The Murphy Builders Site

My Rebel construction is getting to the point where I need to get serious on
the engine decision. I would like to explain my views here, and would
appreciate any and all comments.

I am building my Rebel to carry 2 adults (realistically figuring 200# each),
full fuel, camping gear for several days, and fishing gear without going over
the established 1650# gross weight. I do not have the experience and do not
anticipate flying into STOL situations, and I doubt I would ever put the Rebel
on floats.

While I would like to have 150-160 HP, given these parameters I don't foresee
using the O-320 simply because it weighs to much (255# dry wt). Given the empty
weight figures I've seen for some O-320 equipped Rebels, it seems likely to
reach gross with 2 people and full fuel without any any of the camping/fishing
gear that I'd like to carry. I don't want to have to drain fuel to maintain
gross wt limits. Someone let me know if I'm wrong about this.

However, should I ever sell the aircraft, I think it would have a better resale
value if O-320 equipped.

I like the idea of the Jabiru 3300, 6 cylinder, which the mfg. lists the ramp
weight as 180# with exhaust, carb,starter motor, alternator, ignition system,
and accessory pack. That's 75# lighter than the listed dry weight of the O-320;
39# lighter than the listed dry weight of the Lyc O-235-N2C; and 25# lighter
than the listed dry weight (w/o accessories) of the Continental IO-240-B.

So I am leaning toward the Jabiru 3300. What I'm uncertain about is the higher
RPM's the engine develops (3300 max) and how that might necessitate using a
smaller diameter prop. If I would need a smaller diameter prop, how would that
affect overall performance compared to an engine developing less max rpms but
using a larger diameter prop? Would an in-flight or constant speed prop
(Airmaster or Quinti) overcome some of the performance issues of a smaller
diameter prop?

I found a Propeller Tip Speed Calculator at www.altimizer.com/propspd.html
which says "to produce maximum thrust from your propeller at full power your
tip speed should fall between .88 and .92 mach....This of course varies
depending on your particular propeller and the temperature". Using the
calculator with a 70" prop diameter, 3300 prop rpm's, and ambient temp of 70
deg F produced a tip speed of 0.894 mach. A 72 inch prop under the same
conditions reached 0.919 mach, just shy of the upper limit. I noted that tip
speeds increased as the ambient temp decreased. What ambient temp should you
use to make the proper determination? What happens when prop tips exceed 0.920
mach?

This is all stuff I am trying to understand so that I can make an informed
decision.

So anyway, I would appreciate any discussion anyone might have regarding this.
I searched through the archives for 'Jabiru'. There was some discussion, though
mostly regarding the smaller engine (2200), and at least one other builder
indicated he would be installing the Jabiru 3300.

Roger Hoffman #687R
Eugene, OR USA!





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Empty weights with 0320's really vary depending on equipment. Mine came in
at 925 on wheels using light weight Warp prop, bungee gear, starter,
alternator, and instruments and no fancy finished interior. That still
allowed me plenty of useful load for fuel, heavy people and luggage. And now
that I have mine on amphibs, I can tell you from personal experience, it
flies just fine with really heavy loads.

If you don't care about performance, the 100 hp 912S will give you plenty of
useful load, but it wouldn't be my choice.

I don't know anything about the Jabiru, but would share your concern about
having to use a smaller diameter prop and sacrifice climb power.

JMHO
Walter

-----Original Message-----
From: murphy-rebel@dcsol.com [mailto:murphy-rebel@dcsol.com]On Behalf Of
rognal@dcsol.com
Sent: Sunday, September 22, 2002 2:17 PM
To: murphy-rebel@dcsol.com
Subject: Engine Questions


My Rebel construction is getting to the point where I need to get serious on
the engine decision. I would like to explain my views here, and would
appreciate any and all comments.

I am building my Rebel to carry 2 adults (realistically figuring 200# each),
full fuel, camping gear for several days, and fishing gear without going
over
the established 1650# gross weight. I do not have the experience and do not
anticipate flying into STOL situations, and I doubt I would ever put the
Rebel
on floats.

