Constant Speed Prop For Pusher
Michael &/or Phyllis Entis
project insists that the only way to fly is with a constant speed prop (CSP),
especially for an airplane as clean as the one that I'm building. I would
like to know if anyone out there has had any experience with a CSP on a pusher
type aircraft. I'd sure appreciate the details so that I can intelligently
reply to the next pilot that gives me this recommendation.
Mike Entis
Building a Velocity 173RG/Elite
Rob Cherney
Gerd Mühlbauer makes a model MTV-12 which can be configured
for a pusher. I have seen this 3-bladed prop on a Velocity
at Oshkosh. Gerd's company is called MT Propeller and he
usually runs an ad each month in Sport Aviation; they are
located in Atting, Germany. The bad news is the price --
about US$7,000 -- maybe more with the dip in the dollar.
Give serious thought before spending this, though. You will
be putting a bit more weight in the back of an airplane that
is very sensitive to weight and balance. You are also adding
one more system that can fail -- all for a little more climb
performance over a cruise prop. I'm not sure if it is worth
the effort.
If you do indeed get constant speed prop, consider doing
alot of initial testing with a fixed pitch prop to iron
out the kinks of all of the other systems before installing
the C/S unit. If after testing you are satisfied with the
climb performance, stick with the fixed-pitch prop.
Also, you might need to find an engine that has the prop
governor mounting point next to the prop flange. Most
engines, particularly the straight-valve Lycomings, have
the prop governor mounted near the firewall. If this
is the case, you might have to cut an access hole in the
firewall and build up a cup-like structure behind the hole
to accommodate the governor. If you have not yet purchased
your engine, this is the time to consider these things.
Rob-
+--------------------------------------------------------+
|Robert Cherney Home Phone: (410)465-5598 |
|Ellicott City, Maryland e-mail: che...@clark.net |
+--------------------------------------------------------+
ChaniK
2K. It works well as a ground adjustable now, since the blades are
flexible composite.
MMene90744
hope to use on our 3 cylinder Suzuki Turbo Vari-Eze!
Thanks
Mike
WCeaster
presently running a great american fix pitch and the preformance gain was
great I would estamate 20-30 % and it is not yet C/S but after 5 hr I
noticed cracks and sent my blades back and IVO is making a improved blade
now,The problem was that the blades hit a resonate and the blade would
shake back and forth caused by my200hp engine and all that bad air to the
prop plane even though I had problems I will stick with the program (cost
, preformance, and weight) an inovative design that will be great
Stetson E
will add my 2 cents: For the pusher designs, PLEASE be very careful with
CS props, or non-wood fixed pitch props for that matter. Burt Rutan,
designer of the VariViggen, Defiant, VariEze, Long-EZ and Voyager, was
never able to find a safe, utterly reliable CS prop for his pushers, and
he put alot of research and developmental work into it, particularly for
the Defiant and Voyager. A pusher prop is working in such dirty turbulent
air that tremendous stresses are imposed. Voyager threw a prop blade on
its CS rear prop after less than 100 hours. There have been other reports
of "new" CS props worn beyond service limits after less than 100 hours in
service when installed on pushers. Fixed pitch wooden props are much more
forgiving, and fatigue life of wood greatly exceeds that of metal and (it
appears) of modern composites. That's why you see so many wooden props on
pushers.
Throwing a prop blade is a grave problem. The imbalance, no matter how
quickly you think you can shut the engine down, will likely cause major
engine damage, and that's the least of your worries. The engine flinging
itself off the airframe is also very real possibility. It doesn't take
much imagination to see what the resulting CG shift would do to your
airplane's controllability when the engine decides to take the direct
route to terra firma. Your airframe won't be far behind because its not
an airplane anymore, its now a lawn dart. That's why Rutan recommends
installing an engine retention cable if you plan to install an
inadequately proven prop. That way at least, the engine will more or less
stay with the airframe if you throw a blade and the mounts let go.
As I recall, a VariEze lost a prop blade many years ago. The vibration
from the imbalance disabled the engine controls and broke the magneto
p-leads. The only way the pilot could shut down the engine was with the
fuel selector, which must have taken (to the pilot at least) an eternity.
The pilot made a successful off-airport landing. Upon examination, the
engine was found torn off the mounts and laying deadweight in the lower
cowl. To say this pilot was lucky is an extreme understatement.
