I may do some TSFC test of my own. I use a seed bag scale. It has a 300 pound limit and is accurate to the .01 pound. Sounds like thats what you need :)
Oh and congratulations on a very nice design.
mikhail jones
K-PT 07c thrust fix -- K-PT 07X release
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Re: re: K-PT 07c thrust fix -- K-PT 07X release
Marten -
Impressive work, even considering the many difficulties noted!
Provide a reasonably stout wooden beam with a simple hinge (fulcrum) near the center, with the propane tank near one end and enough counterweight somewhere near the other end to almost balance the weight of the cylinder. As I said, there are NO critical dimensions; the only critical design elements are: (a) The beam must be approximately level between the fulcrum and the weighing device; (b) There must be a narrow "blade" of wood on the underside of the beam to contact the weighing device, and the tank must be as precisely centered over that point as you can get it! - that's literally the only strict "dimension". Once you get that set up, adjust the counterweight back and forth until the weighing device reads nearly but not quite at its upper weight limit. Now, note the weight shown and run your engine for the selected time period (of course, the rule still is, the longer the better for accuracy's sake). At the end of the carefully timed run, note the remaining weight and subtract it from the original figure; the difference will be the weight of the fuel mass consumed.
Again, the only significant error to this method will be bad centering of the fuel weight over the weighing device. If the cylinder is too far out from the fulcrum, it will exaggerate the noted difference; if too far in, it will lie on the low side. In practice, it should not be difficult to get pretty accurate centering over the weighing point, since the cylinder is almost perfectly symmetrical.
This method would be simple to set up and use, and practically fool-proof. All you're doing is using a counterweight to cancel most of the tank and fuel weight during measurement.
L Cottrill
Impressive work, even considering the many difficulties noted!
You can use a simple "see-saw" or "teeter-totter" (I wish I knew the German name!) arrangement with a counterweight to "subtract out" some of the weight, allowing you to use a very accurate but low-range device, such as an electronic postal scale. Interestingly, this can be done with no critical dimensions as follows:mk wrote:*) There was only offered the possibility to measure propane usage via the differencel methode using a bathroom scale. This, as anybody may agree it, makes it difficult to keep the error range low without using lots of of propane. In fact the range of max. possible relative error, which was calculated to ca. 11.5%, was by some >85% caused by that bathroom scale's error. It is not too easy to get a scale which could cary a load of a propane bottle while still being exact to 100 g, rather 50 g or less.
Provide a reasonably stout wooden beam with a simple hinge (fulcrum) near the center, with the propane tank near one end and enough counterweight somewhere near the other end to almost balance the weight of the cylinder. As I said, there are NO critical dimensions; the only critical design elements are: (a) The beam must be approximately level between the fulcrum and the weighing device; (b) There must be a narrow "blade" of wood on the underside of the beam to contact the weighing device, and the tank must be as precisely centered over that point as you can get it! - that's literally the only strict "dimension". Once you get that set up, adjust the counterweight back and forth until the weighing device reads nearly but not quite at its upper weight limit. Now, note the weight shown and run your engine for the selected time period (of course, the rule still is, the longer the better for accuracy's sake). At the end of the carefully timed run, note the remaining weight and subtract it from the original figure; the difference will be the weight of the fuel mass consumed.
Again, the only significant error to this method will be bad centering of the fuel weight over the weighing device. If the cylinder is too far out from the fulcrum, it will exaggerate the noted difference; if too far in, it will lie on the low side. In practice, it should not be difficult to get pretty accurate centering over the weighing point, since the cylinder is almost perfectly symmetrical.
This method would be simple to set up and use, and practically fool-proof. All you're doing is using a counterweight to cancel most of the tank and fuel weight during measurement.
L Cottrill
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re: K-PT 07c thrust fix -- K-PT 07X release
Very nice work. Your diameter ratios are perfect. With some injector development you should be able to get extremely good TSFC.
Eric
Eric
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re: K-PT 07c thrust fix -- K-PT 07X release
Hi Larry,
See-Saw in German is " schaukel "
Al Belli
See-Saw in German is " schaukel "
Al Belli
re: K-PT 07c thrust fix -- K-PT 07X release
Thanks for the replies!
---
Larry,
While the basic principle is quite simple, there seem to be a lot of little things, which would sum up to some relatively large error. At least if not putting quite some effort and money in that see-saw design.
So again, without having gone into detail, the trouble is in the loads being present in opposite to the degree of accuracy needed.
Thereof, I think a seed bag scale as Mikhail Jones suggested, or a postal scale like Bill Hinote used (and/or still uses) would both be suitable solutions. E.g. the suggested degree of accuracy of about 5 g (0.01 lb) would be very good for a max. load of about 136 kg (300 lb)!
Okay some max. load of 40 kg (88 lb) would be enough already. Hmmm.
---
Larry,
While the basic principle is quite simple, there seem to be a lot of little things, which would sum up to some relatively large error. At least if not putting quite some effort and money in that see-saw design.
So again, without having gone into detail, the trouble is in the loads being present in opposite to the degree of accuracy needed.
Thereof, I think a seed bag scale as Mikhail Jones suggested, or a postal scale like Bill Hinote used (and/or still uses) would both be suitable solutions. E.g. the suggested degree of accuracy of about 5 g (0.01 lb) would be very good for a max. load of about 136 kg (300 lb)!
Okay some max. load of 40 kg (88 lb) would be enough already. Hmmm.
mk
Re: re: K-PT 07c thrust fix -- K-PT 07X release
Actually, "schaukel" means swing. "wippe" is see-saw.Al Belli wrote:Hi Larry,
See-Saw in German is " schaukel "
Al Belli
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re: K-PT 07c thrust fix -- K-PT 07X release
Hi Rufus,
Wippe also means balance, which is more descriptive of the mechanism described.
Al Belli
Wippe also means balance, which is more descriptive of the mechanism described.
Al Belli