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Old 03-30-2006, 07:11 PM
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BruceL (and Hobbsy): Are you sure?[8D][8D]
Old 03-30-2006, 07:15 PM
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By the way, I'm going to put some serious hours on my Saito .56 tomorrow, I moved it from my RCM 40 to my Sig LT 40 today. I tried mightily to put the .72 on there but where I have the mount holes drilled in the firewall is just too skinny.
Old 03-30-2006, 07:16 PM
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Dave:

You were included in the address line as a sort of "Info Copy," that's all other than the implicit question about whether the TNC tach has a selexctable gate time.

Bill.

Old 03-30-2006, 07:22 PM
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Gate or no gate it has tached far more Saitos than any other brand.
Old 03-30-2006, 07:38 PM
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ORIGINAL: N3OKI

Hey guy's thanks for the info on the 40. I think after the 2 larger (65in span) profiles are built I will order in a 40 and build the 25 size MoJo. Should be neat to have a small 3d plane.

The wife thought i had lost it yesterday, when upon arriving home from some honey do errands she looked out and saw a new 6x10 enclosed trailer attached to my vehicle. She did not go for the "it followed me home. Can I keep it?" line. So i had to tell her the truth. Hit a hell of a sale att the local Lowes. 2000.00 on sale. They miss priced it. Priced as a smaller trailer. Bt the manager gave it to me as priced. I could not pass it up.
Bill I know exactly what you mean. I told my MFWF (Minister For War and Finance) that I was just driving by the LHS (didn't stop I promise) and this Saito 120 just jumped onto my back seat. When sternly questioned, I cracked under the pressure and admitted that it was on a "end of model runout" sale.

she hit me anyway [&:]

Although my constant griping about how my planes are now too big for the family taxi has elicited the concession that I can now go buy a big trailer (again she balked at the idea of a new pickup) to put them in if I like.

I LIKE!!! I LIKE!!
Old 03-30-2006, 09:14 PM
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Left field?? I don't play left, I'm a right field guy. The only reson I asked the question was no engine will run with at that steady an rpm. There is a thing called standard deviation and by definition the rpm will hover around some base number, say 14,000. So it would be 14,000 + or - a small error. Even closley regulated power supplies have a +or- error and they are extremely accurate. May be small but it's there. Ain't nothing in the world perfect. Even our electronic scales as accurate as they are have an error. Nothing you can do about it. 1/10 of 1% of 10,000 is 10rpm and I know your tach isn't that accurate. You are talking about 1/100 of 1%.

Anyway I just wondered what tach you were using.
Old 03-30-2006, 09:17 PM
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Sure I'm Sure. I use Shure deodorant. We better drop this or suffer the wrathe of the moderator.
Old 03-30-2006, 10:25 PM
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Bill,

I think that you don't need ovens for modern crystal circuitry unless the temp drops quite a bit. I have an oven switch on my R-390A but nobody ever uses it from what I can tell unless in artic conditions. Anyway, not trying to start a p. contest with anyone........
Old 03-30-2006, 10:34 PM
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ORIGINAL: William Robison

In order for any counter to be accurate to a untis count, it has to have a gate time, the counting interval, equal to the period being measured.

In other words, for a tachometer to be correct to ONE revolution per MINUTE it will have to sit there counting for an entire minute before giving a reading. Few people would accept such a thing.

What we actually have are devices that have a much shorter gate time, and obviously, less digits of precision.
Not quite Bill :-)

What modern tachometers do is measure the time interval between when each blade passes in front of the light-sensor.

This means that the accuracy is not dependent on the number of measurements made, providing the engine is holding a constant RPMs.

For example, if your engine is turning at 10,000 RPMs with a 2-bladed prop, there will be 3 milliseconds between each blade passing the light sensor. No matter how long you measure it (providing the revs are constant) there will always be a 3mS interval.

Exactly how many digits of precision are measured depends on the tachometer's time-measuring resolution.

If the tach has a measuring resolution of 3 microseconds then it will be accurate to 3 digits. If it has a resolution of 0.3 microseconds then it'll have a resolution of 4 digits, etc, etc -- no matter how many times you measure that time interval.

What the gate time does is "average" the readings for a given period of time.

A gate time of 1 second will effectively take a minute's worth of pulse-width measurements and return the average of those readings. A six second gate-time will effectively do the same, but over a six-second interval.

The results returned are the *average* RPMs during that time.

This means that a longer gate time may actually produce *less* accurate readings. If you set the gate time to (say) 5 seconds, and your engine has a brief hiccup that causes the revs to drop for a second or two, the average reading will not correspond with either the actual RPMs at the end of the gate period -- just the average -- which will be lower.

Having said all this, most tachs have a gate period of about 1 second or so. This is long enough to provide a relatively stable reading even if the engine RPMs are varying a little (as they inevitably do) but short enough to reflect the effects of any real RPM changes in near enough to real-time.
Old 03-30-2006, 10:58 PM
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YES YES YES and exactly!!!!
Old 03-30-2006, 11:06 PM
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XJet:

You are quite right, sir. I had not thought of measuring the pulse interval. But even a minor clock error in such a tach would lead to a gross error in the rpm reading.

