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>> Telemetry is now reporting receiver battery voltage, some way of
>> reporting fuel level via telemetry would be good. Pressure transducers?
[quoted text clipped - 15 lines]
>
> Marty
Back in the days of bladder tanks, we used a spring loaded flap that
pressed on the tank. When it moved far enough, it caused a microswitch
to operate.
>>Telemetry is now reporting receiver battery voltage, some way of
>>reporting fuel level via telemetry would be good. Pressure transducers?
[quoted text clipped - 15 lines]
>
> Marty
Marty's way puts less load on the airframe which means better performance
for a given engine.
(so says the guy who puts .32's on .19 sized airframes)
YMMV
>> Telemetry is now reporting receiver battery voltage, some way of
>> reporting fuel level via telemetry would be good. Pressure transducers?
[quoted text clipped - 6 lines]
> I doubt we're going to get it down at our level any time
> soon.
I think a lot of the reason that general aviation planes don't have it
is the shape dictated by wing tanks -- sensing the up/down level of fuel
in a wide, low tank ain't easy.
Our tanks are more square -- but our acceleration vector tends to vary a
lot more unless the flight is very boring.
> You should be able to measure what's in the tank on a few
> test flights, extrapolate to an ounces-per-minute number,
> figure your max endurance, and run a timer.
That only works with a predictable throttle profile (like our club
president, whose throttle positions are "full on", "land" and "shut off").
> That seems a whole lot simpler to me than getting sensors
> inside of a tiny little tank!
If you could think up a small accurate flow meter you could integrate
flow -- but the meter wouldn't be trivial.

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Tim Wescott
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Martin X. Moleski, SJ - 05 Jul 2010 05:06 GMT
>> You should be able to measure what's in the tank on a few
>> test flights, extrapolate to an ounces-per-minute number,
>> figure your max endurance, and run a timer.
>That only works with a predictable throttle profile (like our club
>president, whose throttle positions are "full on", "land" and "shut off").
Well, if you calculate the "full on" endurance, every time
you throttle down, you add to your margin of error.
Landing with too much fuel is not usually as troublesome as
landing deadstick (I know that's not true of full-size
airliners, but at our fuel loads, I think it is a reasonably
accurate statement).
>> That seems a whole lot simpler to me than getting sensors
>> inside of a tiny little tank!
>If you could think up a small accurate flow meter you could integrate
>flow -- but the meter wouldn't be trivial.
I thought about a flow-meter, too. I think the mechanism and wiring
would be vastly simpler and more reliable than gauges in the tank.
If you remember to fill your tank every time and reset the fuel
flow meter, it should be fairly accurate. If you know you have
10 oz of accessible fuel in the tank, when the flow meter says
that you've provided 10 oz to the engine, it's time to land.
Our tank designs are so simple that most installations should
provide the full amount of fuel that the tank is rated for.
But that still seems like too much work for too little gain.
Marty

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Tim Wescott - 05 Jul 2010 07:42 GMT
>>> You should be able to measure what's in the tank on a few
>>> test flights, extrapolate to an ounces-per-minute number,
[quoted text clipped - 28 lines]
>
> But that still seems like too much work for too little gain.
It might make sense if you were doing some serious airplane tuning and
wanted to know if you needed to put in a bigger tank or could put in a
smaller one -- but then, you can do that just by going out and flying,
then measuring how much fuel you had left.

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Tim Wescott
Wescott Design Services
http://www.wescottdesign.com
Do you need to implement control loops in software?
"Applied Control Theory for Embedded Systems" was written for you.
See details at http://www.wescottdesign.com/actfes/actfes.html
Six_O'Clock_High - 05 Jul 2010 22:46 GMT
>>>> You should be able to measure what's in the tank on a few
>>>> test flights, extrapolate to an ounces-per-minute number,
[quoted text clipped - 34 lines]
> smaller one -- but then, you can do that just by going out and flying,
> then measuring how much fuel you had left.
This entire discussion is one of the types of things that keep me active in
my flying community, but more importantly reading here. Where else can you
get into a discussion about how many angels can dance on the head of a pin
and not have hurt feelings running rampant?
Martin X. Moleski, SJ - 08 Jul 2010 13:10 GMT
>> ... that still seems like too much work for too little gain.
>It might make sense if you were doing some serious airplane tuning and
>wanted to know if you needed to put in a bigger tank or could put in a
>smaller one -- but then, you can do that just by going out and flying,
>then measuring how much fuel you had left.
I think that's how Maynard Hill did things.
Over and over and over ...
Amazing man!
Marty

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