Fuel dump switch in homebuilt

[Jay]

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. And
since KE is mv^2, you get a proportional benfit from dumping the
weight of the fuel which might be 20% the weight of the airplane, and
the lower weight allows for a slower stall speed which cuts the V
factor, and since thats squared, it counts for a lot. And then of
course you may have a larger glide radius with that reduction in
weight in addition to the reduced fire potential upon landing and
breakup

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.

[Kevin Horton]

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

> After reading some of the transcripts from the "Last Words" website, where
> the flight engineers were dumping fuel when it became evident that an
> emergency 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. And since KE is mv^2, you get
> a proportional benfit from dumping the weight of the fuel which might be
> 20% the weight of the airplane, and the lower weight allows for a slower
> stall speed which cuts the V factor, and since thats squared, it counts
> for a lot. And then of course you may have a larger glide radius with
> that reduction in weight in addition to the reduced fire potential upon
> landing and breakup
>
> 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.

Interesting idea, but I think there are good reasons why people haven't
done this on light aircraft:

1. If you have a major problem and need to do an off-airport landing (e.g.
engine failure, fire, etc), you usually don't have much time to play with,
so you probably wouldn't be able to get rid of enough fuel to make much of
a difference. Anything you do in the design to increase the dump rate
only makes the consequences of an uncommanded fuel dump even worse (see
item 3).

2. If you only have a minor problem (i.e. you have to land, but you are
not in any big rush), then you should have time to get to a suitable
airport where you can safely land at the current gross weight.

3. If you design in the ability to dump fuel, you have added a failure
mode where fuel gets dumped when you don't want it to. This could cause
an off-airport landing. Sure, this failure mode wouldn't happen too
often, but it only has to happen once to really ruin your day.

All things considered, this system would probably decrease the overall
level of safety, not increase it.

Fuel dump systems are on some large jets because of the large difference
between max approved take-off weight and max approved landing weight.
There are also some failures that make it attractive to be able to greatly
reduce the gross weight. E.g. failures of flaps and slats mean up to a 60
kt increase in approach speed on some aircraft. They may also have
partial brake failures to contend with, etc.

Note 1: even though big jets may have a big difference between max
approved take-off weight and max approved landing weight, that does not
mean that it is unsafe to land right after take-off and max approved
take-off weight. You just need to do a smooth landing, and you need a
long runway. Landings at max approved take-off weight are done routinely
during the take-off performance flight testing, as this type of testing
consists of multiple take-offs at max weight, followed a few minutes later
by a landing so the test can be repeated yet again.

Note 2: the glide ratio does not vary with gross weight. I won't try to
explain the math or physics as there are lots of references available on
the web for your googling pleasure.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Holger Stephan]

Kevin Horton wrote:
> Note 2: the glide ratio does not vary with gross weight. I won't try to
> explain the math or physics as there are lots of references available on
> the web for your googling pleasure.

True only in theory (i.e. on high performance gliders). The added drag with
the increased max glide speed will decrease the ratio.

- Holger

[Toks Desalu]

"> since KE is mv^2, .

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

[Drew Dalgleish]

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

>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. And
>since KE is mv^2, you get a proportional benfit from dumping the
>weight of the fuel which might be 20% the weight of the airplane, and
>the lower weight allows for a slower stall speed which cuts the V
>factor, and since thats squared, it counts for a lot. And then of
>course you may have a larger glide radius with that reduction in
>weight in addition to the reduced fire potential upon landing and
>breakup
>
>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.

Probably a lot closer to 10% since most don't take off with full fuel
or have catastrophic failures at that loading. You can keep adding
systems until your plane will never fly.

[Peter Dohm]

Holger Stephan wrote:
>
> Kevin Horton wrote:
> > Note 2: the glide ratio does not vary with gross weight. I won't try to
> > explain the math or physics as there are lots of references available on
> > the web for your googling pleasure.
>
> True only in theory (i.e. on high performance gliders). The added drag with
> the increased max glide speed will decrease the ratio.
>
> - Holger

That could go either way, depending on the porportion of parasitic drag and
induced drag. However, in most cases you are exactly correct that lighter
weight will improve the glide ratio, and that heavier weight will worsen it;
assuming no wind conditions, of course.

