Flying on the Cheap - Instruments

Richard Riley wrote:
RS, it pleases me greatly when I find I've come to the same conclusions
as you.

I'm just finishing work on a cheap slow flier. It's a departure from
standard, at least for the wing, so I've overengineered the safety side
(BRS, 5 point harness and a pilot's parachute). But for
instrumentation, I'm minimal. Handheld GPS and com (since I'm in the
busy traffic of So Cal, I'm addicted to com)

EGT and CHT for the single cylender 2 stroke. RPM. Fuel level is
visible. Altimiter - So I can get a good idea of rate of climb.
Airspeed is a plastic tube with a red plastick floatie disk. That's
it.

OTOH, I have the Uber Panel in the expensive fast flier. Two missions,
two solutions.


I guess I'm a hard headed old coot. (well, DuH!)
I simply won't fly a two-stroke without an EGT.

Problem, though, is that the EGT runs so (you favorite explicative) high
anyway that a micro seizure can put it over the limit in a mater of seconds.
You'd almost have to be staring at it to notice a needle or two width jump.
Specially on the little 2: gauges with a short swing!

I've always wanted to ask Jim if there was a simple circuit that could
monitor the EGT and notice the RATE of increase that would indicate a pending
problem rather that an already existing one. Maybe blink a light, ring a
bell, or apply electric shock as needed?

Jim, anything in you S&M cap that might work here?

Rich(OUCH)ard

Sadism & Machochism?

The problem resolves itself to dicking around with a thermocouple probe that
puts out millivolts and then picking out the microvolt rise that indicates a
rate increase. Can it be done? Sure. Easily? Perhaps. Trivially?
Probably not.

The second problem, generated by the first, is simulating such a rise and
setting the trigger in the simulation. I'm presuming that you don't want to
sacrifice an engine to calibrate the rascal. Then the question becomes,
what rate do you want to trigger? One degree a second? Ten? A hundred?
Or what rise over what time are you interested in?

Form the problem and I'll try and come up with a solution.

Jim


I've always wanted to ask Jim if there was a simple circuit that could
monitor the EGT and notice the RATE of increase that would indicate a
pending
problem rather that an already existing one. Maybe blink a light, ring a
bell, or apply electric shock as needed?

Jim, anything in you S&M cap that might work here?

Rich(OUCH)ard

RST Engineering wrote:

Sadism & Machochism?

The problem resolves itself to dicking around with a thermocouple probe that
puts out millivolts and then picking out the microvolt rise that indicates a
rate increase. Can it be done? Sure. Easily? Perhaps. Trivially?
Probably not.

The second problem, generated by the first, is simulating such a rise and
setting the trigger in the simulation. I'm presuming that you don't want to
sacrifice an engine to calibrate the rascal. Then the question becomes,
what rate do you want to trigger? One degree a second? Ten? A hundred?
Or what rise over what time are you interested in?

Form the problem and I'll try and come up with a solution.

Jim


I see your point, Jim.
I guess the "rate" suggestion is a non-starter as it would also likely vary
considerably between engine types.

Dropping that one and looking at it as a max limit indicator would still
require rather delicate calibration, but would it be more do-able then?

The Leaf catalog doesn't mention EGT limits for the Rotax engines.
I would think a trip point just below MAX EGT (~1100 ~1200 degrees F).

There is also the issue of how and where the EGT probes are installed.
A little closer to the exhaust port will read higher and vice versa.

I dunno, Jim. I'd really like to have something like this (that works!),
but maybe I'm asking for too much?

Richard



There's been a lot of "strangeness" on the net the last few days.
Lot's of 404s and "cannot decrypt document" errors.
Is it me, or the weather still causing problems?

But this one did work...582 max egt = 1200F
FilePath=upload/techdocs/2004611123380.HM11_2.pdf

In article . net,
Richard Lamb wrote:



I dunno, Jim. I'd really like to have something like this (that works!),
but maybe I'm asking for too much?

Richard



When recumbent bike guy was in here, we talked about curing ovens for
composites, and that brought up temperature control units. Those things
use rate of change to avoid temperature overshoot by scaling back power
as the set point is approached.

You do something analogous to this every time you take your foot off the
gas and then begin to brake gently, as you approach a stop sign.

But, the point is, I think you might be able to find an off the shelf
solution. There's nothing terribly sophisticated about a speedometer. In
this case, you want to measure something like degrees per minute instead
of miles per hour.

You mean something like this?
Cabelas.com Item # :IG-521411 or
jcwhitney.com # ZX133955X

Smitty Two wrote:

In article . net,
Richard Lamb wrote:



I dunno, Jim. I'd really like to have something like this (that works!),
but maybe I'm asking for too much?

Richard




When recumbent bike guy was in here, we talked about curing ovens for
composites, and that brought up temperature control units. Those things
use rate of change to avoid temperature overshoot by scaling back power
as the set point is approached.

You do something analogous to this every time you take your foot off the
gas and then begin to brake gently, as you approach a stop sign.

But, the point is, I think you might be able to find an off the shelf
solution. There's nothing terribly sophisticated about a speedometer. In
this case, you want to measure something like degrees per minute instead
of miles per hour.

Good example, but WAY more involved here.

I've fooled around with it some myself, but my experience is in logic design,
not the weird and wonderful world of analog electronics.

Jim's point (as I read it) was that we'd have to notice (and react to) a few
microvolts change - per second - (the RATE question).

But how many mV per second would be considered a threatening situation?
(i.e.: how many degrees per second)

In the automobile example the question might be framed, "What rate of closure
would prompt you to lift the gas pedal and apply the brakes?".

Answer - Depends on how close you are to the thing in front of you.

