:READ THIS FANTASTIC CLAIM: I would be willing to bet that if it were somehow measurable world-wide, the Fun-to-Effort Ratio would be higher for the Short Lady than for any other homebuilt jet ever designed. Won't get me in the Guinness Book of World Records, but it's a comforting thought (or arguably, delusion), just the same ;-)


Larry:

I'm betting you'll be contested on this one! (allow me to be the first)

My M15E motor must surely be close in the fun-to-effort ratio; here's a list of parts, funning from front-to-rear:

1. Intake tube: Off-the-shelf (OTS) exhaust tubing
2. Head plate: OTS large-diameter washer.
3. Combustion chamber: OTS exhaust tubing
4. Transition cone: This is the only part that must be formed--easy, because it's short
5. Throat tube (including u-bend) OTS exhaust tubing
6. Exhaust megaphone: OTS exhaust part, from Burns Stainless
7. Tailpipe final section ("bustle"): OTS exhaust tubing.

Just weld-'er up and go. And it's a strong motor, for its size.

Of course, Mike E. would probably argue that the Pipewood is even easier--which is probably true.
Bill H.
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".......some day soon we'll be flying airplanes powered by pulsejets."
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby James D » Tue Aug 29, 2006 6:04 pm

Eric wrote: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?


Yes it would, the difference is quite alarming.

Eric wrote: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.


Judging by the substantial drop in thrust just from clamping a piece of plate under the intake, you’re probably right, I’ll make a better flare this week.

Eric wrote:How does the sound compare to your first FWE?


It’s difficult to say, a bit louder & harsher sounding than the standard Short Lady probably, but quite similar to the Advanced FWE.
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby larry cottrill » Tue Aug 29, 2006 6:16 pm

James & Eric -

The influence of the 'choke' is very apparent; I expected this, but it looks more dramatic here than what I had envisioned. Wonderful picture, James!

Look at how much influence the air carried back by the intake blast has, even that far back (beyond the aluminum shield) - contrast the top of the cone with the bottom. Amazing!

You've all seen my various pics of the Dynajet static running with the whole pipe red hot. When I flew that engine, more or less at dusk, the cooling at a mere 90 MPH was so good that only about an inch of the pipe was visibly red - the nozzle point at the front end of the tailpipe. A little air moving can pick off radiated heat at an astonishing rate.

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

Postby larry cottrill » Tue Aug 29, 2006 6:30 pm

James D wrote:
Eric wrote: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.


Judging by the substantial drop in thrust just from clamping a piece of plate under the intake, you’re probably right, I’ll make a better flare this week.

James -

Remember, two things are happening here: You've altered the airflow in and (especially) out of the intake; AND, you've caused the tailpipe section to run hotter, on average. If the shell is hotter, the average gas temps inside MUST be higher, at least by a few degrees. Before changing the flare, here's what I'd like to see:

Remove the flat shield and substitute a long piece of 1 or 1.5 inch tubing behind the intake - just wire it on or something, and leave about a 1-inch gap at the flare for breathing. Don't try to consciously make an 'augmentor', just a sort of crude 'thrust tube' for the ejected intake air. See if the engine runs weaker yet, just by shielding the whole tailpipe from the influence of cooling air. And, photograph again, of course.

What I'm getting at is, let's try to determine whether the engine might actually be "de-tuned" slightly by the higher running temperature. Also make careful note of the running frequency that's established, and how much it drifts from the starting 'cold pipe' frequency!

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

Postby Graham C. Williams » Tue Aug 29, 2006 6:34 pm

Dear James.
Great shot. The heat pattern is a real eye opener!
Along with the reduction in Thrust did you notice any change in operating frequency?

Thanks
Graham.

P.S. Ok Larry I see you've beat me to the question.
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby James D » Tue Aug 29, 2006 7:31 pm

I've attached a video clip to show running with & without the deflector, the frequency is very similar in both clips. After 1 minute of running at a moderate thrust level it settles at 323 Hz.
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re: Prettiest FWE (?) - the 'Lady Anne Boleyn'

Postby Graham C. Williams » Tue Aug 29, 2006 8:25 pm

Dear Eric.
Do you think that your comments about the intake flair could also apply to the tailpipe? Most motors do not have a lip on the exhaust so I guess it makes little effect.

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

Postby mk » Tue Aug 29, 2006 9:04 pm

Very cool! Congratulations to all of you!

It's very interesting to follow up this thread.

Also, I must admit, that I pretty much like the quality work in every aspect.
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