While I would like to have 150-160 HP, given these parameters I don't
foresee
using the O-320 simply because it weighs to much (255# dry wt). Given the
empty
weight figures I've seen for some O-320 equipped Rebels, it seems likely to
reach gross with 2 people and full fuel without any any of the
camping/fishing
gear that I'd like to carry. I don't want to have to drain fuel to maintain
gross wt limits. Someone let me know if I'm wrong about this.

However, should I ever sell the aircraft, I think it would have a better
resale
value if O-320 equipped.

I like the idea of the Jabiru 3300, 6 cylinder, which the mfg. lists the
ramp
weight as 180# with exhaust, carb,starter motor, alternator, ignition
system,
and accessory pack. That's 75# lighter than the listed dry weight of the
O-320;
39# lighter than the listed dry weight of the Lyc O-235-N2C; and 25# lighter
than the listed dry weight (w/o accessories) of the Continental IO-240-B.

So I am leaning toward the Jabiru 3300. What I'm uncertain about is the
higher
RPM's the engine develops (3300 max) and how that might necessitate using a
smaller diameter prop. If I would need a smaller diameter prop, how would
that
affect overall performance compared to an engine developing less max rpms
but
using a larger diameter prop? Would an in-flight or constant speed prop
(Airmaster or Quinti) overcome some of the performance issues of a smaller
diameter prop?

I found a Propeller Tip Speed Calculator at www.altimizer.com/propspd.html
which says "to produce maximum thrust from your propeller at full power your
tip speed should fall between .88 and .92 mach....This of course varies
depending on your particular propeller and the temperature". Using the
calculator with a 70" prop diameter, 3300 prop rpm's, and ambient temp of 70
deg F produced a tip speed of 0.894 mach. A 72 inch prop under the same
conditions reached 0.919 mach, just shy of the upper limit. I noted that tip
speeds increased as the ambient temp decreased. What ambient temp should you
use to make the proper determination? What happens when prop tips exceed
0.920
mach?

This is all stuff I am trying to understand so that I can make an informed
decision.

So anyway, I would appreciate any discussion anyone might have regarding
this.
I searched through the archives for 'Jabiru'. There was some discussion,
though
mostly regarding the smaller engine (2200), and at least one other builder
indicated he would be installing the Jabiru 3300.

Roger Hoffman #687R
Eugene, OR USA!



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For what it's worth, My Rebel "652" completely finished (upholstered
interior and paint) with basic VFR instruments, complete engine instruments,
ELT, bungee gear and O320 H2AD came in at 978 LBS. That also included a 36
LB Senenich prop. This gives me 672 lbs of useful load with the confidence
one needs to fly any where. Is this not enough? I have seen to often the
sacrifices of reliability trying to save a couple of pounds. Besides 1650
gross is calculated at "0" G's and the airframe is rated at "+6 need I say
more.




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Hi Roger

I don't have hands on experience with any of the engines mentioned but I
like to compare engine power at 2400 to 2500 rpm. In the majority of
cases that is about all you'll be seeing while trying to climb over that
fence or those trees. Maybe you can do a bit better with a variable
pitch prop but I wouldn't count on it. At Rebel climb speed a larger
prop will produce somewhat more thrust per horsepower than a smaller
diameter prop. I suspect a 912S might outperform that J-3300. In
addition of course fuselage drag goes up with a smaller prop due to
higher speed airflow over the fuselage and the fuselage cross section
area being a higher percentage of the prop disk area.

At .9 mach tip speed I feel you are losing a bit too much power due to
high prop tip drag and you are making some serious noise. The number I
settled on for a takeoff target was .8 mach tip speed. I didn't check to
see if the calculator that you mentioned considers it but tip mach also
rises with forward airspeed of course.

These comments are for a Rebel and may not be as applicable to a higher
speed aircraft.

Ken

rognal@dcsol.com wrote:

My Rebel construction is getting to the point where I need to get serious on
the engine decision. I would like to explain my views here, and would
appreciate any and all comments.

I am building my Rebel to carry 2 adults (realistically figuring 200# each),
full fuel, camping gear for several days, and fishing gear without going over
the established 1650# gross weight. I do not have the experience and do not
anticipate flying into STOL situations, and I doubt I would ever put the Rebel
on floats.

