RV-9A's wing with Rotax 914?

[Shin Gou]

Looking at RV-9A's specification (weight, engine, etc.), I think a
Rotax 914 can power it very well, may give a better performance than
O-235. However, the problem is Rotax is far to light to be installed
on RV-9A.

So I just can't help thinking, well, why not a new design around
RV-9A's wing and Rotax 914. The design will be pretty much on
fuselage. The benefits of this designe of new fuselage+RV-9A
wing+Rotax 914 should be:

1) the basic empty weight should be 100-150 lbs lighter than RV-9A.
Rotax 914's wet installation weight is about 80 lbs lighter than
O-235. There should be more or less some structural weight saving from
the lighter engine installation and lighter gross weight.

2)Rotax 914 has constant 100 hp output up to 12,000 feet so it gives
more horsepower at 8000 feet than O-235.

3)The fuselage, if built in composite, can be sleeker(not necessarily
much lighter though)

Overall, lighter weight+more horsepower at altitude+sleeker fuselage
should make this new fuselage+RV-9A wing+Rotax 914 design at least as
good as RV-9A with O-235.

Prove me wrong please.

Shin Gou

[[email protected]]

"Shin Gou" > wrote in message
om...
> Looking at RV-9A's specification (weight, engine, etc.), I think a
> Rotax 914 can power it very well, may give a better performance than
> O-235. However, the problem is Rotax is far to light to be installed
> on RV-9A.
>
> So I just can't help thinking, well, why not a new design around
> RV-9A's wing and Rotax 914. The design will be pretty much on
> fuselage. The benefits of this designe of new fuselage+RV-9A
> wing+Rotax 914 should be:
>
> 1) the basic empty weight should be 100-150 lbs lighter than RV-9A.
> Rotax 914's wet installation weight is about 80 lbs lighter than
> O-235. There should be more or less some structural weight saving from
> the lighter engine installation and lighter gross weight.
>
> 2)Rotax 914 has constant 100 hp output up to 12,000 feet so it gives
> more horsepower at 8000 feet than O-235.
>
> 3)The fuselage, if built in composite, can be sleeker(not necessarily
> much lighter though)
>
> Overall, lighter weight+more horsepower at altitude+sleeker fuselage
> should make this new fuselage+RV-9A wing+Rotax 914 design at least as
> good as RV-9A with O-235.
>
> Prove me wrong please.
>
> Shin Gou

I've had similar thoughts along the lines of sticking a 914 in either an
RV-3 or an RV-9. Why not just extend the forward fuselage to get the w/b
correct? You'd also want to verify your stability margins because the longer
forward fuselage will tend to be destabilizing. Lengthening the fuselage
will cost you some weight in additional structure, but you should still end
up with a lighter airframe that uses less fuel.

On the other hand, why not build it with the 0-235 and go flying a year or
two sooner?

KB

[Pete]

The plane you describe already exists - the Europa.

www.europa-aircraft.com

Faster (at altitude) and lighter than an RV9 with an O-235

Better yet, the wings unplug, and you can swap in the glider wings (ala U-2)
to cruise _really_ high :-)

Cheers,
Pete
Europa Builder (both wings)


"Shin Gou" > wrote in message
om...
> Looking at RV-9A's specification (weight, engine, etc.), I think a
> Rotax 914 can power it very well, may give a better performance than
> O-235. However, the problem is Rotax is far to light to be installed
> on RV-9A.
>
> So I just can't help thinking, well, why not a new design around
> RV-9A's wing and Rotax 914. The design will be pretty much on
> fuselage. The benefits of this designe of new fuselage+RV-9A
> wing+Rotax 914 should be:
>
> 1) the basic empty weight should be 100-150 lbs lighter than RV-9A.
> Rotax 914's wet installation weight is about 80 lbs lighter than
> O-235. There should be more or less some structural weight saving from
> the lighter engine installation and lighter gross weight.
>
> 2)Rotax 914 has constant 100 hp output up to 12,000 feet so it gives
> more horsepower at 8000 feet than O-235.
>
> 3)The fuselage, if built in composite, can be sleeker(not necessarily
> much lighter though)
>
> Overall, lighter weight+more horsepower at altitude+sleeker fuselage
> should make this new fuselage+RV-9A wing+Rotax 914 design at least as
> good as RV-9A with O-235.
>
> Prove me wrong please.
>
> Shin Gou

[Bob Kuykendall]

Earlier, (Shin Gou) wrote:

> ...Prove me wrong please.

