Fuel dump switch in homebuilt

On 1 Dec 2003 02:55:01 GMT, Del Rawlins
wrote:

On 30 Nov 2003 01:49 PM, Jay posted the following:
After reading some of the transcripts from the "Last Words" website,
where the flight engineers were dumping fuel when it became evident
that an emergecy landing was a certainty, it dawned on me that there
might be some benefit for a small plane as well. The less energy you
carry into a crash landing the better off you're going to be.

If you are making an emergency landing in a small plane, chances are
that you don't have any fuel left on board to dump.

Well... as far as homebuilts are concerned, fuel exhaustion (defined as the
pilot running the airplane out of fuel) plays only a minor role in the
overall accident rate. During 1998-2000, only 4.5% of all homebuilt
accidents involved fuel exhaustion (including some accidents that occurred
during precautionary landings due to a low fuel state).

Ron Wanttaja

"Kevin Horton" wrote ...
The higher speed also gives more lift, and the lift to drag ratio (and
hence the glide ratio) remains the same. This assumes that both
conditions are at the same angle of attack, and the the changes in
Reynolds number and Mach number don't change the airfoils CL and/or CD.
This should not be a problem with typical light aircraft at their best
glide speeds at typical light aircraft altitudes.

You're ignoring aeroelastic effects. Some of the plastic airplanes can bend
quite a bit.

Rich

On 30 Nov 2003 14:49:37 -0800, (Jay) wrote:



Maybe a fuel selector switch that ports to a low pressure area near
the tail would act as a light weight solution to draw out the fuel
from the tanks. A safety wire that would have to be broken would be a
good idea so it isn't accentally selected. Like the WEP setting on
the WW2 fighters with water injection.

Jay I have thought about this myself in view of the astronaut doctor
and pilot owner who died from burns learning to fly my type of
aircraft.

in reality though, if you weigh up the situation in a balanced way,
you are far better leaving off the contraption, having a simpler
lighter aircraft and spending all of your efforts in preventative
maintenance.

with good maintenance and considerate operation by the pilot any
certified aircraft engine will run way beyond it's tbo.

if you fly as often as the finances will allow, your skills will keep
you from ending up in the situation where fuel would need to be
dumped.

Stealth ( I didnt fit one) Pilot
Australia

You are correct sir, I didn't include the constant because I was
concentrating what the relative benefit of changing the factors of the
expresion rather than calculating the absolute energy. Maybe I should
have said the energy was directly proportional to mv^2.

And I'd like to hear some other possible light weight implementations
or examples in place today. The solution I suggested adds another
port on the fuel selector valve, and a piece of plastic tubing to the
low pressure port.

"Toks Desalu" wrote in message news:vGwyb.263612$mZ5.1937460@attbi_s54...
" since KE is mv^2, .

Small correction: KE is (1/2 mv^2)

Ron Wanttaja writes:

If you are making an emergency landing in a small plane, chances are
that you don't have any fuel left on board to dump.

Well... as far as homebuilts are concerned, fuel exhaustion (defined as the
pilot running the airplane out of fuel) plays only a minor role in the
overall accident rate. During 1998-2000, only 4.5% of all homebuilt
accidents involved fuel exhaustion (including some accidents that occurred
during precautionary landings due to a low fuel state).

How many of "all homebuilt accidents" involved an "emergency landing"?
(I don't think we mean "landing" to include "falling to earth in pieces".)

BTW, do any homebuilts use easily-sheared tip-tanks (like some Cessnas and
Lears do)?

--kyler

Earlier, (Jay) wrote:

...The solution I suggested adds
another port on the fuel selector valve,
and a piece of plastic tubing to the
low pressure port.

Well, even with a bit of help from a low-pressure area, you're going
to need additional pumping capacity to get the fuel overboard in a
reasonable amount of time.

According to _Firewall Forward_, FAR part 23 guidelines specify that
pumped fuel system be capable of delivering 125% of the takeoff power
fuel flow, and gravity flow systems 150%. That's open-port flow with
zero backpressure.

For example:

Say you're using a 180 h.p. or so motor that draws 18 gallons per hour
at max takeoff power (let's say). The most you can expect the
appropriately-sized fuel pump to move is about 25 gallons per hour.

But, more likely, you haven't got an hour. The vast majority of
concievable small aircraft emergencies are likely to be over in 15
minutes or less. That means you only have time to send 25/4 or about
6.25 gallons (37.5 lbs) of fuel overboard.

And that's if the pump runs wide open at the outlet. With any
substantial backpressure, the flow rates will be much lower. And you
might happen to need some of that pressure to apply fuel pressure to
the engine fuel system inlet. I suppose that you could add a rate
restrictor to the overboard port, so that fuel pressure is maintained
even while dumping. But that's going to cut the dump rate
substantially.

Of course, both of these points can be easily addressed. You can add a
separate dumping pump just to pump fuel overboard, and you can size it
to achieve the desired rates. You can also give the pump its own fuel
supply and overboard plumbing, again sized for the desired dump rate.
You can even plumb the dump system with a standpipe so you can't
inadvertantly run the tanks completely dry with it.