Thanks for telling me about the alternate method of measuring. But then you go on to mention the one second gate time, so I'll guess what we have are totalizers as I was mentioning, rather than the intervalometers measuring the time?
--------------------
Barry:

I haven't seen an R-390 for years. A real boat anchor that would heat your house in the dead of winter, but if you had one working right you couldn't ask for a better HF radio than Mr. Collins' big box.

My old frequency counter, ten digit, was certified down to one cycle on readings up to 99.999999 Mhz, but only if I gave it a 30 minute warm up of the crytal oven. It did have selectable gate times of 1.0, 0.1, 0.01, and 0.001 seconds, with auto decimal placement.

Bill.
Old 03-31-2006, 02:13 AM
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We know Bill has been around awhile but I think his tach has been around longer then he has.
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Old 03-31-2006, 05:08 AM
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Default RE: Welcome to Club SAITO !

Speaking of "old tachs" (and Saitos of course), I wonder if those old reed-based tachos would read half RPMs on a 4-stroke because it only fires once every two RPMs?

Does anyone (apart from me) remember those old reed tachs?
Old 03-31-2006, 08:12 AM
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I have one of those old reed jobs. Seemed to be sympathetic to harmonics

http://www.humboldtmfg.com/c-2-p-284-id-2.html

H 3753 $29.95 is the third item down.

These things were sold in the model magazines in the 50's - 60's for around $19.95

I have one. It is actually rather crude compared with today's electronic tachs.

It takes more skill to use one than the current electronic tachs

To try to keep down harmonic sympathy, you slide the wire all the way out before holding close to the engine.

You then draw the wire back slowly into the holder. At a certain point, the wire will wave back and forth at the same frequency as the engine. You seek the widest sympathy vibration. Then read the rpm off the calibrated scale on the holder.

The device had a pocket clip so you could carry it in your shirt pocket. Mine came in a leather belt clip pouch.

It was called the Vibra Tach and was very durable if taken to the field.

The link above is advertising the device for use with concrete vibrators. This is a rugged environment. The Vibra Tach is the best device for this application due to its ruggedness.
Old 03-31-2006, 09:15 AM
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ORIGINAL: EMVIN

#237

mwarren400, I'm glad to hear the good news, I have a 220 and will be fireing it up this weekend for the first time. What size prop did you use? What kind of fuel?

Used a 20x8 Master Airscrew Classic (only thing available in that size) with 15% Cool Power and 4 ounces of Castor mixed in to the gallon
Old 03-31-2006, 09:21 AM
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What RPM did you get?
Old 03-31-2006, 11:09 AM
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Bill
Re: intake stacks ( sorry to rehash this old stuff )
quote:

Sealing the intake stack
I never said anything in particular about the o-rings, only that the gap between the carb body and the stack had to be sealed for it to work properly.

Once I got the part I had a better picture of what in does. I read back through the "Bill's Guide" notes ( thanks ) and I have to ask....not being a smart azz....does the Saito Intake Stack have air leaks by design ? I take it that the part is not made work like a sealed intake air box / filter on a gas engine, rather to catch fuel spray/fog and is just not that critical to be sealed. Thanks, sorry to drag this out.

over and out![8D]
Drums

Great Weekend to All!!


Bill
Old 03-31-2006, 03:28 PM
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BillD:

The gap remains from the early days when all the Saitos had a sliding choke plate in that gap.

The manual chokes have been discontinued, but the stacks have not been redesigned to close the gap. So we have to cobble up some sort of seal between the carb and the base of the stack.

Bill.
Old 03-31-2006, 03:52 PM
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>>> Saito-220 18x8, 19x8, 20x8

Try the APC 32x4W for funfly.

Ernie
Old 03-31-2006, 04:22 PM
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What causes the engine to start backwards? New Saito 125.
Jerry
Old 03-31-2006, 04:29 PM
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Jerry:

What causes the engine to start backwards? New Saito 125.
Generally, not enough prime, or the throttle not far enough open.

Do be careful, with a full tank the engine can draw fuel through the pressure line and keep running. The exhaust heat going out through the carb can damage the o-rings, don't let it keep going. I have actually melted the element out of the Bru-Line air filter with just a couple seconds reverse running.

Bill.

Old 03-31-2006, 04:48 PM
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I have a 20x6 on right now.. should be breaking it in tonight......If i can escape the wife for a while.........
Old 03-31-2006, 06:55 PM
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All Saitos didn't have a choke plate in some gap or even a gap. The original 30, 40, 45, 80twin had a clamp on choke that was held by an allen screw. The twin carb 80 and 90 twins didn't have a choke at all. Just my finger.
Old 03-31-2006, 07:31 PM
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Four strokes will often start before the piston gets to top dead center. If so the engine may run backwards.

Not only does it get the intake hot, the plane tries to back away from you.
Old 03-31-2006, 08:37 PM
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At Ford NVH (noise, vibration and harshness) school we played quite a bit with the reed tachs. With carefull adjustment you could isolate Crankshaft and Camshaft freequency, independent cylinder firing and even auxillery frequencies. Interesting thing is that to get a tool that would do everything a $10 Reed Tach, available at any small equipment shop, is capable of, you had to spend thousands from a specialty dealer. Of course the expensive unit would do so much it was silly, and invaluable.

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