Peter

[Vaughn]

"Holger Stephan" > wrote in message
...
> Kevin Horton wrote:
> > Note 2: the glide ratio does not vary with gross weight. I won't try to
> > explain the math or physics as there are lots of references available on
> > the web for your googling pleasure.
>
> True only in theory (i.e. on high performance gliders). The added drag
with
> the increased max glide speed will decrease the ratio.

From what I have been taught (and teach my students) Kevin is quite
right. Just because glide ratio (best L/D) does not change, that does not
mean that the aircraft performance is unchanged by gross weight. At a
higher weight, best L/D comes at a higher airspeed. If you happened to be
downwind of your intended landing area, you would be better off (very
margionally) by hanging on to the extra weight. As already mentioned, stall
speed decreases with weight and using that same formula (1/2 MV^2) reducing
the velocity on an off-field landing drastically reduces the energy that
must be disipated after landing.

On balance, I believe that fuel dumps in small aircraft are a bad idea.

Vaughn


>
> - Holger
>

[Del Rawlins]

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.

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

[Kevin Horton]

On Sun, 30 Nov 2003 16:51:58 -0800, Holger Stephan wrote:

> Kevin Horton wrote:
>> Note 2: the glide ratio does not vary with gross weight. I won't try to
>> explain the math or physics as there are lots of references available on
>> the web for your googling pleasure.
>
> True only in theory (i.e. on high performance gliders). The added drag
> with the increased max glide speed will decrease the ratio.
>
> - Holger

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.

But, if we have a windmilling prop, the windmilling rpm will go up
with speed, and the windmilling drag could increase quite a bit, and that
could affect the results. So, add an assumption of a stopped prop.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

[Eric Miller]

"Drew Dalgleish" > wrote
> Probably a lot closer to 10% since most don't take off with full fuel
> or have catastrophic failures at that loading. You can keep adding
> systems until your plane will never fly.

At which point it is finally safe! =D

Eric

[Ron Wanttaja]

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

[Richard Isakson]

"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

[Stealth Pilot]

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

[Jay]

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)

[Kyler Laird]

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

[Bob Kuykendall]

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.

[Ron Wanttaja]

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

[Del Rawlins]

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/

[Ed Wischmeyer]

> >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

[Ron Wanttaja]

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

[Kyler Laird]

Ron Wanttaja > writes:

>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.

So are you saying that there's a 1:1 relationship between losing power and
making an emergency landing? No one loses power and performs a stall/spin
return to the ground?

I'm just trying to get back to the point about fuel probably being already
exhausted when an emergency landing is executed. Are you saying that three
of every four emergency landings are made with significant quantities of
fuel on board? (Another complication is that it's fairly common to still
have gobs of fuel on board even when fuel starvation is the cause of the
accident.)

--kyler

[Kyler Laird]

Ed Wischmeyer > writes:

>> >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?

No source. I just heard that that's the way they were designed. I assume
they shear a lot more easily than the tanks in my wings do.

--kyler

[Ron Wanttaja]

On Tue, 02 Dec 2003 17:09:41 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.
>
>So are you saying that there's a 1:1 relationship between losing power and
>making an emergency landing? No one loses power and performs a stall/spin
>return to the ground?

Certainly, to a depressing extent, especially when the engine failure
occurs on takeoff. I apparently didn't make my point clear: Another
poster commented that "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." My
response was meant to counter this, in that fuel-exhaustion-related
accidents were a relative minority.

>I'm just trying to get back to the point about fuel probably being already
>exhausted when an emergency landing is executed. Are you saying that three
>of every four emergency landings are made with significant quantities of
>fuel on board?

No. All I said on my original posting was that 4.2% (I posted "about
4.5%") of all homebuilt accidents in the January 1998 to December 2000 time
period (29/692) involved fuel exhaustion. I make no claim about how much
fuel remained in the remaining 660-odd accidents that year, other than to
guess that the NTSB investigator apparently considered there was sufficient
fuel on board to rule out lack of fuel as a reason for a loss of power
situation.

