Why two needle valves working in unison?
I suspect your missing the function of the needle valve.
It is only a fine adjustment on the mixture. One will do.
You can use two (one per rotor) but they must be individually
adjustable.
The slide in the slide throttle does the gross adjustment
to the amount of fuel as a function of the area of the
slide opening.
--
Paul Lamar ...No rotor no motor.
Paul
This valve idea I sent was more in responding to Gordon's post on the
Constant Flow Fuel Injection post thread about a separate injection
system
but could also be be incorporated into your slide throttle.
As you have modeled the slide throttle, getting fuel to flow evenly
to the
separate ports will be challenging to say the least. To assure this,
both
passages from the point the fuel leaves the singular valve port must
have
the same dimensions, lengths, bends etc. Hence two needle valves,
each one
dedicated to a port on your slide throttle. IMHO the brilliant part of
slide throttle fuel delivery system is that fact that you have in
essence a
variable size orifice system. I believe this was your original
design. Say
at any time at least one jet and sometimes two opened. This allows
you to
drill progressively bigger holes. I am not sure how this will be
accomplished yet but the idea has lots of promise.
Perhaps the double needle valve has a use in Gordons' way as well.
Bear with
me a moment and lets examine this half baked midnight madness idea.
Gordon introduced a system that seems interesting and had many variables
introduced into managing fuel flow. The device he showed had a mechanism
that bypassed unneeded fuel through one of eight selected orifices thus
controlling the pressure and flow on the system. It seemed
complicated in
the plumbing and because engine rpm and pump flow curves are never very
linear. In essence the multi-orifice valve becomes a little pressure
accumulator and the outlet orifices are part of by pass system.
One needle valve could do the same thing as well.
Background thinking:
As you might know, with the SeaWind, the standard LycCon engine
mounted fuel
pump can not pull the fuel ten feet in length and six feet in
elevation when
the airplane climbs to over 8,000' The system therefore needs a altitude
electric boost pump. Correct me if I am wrong but any mechanical
based fuel
delivery system is going to have to be a back-up low altitude unit
to keep
my feet dry :)
Hence high altitude flight depends on having electricity for me. If the
mechanical pump was served by an electrical booster pump then electrical
failure mode would mean a decent to under 8,000'. The mechanical pump
feeding constant flow, high pressure mechanical injectors could possible
operate with some sort of mechanical by pass valve. If you mechanically
adjust the setting of this valve (actually a screw adjusting spring
pressure) in essence vary the outlet line pressure and hence the flow
quantity. It becomes a fuel throttle.
Said another way the mechanical pump is over sized but reacts to
pressure
head and by passes fuel from the outlet side back to the inlet side
essentially unloading the pump a bit and eliminating the need of a
return
line. Nothing new here folks. Similar systems are usually built into the
carb. as a float (flow) or as a pressure regulator in Ellison I
suppose. It
doesn't have to be though.
I think the ultimate efficient setup would be to have the electrical
fuel
pump, small pressure tank and the pressure regulator installed in or
around
the vicinity of the header tank. A analogous system would be how
portable
air compressors or home water well pressurized systems work.
The pressure tank needs a sensor which tells the electric pump to
turn on
and run until the fuel volume and pressure in the pressure tank
reaches a
preset value. The pump doesn't run when there is no demand for fuel
hence
the line pressure after the regulator remains low. In this case the fuel
pressure regulator is separate from the air throttle and can be linked
electronically or mechanically.
Perhaps for me a combination would work the best. That is a electrically
driven pump/pressure tank, with cut off sensor supplying the mechanical
engine driven pump. This way the engine mechanical pump could be biased
towards output pressure.
Darn now where did I file the picture of the 300hp P port racing
engine with
the mechanical fuel pump and injectors spraying into the bell mouths?
Doug Fir
---------------------------------------------------------
"As you have modeled the slide throttle, getting fuel to flow
evenly to the separate ports will be challenging to say the least."
Not true if you use two separate leaning valves as I have already
suggested several times.
In fact you may not want to have fuel to flow evenly to the
separate ports. What you want is the RIGHT amount of fuel
to flow to each rotor depending on the individual characteristics
of each rotor. Typically the EGT's are not the same due to
many factors in most A/C installations. This is also true
for most EFI systems.
Yes the holes can be tailored but probably unnecessary as
the latest design uses many holes of the same size. More and more
are connected as the slide is opened. I have updated the
web site with the new design.
http://www.rotaryeng.net/bunch-of-holes-SLT.jpg
http://www.rotaryeng.net/bunch-of-holes-SLT2.jpg
http://www.rotaryeng.net/spacer-slot-detail.jpg
Your needles are too short for a typical 3 inch travel leaning
cable and rapid control. The advantage to the vernier AND three inch
travel needles is you can make rapid gross changes or cut off the
fuel completely by pushing or pulling the knob.
Twisting the knob gives a fine mixture adjustment. You set the
mixture full rich for starting and you shut off the fuel supply
for stopping the engine. Just like any Cessna.
Your approach is way more costly. By using SS tubing and SS jic
1/8th plumbing fittings the cost of my needle valves can be just
a few dollars using only a lathe to cut the needles.
