Hey guys, my crazy side visited me last night while I slept and
planted a seed. Here is what my alter ego said-
If we are going to end up with a functioning EFI, why not use it to
set the RPM we want like jet engines do? We could have say 3 or 4
detents or set points, WOT, cruise, flight idle and ground idle and
let the engine control the rest of it automatically. No more prop
overspeeds, etc. Set the RPM at 6000, start a climb and the computer
would keep the 6000 by adding more throttle. Start a descent, same
thing but backwards, the EFI would throttle back to keep 6000.
It would require a servo motor on the throttle, and not much else.
The throttle cable could still be there for manual over ride if the
servo motor failed. Kind of like cruise control in cars. Turn it on
and its on, tap the brakes and its off.
Kevin Alderman
Now this sounds like a great idea. A good way to reduce pilot
work load at high load moments.
- Mark LaPierre
I am not building an RV, so flutter is not one of my primary
concerns, but it is always a potential problem. I am building a
composite, and reinforced the dickens out of the tail/ fuselage
intersection and spent way too many hours balancing my control
surfaces. The overspeed (RPM) came from observing students at the
local flight school where I rent planes. I have noticed that quite
a few pilots will overspeed an engine in emergency situations- like
practicing emergency descents- they tend to push the nose down and
then sometime after worrying about Vne figure out that the engine
has passed redline. Not an everyday event, but it does happen in particular
with a carbed Cherokee P28-140, poor abused plane. One student at
the school has locked the brakes twice on this plane on landing and
once on the 172 to the point of blowing out the tires on the runway.
The wheel pants have been gone for a while. Not that this idea
would be for students, but we have the system, all that would be
needed would be a servo motor, a controller and a few more lines of
code. And just like cruise control, any pilot input would over ride
the system.
As I get more toward completion of my toy, I will put some more
thought into this. Since performance will vary with each plane, the
RPM would be programmable by the owner in say 4 places. Pull from
WOT to the first detent and then she goes into flight cruise mode
with auto leaning to a point say 10% rich. You can further lean if
you like, or maybe normal cruise mode would lean to peak EGT after
finding a way to read it. The next detent is cruise descent, the
next could be flight idle. All of this could be managed with
microswitches at the detent points. Spend say 4 seconds at the
detent and the system takes over automatically. Move it from the detent
and its all yours again.
My OCD nature will push this thing straight to a FADEC, so I might
as well look at it this way from the beginning- if the other sensors
aren't there the system can compensate for it and let the pilot do
the leaning, adjustments, etc.
I will keep you posted. In the meantime, throw ideas at me and I
will see how it can go into the system.
KA
I see no reason that an automotive cruise control could be adapted to fly the
planes RPM. You just need to adapt the speedometer cable drive. I forget the
speedo cable RPM at 60MPH. You would want to shoot for that cable RPM for your
flight conditions, 6000RPM. Simple toggle switches for set, resume, increase
and decrease the same as in your car. It is winter now. Probably a good time
to disable your wife's cruise before she hits ice and wrecks the SUV anyway.
OOPs, I think I stepped in it now :-))).
Dale Davies
One of the clues when flying in IMC without a attitude gyro or a failed gyro and
a non constant speed prop is the RPM increases while diving. A good thing
as it helps the pilot to maintain a level attitude.
The early V Tail Doctor Killers (AKA Bonanza) would pick up speed fast
in a dive. (Constant speed prop). The AC was very clean aerodynamically.
Then the aircraft would exceed VNE and the V tail would flutter and come
off. The next thing that would quickly happen is the AC would pitch down to
90 degrees. The CG was well forward of the center of lift. This is normal but
the down force on the tail normally holds the nose up. The G forces
were enormous. This would severely overload the wing spar causing aircraft
break up. The high G forces on the people inside probably spit them out through
the cabin roof.
The wing area is 177 square feet. Dynamic pressure at 250 MPH is
160 pounds per square foot. That is a down force on the wings of
28,000 pounds. About 9.6 G's. The seat belts or seat mounting probably
could not stand 9.6 G's.
Beech Craft eventually figured it out and retrofitted a tail beef up.
http://www.tsgc.utexas.edu/archive/general/ethics/vtail.html
Paul Lamar
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