Standby vacuum recommendation needed
Harvey M. Spencer
System that taps off of the engine manifold and has a t-fitting to switch
from the engine driven vacuum pump to the standby one. I know I will have to
reduce throttle at altitude to maintain an adequate vacuum differential. Does
anyone know how many RPM (approx) I would be carrying with a fixed pitch prop
and Lycoming O320 150HP engine that I have at say 5000 feet to yield enough
vacuum? Would I be able to maintain altitude? How about the service ceiling
for maintaining vacuum? If anyone has actually installed and used this system
I would like to hear your experiences. It seems good insurance at about $300.00.
Craig Wall
>
>I fly my Glasair IFR frequently.
(engine plumbing described)
>It seems good insurance at about $300.00.
Why don't you install a relief tube with a venturi
strong enough to run a gyro? Then all ya gotta do
if the pump goes Tango Uniform is yank a hose off
one thing and plug it into something else...
Craig (...simplicate and ...nevermind....) Wall
(Sell ya one for $299.95. The installation doesn't
involve drilling holes in yer engine...and you
can *Pee* in it, if you get the urge...)
(I mean it wouldn't have to be _very_ big on a high
speed lead sled like a Glasair, now *would* it?...
the venturi, I mean...and you could even retract it.)
myc...@clark.net
>I've been waiting for this thread!
>
>Why hasn't anybody stuffed a venturi up an exhaust stack? You'd have high
>velocity gases that should create enough vacuumn to suck the chrome off a
>trailer hitch. As long as your engine's running, you wouldn't have to worry
>about icing on the venturi either.If you're IFR and no engine you probably
>won't be wondering if your venturi was going to ice up.
Why not. The same trick has been used in reverse to augment cooling in some
aircraft like the Apache 160's. Except there the exhaust was fed through the
center to draw the air along.
Even though I depend on Bernouli to keep me in the air I don't know I
would want to use a relief tube hooked to this arangement.
On the more serious side wouldn't making a venturi that could consistently
handle exhaust gas temperatures and wouldn't corrode quickly be a bit
expensive?
Mike Bevan CP CFI etc.
John Burnaby
Craig Wall
>
>Even though I depend on Bernouli to keep me in the air I don't know I
>would want to use a relief tube hooked to this arangement.
Uh, noooo....Mike- you don't hook the *relief* tube to the gyro;
you unhook it and connect the *venturi* to the gyro. *It* sucks,
and then like a good CFI you can call ATC on the relief tube...
and let the *venturi* do the work.
(*sheesh*)
Craig (I mean, on a Glasaire the venturi would be less than an inch
in diameter- you could make it out of stainless steel.) Wall
myc...@clark.net
>In article <48nonh$h...@clark.net>, myc...@clark.net says...
>
>>
>>Even though I depend on Bernouli to keep me in the air I don't know I
>>would want to use a relief tube hooked to this arangement.
>
>
> Uh, noooo....Mike- you don't hook the *relief* tube to the gyro;
> you unhook it and connect the *venturi* to the gyro. *It* sucks,
> and then like a good CFI you can call ATC on the relief tube...
> and let the *venturi* do the work.
>
>
I hope I'm not starting a flame war, but I just meant that I didn't know
I would want to have a relief tube hooked into my exhaust, independent
of it's use as an emergency vacuum system. I have no desire to do
anything risking getting corrosive fluids into my gyros.
Mike (Not wanting to expose delicate parts of my anatomy to hot exhaust)
Bevan :-)
sl...@ebtech.net
Most likely because of the back pressure inside the exhaust system
would counteract the venturi's suction. Unless your running a tuned
cross-over exhaust, with little or no back pressure. But you would
definately lose performance by stuffing a ventury up your
stack.(exhaust stack, that is)
I have had a vaccum pump give-up on me. I continued on, IFR, with the
other instruments. (Remember that partial panel training when you went
after the IFR ticket?)
Marc Rodstein
says...
Attitude Indicator. They cost about $1300, though, and you need
a free hole to put them in your panel.
A chepaer way is the Precise Flight system that uses engine
vaccum and sells for about $400, but this system requires that
you use reduced engine power above 2000 or 3000 feet of
altitude, in order to produce enough vaccum.
--
Marc Rodstein
Boca Raton, Florida
stephen j beaver
>In article <48j6m0$6...@sun2.ccf.swri.edu>, cw...@swri.edu (Craig Wall) says:
>>
>>In article <48j4n9$6...@hacgate2.hac.com>, hspe...@igate1.hac.com says...
>>>
>>>I fly my Glasair IFR frequently.
>>
>>(engine plumbing described)
>>
>Why hasn't anybody stuffed a venturi up an exhaust stack? You'd have high
>velocity gases that should create enough vacuumn to suck the chrome off a
>trailer hitch. As long as your engine's running, you wouldn't have to worry
>about icing on the venturi either.If you're IFR and no engine you probably
>won't be wondering if your venturi was going to ice up.
Once apon a time, I had a Navion with an E225 engine and no vaccum pump or
provision for the installation thereof. It's instruments were venturi powered and I
wanted to fly it IFR. One day, I saw an item in the aviation consumer about a standby
vaccum system which had been developed for early Bonanzas (which the same problem)
Although the system was only STC'd for the Bonanza, I had no trouble getting field
aproval (337) for the NAvion. I think the system was (is) called the AutoVac IV.
In the magazine, it said that the developer had wanted to certify a simple manifold vaccum
adapter, an external venturi and an automatic change-over switch but the FEDs objected
because if the venturi failed because of ice, a person might need full power to overcome
the effect of airframe ice and at full engine power there would be no manifold vaccum to use.
Next, it said, he wanted to put the venturi in line astern with the exhaust to keep it warm but
again it was nixed, I think because icing might cause the engine to stop and remove the
source of heat.
The product that was finally certified and which I installed and used for several years was
an electrically heated verturi, a manifold adapter and a pressure switch.
The pneumatic switch automatically selected the source with the most suck and
illuminated a light to tell you what was happening. The heater could be turned on manually
from a switch in the cockpit. All this resulted in a dual redundant vaccum system with no
moving parts which provided all the suck a person could want in any amaginable
circumstance.
Finally, how about this for an idea (especially for a Glassair). Why not build into the cowl,
just ahead of the firewall, a flush venturi. This could be made (I should think) by placing
two NACA fluch inlets back to back, one to accelerate the air and produce the vaccum,
the other to deccelerate it. This should produce enough vaccum, be of very low drag
and be kept warm enough by radiated engine heat. What do you think?
Steve
Sven Jerlhagen AR/AF Soft Support
>
> I am thinking of installing the Standby Vacuum
The answer can be had by looking at your manifold pressure gauge.
If you don't have one, install one temporarily.
Another idea is a venturi on a gear leg. No additional drag
when retracted, extend the gear when the vacuum pump fails.
/Sven Jerlhagen
Craig Wall
>Another idea is a venturi on a gear leg. No additional drag
>when retracted, extend the gear when the vacuum pump fails.
>
Or when you have to go to the bathroom...
Craig Wall
.
Craig Wall
That's hilarious, Mike. I concede. Bwahahaha!!!
Craig
.