Mechanical rotary fuel pumps are expensive and they must be driven
somehow from the engine with the proper gearing.
To implement a simple, low cost, low pressure system you have a
high tail that you could put a sump tank in with a stand pipe in
it that would return excess fuel to the main tank as in this
Aerocarb diagram. Use one or more cheap Facit electric boost pumps
to keep
the sump tank full. A hand wobble pump would work in an emergency.
If the vents in your main tanks point forward they too could
provide dynamic pressure to help transfer fuel up to the sump tank.
The old air cooled VW bug used a similar stand pipe in the main
fuel tank. When the fuel level got below the top of the stand
pipe you switched over to another reserve line plumbed to the
bottom of the main tank.
I can sympathize with you on why you want a fly by wire system on
the remotely mounted engine on a SeaWind but even a
B747 uses steel throttle cables. BTW UAL had a cowl come off
an Airbus at LAX on take off. When the cowl departed it
took the fly by wire throttle control with it. The pilot
had to cut the fuel supply to the engine to shut it down
so he could land.
The picture you speak of is on the web site.
http://www.rotaryeng.net/mech-fuel.html
--
Paul Lamar ...No rotor no motor.
Doug and Paul,
The idea behind the flywheel magneto and constant flow fuel
injection is to apply the design philosophy behind the piston
aircraft engine -- very simple and reliable fuel and ignition
system that will keep working as long as the engine is turning.
In other words, it would take a catastrophic structural failure to
stop the engine -- such as a broken crankshaft, dropped valve, blown
cylinder, or thrown rod.
In fact such big structural failures happen more frequently than
failure of the magnetos or carb/fuel injection in aircraft engines.
This tells us how successful this design approach is. The weak link
is the actual piston engine structure. With the rotary, engine
structure is much stronger and potentially break-proof.
So if we take the very high-reliability fuel and ignition form the
piston engine and combine it with the very high structural
reliability of the rotary engine, we have a better mousetrap.
With a flywheel magneto and a carb or simple contstant flow
injection, the only thing that will stop a rotary engine is some
kind of catastrophic structural failure. Barring that, as long as
the engine turns, you will have fuel and spark. This is a very
pragmatic and powerful design philosophy for an aircraft engine.
When you have ignition and fuel dependent on electrical system, you
have a whole bunch of failure points. The alternator, the alternator
belt or pulleys, wiring, connectors, switches, engine computers,
ingition controllers and on and on. It does not take a genius to see
that there are many more things that can go worng.
In fact when things do go wrong with auto engines in airplanes it is
with little things like wiring, connectors and such. A simple bad
wire connection or bad switch can stop your airplane engine dead at
the worst possible time.
Most of us look at today's computer-controlled car engines and see
great reliability. This is very true. Al Wick who flies a
Subaru-powered Cozy has done a good study of Subaru car failures
using empirical repair data and found that the reliability of the
engines and electronics is very high, with mean times between
failure of many thousands of miles driven.
This is all well and good. A late model car engine can work just as
reliably in an airplane if we limit our airplane use to taxiing it
around the airport. But as soon as we leave the ground, we are
operating in different kinds of conditions. The atmosphere is much
different even at 10,000 feet than it is at sea level.
That is not to say that stock auto engines can't work. They can. Al
Wick has had very good reliability using the completely stock Subaru
engine, with just a redrive on it. Not conicidentally, the only
problems he ever had was with the redrive.
My own view is that I would go either with a completely stock late
model engine, with the stock computer, EFI, ignition, etc and impose
a reasonable ceiling of about 10,000 feet. Use this in a design with
low landing speeds to make off-airport landings more survivable.
The other choice for me is to come up with a flywheel magneto and
carb or constant flow injection. Provided those systems are designed
and fabricated properly, it could be a great aircraft engine.
But creating a hybrid between the two is where I see problems. Look
at the EFI injectors, for instance. Do we even know how their
operation is affected by altitude? Or the engine computer?
We talk regularly here about turbocharging and turbocompounding and
flying at 15,000 and 20,000 feet. In an engine that relies
completely on electronics I would feel much better if I knew
positively that those electronics work reliably at the temperatures
and pressures we see at those altitudes.
As far as I know nobody has ever carried out such tests. So when you
start flying such an airplane you are the test pilot.
The other issue with a lot of electronics is in-flight ememrgency
procedures. Complex systems have complex troubleshooting procedures.
Again, look at piston airplanes. If there is a problem with the
engine, the procedures are pretty straightforward: cycle the magneto
switch, fuel boost pump, check for carb heat, fuel selector valve, etc.
Now when you have a lot of electronics, how do you come up with
emergency procedures for an engine out? Since you are the designer
of the plane, you have to come up with those procedures.
The turth is, most people don't even think about coming up with a
procedure. So what happens, worst-case, if you are in IMC and you
have an engine-out? Do you start just madly flailing about, flipping
switches and pressing buttons? That's when you realize that all of
those electronic gizmos that your engine relies on to keep running
could be a liability.
Regards,
Gordon.
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