>(Another complication is that it's fairly common to still
>have gobs of fuel on board even when fuel starvation is the cause of the
>accident.)

Out of the 29 cases of fuel exhaustion, two cases involved a crash during a
precautionary landing due to a low fuel state, one involved the fuel tank
unporting when the pilot maneuvered at low attitude with a low fuel state,
one had a bad header tank, and one pilot failed to select his reserve tank
when the main tank ran dry. Three cases of extremely low fuel, two of some
amount of fuel. In the remaining 24 cases, the engines quit because the
pilot used up all his or her usable fuel (one case included a leaking fuel
tank). That would still leave several gallons aboard each aircraft.

In ~660 accidents, then, the airplane crashed with sufficient fuel on board
to have enabled continued flight. I personally don't think a fuel-dump
valve would have helped in most of these cases. But I suspect it's like
the ballistic parachute argument; if you need one, then you REALLY need
one. :-)

Ron Wanttaja

[Jay]

Thanks, Bob K, or your insightful contribution to the discussion.

Thats good data to have about the fuel pump requirements for the pump
that feed the engine. Have recently done some looking into of pumps
for a diesel to veg oil conversion project and I've discovered that
you really design pumps differently depending on what your goal is.
For a fuel pump, you want to deliver small volumes at high pressure.
In contrast for dumping fuel you want to move large amounts to a
negative pressure. Have you seen any of the pumps they use in washing
machines?

But since its a negative pressure system, technically speaking, you
don't need a pump at all to drain the tank. The only question, is how
fast do you need to let it go, that will dictate how big a pipe do you
need from the tank to the valve to the low pressure port on the
surface of the fuselage. Of course the bigger the pressure
differential you can find the better.


(Bob Kuykendall) wrote in message >...
> 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.

[Mark Hickey]

Ron Wanttaja > wrote:

>No. All I said on my original posting was that 4.2% (I posted "about
>4.5%") of all homebuilt accidents in the January 1998 to December 2000 time
>period (29/692) involved fuel exhaustion. I make no claim about how much
>fuel remained in the remaining 660-odd accidents that year, other than to
>guess that the NTSB investigator apparently considered there was sufficient
>fuel on board to rule out lack of fuel as a reason for a loss of power
>situation.
>
>>(Another complication is that it's fairly common to still
>>have gobs of fuel on board even when fuel starvation is the cause of the
>>accident.)
>
>Out of the 29 cases of fuel exhaustion, two cases involved a crash during a
>precautionary landing due to a low fuel state, one involved the fuel tank
>unporting when the pilot maneuvered at low attitude with a low fuel state,
>one had a bad header tank, and one pilot failed to select his reserve tank
>when the main tank ran dry. Three cases of extremely low fuel, two of some
>amount of fuel. In the remaining 24 cases, the engines quit because the
>pilot used up all his or her usable fuel (one case included a leaking fuel
>tank). That would still leave several gallons aboard each aircraft.
>
>In ~660 accidents, then, the airplane crashed with sufficient fuel on board
>to have enabled continued flight. I personally don't think a fuel-dump
>valve would have helped in most of these cases. But I suspect it's like
>the ballistic parachute argument; if you need one, then you REALLY need
>one. :-)

Let's not rule out the one advantage of the fuel dump we haven't
discussed - that anyone who had to deadstick in due to fuel starvation
could then claim he had dumped the fuel to prepare for the deadstick
landing. Sure, he'd have some 'splainin' to do when the beast fires
right up when resupplied with go-juice, but he could always pull a
Unka BOb and claim it was just one of those evil intermittent auto
engine systems.

Mark Hickey

[RR Urban]

>Let's not rule out the one advantage of the fuel dump we haven't
>discussed - that anyone who had to deadstick in due to fuel starvation
>could then claim he had dumped the fuel to prepare for the deadstick
>landing. Sure, he'd have some 'splainin' to do when the beast fires
>right up when resupplied with go-juice, but he could always pull a
>Unka BOb and claim it was just one of those evil intermittent auto
>engine systems.
>
>Mark Hickey
++++++++++++++++++++++++++++++

All machinery has the capacity to be evil.
*Certified* is just less evil in competent hands.


