> > 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 alumininum 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 Aelerons 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 powerplant 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 fabricaton 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,
I own a flying Dragonfly MK-IIH (and 4 Dragonfly projects). I am the
Dragonfly Builders and Flyers Newsletter (DBFN) Editor, I manage the
Dragonfly email list, and I have been designated as the US representative
for the Dragonfly by the new owners from South Africa. I have about 150
hours of time in tail wheel Dragonfly's (MK-II and MK-IIH) and based on my
personal experience and research, I do not think a 2 rotor 13b with a
redrive would be a very good engine choice for the Dragonfly.
The original Dragonfly MK-I (landing gear at the end of the canard tips)
prototype flew with a 45 HP 1600 cc VW with no electrical system. They
switched to a 56 HP 1835 shortly thereafter (the Hapi 1835 would later be
rated at 60 HP). The Dragonfly was designed to be an economical aircraft
(to build and fly) with decent cross country speed.
The original MK-I had an empty weight of 590 pounds with the 1600 VW and 605
pounds with the 1835 VW. While it is possible to build a light Dragonfly,
most people today are going to install things like radios, transponders,
lights, seat cushions, ELT's, and starters. A typical modern MK-II (22'
canard with inboard landing gear) with a VW is usually going to weigh
between 730-780 pounds. The original MK-I maximum gross weight was 1075. A
carbon fiber spar cap lay-up schedule change was made and in the Fall of
1984. The maximum gross weight was later increased to 1150. The maximum
gross weight was later increased to 1300 pounds. Aircraft with the inboard
landing gear have not had problems at these higher weights.
The typical Dragonfly has a fuel capacity of about 15-17 gallons. My
Limbach L2000 engine rated at 80 HP has a fuel burn of about 3.5-4 GPH in
typical cruise and I see about 140 MPH IAS. The empty weight on my MK-IIH
(fiberglass hoop landing gear attached to the fuselage) is 797 pounds.
Initially the designer "strongly" recommended against installing a VW engine
larger than an 1835. They later went on to install a 2180 and were
basically put out of business when the 2276 cc engine started breaking
crankshafts. Since the Dragonfly "factory" was owned by Hapi engines, it is
only natural that they did not support or suggest installing anything except
a Hapi engine.
Aerodynamic changes like adding flaperons should not be taken lightly. The
Dragonfly is an equal span tandem wing airplane. If you start doing things
to reduce the stall speed of the canard you also have to do them to the
wing. Although a deep stall is theoretically not as bad as it would be in a
Velocity or Eze, it is still something that should not be taken lightly. To
my knowledge, only one Dragonfly has ever been deep stalled (on purpose in
flight testing by a Naval test pilot wearing a parachute at high altitude)
and the pilot was able to recover the airplane without difficulty. Pretty
soon you will have an airplane that will be very complex and heavy.
With a 100 HP engine the Dragonfly can easily exceed the never exceed speed
in level flight. I guess you could use the extra power for take-off and
climb and then throttle back to 40% power to keep it below VNE. I do not
remember seeing a HP vs fuel flow chart on the 13B so I can not comment as
to whether or not this might even be feasible. The never exceed speed of
the Dragonfly is 180 MPH (Dragonflyer newsletter #4 page 12).
Landing on a 2,500' strip is not out of the question for a Dragonfly. I
would not even consider landing on a grass strip with a MK-I. I fly out of
a 3,420' paved airport that is 1,020' MSL. If I am on my game, I can land
in less distance than it required for take-off. There will probably be a
time when that 2,500' grass strip will not be long enough to land on, you
will certainly want to practice a lot on longer runways. With lots of
practice you will probably be able to land your Dragonfly at 65 MPH, maybe a
couple MPH slower if you install VG's (at 50% chord line on the canard - not
10-15%) depending on your weight and CG. The Dragonfly is not a STOL
airplane.
The CG and weight are going to be big concerns, even if you could get the
FWF package down to 240 pounds. You will almost certainly have to mount the
radiator aft of the CG. After spending thousands of $ on an exotic
lightweight 13B you will be no better off than if you would have just bought
an O-200 or 3300 Jabiru. You might get by with $9K for the basic exotic
13B, but then you will have to buy an engine computer, custom radiator,
engine mount, engine cowl, radiator scoop for the belly of the a/c....if you
could get by for much less money than good used zero SMOH O-200 set-up I
would be really surprised. A good solid 100 HP will be more than enough for
any Dragonfly. I would strongly recommend an EJ-22 or (SOHC) EJ-25 long
before I would recommend an exotic 2 rotor 13B.
I do believe that a single rotor engine would be a good alternative for the
Dragonfly (or almost any aircraft that needs about 100 HP), in fact I own a
single rotor 12A with a Ross PSRU. I bought the engine last year with the
intention of installing it on my MK-III (tricycle gear). To the best of my
knowledge this engine has never been run. I think I am quite a ways off
from working on the engine.
Several years ago I was looking at the possibility of running a direct drive
2 rotor 13B to get about 100 HP. The Dragonfly is limited to about a 52"
prop, so there is not an issue running the engine at 4000 RPM. This is not
uncommon for a direct drive Subaru and only a few hundred more RPM than many
VW's run. I was discouraged by a couple experienced rotary powered airplane
guys from considering this set-up.
I had the opportunity to fly with Rich Goldman (in fact I was his first
passenger) a few years ago (I think it was in 2003 at Mattoon, IL tandem
wing fly-in) when he had about 50 hours on his airplane. The engine was
very smooth, but we had to cut the flight short due to cooling concerns. I
hosted the 2003 (also the 2004 and 2005) national tandem wing fly-in at
Sullivan, MO and on the way to Sullivan Rich had an (apparent) engine
computer failure and he was forced to land on a sod farm. The airplane was
damaged beyond (economical) repair. He reduced power north of Peoria to
descend below a cloud deck and when he attempted to increase power to arrest
his rate of descent the engine would not respond. He reset the computer (a
couple times), but the engine would not increase above idle power.
The pictures that you sent do not match the text description of your landing
gear configuration. From your description I would say that you have a
MK-IIH, not a MK-II, but the pictures indicate that you have a MK-II. A
MK-II has fiberglass (or steel) legs that come out of the bottom of the
canard (not called the front wing). The MK-II legs are not a hoop, but
rather a flat leg that has a 90 degree twist about 1/2 way down the leg.
The MK-IIH (not an official factory designation or supported modification)
has a fiberglass (or aluminum) hoop landing gear that is attached to the
fuselage.
FYI - There are 4 Dragonfly landing gear configurations:
MK-I - wheels at the tips of the canard
MK-II - inboard fiberglass (or steel) landing gear coming out the bottom of
the canard
MK-IIH - fiberglass (or aluminum) hoop landing gear attached to the fuselage
(not an original configuration supported by the "factory")
MK-III - tricycle gear
Before you start making radical changes to your Dragonfly (like pneumatic
airbrakes) I suggest that you get a flight in a Dragonfly first. You will
have the first Dragonfly with a BRS. I would also suggest that you start
subscribing to the DBFN, purchase the DBFN archive (all 124 Dragonfly
newsletters dating back to 1980), and join the Dragonfly email list on Yahoo
Groups. If you let me know where you are located I might be able to put you
in contact with a Dragonfly owner near you.
Jeff LeTempt
Rolla, MO
The Rotary Engine NewsLetter. Powered by Linux.
ACRE NL web site.
http://www.rotaryeng.net
Copyright 1998-2006 All world wide rights reserved.