However, that pump weighs something, and the fuel, electrical, and
mechanical connections that service it also weigh something. And when
you add up all that weight, it is substantial, and it will have a
measurably deleterious effect on takeoff, cruise, and landing
performance. It also adds many points of potential failure, both
mechanical and human. And for those accidents caused by fuel
exhaustion (a big slice of the pie), it means that the airplane hits
the ground with more weight and energy, not less.

What you end up with is a compromise that balances constant and
measurable penalties (weight and complexity) against hypothetical
gains (safety).

Thanks, and best regards to all

Bob K.

On Mon, 01 Dec 2003 20:09:35 GMT, Kyler Laird
wrote:

Ron Wanttaja writes:

Well... as far as homebuilts are concerned, fuel exhaustion (defined as the
pilot running the airplane out of fuel) plays only a minor role in the
overall accident rate. During 1998-2000, only 4.5% of all homebuilt
accidents involved fuel exhaustion (including some accidents that occurred
during precautionary landings due to a low fuel state).

How many of "all homebuilt accidents" involved an "emergency landing"?
(I don't think we mean "landing" to include "falling to earth in pieces".)

About 20% of the homebuilt accidents in that period involved a loss of
power due to mechanical failure of the engine or fuel system (vs. pilot
mismanagement of fuel or power system). About 15% engine related, about 5%
fuel-system related.

BTW, do any homebuilts use easily-sheared tip-tanks (like some Cessnas and
Lears do)?

Closest thing I'm aware of is the droppable fuel tank used in the O'Neill
Magnum...

Ron Wanttaja

On 01 Dec 2003 06:07 PM, Ron Wanttaja posted the following:
On Mon, 01 Dec 2003 20:09:35 GMT, Kyler Laird
wrote:

Ron Wanttaja writes:

Well... as far as homebuilts are concerned, fuel exhaustion (defined
as the pilot running the airplane out of fuel) plays only a minor
role in the overall accident rate. During 1998-2000, only 4.5% of
all homebuilt accidents involved fuel exhaustion (including some
accidents that occurred during precautionary landings due to a low
fuel state).

How many of "all homebuilt accidents" involved an "emergency landing"?
(I don't think we mean "landing" to include "falling to earth in
pieces".)

About 20% of the homebuilt accidents in that period involved a loss of
power due to mechanical failure of the engine or fuel system (vs.
pilot mismanagement of fuel or power system). About 15% engine
related, about 5% fuel-system related.

Is "running out of gas' considered pilot mismanagement of the fuel
system in the accident report data? Also, I realize that the accident
data is what you have available, but data showing the causes for forced
landings (which may not necessarily generate an accident report) might
be more appropriate.

----------------------------------------------------
Del Rawlins-
Remove _kills_spammers_ to reply via email.
Unofficial Bearhawk FAQ website:
http://www.rawlinsbrothers.org/bhfaq/

BTW, do any homebuilts use easily-sheared tip-tanks (like some Cessnas and
Lears do)?

Easily sheared Cessna tip tanks, like on a twin? Don't think the
accidents show that those shear... what's your source?

thanks

Ed Wischmeyer

On 2 Dec 2003 03:31:39 GMT, Del Rawlins
wrote:

How many of "all homebuilt accidents" involved an "emergency landing"?
(I don't think we mean "landing" to include "falling to earth in
pieces".)

About 20% of the homebuilt accidents in that period involved a loss of
power due to mechanical failure of the engine or fuel system (vs.
pilot mismanagement of fuel or power system). About 15% engine
related, about 5% fuel-system related.

Is "running out of gas' considered pilot mismanagement of the fuel
system in the accident report data?

It isn't on my analysis. My primary interest is mechanical failures
related to accidents, but I've done some breaking-out of the pilot-related
causes. I have one catch-all category for the pilot losing control or
mishandling the airplane (with subsidiary fields for winds, etc.), and
separately track items like fuel exhaustion, VFR to IFR, pilot
disorientation and Incapacitation, wake turbulence, deliberate maneuvering
at low altitude, failure to recover from aerobatic maneuvers,
builder/manufacturer error, inadequate preflight, out of weight or CG
range, and suicide.

It's all leading to a KITPLANES article, once I'm done refining the output.
Ran a CD backup of the directory last night, it was about 250 Mb. Been a
busy boy.

Also, I realize that the accident
data is what you have available, but data showing the causes for forced
landings (which may not necessarily generate an accident report) might
be more appropriate.

Agreed. About twenty years back, my EAA chapter was having a picnic at an
airpark home of a member. He went to take some passengers up in his
homebuilt, and lost the engine right after liftoff. He got the plane
stopped before going over the bluff at the end of the runway, but had to
ground-loop it and wipe the gear off. The chapter members ran to the
wreck, piled it on a convenient trailer, and had it back in the hangar
(door closed) before the cops got there. "What accident?" :-)

Then there was the case about seven years ago, when a news crew asked a man
coming out of a patch of woods whether he knew anything about a nearby
plane crash. He denied it. But he didn't explain why one arm was in a
sling and there was crumpled Fokker rudder tucked under the other arm....

However, my primary interest is the accident rate of homebuilts vs.
production aircraft, and the relative occurrences of the various causes.

Thanks again to whoever pointed me at the NTSB database files, they're
wonderful. Beats weeding through the online narratives. I thank you, and
my ophthalmologist will thank you. :-)

Ron Wanttaja