While I would like to have 150-160 HP, given these parameters I don't foresee
using the O-320 simply because it weighs to much (255# dry wt). Given the empty
weight figures I've seen for some O-320 equipped Rebels, it seems likely to
reach gross with 2 people and full fuel without any any of the camping/fishing
gear that I'd like to carry. I don't want to have to drain fuel to maintain
gross wt limits. Someone let me know if I'm wrong about this.

However, should I ever sell the aircraft, I think it would have a better resale
value if O-320 equipped.

I like the idea of the Jabiru 3300, 6 cylinder, which the mfg. lists the ramp
weight as 180# with exhaust, carb,starter motor, alternator, ignition system,
and accessory pack. That's 75# lighter than the listed dry weight of the O-320;
39# lighter than the listed dry weight of the Lyc O-235-N2C; and 25# lighter
than the listed dry weight (w/o accessories) of the Continental IO-240-B.

So I am leaning toward the Jabiru 3300. What I'm uncertain about is the higher
RPM's the engine develops (3300 max) and how that might necessitate using a
smaller diameter prop. If I would need a smaller diameter prop, how would that
affect overall performance compared to an engine developing less max rpms but
using a larger diameter prop? Would an in-flight or constant speed prop
(Airmaster or Quinti) overcome some of the performance issues of a smaller
diameter prop?

I found a Propeller Tip Speed Calculator at www.altimizer.com/propspd.html
which says "to produce maximum thrust from your propeller at full power your
tip speed should fall between .88 and .92 mach....This of course varies
depending on your particular propeller and the temperature". Using the
calculator with a 70" prop diameter, 3300 prop rpm's, and ambient temp of 70
deg F produced a tip speed of 0.894 mach. A 72 inch prop under the same
conditions reached 0.919 mach, just shy of the upper limit. I noted that tip
speeds increased as the ambient temp decreased. What ambient temp should you
use to make the proper determination? What happens when prop tips exceed 0.920
mach?

This is all stuff I am trying to understand so that I can make an informed
decision.

So anyway, I would appreciate any discussion anyone might have regarding this.
I searched through the archives for 'Jabiru'. There was some discussion, though
mostly regarding the smaller engine (2200), and at least one other builder
indicated he would be installing the Jabiru 3300.

Roger Hoffman #687R
Eugene, OR USA!

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RJohnson-

This was one of the points I was trying to make. You have 672 lbs of useful
load. I want to carry two people (400#), and full fuel(264#). If I want to make
a flight to Oshkosh, I've got 8 lbs left for gear/luggage. Again, I do not
choose to exceed gross wt limits and I don't want to have to drain fuel to gain
payload.

Thanks for your comments.

Roger #687R
Eugene, OR USA





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Hi Roger
I've an 0-290 lyc. in my rebel. The origional empty weight was 850lbs. I
think I've probably added about 50lbs. to that since completion. I rarely
carry full fuel. Full fuel gives me about 7hours endurance. The longest
I've ever flown my plane was 3.9hrs. and I was glad to land and strech my
legs (and unstrech my bladder) after that.
Drew Dalgleish

At 08:47 AM 9/23/2002 -0800, you wrote:

RJohnson-

This was one of the points I was trying to make. You have 672 lbs of useful
load. I want to carry two people (400#), and full fuel(264#). If I want to

make

a flight to Oshkosh, I've got 8 lbs left for gear/luggage. Again, I do not
choose to exceed gross wt limits and I don't want to have to drain fuel to

gain

payload.

Thanks for your comments.

Roger #687R
Eugene, OR USA



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G'day Roger !

We fitted a "souped up" , but light weight ( light weight starter, alternator, no vacuum pump & one mag' replaced by an electronic system) version of an 0-235 ( about 130 HP) , to our Rebel (it weighs in at around 950 lbs with a pretty good panel).... and we are very happy with our performance.

I weigh 300 lbs and the Rebel lifts me & a large friend & lots of gear besides and doesn't even notice the extra weight ! :-)

I am not in love with the Jabiru 6 Cylinder for a number of reasons (too many hometown stories.... write to me & I'll tell you about some )

The whole high revving / small diameter prop' IS a real issue on a large fronted plane like a Rebel .... I reckon you would be better off with a geared down 912S swinging a larger prop !