Unka BOb --

[Ron Wanttaja]

On Wed, 03 Dec 2003 10:59:02 -0700, Mark Hickey > wrote:

>Let's not rule out the one advantage of the fuel dump we haven't
>discussed - that anyone who had to deadstick in due to fuel starvation
>could then claim he had dumped the fuel to prepare for the deadstick
>landing. Sure, he'd have some 'splainin' to do when the beast fires
>right up when resupplied with go-juice, but he could always pull a
>Unka BOb and claim it was just one of those evil intermittent auto
>engine systems.

Actually, he might not have to explain too much. This sort of scenario
does happen (where the engine runs OK afterwards), and the NTSB usually
just chalks it up to "Engine failure for undetermined reasons."

Ron Wanttaja

[sean trost]

or one could say it was certifiably evil.....:)
Sean


RR Urban wrote:
>>Let's not rule out the one advantage of the fuel dump we haven't
>>discussed - that anyone who had to deadstick in due to fuel starvation
>>could then claim he had dumped the fuel to prepare for the deadstick
>>landing. Sure, he'd have some 'splainin' to do when the beast fires
>>right up when resupplied with go-juice, but he could always pull a
>>Unka BOb and claim it was just one of those evil intermittent auto
>>engine systems.
>>
>>Mark Hickey
>
> ++++++++++++++++++++++++++++++
>
> All machinery has the capacity to be evil.
> *Certified* is just less evil in competent hands.
>
>
> Unka BOb --

[sean trost]

or one could say it was certifiably evil.....:)
Sean

[David O]

Mark Hickey > wrote:

>Let's not rule out the one advantage of the fuel dump we haven't
>discussed - that anyone who had to deadstick in due to fuel starvation
>could then claim he had dumped the fuel to prepare for the deadstick
>landing.

I am reminded of the following accident report which I found quite
humorous. This is a partial quote from an NTSB accident report of a
C-150 forced landing near Four Corners Regional Airport, Farmington,
New Mexico circa October 2003,

"According to the tower operator at FMN, as the airplane was entering
a left base for runway 07, a expletive was heard over the tower
frequency and shortly thereafter an emergency locator transmitter
(ELT) signal was heard. According to emergency personnel, when they
arrived on scene, they found the pilot had already pulled himself out
of the inverted airplane and was sitting on the wing. The pilot told
them "don't worry about a fire, there's no fuel."

David O -- http://www.AirplaneZone.com

[Stealth Pilot]

On Thu, 04 Dec 2003 02:11:16 GMT, Ron Wanttaja >
wrote:

>On Wed, 03 Dec 2003 10:59:02 -0700, Mark Hickey > wrote:
>
>>Let's not rule out the one advantage of the fuel dump we haven't
>>discussed - that anyone who had to deadstick in due to fuel starvation
>>could then claim he had dumped the fuel to prepare for the deadstick
>>landing. Sure, he'd have some 'splainin' to do when the beast fires
>>right up when resupplied with go-juice, but he could always pull a
>>Unka BOb and claim it was just one of those evil intermittent auto
>>engine systems.
>
>Actually, he might not have to explain too much. This sort of scenario
>does happen (where the engine runs OK afterwards), and the NTSB usually
>just chalks it up to "Engine failure for undetermined reasons."
>
>Ron Wanttaja

in australia it is usually chalked up to carby ice.
Stealth Pilot

[Andrew Rowley]

(Jay) wrote:

>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.

I think I'd prefer to maximise the chances of keeping all the
remaining fuel safely in the tanks after landing. My view is that any
reduction in landing weight is more than offset by the chances of
having fuel still in the dump system on landing and making fire more
likely.

[Kyler Laird]

Andrew Rowley > writes:

>I think I'd prefer to maximise the chances of keeping all the
>remaining fuel safely in the tanks after landing. My view is that any
>reduction in landing weight is more than offset by the chances of
>having fuel still in the dump system on landing and making fire more
>likely.