Another EZ had a failure of a homebuilt kevlar fixed pitch prop. The
pilot suffered serious injuries. Total time on the prop was approximately
3 minutes. Yet another EZ failed a purchased molded plastic fixed pitch
prop. I believe total time on this one was under 10 minutes. And there
are numerous other prop failure accounts discussed in Rutan's Canard
Pusher Newsletter over the last 20 years, many of which were constructed
of composite, metal, or were CS, or a combination of the three.
Even certified props aren't the answer if they aren't properly tested.
Hartzell cautions airframe makers to do vibration analysis studies on
every prop/airframe combination that incorporates a Hartzell prop. With
proper testing, its obvious that a CS prop can be made to work on a pusher
- just look at the Cessna Skymaster. But which homebuilt prop
manufacturer has the resources to do the proper testing for every pusher
design?
I believe that on a pusher, it is prudent to regard CS props, and even
metal or composite fixed pitch props, the same way most people regard auto
conversions - Lets see 20 or more in service for 1000 hours each without a
major failure - then we'll talk.
On a related subject - those of you building or flying a pusher of any
design should consider getting a set of Rutan's Canard Pusher Newsletters.
They contain 20 years worth of pusher experience. Find an EZ
builder/flyer in your local EAA chapter and make a copy of his/her set
(this is authorized by Rutan). Or call Rutan Aircraft Factory for back
issues (do-able, but expensive). Or email me, and I'll make xerox copies
for you at my cost. I also have the text of the newsletters on disk if yo
ChaniK
acts as a dampener on any reasonance modes resulting from the dirty
airflow back of the airframe. I've had no problems with the prop on my
Varieze.
Bruce Frank
: I recently Bought a IVO magnum prop for my Prescot Pusher where I was
Neither IVO nor Warp Drive have a succesful history in a pusher config.
Let me know the results after 50 hrs.
Bruce A. Frank, "Ford 3.8L Engine and V-6 STOL
b...@marlin.ssnet.com Homebuilt Aircraft Newsletter"
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\ (-o-) / AIRCRAFT PROJECTS CO.
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O O
David M Parrish
>Actually, I have had my Magnum on my Varieze for about 50hrs with no
>problems. The loose bushing problem is with the o-360 engines, not
>pushers in general.
That made me think about my particular problem. I'm building a Velocity
and plan to use a Subaru SVX engine. Most Velocitys use an IO-360, which
gives only two very large impulses per engine/prop revolution. I'd think
that would perfect to excite destructive resonances in a prop.
(Graphite/epoxy may be very strong, but it isn't as tough as wood.)
But what about my combination? The SVX is a six cylinder, so there are
three impulses per engine revolution. With a Ross 2.17 reduction, the
prop sees 6.51 impulses per prop revolution, possibly raising the
frequency above the major resonant frequencies of a graphite prop.
---
David Parrish
Damn. Another decision...
ChaniK
will not be a problem for the MAgnum. It runs fine on 350hp V-8s, too.
The O-360s can hurt the bushings because they can actually drive reverse
torque on the trailing bolts since their impulses are huge. And BTW, the
composite blades are much tougher than wood. On a static pull, the prop
blades can take over 60,000lbs pull, but, as any engineer can tell you,
it's the reasonant modes that can get you.
David M Parrish
>I am interested in the SVX for my Glasair. I did not hear from the
>Velocity people in the last 2 years about their testing and I wonder where
>it stand. Do you know of some experience with this engine. Do you know
>how to approach the computer problem (the computer cut off the power to
>some 30% if there is a problem with the O2 sensors or something like that)
The engine they were using is the one I bought. They'd had quite a bit of
teething troubles with it and finally decided it was just taking too much of
their time to fool with it. Their problem with the O2 sensor was 100LL. Real
big no-no. Their finial flight with it ended with the engine in "limp-home"
mode and not generating full power. Duane thought it might of been due to
the high coolant temps he was running. The electronic controller is
definitely one area I need to look at. (Even though I'd hate to switch to
a carb and distributor and cringe at the cost of aftermarket systems.)
>The other issue is where to get one. I understand that Subaru will not
>sell you an engine. (never mention the word aircraft with them BTW.) The
>Ross redaction system looked to me like the best one too. I will be
>interested to learn from your experience.
It's definitely not an easy engine to get. The main source is the wrecking
yard and the SVX is a pretty rare car. Expect to pay $5K just for the
engine alone. I have heard there are other sources for this engine, and
Ross could probably direct you to where.