Well, I'm not in any position to prove you wrong or right, but my
opinions are:

* Based on my relatively meager composites experience, making a nice
composite fuselage from scratch is several times harder than riveting
together one of Vans' fuselage kits. To get a nice shape _and_ light
weight, you find yourself drawn towards using female-molded parts like
I'm developing for the HP-24 kit sailplane fuselage. And once you get
that deep into it, you're pretty much in the business.

* Based on my personal prejudice, and on many conversations with the
aeronautic engineer who designed the wing profile for the RV-10, I
don't feel so enthusiastic about the RV-9 wing as that I'd go to the
trouble of adapting it onto a different airplane. Don't get me wrong;
the RV-9 wing is a fine solution to the original set of constraints.
But I'd prefer to start with a blank sheet, and not be constrained by
the limitations imposed on the wing by a prior fuselage design.

* Based on other personal prejudices, I prefer airplanes that are
generally relatively homogenous in terms of construction methodology.
That is, metal fuselages with metal wings, and composite fuselages
with composite wings. Sure, there are often compelling reasons not to
hold with that - the HP-18 kit sailplane is a good counterexample. But
I think that people do better work, and enjoy it more, when they're
not always "shifting gears" and re-climbing learning curves as they
change between metal techniques and composite techniques.

And again, those are just my opinions.

Thanks, and best regards to all

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

[nauga]

Shin Gou wrote:

> Overall, lighter weight+more horsepower at altitude+sleeker fuselage
> should make this new fuselage+RV-9A wing+Rotax 914 design at least as
> good as RV-9A with O-235.
>
> Prove me wrong please.

No right or wrong from me, but if you're going to all
that time and trouble, why not design a whole new
airframe for the envelope you intend and the performance
you want. RV wings or not, what you propose will almost
certainly take longer and be more expensive than an RV.
I'd also bet that you wouldn't see enough performance benefit
to warrant all the changes strapped to the same RV wing.

Interesting project from an engineering point of view,
but not very practical, IMO.

Dave 'clean sheet' Hyde

[Richard Lamb]

nauga wrote:
>
> Shin Gou wrote:
>
> > Overall, lighter weight+more horsepower at altitude+sleeker fuselage
> > should make this new fuselage+RV-9A wing+Rotax 914 design at least as
> > good as RV-9A with O-235.
> >
> > Prove me wrong please.
>
> No right or wrong from me, but if you're going to all
> that time and trouble, why not design a whole new
> airframe for the envelope you intend and the performance
> you want. RV wings or not, what you propose will almost
> certainly take longer and be more expensive than an RV.
> I'd also bet that you wouldn't see enough performance benefit
> to warrant all the changes strapped to the same RV wing.
>
> Interesting project from an engineering point of view,
> but not very practical, IMO.
>
> Dave 'clean sheet' Hyde
>


I'd have to agree with Dave on this one.
Using a lighter engine would allow for a lighter airframe.
AND lighter wings...

As a fer instance, look at the differences between an RV and
a Zenith Zodiac.

The Zodiac was designed around a smmaller lighter engine to good
advantage.

Richard

[Shin Gou]

(Bob Kuykendall) wrote in message >
> Well, I'm not in any position to prove you wrong or right, but my
>
> * Based on my personal prejudice, and on many conversations with the
> aeronautic engineer who designed the wing profile for the RV-10, I
> don't feel so enthusiastic about the RV-9 wing as that I'd go to the
> trouble of adapting it onto a different airplane. Don't get me wrong;
> the RV-9 wing is a fine solution to the original set of constraints.
> But I'd prefer to start with a blank sheet, and not be constrained by
> the limitations imposed on the wing by a prior fuselage design.
>

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

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?

BTW, I like Europa very much too. Actually I was going back and forth
between Europa and RV-9A. THe only problem of Europa for me is its
price: near $29k for a complete kit while RV-9A's wing kit costs only
$5400. I am just wondering why there's no head-to-head comparison
between these two aircrafts whose missions and performances are so
similar.

