Engine failure on approach

> Suppose, just suppose that you’re in your RV-8 on speed, full flaps turning
> base to 1/2 mile final and the engine quits. You are pretty sure that you
> have the runway made but you want to extend your glide as much as possible.
> Do you leave the flaps where they are or do you raise them and if so how
> much? Thought about this yesterday as I turned final.

As you know, the glide ratio (i.e the distance traveled for a given
amount of altitude) will be better with the flaps up than with them
extended, assuming that you are at the best glide speed for each
configuration. So, at the moment that the engine failed, if you were
at the best glide speed for flaps up, or faster, there is an
advantage to raising the flaps, no matter what your altitude is.

But, if you are flying slower than the best glide speed for flaps up,
you are going to need to push over to accelerate, and you will lose
some altitude to do this. At the moment where you attain the best
glide speed for flaps up, you will probably be below the flight path
you would have followed if you had just left the flaps down. But the
improved glide performance with flaps up will soon let you get above
the flight path you would have followed if you had left the flaps down.

If you were flying below the stall speed for flaps up when the engine
failed (which is a lot slower than you should be flying on final),
you could still raise the flaps, but you would have to push as you
did so, to keep the angle of attack less than the stalling angle of
attack. This implies that you will be at much less than one g load
factor, and you will be falling from the sky like the proverbial
brick until you get some speed back and can then allow the g to
increase. This would be a bad situation if you were at low altitude,
as you might not get enough speed to allow you to pull g and break
the rate of descent before you hit the ground.

In general, for any given speed, there is an altitude at which it
doesn’t matter whether you retract the flaps or leave them down – you
will hit the ground at the same point. If you are above this
altitude, it makes sense to retract the flaps. If you are below this
altitude it makes sense to leave them down.

All of the above assumes you know the speed for best glide ratio with
the flaps up and down, and that you know the stall speed for flaps up
and down. You should have determined all those numbers during your
flight test program. Then you should simulate engine failures
starting from various conditions. Put the flaps down, stabilize at
airspeed X using whatever rpm you normally use on base leg. Then
pull the throttle to idle, push over, retract the flaps, and note how
much altitude you lose before you get to best glide speed for flaps
up. Add a bit of a buffer to this altitude, and it will give you a
reasonable minimum altitude at which you should consider retracting
the flaps. Repeat this at different airspeeds, and note how the
altitude required to achieve best glide speed varies with the speed
at engine failure.

Kevin Horton

Kevin wrote a excellent description of the technical aspects of engine out
glide path. I’ll take a different approach.

Certainly I can not, and few other pilots that I know, except my Test Pilot
Hero 😉 Kevin Horton, can call up that info and process it, while turning
directly to the airport property and trying to figure out why the engine
quit and whether to pull the prop back, switch tanks, maintain best glide,
find a place to park, check the boost pumps, tighen up your shoulder
harness, hit the starter, all this while soiling your undergarments.

I offer a different question and some answers.
What can we do to improve our safety while flying in the pattern?

Tighten up our patterns. An engine failure in the pattern should never
result in an off airport landing. (maybe off the runway, but on the airport
property.) We should talk to our friends about the bomber patterns we all
see at our airports and set a good example, by flying nice tight patterns.

Never Turn back to the runway on an engine failure after take-off.

Shock cooling be damned, approaches should be made at idle power.

Aim for the 1000 ft markers, not the end of the runway.

Don’t get slow!

Every power change in the pattern should be a reduction. Not counting ATC,
adding power in the pattern should be considered poor planning and an error.

Every one should have an engine failure checklist committed to memory. Mine
is an old WWII checklist:

Glide – pull or push to best glide speed
Gear – Up or down, up is default unless you are willing to bet your life
that the ground is hard
Gas – Pump on and Try all Selector all positions including OFF, ( I had
one quit, right after annual, and it ran in OFF )
Ignition – try all positions including OFF
Heat – Carb Heat on
Mixture – Rich or maybe leaned on an injected eng.
Prop – Low RPM or Feather
Canopy – open(or doors unlatched) before impact
Harness – Seat and shoulder harness locked and tight

Finally when the end is near,
Mixture, Master & Mags off for impact

You notice flaps did not even make the list.

To answer the original question, If I was high enough to do everything else
that is more important, then I would raise the flaps. There is more
important work to do than raising the flaps. The most important thing, FLY
the airplane to the ground. Airplanes that arrive at the accident site
under control with the wings level usually have survivors onboard. You will
notice Glide is first on the list, and the only thing on the list that I did
when my engine quit.

Tailwinds,
Doug Rozendaal