RV-9A's wing with Rotax 914?

Earlier, (Shin Gou) wrote:

Bob, could you tell me more about the constrains of the RV-9A wing on
its current fuselage?

An RV builder who is familiar with both RV-6 and RV-9 could tell you
more about that than I ever could.

In specific, I can only repeat some of what I've heard that seems to
make sense. That is, that the longitudinal location of the RV-9 spar
is constrained lightly by the original design of the RV-6 fuselage
(elements of which of course Vans is at liberty to change) and
constrained more tightly by the size and shape of the pilot and their
relationship with the seat and controls. A similar fuselage design
will have similar general constraints - but the devil is in the
details.

I like Rotax 914/912s and Jabiru 3300 for their light weight and fuel
efficiency. If a lighter and better engine can do the same job as an
O-235, why not?

Having spent well into the five digits on composite aircraft tooling
and with the end barely on the horizon, here's the one bit of specific
advice I feel qualified to give:

If the RV-9 is anywhere near what meets your needs, buy the kit and
build it as shown in the plans. Take the extra money you would have
spent developing a new fuselage, and put it in the bank. It will way
more than cover the extra fuel burned by the O-235. The O-235 might
seem old-tech and sound like a tractor. But its extra oomph below
10000 feet will make more difference than you might expect in how the
airplane feels like it performs.

You will have the good feeling that comes from building airplane
parts, and you will not have the many sleepless nights that come from
wondering whether something you are developing is going to work as
planned. Be guided by the hand; your building experience will be
happier, quicker, and more peaceful if your mind is at ease and your
fingers are busy.

Thanks, and best regards to all

Bob K.
http://www.hpaircraft.com/hp-24

VideoFlyer wrote:

Well, considering the differences in chord, span and thickness,
my guess is - it won't fit.


Well duh.

Dang...there go my plans for this weekend! LOL!

I realize that it wouldn't fit. I guess my question is more along the lines
of:

"With a thinner wing, more like the one on an RV, would the Zodiac XL have
higher speeds? (both cruise and stall?)

Or more simply, why is the XL so much slower than the RV? Is the thick wing
the MAIN reason? (I realize there are many reasons) More horsepower does not
necessarily net higher speeds. Reducing drag does.


Well, the Z is an 80 to 100 hp airframe.
The RV is a150 to 200 ho airframe.
That might have SOME effect on speed.

Lessee, I think the RV has a lot more wing area,
(certainly more than the HDS anyway)
But it's a lot heavier too.

That fat airfoil on the Z makes for a lighter wing structure.

Also, compare stall speeds as well as cruise speeds.

One is a bigger heavier airframe and it NEEDS more power to fly.

The other is smaller, lighter, and has a higher lift wing.

Richard

In all likelyhood the answer is yes, it would be faster, both in
cruise and stall. I've flown a Zodiac and it was not a fast airplane,
man that wing is THICK.

And to answer the question about putting the turbo normalized Rotax
engine on an RV wing. Why not just build a longer (custom) engine
mount on the standard RV airframe and redo the fiberglass cowling.
You'd end up with a lighter plane and have the CG where you wanted it.
Also the longer nose (besides looking turbine cool) will save drag
because you're getting the prop a little further from the canopy and
wing roots. And yes the longer moment arm will increase the time
required for spin recovery, but it will also make it a more stable IFR
platform in pitch and yaw.

Also, the big difference between the RV and Europa on kit price is the
amount of labor you're going to have to put in. Assuming people with
equal skill in the respective contsruction materials, you're going to
be done faster with the Europa. The Europa is top of my list right
now because my time is more limited than my budget.

Regards



(VideoFlyer) wrote in message ...
Well, considering the differences in chord, span and thickness,
my guess is - it won't fit.


Well duh.

Dang...there go my plans for this weekend! LOL!

I realize that it wouldn't fit. I guess my question is more along the lines
of:

"With a thinner wing, more like the one on an RV, would the Zodiac XL have
higher speeds? (both cruise and stall?)

Or more simply, why is the XL so much slower than the RV? Is the thick wing
the MAIN reason? (I realize there are many reasons) More horsepower does not
necessarily net higher speeds. Reducing drag does.

On Wed, 03 Mar 2004 12:46:45 -0800, Jay wrote:

And to answer the question about putting the turbo normalized Rotax
engine on an RV wing. Why not just build a longer (custom) engine mount
on the standard RV airframe and redo the fiberglass cowling. You'd end
up with a lighter plane and have the CG where you wanted it.
Also the longer nose (besides looking turbine cool) will save drag
because you're getting the prop a little further from the canopy and
wing roots. And yes the longer moment arm will increase the time
required for spin recovery, but it will also make it a more stable IFR
platform in pitch and yaw.


