From: "David Leonard wdleonard@gmail.com" <flyrotary@lancaironline.net>
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Date: Fri, 8 May 2020 06:17:00 -0700
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Subject: Re: [FlyRotary] Turbos
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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Hi Neil,
It all depends on how you size and operate your turbo.
In general, the pressure relief, or pop-off valve is not needed in
aircraft.  Those come more into play during the fast throttle closures that
occur in highly boosted race cars during shifting.  They spend almost all
of their time closed.  These valves are not intended to be the primary
pressure regulation and would not function well in such a capacity. They
only limit peak pressure but do not do so with a high level of accuracy or
control ability.  They would also be highly inefficient if used in this
manner, as the turbo would be producing continuously higher back pressure
than needed.  The turbo would be short lived and your fuel consumption
would suffer greatly.

The wastegate issue is a much bigger question but the short answer is that
yes, you probably want/need one.  The only exception might be a large
turbine turbo that is sized so big that the max boost was only achieved at
WOT operating conditions.  Even then, you would be limiting the usefulness
of your turbo at altitude because if it were sized for WOT at sea level, it
would not be very useful at altitude.  If sized for WOT at altitude you
could use throttle to control boost down low, but you always run the risk
of overboost.  Similarly, a fixed exhaust bypass would allow a smaller
turbo to be used in the same manner but with less efficiency and shorter
life.  I have experimented with my turbo in this configuration.  By
removing the flapper valve from my wastegate and creating a fixed bypass I
was able to run at WOT and have approximately the boost I wanted, but only
at a very specific altitude.  Any higher and boost drops off
precepitously.  Any lower and throttle is needed to control boost.  There
is not much of a sweet spot as the natural variations in conditions created
a oscillating situation that is simply not tolerable.  But for maximum
benefit from your turbo, longest life and efficiency there is no substitute
for a wastegate of some sort.

Dave Leonard
N4VY, Turbo Rotary RV-6

On Thu, May 7, 2020 at 2:47 PM 12348ung@gmail.com <
flyrotary@lancaironline.net> wrote:

> Can anyone help me with the following?    With a turbo, can I just use a
> pressure relief valve and negate the wastegate totally??    Looking for
> simplicity and weight saving.   Neil.
>

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<div dir=3D"ltr">Hi Neil,<div>It all depends on how you size and operate yo=
ur turbo.<br><div>In general, the pressure relief, or pop-off valve is not =
needed in aircraft.=C2=A0 Those come more into play during the fast throttl=
e closures that occur in highly boosted race cars during shifting.=C2=A0 Th=
ey spend almost all of their time closed.=C2=A0 These valves are not intend=
ed to be the primary pressure regulation and would not function well in suc=
h a capacity. They only limit peak pressure but do not do so with a high le=
vel of accuracy or control ability.=C2=A0 They would also be highly ineffic=
ient if used in this manner, as the turbo would be producing continuously=
=C2=A0higher back pressure than needed.=C2=A0 The turbo would be short live=
d and your fuel consumption would suffer greatly.</div></div><div><br></div=
><div>The wastegate issue is a much bigger question but the short answer is=
 that yes, you probably want/need one.=C2=A0 The only exception might be a =
large turbine turbo that is sized so big that the max boost was only achiev=
ed at WOT operating conditions.=C2=A0 Even then, you would be limiting the =
usefulness of your turbo at altitude because if it were sized for WOT at se=
a level, it would not be very useful at altitude.=C2=A0 If sized for WOT at=
 altitude you could use throttle to control boost down low, but you always =
run the risk of overboost.=C2=A0 Similarly, a fixed exhaust bypass would al=
low a smaller turbo to be used in the same manner but with less efficiency =
and shorter life.=C2=A0 I have experimented with my turbo in this configura=
tion.=C2=A0 By removing the flapper valve from my wastegate and creating a =
fixed bypass I was able to run at WOT and have approximately the boost I wa=
nted, but only at a very specific altitude.=C2=A0 Any higher and boost drop=
s off precepitously.=C2=A0 Any lower and throttle is needed to control boos=
t.=C2=A0 There is not much of a sweet spot as the natural variations in con=
ditions created a oscillating=C2=A0situation that is simply not tolerable.=
=C2=A0 But for maximum benefit from your turbo, longest life and efficiency=
 there is no substitute for a wastegate of some sort.</div><div><br></div><=
div>Dave Leonard</div><div>N4VY, Turbo Rotary RV-6</div></div><br><div clas=
s=3D"gmail_quote"><div dir=3D"ltr" class=3D"gmail_attr">On Thu, May 7, 2020=
 at 2:47 PM <a href=3D"mailto:12348ung@gmail.com">12348ung@gmail.com</a> &l=
t;<a href=3D"mailto:flyrotary@lancaironline.net">flyrotary@lancaironline.ne=
t</a>&gt; wrote:<br></div><blockquote class=3D"gmail_quote" style=3D"margin=
:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"=
><div lang=3D"EN-US"><div class=3D"gmail-m_-8899553916149376526WordSection1=
"><p class=3D"MsoNormal"><span lang=3D"EN-AU">Can anyone help me with the f=
ollowing?=C2=A0=C2=A0=C2=A0 With a turbo, can I just use a pressure relief =
valve and negate the wastegate totally??=C2=A0 =C2=A0=C2=A0Looking for simp=
licity and weight saving.=C2=A0=C2=A0 Neil.<u></u><u></u></span></p></div><=
/div></blockquote></div>

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