Jim's response was
It seems like a fairly simple request on the surface, but too many undefined
variables for a simple answer.

There is going to be a bit of research involved before this one can be worked
out.

Richard

My ex has a cute "old saying" that she came up with.

"Two weeks in the lab will save you three days in the library
every time".

In article et,
Richard Lamb wrote:



When recumbent bike guy was in here, we talked about curing ovens for
composites, and that brought up temperature control units. Those things
use rate of change to avoid temperature overshoot by scaling back power
as the set point is approached.

You do something analogous to this every time you take your foot off the
gas and then begin to brake gently, as you approach a stop sign.

But, the point is, I think you might be able to find an off the shelf
solution. There's nothing terribly sophisticated about a speedometer. In
this case, you want to measure something like degrees per minute instead
of miles per hour.

Good example, but WAY more involved here.

I've fooled around with it some myself, but my experience is in logic design,
not the weird and wonderful world of analog electronics.

Jim's point (as I read it) was that we'd have to notice (and react to) a few
microvolts change - per second - (the RATE question).

But how many mV per second would be considered a threatening situation?
(i.e.: how many degrees per second)

In the automobile example the question might be framed, "What rate of closure
would prompt you to lift the gas pedal and apply the brakes?".

Answer - Depends on how close you are to the thing in front of you.

Jim's response was
It seems like a fairly simple request on the surface, but too many undefined
variables for a simple answer.

There is going to be a bit of research involved before this one can be worked
out.

Richard

My ex has a cute "old saying" that she came up with.

"Two weeks in the lab will save you three days in the library
every time".

Richard,

If it helps you to see this as a very difficult challenge, then go
ahead. I know what the "H" in RAH stands for, but if designing your own
circuit from discrete transistors that you've carved out of wood is
beyond your interest, then why not look around for a plug 'n' play
option? Have you *really* already done that and come up empty handed?
I've got a shelf full of catalogs of temperature control hardware. I
haven't actually looked for one with a rate alarm option, but since rate
is monitored and used by the controller, I don't see why someone
wouldn't offer such an alarm as an option.

If it helps you to see this as a very difficult challenge, then go
ahead. I know what the "H" in RAH stands for, but if designing your own
circuit from discrete transistors that you've carved out of wood is
beyond your interest, then why not look around for a plug 'n' play
option? Have you *really* already done that and come up empty handed?
I've got a shelf full of catalogs of temperature control hardware. I
haven't actually looked for one with a rate alarm option, but since rate
is monitored and used by the controller, I don't see why someone
wouldn't offer such an alarm as an option.

Ok, Smitty.

Nope, not at all interested in carving transistors out of wood.

Since you have all the catalogs, my suggestion is to "go for it".

When you are all done, we can compare "budgets" and judge accordingly.
Budgets?

First, obviously, would be cost.
I'm pretty sure, should he decide to bite, Jim's solution would come in
for under 50 bucks.

Power budget?
We can assume we have a 12 volt DC electrical system. How many amps
will you need? Jim probably wouldn't need over 100 mA or so, if that.

Weight budget? (Oh Sh*t, not that again!)
What say, Jim? 3 or 4 ounces?

And then come the electrical issues!

It's a thermocouple. Output is in the millivolt range.
AND, to monitor RATE of change over a very short time (seconds) we'd
have to get down to the microvolt level!

To be able to use that, it will have to be scaled up - gain of roughly
one million or more? No freakin' way *I* would try that with desecrate
(or even wooden) transistors.

Again, it's a thermocouple!
How do you propose to "interface" to it? Single side ain't gonna get it.
You would wind up amplifying the noise as much or more than the signal!
Differential low noise high gain op amp seem to be the best solution here.

Nope, this simple circuit is way beyond anything this ol' logic mechanic
would be able to do. And, not ashamed to admit it, either.

So, let's see whatcha got there Smitty?

Richard

RST Engineering wrote:
Sadism & Machochism?

The problem resolves itself to dicking around with a thermocouple probe that
puts out millivolts and then picking out the microvolt rise that indicates a
rate increase. Can it be done? Sure. Easily? Perhaps. Trivially?
Probably not.

The second problem, generated by the first, is simulating such a rise and
setting the trigger in the simulation. I'm presuming that you don't want to
sacrifice an engine to calibrate the rascal. Then the question becomes,
what rate do you want to trigger? One degree a second? Ten? A hundred?
Or what rise over what time are you interested in?

Form the problem and I'll try and come up with a solution.

Jim

Tie the engine temp to a flashing LED or maybe an audible beep. Rate of
flash/beep increases as temp rises. Thing goes crazy as it's warming
up, but a button allows you to set the "this is good" steady state. If
the temp rises after that, the beeping/flashing starts going again.
Maybe the pilot wants to just shut it off again...maybe he decides that
danger is clear and present.

--
This is by far the hardest lesson about freedom. It goes against
instinct, and morality, to just sit back and watch people make
mistakes. We want to help them, which means control them and their
decisions, but in doing so we actually hurt them (and ourselves)."

Richard Lamb wrote:


I've always wanted to ask Jim if there was a simple circuit that could
monitor the EGT and notice the RATE of increase that would indicate a
pending
problem rather that an already existing one. Maybe blink a light, ring a
bell, or apply electric shock as needed?

Rich(OUCH)ard

That electric shock might be a good last warning that you are about
to land wheels up. Just short one of the magnetos to a plate under
the pilots seat until the revs increase, or the wheels come down ;-)

For those that argue that you might be purposely landing wheels up,
I'd add that it would be a good reminder to kill the engine before
attempting a belly landing ;-)

Don W.