Yeah, but think of the path of that fire (as it spreads to the areas
now peppered with fuel). It'd be like a big burning arrow pointing
right at your plane. It should make it easy to find your body.

--kyler

[Ron Wanttaja]

On Thu, 04 Dec 2003 18:06:19 +0800, Stealth Pilot >
wrote:

>>
>>Actually, he might not have to explain too much. This sort of scenario
>>does happen (where the engine runs OK afterwards), and the NTSB usually
>>just chalks it up to "Engine failure for undetermined reasons."
>
>in australia it is usually chalked up to carby ice.

If the conditions were favorable for carb ice, the NTSB reports usual say
so, and often ascribe the accident to it. But in a lot of cases, they
don't mention it; they just do the "undetermined" shrug.

Ron Wanttaja

[Jay]

Regarding how data for incident reports are gathered. Someone had
mentioned the experimental that ground looped and was whisked away
before any pesky official types nosed around. Another guy I know lost
an oil line on his Rotax 912 and, after the engine siezed, landed in
the brush out near Hemet. He hiked out, and came back with a trailer,
nothing reported even though he made a call on the radio on his glide
down from 6,000 AGL.

I also understand that an emergency off airport landing is not a
reported incident if there is no property damage. So if I lose power
and land on a freeway, as long as I'm able to merge with traffic and
not hit anything, it doesn't end up in the statistics. So this means
the incident stats are showing a more rosey impression than is real of
the state of reliability of GA.

Ron Wanttaja > wrote in message >...
> On Wed, 03 Dec 2003 10:59:02 -0700, Mark Hickey > wrote:
>
> >Let's not rule out the one advantage of the fuel dump we haven't
> >discussed - that anyone who had to deadstick in due to fuel starvation
> >could then claim he had dumped the fuel to prepare for the deadstick
> >landing. Sure, he'd have some 'splainin' to do when the beast fires
> >right up when resupplied with go-juice, but he could always pull a
> >Unka BOb and claim it was just one of those evil intermittent auto
> >engine systems.
>
> Actually, he might not have to explain too much. This sort of scenario
> does happen (where the engine runs OK afterwards), and the NTSB usually
> just chalks it up to "Engine failure for undetermined reasons."
>
> Ron Wanttaja

[andy asberry]

On Thu, 04 Dec 2003 13:09:52 GMT, Kyler Laird >
wrote:

>Andrew Rowley > writes:
>
>>I think I'd prefer to maximise the chances of keeping all the
>>remaining fuel safely in the tanks after landing. My view is that any
>>reduction in landing weight is more than offset by the chances of
>>having fuel still in the dump system on landing and making fire more
>>likely.
>
>Yeah, but think of the path of that fire (as it spreads to the areas
>now peppered with fuel). It'd be like a big burning arrow pointing
>right at your plane. It should make it easy to find your body.
>
>--kyler

Giving one of those redwood tree squatters a fuel shower might tick
him/her off enough to put the spark to your flaming arrow. Watch your
six!

[Ron Wanttaja]

On 4 Dec 2003 09:34:35 -0800, (Jay) wrote:

>I also understand that an emergency off airport landing is not a
>reported incident if there is no property damage. So if I lose power
>and land on a freeway, as long as I'm able to merge with traffic and
>not hit anything, it doesn't end up in the statistics. So this means
>the incident stats are showing a more rosey impression than is real of
>the state of reliability of GA.

NTSB Part 830 specifies when accidents are reportable. Reportable
occurrence must include one of the following:

1. Death
2. Serious injury
3. "Substantial damage" to the aircraft.

Without one of these events occurring it's considered an incident and thus
not required to be reported. However, incidents involving:

- Flight control system malfunction or failure
- Crew incapacitation
- Turbine engine structural failure
- In-flight fires
- Midairs
- Damage to property other than the aircraft exceeding $25k

....also must be reported (plus other events for large multiengine
aircraft). Engine failures, per se, are not required to be reported if the
damage is limited to the engine.

Ron Wanttaja