>
>> > > I am 90% done with the airframe of my dragon fly I
>> >
>> > am intending to
>> >
>> > > power it
>> > > with a 13b. Any comments? Anyone seen a rotary
>> >
>> > powered dragonfly?
>> >
>> > > would make
>> > > quite a buzzz.....
>> > > --
>> > > Thanks,
>> > > Brent Hasty
>> > >
>> > > Isn't it a bit heavy Brent?
>> > >
>> > > Paul Lamar
>
> --------------------------------------------------
> vw engines are around 165 lb average see:
>
http://www.greatplainsas.com/specsfd.html
>
> I initially began to think about repowering with a rotary when on
the
> list
> someone sent out a link to an outfit making aluminum side
plates, this
> makes it around just 50lbs heavier than a vw for well over twice
the hp,
> not
> to mention reliability issues...
> What are other means to put a 13b on a diet, if one were willing to
> sacrifice
> a little bit of horse power?
>
> I do not think a rotary powered dragonfly is insurmountable.
>
> ------------------------------------------------
>
>> > I'd think so.. I just about bought a Dragonfly
>> > project, but was
>> > discouraged by the weight limit for an engine, and
>> > who wants to
>> > fly behind a VW motor?.. If memory serves me
>> > correct, a c-85 was
>> > to much weight. A single rotor would fit, but that
>> > might mean a
>> > bit of a wait until they get on the market..
>> >
>> > Jarrett
> --------------------------------------------------------------
> What are the dynamics of aircraft performance that are affected by a
> engine
> weight increase like I am discussing?
>
> Consider the reduction of stall by modifying the Ailerons with a
flaperon
> mechanism similar to the kitfox and avid?
> ---------------------------------------------------------------
>
>> I owned and flew a Dragonfly for many years. The 13B
>> is too heavy and powerful for that design.
>
> -------------------------------------------
> How can one ever have too much power?
> -----------------------------------------
>>It was
>> designed around a 1600cc vw, but others have installed
>> c-85/O-200, Jabiru, Subaru, etc, up to about 135hp.
>> Mine was powered by the humble VW for 240 hrs or so,
>> then switched over to a turbocharged Subaru EA81.
>> Performance increased significantly, and no more 50 hr
>> valve jobs req'd.
>
> -------------------------------------------------------------
> At 200lbs the weight of a 13b-aluminum is equal to the ea81 with
> significantly
> more power.
>
> Any clue the VNE of the dragonfly airframe? (cant find it on google)
>
> ------------------------------------------------------------
>
>> There was one fellow out near Mojave somewhere that
>> had built a single-rotor power plant for the DF. I
>> visited his hangar back in the mid-90's. I have no
>> idea if it ever flew with that engine.
>
> -------------------------------------------------------------
> I have a farm I bought to put a fabrication shop on that is 2500 feet
> long, I
> hope to be able to get in and out with the dragonfly.
>
> The extra power will help to leap off the ground, but I will have
to deal
> with
> a hot landing...... Again the flaperon idea may help.
>
>
>
> Thanks,
> Brent Hasty
Brent, it's great that your considering a rotary for your project, and
usually I would promote the installation, however in this case I don't
think you'll be well served to do this installation. There are numerous
reasons not to. Remember the sqr'd rule, double the weight, it takes 4
times to get to speed under the same power [ and 4 times more runway].
Granted, you'll have more horsepower, so lets say twice as much time and
twice as much runway instead. I found an article on EAA's site which
I've
copied below to give you another author's perspective. The points
that come
to light are very important to note.
So weight's as I've found off the net..
VW- 140-190lb's depending on how 'custom' it is.. We'll split the
difference and call it 165lb's
Ea-81- 220lb's installed..[185 for the basic engine block]
13B- ~300lb's installed.. [Paul will correct me if I'm wrong..as this is
from memory]
Horsepower..?
