Where did all the kits go?

WS = 48 > Definately interested in getting a DWG file.

Can make a dwg of the preliminary file as I have now. Finished plan looks a bit different, like a tapered wing instead of a hershey ba wing, and a full swinging rudder. Like always, a lot of little moddin here and there.

Send me a PM with your e-mail. DWG format is ACAD 2000, or what ca you work with

-- indoruwe

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Thanks mate - very helpful as I was trying to get a good idea of max current the supply needed to be able to put out

David

Branko wrote:

I've been thinking about making up a glow driver circuit - I like the idea of a constant voltage supply, since it would behave like a NiCad driver - it will increase the current if the plug is flooded to help burn off the fuel. Also, an ammeter connected to the supply would give a lot of information about the state of the plug.

However, compared to a simple pulsed 12v supply, a constant-voltage drive is considerably more complex, requiring a DC-DC converter and reference voltage, and will generate considerable EMF which might disturb nearby radios, not the best thing at a flying field really.

What have others done? Would constant voltage be worth the effort?

Ed, I am not sure you are as right as we both wish you were. Let me share with you some comments about discontinued kits I got from Midwest a couple of years ago when I was discussing modifications that needed to be made in the construction manual to make the aircraft a safer model.

The guy I was talking to (on my dime) told me that they sold out of that kit and it would not be offered again. I asked why and what he told me is still rocking my thought processes. He said that the rate of return on the investment for that kit was too low. I did question him in general because the exact numbers were company close held information and he did answer me in general terms. It seems that his company invested $X to kit said airplane. It cost $Y to keep the completed kits on the shelf. When $X+$Y+Profit could not be recovered within an acceptable period of time, that aircraft kit was discontinued. I asked what controlled the process and he replied 'sales rate'.

In short I am afraid that because many are no longer building kits, they may no longer be available in the near future. I wish I knew a way to change that..without making a small fortune in the R/C world. Small fortunes are made in the R/C world from big fortunes...

"Six_O'Clock_High" >> draw the plans myself and kit the bugger. You'd be surprised how

I hear you, Jim. Have you ever noticed how most small businesses have a lifetime, just like we humans?

Midwest was near the top of the heap for a while, then it grew old and faded into the background. Just like RCM and legions of other hobby related businesses.

I understand that no one would be expected to keep producing a product that was not providing sufficient income to justify its existence. After all, the bottom line is profit, as you have pointed out so well.

However, what if the kits begin to trickle in from China? Imagine the low cost and good quality of said kits. It would not surprise me if I learned that some enterprising Chinese entrepreneur has been buying up plans and designs of past favorites. What is not profitable at Midwest, may be very profitable in a Chinese manufacturing environment.

Chinese motorcycles are about to collapse the previously Japanese dominated market paradigm. Some of the Chinese motorcycles are part-for-part clones (Lijan 250cc V-twin of the Yamaha Virago 250cc V-twin) of Japanese motorcycles. The feedback that I have heard so far have been very positive.

We in the US should begin investigating how England survived, more or less intact, its removal from manufacturing dominance a couple of centuries ago. I do not see the trend turning around for us any time soon. By the time it does, the jobs will have moved from the poor folks in South Africa (previously in Bangladesh) to the poor folks in North America. Fortunately, I won't be here to see it. Neither will you.

Ed Cregger

| What have others done? Would constant voltage be worth the effort?

Personally, I don't even think a power panel is worth the effort.

My glow plug driver has a subC cell in it. My electric starter has a battery too. I use a hand powered fuel pump. No power panel.

I can see where only one battery to charge would be convenient, but I don't like the wires -- just something else to get snagged in the prop.

I plan to do some experimenting with modifying one of those car mobile phone power supplies - they can easily be modified to change their output voltage, but am not sure how much current they can handle - but since they are cheap (from the tip) playing will not be expensive.

If all else fails I will build a 'proper' supply as per one of the circuits from the rc circuits sites - high power bits from computer power supplies (again from the tip) might work

I dont know about the interference, but I can check that on the bench, I think

David - who has not much cash, but time to play with stuff

Poxy wrote:

I use a nicad starter normally, but there are 2 situations where it'd be useful to have a 12v-driven one on hand - for when the nicad starter is flat (which seems to happen far too often), and for when you want to diagnose a plug problem without removing the plug. Because the drive voltage is accurately regulated, any change in the plug would be reflected by a change in current draw. For example, a dead plug draws no current, a flooded one draws excessive current, a worn-out one would use less current.

| > I can see where only one battery to charge would be convenient, | > but I don't like the wires -- just something else to get snagged | > in the prop.