As to my experience, well, I haven't done much with the engine as yet, other
than to strip the wiring harness off so I can rewire the engine with mil
spec wire. I hope to do some dyno testing and make a lighter weight intake
manafold. (The stock manafold weighs about fifteen pounds, with another
seven for the throttle body.) If I get really ambitious, I may even try
designing a new ignition/injector controller.
---
David Parrish
Currently REdoing my winglets.
TeddyDBear
Parrish) writes:
>That made me think about my particular problem. I'm building a Velocity
>and plan to use a Subaru SVX engine.
I am interested in the SVX for my Glasair. I did not hear from the
Velocity people in the last 2 years about their testing and I wonder where
it stand. Do you know of some experience with this engine. Do you know
how to approach the computer problem (the computer cut off the power to
some 30% if there is a problem with the O2 sensors or something like that)
The other issue is where to get one. I understand that Subaru will not
sell you an engine. (never mention the word aircraft with them BTW.) The
Ross redaction system looked to me like the best one too. I will be
interested to learn from your experience.
Thanks
Ted (KMAO)
Big EZ 13AU
Super Acro Sport 3GV
Glasair (In the garage)
Dana Aviat
which are really spinnung in turbulent air?
TeddyDBear
Parrish) writes:
>The engine they were using is the one I bought. They'd had quite a bit of
>teething troubles with it and finally decided it was just taking too much
of
>their time to fool with it. Their problem with the O2 sensor was 100LL.
Real
>big no-no. Their finial flight with it ended with the engine in
"limp-home"
>mode and not generating full power. Duane thought it might of been due to
>the high coolant temps he was running. The electronic controller is
>definitely one area I need to look at. (Even though I'd hate to switch to
>a carb and distributor and cringe at the cost of aftermarket systems.)
This is really interesting I will want to follow up with you on your
progress.
I heard there is a guy in AZ that is doing a bypass of this function of
the computer while still maintaining the sensors auto mixture function. I
obviously do not know enough about it. There is a guy in Chattanooga TN
who is very productive builder he builds a Lancair 4P and a Defiant and
have 2 SVX for it if I am not mistaken. He will be a good person to talk
to. He use to be the local EAA president very nice guy you should not
have a problem localizing him. The guy that build that electronic
ignition in Chattanooga TN knows him too and between this two you should
be getting some help. I thought that this engine will be great for my
Glasair but I think we got to be very cautious we are experimenting enough
in the aircraft that I will want to be careful with the engine and put
only one that there is a lot of experience with. Just couple month ago
the PMA engine of the guy with the Venture broke in flight and took the
guy with him. I fill that we need to be very careful with how much we
experiment. The SVX looks really very reliable but some times small
peripheral things can get you. Any how that’s how progress is being made,
just be careful.
What do you do with your winglets? I just shaved off the lower portion of
mine I will be happy to compare notes with you on that.
(I am living this in the “public domain” and E-mail you so every body can
participate)
Thank you
Ted
Big EZ 13AU
Super Acro Sport 3GV
Glasair (in the garage)
TeddyDBear
Parrish) writes:
>>in the aircraft that I will want to be careful with the engine and put
>>only one that there is a lot of experience with. Just couple month ago
>>the PMA engine of the guy with the Venture broke in flight and took the
>>guy with him. I fill that we need to be very careful with how much we
>
>From what I've heard, that was a clear case of VFR into IMC and not a
>failure of the aircraft. (OK. It did break up when it hit the trees...)
>
>
My understanding (being a just a Country Doc though its limited :-) ) is
that the crankshaft broke in flight. I have heard that continental have
warren the guy that something about the strength of it is limited.
As always I do not know enough about it, but I have an opinion.
Are you keeping the lower winglets?
Ted (KMAO)
Dennis Callahan
FWIW, there are a lot of active Glassair builders on cserve in the
AVSIG forum. There seem to be at least 3 Glassair threads running
constantly.
Charles K. Scott
d...@bmesun1.MCG.EDU (David M Parrish) writes:
> >in the aircraft that I will want to be careful with the engine and put
> >only one that there is a lot of experience with. Just couple month ago
> >the PMA engine of the guy with the Venture broke in flight and took the
> >guy with him. I fill that we need to be very careful with how much we
>
> From what I've heard, that was a clear case of VFR into IMC and not a
> failure of the aircraft. (OK. It did break up when it hit the trees...)
David, you've got two accidents confused. The Venture was a broken
crank. The NSI Kitfox demonstrator was a low altitude tree strike in
IMC.
Corky Scott