Putting a lighter engine further forward will probably increase the polar
moment of inertia slightly, which would tend to very slightly slow the
aircraft's response in pitch and yaw. But from a stability point of view,
the extra area forward will have roughly the equivalent effect to reducing
the area of the vertical and horizontal stabs. Thus it will reduce the
static longitudinal and directional stability, which would make it a less
stable IFR platform.

In pitch, the fix may be to move the CG aft limit a bit forward, or
maybe it will be OK as is. In yaw, flight tests would determine whether
it was necessary to add vertical stab area, possibly via a dorsal fin.

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Jay wrote:

And yes the longer moment arm will increase the time
required for spin recovery, but it will also make it a more stable IFR
platform in pitch and yaw.

Whoa there. A longer nose moment arm will _decrease_
stability, not increase it. As for spin recovery, increasing
or decreasing depends on the weight of the engine and the
moment arm (or arm^2, technically).

Dave 'sluggo' Hyde

Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction.
Think of the stability of an arrow vs. a badmitton birdy. The birdy
always points into the wind, but any little disturbance causes it to
wiggle, like your C150 with the engine 3' from the CG, when you hit
rough air, the tail bobs around.

Regarding the fus. area in front of the CG, the Rotax engine is
smaller than the Lycoming its replacing, so you could make the cowling
smaller. And we're really only talking about 2' max on the extension.

Dave,
I think we're saying the same thing, moving a lighter weight out
further from the CG will increase the moment of inertia.



"nauga" wrote in message thlink.net...
Jay wrote:

And yes the longer moment arm will increase the time
required for spin recovery, but it will also make it a more stable IFR
platform in pitch and yaw.

Whoa there. A longer nose moment arm will _decrease_
stability, not increase it. As for spin recovery, increasing
or decreasing depends on the weight of the engine and the
moment arm (or arm^2, technically).

Dave 'sluggo' Hyde

"Jay" wrote in message
om...
Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction.
Think of the stability of an arrow vs. a badmitton birdy. The birdy
always points into the wind, but any little disturbance causes it to
wiggle, like your C150 with the engine 3' from the CG, when you hit
rough air, the tail bobs around.

Regarding the fus. area in front of the CG, the Rotax engine is
smaller than the Lycoming its replacing, so you could make the cowling
smaller. And we're really only talking about 2' max on the extension.

Dave,
I think we're saying the same thing, moving a lighter weight out
further from the CG will increase the moment of inertia.



You're right about the moment of intertia, but that is only one of the
forces here. Don't forget about aerodynamically destabilizing effect of
adding that surface area forward of the CG (The plug you need to add to the
forward fuselage adds, right?). Heck, Van's used to be concerned about the
impact of adding wider than stock gear leg fairings, and we're talking a
relatively small area, located near the CG...

KB

On Thu, 04 Mar 2004 09:52:34 -0800, Jay wrote:

Regarding earlier comment...
A tight rope walker uses a 30' balance pole, not a 2' pole. The large
moment makes everything happen slower, disruption AND correction. Think of
the stability of an arrow vs. a badmitton birdy. The birdy always points
into the wind, but any little disturbance causes it to wiggle, like your
C150 with the engine 3' from the CG, when you hit rough air, the tail bobs
around.

Regarding the fus. area in front of the CG, the Rotax engine is smaller
than the Lycoming its replacing, so you could make the cowling smaller.
And we're really only talking about 2' max on the extension.


You are confusing inertia with stability. They are not the same thing at
all. You need to learn what stability means before you can deduce what
effect a particular modification is likely to have on the stability of
the aircraft.

Read and understand the info at the following links, then we can have a
useful discussion. It is not possible to have a productive discussion
when one party does not understand the terminology used.

http://142.26.194.131/aerodynamics1/...ity/Page3.html
http://142.26.194.131/aerodynamics1/.../Negative.html
http://142.26.194.131/aerodynamics1/...y/Neutral.html
http://142.26.194.131/aerodynamics1/.../Positive.html
http://142.26.194.131/aerodynamics1/...ity/Page4.html

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/
e-mail: khorton02(_at_)rogers(_dot_)com

Jay wrote...

Dave,
I think we're saying the same thing, moving a lighter weight out
further from the CG will increase the moment of inertia.

We're saying the same thing about moment of inertia. That's got
plenty to do with achievable angular acceleration but nothing
to do with stability. Additional area ahead of the CG is
DEstabilizing, not stabilizing, as you stated.

Dave 'co-efficient' Hyde

Kevin Horton wrote...

It is not possible to have a productive discussion
when one party does not understand the terminology used.

My hovercraft is full of eels.

Dave 'tobacconist' Hyde