Of course, the #1 thing to get snagged in a prop is my fingers/hand, but I digress :)

| I use a nicad starter normally, but there are 2 situations where | it'd be useful to have a 12v-driven one on hand - for when the nicad | starter is flat (which seems to happen far too often)

I keep more than one on hand, which pretty much solves that problem.

| and for when you want to diagnose a plug problem without removing | the plug. Because the drive voltage is accurately regulated,

I'm not so sure it's the voltage, but the duty cycle that's regulated.

| any change in the plug would be reflected by a change in current | draw. For example, a dead plug draws no current, a flooded one draws | excessive current, a worn-out one would use less current.

A worn out one uses the same current. It's not the coil that wears out, it's the catalyst coating that gets fouled.

Not sure about a flooded one, but I'll take your word for it.

Personally, my favorite nicad starter has a current meter built in. The battery has already worn out once, but it wasn't hard to solder in a new one.

I have 2, a new one with a meter in the top, which is nice but my engine is inverted so I can't see it, and one which is about 15 years old and seems to hold its charge better than the new one. That said, I've managed to succeed in having both flat a number of times.

Broadly speaking there are 2 kinds of electronic glow driver, the most common is pulsed 12v where, as you suggest, the amount of current through the plug is governed by the duty cycle of the pulses. However, these are rarely regulated - that is, there is no feedback from the plug that varies the duty cycle. Rather you set a fixed rate.

The other type of driver is what I'm considering. It's a little more sophistcated in that it uses a DC-DC converter to produce a fixed voltage which youy can set, say 1.25v. Using its own accurate voltage reference, it monitors the output voltage and has a feedback loop that varies the duty cycle of the converter to maintain that voltage. Thus, let's say a plug driven at 1.25V draws 2.5A when it's glowing, however, if it beomes flooded, the metal will cool, decreasing its resistance. In an unregulated circuit, this would cause the voltage to drop as the load has increased, however with this circuit, the DC-DC converter will wind upthe duty cycle to maintain

1.25V and the current rises to, say, 4A while the fuel is boiled off, then as soon as the fuel is gone and the plug is glowing again, the circuit drops the duty cycle.

The latter kind is in some ways similar to a simple pulsed 12V supply, but where the pulsed units operate at about 100Hz, DC-DC converters tend to operate in the 100KHz or higher range - some as high as 1MHz leading to issues of RF radiation

You might be right - I always assumed the wire got thinner thus increasing resistance, meaning the plug wouldn't glow as brightly.

I also assumed that glow plug wire was solid platinum, and that was the catalyst?

Not pure platinum. George Aldrich told me the good ones have rhobidium and other precious rare metals.

As for the wear out question, it is not a catalyst issue but a contamination issue that Doug addressed.

"Importing Kits" from China......an interesting concept to say th

least!!!

Jerr

-- tailskid

Been modeling since '49 - which makes me an Old Fart

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Why not? I know it sounds strange because of the current trends, but AK Models said they had some kits for sale. I didn't look any further for them once I saw the Christen Eagle ARF with a fiberglass fuselage.

As we all know, the Chinese, like us, are in it for the money. If they become convinced that there is a market, you can be sure that they will fill the niche'.

Ed Cregger

Thanks for the clarification.

A pulsed system will behave the same way, each pulse will deliver as much more current to a cold plug (proportionally) as would the DC.

When I assembled my driver, it occurred to me that a piezo transducer across the drive transistor or the plug could provide audible feedback, but I haven't tested this idea.

I was inspired to make a pulse driver after seeing a circuit on the WWW. Hint: A.T's site has links to other RC electronics pages. I posted a word picture of my circuit to this news group a couple of years ago, would you like a repost?

I had thought that, although there still would be a slight voltage drop and thus a drop in current, which attracted me to the idea of the precision of a constant voltage circuit. In the latter case, an ammeter would give a very accurate indication of the state of the plug. Of course, that depends on the resolution of the ammeter, and since I was thinking of using a 3914 driving a bunch of LEDs. I guess the resolution isn't going to be that great.

Sure - it'd be great to see what you did. If I went the pulsed route I had planned to use a 555 timer and a mosfet.

| > A worn out one uses the same current. It's not the coil that wears | > out, it's the catalyst coating that gets fouled. | | You might be right - I always assumed the wire got thinner thus increasing | resistance, meaning the plug wouldn't glow as brightly. | | I also assumed that glow plug wire was solid platinum, and that was the | catalyst?

I doubt the wire is (mostly) made of anything special, probably just nichrome.

But the insides of the glow plug, and maybe the wire too, are coated with a material that acts as a catalyst. I think there's some platinum in it, but there's other things too. The wire gets it hot to start out, and the catalyst keeps it hot by making sure that small amounts of fuel keep burning there.

Either part can fail, though usually it's that something happens to the catalyst that stops it from doing it's job. I suspect it been contaminated, but I'm not sure of the specifics.

In any event, the symptoms of that are pretty obvious -- the engine dies as soon as you remove the glow driver, but it works fine up until then.

I doubt the current draw changes at all if the glow plug is fouled our not.

How long do you think it will be before they own us??

Randy Model Airplane Engineering

What do you mean by "before"?

Ed Cregger