Ram air

On Jun 2, 12:46 am, wrote:
On Jun 1, 6:35�am, Tina wrote:

What makes me wonder about it is, even at 60 mph holding your hand out
of the window of a car subjects it to a significant backward pressure,
so the energy must be there.

The energy is there and in a simplified discussion it is called
stagnation pressure, the sum of static pressure and ram air
pressure. As you go faster, static stays the same, ram goes up with
the square of velocity, as discussed already. Your airspeed
indicator uses the two pressures and does the math for you. On the
Tango 2, a homebuilt, we have a ram air scoop below the spinner and a
Y-valve and door for filtered or ram air. When I go to ram air at
150 kias, my manifold pressure goes up about .6 inch. Theoretically I
should recover 1.08 inches. I only have a single buttlerfly Y-valve;
we think some of the air is following the path of least resistance and
going back up the filtered tube. Another Tango 2 has a double
butterfly Y-valve that close off the escape route back through the
filter. His ram rise is about 1.1 or 1.2 inches, which is more than
stagnation. We put his ram air tube a little lower and closer to the
prop as discussed in SPEED WITH ECONOMY by Ken Paser. This seems to
capture the increased pressure behind the blade as it passes the
inlet, timed with the intake valve opening. When we are side by side,
flat out, when he goes ram air he pulls away from me.
I normally don't go ram until I climb above the haze layer and my
power drops below %75. At that point the power goes up about 4-5% and
I can feel the acceleration.
As someone else mentioned, you can't put a funnel out there and
get even more boost. Any excess will just flow around the inlet and
possibly increase drag. We don't know if our setup is optimum, but it
helps. Other homebuilters I've talked to report similar results. Oh,
for a wind tunnel and a lot of money.

Denny
Team Tango

Thanks, Denny. I thought if anyone would extract the last bit gain it
would be someone with a home built.