"Parlow, Eric (Turbos-Asheville)" wrote:
I'm building a RV-8A.
I would like to use a turbocharged 20B with 2.85:1 and CS prop.
Planning for 350 bhp climb & 200 bhp cruise to 12k ft.
What challenges am I facing?
Eric Parlow
RV-8A
In regard to the engine not many. You need a motor mount and
cooling
system. As I recall Tracy Crook is building a similar but NA
combination. Feel free to ask any questions on here. The big thing
before you start is build a full size mock up or get 3D software
to make sure everything fits where you think it is going to fit.
You will have to build a 20B turbo manifold because as far as
I know there is nothing off the shelf. There are signs that
there will be a low profile intake manifold available.
Paul Lamar
That's going to be a real performer Eric!
Just wondered about your choice of the 2.85 ratio. Some people want
the
additional engine rpm that a 2.85 ratio will allow (for more HP) but
since
you are turbocharging, you can easily meet your HP goals without
reving
the
engine past 6000.
Also, ask a few prop makers what they have available that would work
efficiently at 74" long , 2100 rpm and 350 HP. You may be surprised
at
the
answer.
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
Why are 2100 RPM and 74 inch props magic numbers Tracy?
You have my mystified.
Paul Lamar
Just the usual operational reasons.
6000 / 2.85 = 2105 rpm
74 inches is the largest prop diameter recommended for the RV for
ground
clearance reasons.
Sure, you can run the engine faster but if you can easily meet or exceed
the
HP targets at a lower rpm, why do it?
Tracy Crook
tcrook@rotaryaviation.com
www.rotaryaviation.com
I am not arguing the turbo charger bit. You can always taylor
the turbo charger to give you all the boost you want at almost
any RPM you want. What I am saying is you can always get more
power with a NA rotary, P-port or street port, by running it faster.
Up to the limits of the rotor bearing which seems to be around
9200 for the current rotors. The RX 8 rotors are lighter
and the limit there may be over 10,000 RPM.
Make the prop smaller in diameter and use wider blades
if necessary to absorb the additional HP.
Klause runs his prop at over 3500 RPM at 250 MPH.
Paul Lamar
I think perhaps Paul & Tracy have overlooked the obvious BIG challenges you
are going to face: Space and weight. That 20B, especially with a turbo
hanging on it is going to be both heavy and bulky compared to the 4 cyl Lyc
the RV-8 was designed to carry.
Weight wise, you can probably make it work by flying from the back seat and
nobody in the front seat. Firewall & mount (and landing gear, etc.) will
need to be designed / reinforced for the greater stresses they will see, as
may the central fuselage. Wings & spars should be OK (although Tracy is
lengthening his wings... to carry the weight of a "full" load plus heavier
engine?)
The 20B is 50% more engine than a 13B. Include the volume of a 50% larger
rad, oil cooler, and an appropriately sized intercooler, and there may not
be enough room under the cowl. Best to sound this one out with Tracy and
others with experience cramming one of these larger engines into a small
airframe.
Tom Kendall
Good points Tom.
If somebody sends me a drawing on the RV8 firewall and a sketch
of the stock cowl I will see what fits using Rhino.
What are the dimensions of your rad and oil cooler Tracy.
Paul Lamar
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