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timwhalen

Tuned Pipe Wave Velocity

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23 hours ago, LohringMiller said:

EngMod2T has Tom's tuning calculations included.  Some other interesting tools are available on this site.  The dyno software can be used with an inertial dyno but not for a boat.  The drag is too hard to estimate accurately enough.   We verified the simulations on an inertial dyno as well as with Eagle Tree data loggers in the boats.  The inertial dyno software and data logger costs around $1000.  We machined the flywheel, but I would expect you could have it made by a machine shop for around another $1000.  An article on all this is available from Model Engine Maker issue 15.  There's a lot of on line information as well.  I have a spreadsheet for size and stress calculations.  The best article on one of our engine modification programs is here.  Another article on our gasoline test series in a modified Zenoah is here

We ran the simplest Eagle Tree data logger with an rpm and GPS module.  That gives all the information you need but I have measured EGT both on the dyno and in the boat.  It wasn't particularly useful at our state of sophistication.  The rpm vs time curve on an accelerating boat has a very similar shape to the rpm vs time curve on the inertial dyno.  Power is a very sensitive indicator of scavenging efficiency in a two stroke.  Gordan Blair went a lot farther at Queens University of Belfast with his Yahama 250 cylinder test series. Even so, he verified the scavenging rig results with inertial dyno testing.  Some of the designs tested are below.  With very few exceptions, model engines have the poorest transfer passage designs.

Lohring Miller

YAM 2 through 10.jpg

YAM 12, 14&15.jpg

Thank you, Lohring...much appreciated.

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23 hours ago, Mike Rappold said:

Tim,

On the Eagle Tree logger, the thermocouple expansion board can handle two thermocouples. So you only need one of those. The thermocouples are up to you. I did not use the Eagle Tree ones but bought from another source. I used a thermocouple supply company.  The EGT sensor with compression fitting from Eagle Tree seems to large to fit in the side of a thin walled tuned pipe - something to consider.

The Cylinder head temp sensor is very similar to the one I use.  The one I use is smaller in length eyelet. The cooling heads on the engines need to be modified to fit the eyelet and allow for the glow ignitor to fit around the glow plug. let me know if you need more details on this.

I have never tried the pitot tube for speed measurement - have only used the GPS module.

 

Also to backup what Lohring said about measuring EGT in the boat. I have not found EGT particularly useful as a tuning aid yet. The Cylinder Head Temp has been very useful. If I meter the water more/less to adjust the temp plus work the needle valve, this works the best. The EGT then becomes a secondary reference point - have to have the correct engine temp/needle first and then the EGT follows - if that makes sense. 

EngMod2T simulation program is powerful program but does have a  learning curve. The program does have a glow ignition feature. I am using it on .21 RC drag car engines. Take data from the Eagle Tree logger to help feed some of the software inputs. Have not tried it on boat engines yet though.

Mike

 

Thanks, Mike... now, to find the thermocouple expansion board.

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We never had problems with the magnetic sensors except on the electric hydro.  There we ran the sensor on the propeller shaft because the motors magnetic field overwhelmed anything the tiny magnets put out.  We still ran it close to some big magnetic fields.  The little wire on the last picture is the Hall sensor wire.  The big wires were sized for 1000 amps. 

I ran magnetic sensors on model outboard flywheels as well as the shaft coupler on Zenoahs.  See below.  I included the thermocouple holder I made for EGT sensing.  It's pictured on a crackerbox exhaust extension.  Maybe you have a bad unit or Hall sensor.  Eagle Trees are model, not aircraft grade grade.  We've gone through several, especially when they got wet.

Lohring Miller

Crackerbox EGT.JPG

Magnet mounting.JPG

Nelson with sensors hi res.JPG

Motor Wiring.jpg

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Terry

Thy do show ragged but I don't think it is the sensor fault. How much RPM change you think are small eng can do in 1 second? 

blip the throttle and count to 1001. Bet it can do the whole RPM rang in that small time frame. 

So put that in context to what you see on the graft.

Now may be a filter on the signal can make a better looking graft?

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18 hours ago, dwilfong said:

Terry

Thy do show ragged but I don't think it is the sensor fault. How much RPM change you think are small eng can do in 1 second? 

blip the throttle and count to 1001. Bet it can do the whole RPM rang in that small time frame. 

So put that in context to what you see on the graft.

Now may be a filter on the signal can make a better looking graft?

 

It could be the motor to some extent but it's mostly "noise" IMHO.  I'm only using 10 hz here as that's what the LCD panel wants, but I have tried 50 hz and it's not much better.

I doubt a motor could actually jump from 9-14K in 0.1sec. unless it's hitting the pipe.  (199.9 - 200.0 sec.).

Funny tho it is pretty smooth coming on pipe from 15-23K. :)

 

043012-10trim.jpg

 

Edited by Terry Keeley

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17 hours ago, Terry Keeley said:

 

It could be the motor to some extent but it's mostly "noise" IMHO.  I'm only using 10 hz here as that's what the LCD panel wants, but I have tried 50 hz and it's not much better.

I doubt a motor could actually jump from 9-14K in 0.1sec. unless it's hitting the pipe.  (199.9 - 200.0 sec.).

Funny tho it is pretty smooth coming on pipe from 15-23K. :)

 

043012-10trim.jpg

 

Yes it is funny that as soon as the boat catches up to the eng it gets erratic.

Might need a little more load on the eng.

Edited by dwilfong

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Terry what material and how thick are you using to mount your hall affect sensor? On all my heli’s I’ve used G10 -1/16” or 3/32” depending on how far it has to reach the magnet. Always mounted to the engine lug. As you know the magnets also have to have the correct pole facing the pickup. I always epoxied the magnets in the flywheel and used lead shot of the same weight to balance the other side.

 Thanks John 

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Thanks guys. That's an old mount in the pic, I've made a newer solid aluminum one and even tried a rubber insulator mount with the same results.  The only thing left I might try is a noise reducing circuit from the sensor mfg but I'm not holding my breath.  Optical IR is supposed to work very well as long as there's a good flat black section. 

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