Vw- 85-140 [ we'll say 125 as I've heard that w/out considerable
mods they
can't produce more than 100 due to cooling airflow/fins]
Ea-81- 100hp
13B [if you do it right w/ a P-port I'd guess 225-250hp.. we'll say
225 to
be conservative]
I don't think I'd want to fly in an airframe which has that much extra
engine weight.. but that might be just me..
WHAT ENGINE DOES THE DESIGNER RECOMMEND?
Each aircraft design is developed around certain engine options. A good
clue as to the engine best suited for your project might be ascertained
from the engine the designer installed in his prototype. In
addition, his
literature will undoubtedly stipulate the horsepower range the
aircraft was
designed to safely accommodate.
Some builders are bad about ignoring the designer's horsepower
limitations
and often go ahead on their own and install a much larger engine -
with or
without the designer's approval - hoping to achieve superior
performance.
This can be a dangerous thing to do. Why? I'll try to tell you why by
citing a few worst case scenarios as examples.
It is unlikely that your aircraft's structure was designed to handle
engines much heavier and more powerful than those few recommended.
Anyone building from a kit quickly learns that any small
modification you
make seems to compound problems and affect other parts. For instance, if
you elect to install a larger engine you will find that the furnished
cowling will not fit it without major surgery. The exhaust system,
too, may
have to be modified.
Be advised that engines more powerful than those specified by the
designer
will produce higher thrust and torque loads than those the structure was
designed to handle safely. To avoid exceeding the gross weight and G
loads
specified, such an engine should be derated with mechanical control
stops.
In addition, substituting a heavier engine will upset the design
weight and
balance calculations, and may force you to reduce or eliminate the
baggage
allowance. Furthermore, you might have to redesign and build a shorter
engine mount . . . and maybe add ballast (that's dead weight, son).
Carrying this line of thinking further, a larger more powerful
engine will
require a larger propeller. To accommodate that increased propeller
diameter, longer landing gear legs may have to be built in order to
assure
a safe ground clearance for the propeller.
And that is not all. A more powerful engine will ordinarily cost more,
initially, and will gulp down more fuel. Therefore, unless you also
increase the aircraft's fuel capacity somehow, the aircraft's flight
duration will be definitely reduced.
Increasing the fuel capacity can solve that problem but creates another.
You will be adding still more structural and fuel weight. Consequently,
although the aircraft's range may be increased with the added fuel
capacity, the overall performance may suffer because your payload
will be
reduced and/or your gross weight will be increased beyond its design
limit.
Here's still another glitch. Although an increase in horsepower
generally
produces a shorter take-off, and a better climb, don't think for a
minute
that the attendant increase in top speed will be something
phenomenal. It
won't be. The reason, of course, is well known.
Doubling the horsepower will not double the top speed . . . far from it.
The boost in top speed is often disappointing and seldom does a
builder see
anything over a 25% increase . . . and that would be with the fuel
flowing
through the engine like a stream of water flushing down the toilet.
Consider this observation for the overkill. Most of the more powerful
engines are high compression engines and have to be fed that
expensive 100
octane low lead aircraft fuel. That means you may not be able to use
auto
fuel in your airplane . . . and you know what that will do for your fuel
costs when you are burning over 10 gph.
I say, build it light and you'll get way better performance rather than
heavy and over powered..
Btw.. what is the listed max FWF weight for a Dragonfly?
Don't get me wrong here, I'm not saying the rotary is a bad engine,
I just
don't think its the proper engine for that airframe.. I'd hate to
hear that
it wasn't all you'd hoped it would be after getting it installed..
Ok.. thats my two cents.. [ for what its worth.. :-) ]
Jarrett
Brent! As a dragonfly builder and -pilot for many years,I have followed
this design since 1984.(using VW since first flight) I have been in
contact with a man flying behind a Norton Wankel for quite some
time.Unfortunately ,the engine stopped (ignition problem)and the
Dragonfly was destroyed,still he survived.Good luck with your
Dragonfly,with or without a Wankel! It`s a great airplane!
Torvid
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