Shin

[VideoFlyer]

What would happen if you put an RV wing on the Zodiac XL? Would the thinner RV
wing provide less drag....therefore higher speeds?

[Richard Lamb]

VideoFlyer wrote:
>
> What would happen if you put an RV wing on the Zodiac XL? Would the thinner RV
> wing provide less drag....therefore higher speeds?

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


Well duh.

[VideoFlyer]

>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.

[Bob Kuykendall]

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

[Richard Lamb]

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

[Jay]

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.

[Kevin Horton]

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

[nauga]

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]

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 .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
>

[[email protected]]

"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

[Kevin Horton]

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

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

[nauga]

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

[nauga]

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

[Jay]

After control system theory in engineering school and designing PID
systems for work I know what stability means, but thanks for the links
anyway. I wasn't talking about the engineering definition, I was
referring to what lay people usually refer to as a feeling they call
"stability". I didn't want to bore people defining terms when we're
really talking about how something feels to a pilot.

[Snowbird]

"nauga" > wrote in message .net>...
> 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
>

??? 'tobacconist' think you misspelt 'obfuscationist'?

Sydney

[nauga]

Jay wrote...

> I wasn't talking about the engineering definition, I was
> referring to what lay people usually refer to as a feeling they call
> "stability". I didn't want to bore people defining terms when we're
> really talking about how something feels to a pilot.

Regardless of how you intended to refer to it,
more area in front of the CG will reduce both the
stick force per g and the stick force per unit
airspeed deviation. Both of these effects are
detrimental to handling in IMC (for an airplane
that's originally suited for it), and neither
are effected by the mass distribution other than
the effect that distribution has on CG. Inertia
doesn't enter into the picture in these effects.

What _hasn't_ been said here is that if you
add more aerodynamic are in front you can compensate
by moving the CG forward, but (a) that's not always
easy, and (b) you then effectively lengthen the
tail arm, which has a similar effect on handling.

Dave 'TANSTAAFL' Hyde

[Big John]

Kevin

Read where Canada may close Goose Bay, 'Bag' Town and others. Looks
like your Political's will strip you like ours have/did.

Big John

[Kevin Horton]

On Fri, 05 Mar 2004 13:24:05 -0800, Jay wrote:

> After control system theory in engineering school and designing PID
> systems for work I know what stability means, but thanks for the links
> anyway. I wasn't talking about the engineering definition, I was
> referring to what lay people usually refer to as a feeling they call
> "stability". I didn't want to bore people defining terms when we're
> really talking about how something feels to a pilot.

OK, if you don't want to talk about stability, try to find some other
words to describe what you want to say. Otherwise if what you are trying
to mean doesn't match the words you use it is like trying to have a
discussion with my wife when she gets in one of those moods. It ends up
with a lot of words being said, but no communication occurring.

There is a very good relationship between quantitative measures of
stability and how the aircraft will "feel" to the pilot. Adding area
forward to accommodate a lighter engine on a longer engine mount will make
the aircraft a worse IFR platform, as there will be less of a tendency
for the aircraft to return to the trimmed condition if it is disturbed in
pitch or yaw. There will also be lower stick force cues if you get off
the trimmed speed, which will increase the workload when trying to fly a
desired speed, like when you are on final approach.

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

[Richard Lamb]

Jay wrote:
>
> After control system theory in engineering school and designing PID
> systems for work I know what stability means, but thanks for the links
> anyway. I wasn't talking about the engineering definition, I was
> referring to what lay people usually refer to as a feeling they call
> "stability". I didn't want to bore people defining terms when we're
> really talking about how something feels to a pilot.

This IS a fairly technical forum.

What the great unwashed masses think about aerodynamic stability
would probably confuse me badly...

Richard

[Big John]

Kevin

Do you think my wife and yours came from the same family tree?

BJ

On Sat, 06 Mar 2004 03:12:07 GMT, Kevin Horton > wrote:

----clip----

----clip---- Otherwise if what you are trying
>to mean doesn't match the words you use it is like trying to have a
>discussion with my wife when she gets in one of those moods. It ends up
>with a lot of words being said, but no communication occurring.

----clip----