From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: Turbos
Date: Sat, 9 May 2020 07:15:10 +0800
References: <list-223039@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-223039@logan.com>
Message-Id: <C6842B1C-E300-4881-BA8D-F102BEAA98D6@gmail.com>

Hi guys.
Another turbo question.
Do you guys just use a standard waste gate actuator (perhaps with basic =
controller allowing different boost settings) and run out of boost at x =
altitude, or do you have some kind of altitude compensation?
Thanks
Steve Izett


> On 9 May 2020, at 6:24 am, 12348ung@gmail.com =
<flyrotary@lancaironline.net> wrote:
>=20
> Dave and contributors,
>                                            Spent yesterday finally =
getting specific answers that I should have had 12 months ago.  The guru =
that I sent the stock turbo to in the end had no idea as to an upgrade =
for temp in the hot section.  The up grade that Dave suggested is =
approx. $900 USD.  Real problem at the moment is the exchange rate with =
all the bank charges,  the great Ozzie dollar is approx. half.  Then =
freight----  I see freight on a turbo from the US at up to $800 Oz =
dollars!!   Then internal freight in OZ, plus labour costs  ---  I will =
have to sell 2 kidneys!
>                 Then considering I do not have a stock RX7 manifold to =
bolt the turbo to =E2=80=93 I am manufacturing an adaption of the stock =
Renesis  manifold, so whatever turbo I get it means work to make it fit =
and I am =C2=BE down that path.  So having already having a =E2=80=9Cdummy=
 spit=E2=80=9D due to 12 months lost, I lauch out to find a new turbo in =
OZ.  I find that Garret and others have a hot section wheel that will =
stand 1050 degrees C!!  Wow that fixes anything that the rotary puts out =
with no phone calls involved trying to explain.    Once again I make the =
usual; mistake telling the company with all these shiny new turbos that =
I want it for a drone!!  Thought that would by pass the usual =
arguments---- silly boy, NO they do not supply for aeronautical =
applications!!  So I am back to =E2=80=9Cdune buggy=E2=80=9D even though =
the nearest beach is 300 miles away.  Seems the turbo I require is the =
smallest they make.  Price is yet to enter the discussion.
>                 Will update as I get abused.  I am asked continually =
for Make, Model, Vin Number, year of manufacturer!  All I want is a =
turbo!
> Thanks to all,
> Neil.
> =20
> From: Rotary motors in aircraft <flyrotary@lancaironline.net>=20
> Sent: Friday, May 8, 2020 11:17 PM
> To: Rotary motors in aircraft <flyrotary@lancaironline.net>
> Subject: [FlyRotary] Re: Turbos
> =20
> 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.
> =20
> 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.
> =20
> Dave Leonard
> N4VY, Turbo Rotary RV-6
> =20
> 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.