Rebuilding project questions
David J. Ervin
I've been watching here for awhile quietly
learning. Last weekend I took the plunge and
bought a "slightly" damaged ultra light plane. I
have looked out in web space and can't find the
answers to some questions I hope someone can help
me with. Here they are.
1. The new specs in the plans call for a Hirth
2704 engine. Currently the plane has a Rotax 377
with a b drive and electric start. Hirth's web
page shows the weight for their complete setup at
96 pounds for all. I can't find the total weight
of the Rotax setup anywhere. Anyone know where I
can find these stats on this engine setup and a
similarly equipped 503, or do one of you keep this
information handy in your frontal lobe?
2. Are physical dimensions and bolt patterns of
the two brands of engines available anywhere?
3. Can a Rotax 503 and my current 377 exchange any
parts such as the starter, gearbox or exhaust
pipe?
4. What are the advantages/disadvantages of two
blade prop vs three blade prop.
5. What are the advantages/disadvantages of fixed
pitch vs ground adjustable.
6. Who is recommended for Rotax rebuilds?
--
David J. Ervin
"The difference between genius and stupidity is
that genius has its limits"
-Albert Einstein
David Ohnsager
says...
> Hello group!
>
> I've been watching here for awhile quietly
> learning. Last weekend I took the plunge and
> bought a "slightly" damaged ultra light plane. I
> have looked out in web space and can't find the
> answers to some questions I hope someone can help
> me with. Here they are.
What kind of ultralight is it? What's its name?
What parts are slightly bent? I hope you replace them with the right
stuff. Not doing so can be hazardous to your health.
Are you a pilot? You need training in a UL whether you are or not. I
trust you have a good instructor lined up? If so, welcome to the sky and
happy aviating!
>
> 1. The new specs in the plans call for a Hirth
> 2704 engine. Currently the plane has a Rotax 377
> with a b drive and electric start. Hirth's web
> page shows the weight for their complete setup at
> 96 pounds for all. I can't find the total weight
> of the Rotax setup anywhere. Anyone know where I
> can find these stats on this engine setup and a
> similarly equipped 503, or do one of you keep this
> information handy in your frontal lobe?
This is interesting. It has a 377 but the plans call for a 2704? A 377 is
a 35HP motor while a 2704 is 50HP. Either it is pretty doggy with the
377, or it will be rather spritely with a 2704. Ya can't add 43% more
horsepower (or take away 30%, depending on which way you look at it)
without noticing!
96 LB is about right for the Hirth. The LEAF 95-96 catalogue says a 503
DCDI weighs 110 lb w/ a C-box and electric start, and a 377 weighs about
85 lb w/ a b-box and no electric start. If you assume the electric start
option adds about 8 lb to a 377 (like it does for the 503) then the
weight comes to 93 lb. Hirth comes standard with electric start.
>
> 2. Are physical dimensions and bolt patterns of
> the two brands of engines available anywhere?
Not for the Hirth unless Rec Power or Eastside Engines has come up with
them. The old catalog the Canadians used had them, but they were pretty
much illegible (poor quality photocopying).
Try a LEAF catalogue for Rotax dimensions. It has them all.
>
> 3. Can a Rotax 503 and my current 377 exchange any
> parts such as the starter, gearbox or exhaust
> pipe?
Nope. At least it wouldn't be a good idea what with the difference in
power and all. I wouldn't want to run a b-box on a 50 HP motor, wouldn't
feel comfortable with it. The exhaust will not be tuned for the larger
motor and will reduce power. The starter.... who knows?
>
> 4. What are the advantages/disadvantages of two
> blade prop vs three blade prop.
Advantage of a 2-blade is efficiency. Period.
Advantages of 3-blade is smoother running, quieter, less vibration, more
thrust if prop size is restricted (like on a Challenger), and they look
cooler.
>
> 5. What are the advantages/disadvantages of fixed
> pitch vs ground adjustable.
Don't waste your time with fixed pitch. Unless you are lucky your fixed
pitch prop will not be optimal for your bird. Look at any of the
catalogues and see how many different fixed pitch props are available and
recommended for any given engine. There are several for any given engine
and airframe combination, too. So how do you know which one is right for
YOU? You don't. Not without trying them, and that can get expensive.
Get a good ground adjustable prop and adjust it until it works best with
your airframe (which was WHAT, again?) and engine. Remember, your engine
will change as it breaks in (and wears out), and the weather will change
over the year, and you will also change. An adjustable pitch prop can
change with you.
My first UL had a 377 with a fixed pitch 2-blade wood prop. It flew and I
was in 7th heaven. Then I replaced it with an adjustable pitch 3-blade
prop. The change in performance, smoother operation, quietness, etc,
showed me that I hadn't even been on the STAIRWAY to heaven before. Go 3-
blade adjustable pitch. You won't regret it.
>
> 6. Who is recommended for Rotax rebuilds?
Don't know. Others will have to help with this one. Good luck.
> --
> David J. Ervin
>
> "The difference between genius and stupidity is
> that genius has its limits"
>
> -Albert Einstein
>
>
>
Hope your project turns out well and you enjoy many seasons of happy
flying!
Regards,
DAO