Drop us a line if you want more info "

Rick & Wendy Harper
16 Tor rd, Dee Why
N.S.W. Australia 2099
Ph: 02 9971 7889
O'seas: 612 9971 7889
Mbl: 0416 041 007
O'seas: 61416 041 007

----- Original Message -----
From: rognal@dcsol.com (rognal@dcsol.com)
To: murphy-rebel@dcsol.com (murphy-rebel@dcsol.com)
Sent: Monday, September 23, 2002 7:16 AM
Subject: Engine Questions


My Rebel construction is getting to the point where I need to get serious on
the engine decision. I would like to explain my views here, and would
appreciate any and all comments.

I am building my Rebel to carry 2 adults (realistically figuring 200# each),
full fuel, camping gear for several days, and fishing gear without going over
the established 1650# gross weight. I do not have the experience and do not
anticipate flying into STOL situations, and I doubt I would ever put the Rebel
on floats.

While I would like to have 150-160 HP, given these parameters I don't foresee
using the O-320 simply because it weighs to much (255# dry wt). Given the empty
weight figures I've seen for some O-320 equipped Rebels, it seems likely to
reach gross with 2 people and full fuel without any any of the camping/fishing
gear that I'd like to carry. I don't want to have to drain fuel to maintain
gross wt limits. Someone let me know if I'm wrong about this.

However, should I ever sell the aircraft, I think it would have a better resale
value if O-320 equipped.

I like the idea of the Jabiru 3300, 6 cylinder, which the mfg. lists the ramp
weight as 180# with exhaust, carb,starter motor, alternator, ignition system,
and accessory pack. That's 75# lighter than the listed dry weight of the O-320;
39# lighter than the listed dry weight of the Lyc O-235-N2C; and 25# lighter
than the listed dry weight (w/o accessories) of the Continental IO-240-B.

So I am leaning toward the Jabiru 3300. What I'm uncertain about is the higher
RPM's the engine develops (3300 max) and how that might necessitate using a
smaller diameter prop. If I would need a smaller diameter prop, how would that
affect overall performance compared to an engine developing less max rpms but
using a larger diameter prop? Would an in-flight or constant speed prop
(Airmaster or Quinti) overcome some of the performance issues of a smaller
diameter prop?

I found a Propeller Tip Speed Calculator at www.altimizer.com/propspd.html
which says "to produce maximum thrust from your propeller at full power your
tip speed should fall between .88 and .92 mach....This of course varies
depending on your particular propeller and the temperature". Using the
calculator with a 70" prop diameter, 3300 prop rpm's, and ambient temp of 70
deg F produced a tip speed of 0.894 mach. A 72 inch prop under the same
conditions reached 0.919 mach, just shy of the upper limit. I noted that tip
speeds increased as the ambient temp decreased. What ambient temp should you
use to make the proper determination? What happens when prop tips exceed 0.920
mach?

This is all stuff I am trying to understand so that I can make an informed
decision.

So anyway, I would appreciate any discussion anyone might have regarding this.
I searched through the archives for 'Jabiru'. There was some discussion, though
mostly regarding the smaller engine (2200), and at least one other builder
indicated he would be installing the Jabiru 3300.

Roger Hoffman #687R
Eugene, OR USA!



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Roger,
Put in the 150 hp O-320, carry 4 hrs of fuel and plan 3 hour maximum bladder
capacity flights at 7.5 gal/hr x 4 =180 lbs + unusable (2 gal each tank?)24 lbs =
204, (if you are not instrument equipped and proficient it is not that often that
you will get a straight shot at more than three hours anyway, not in the northeast
anyway), lose 20 lbs, convince your friend to lose 20 lbs, this would give you
about 90 lbs of baggage capacity assuming that the A/C comes in at 1000 lbs.
Other suggestions, Put in the 912 and pick up 100 lbs but sacrifice
performance. (You will have to fly the wing.) Ship your stuff to OSH. Leave your
friend (wife?) behind and enjoy the true solitude and enjoyment of flight. Scrap
the Rebel (you should have figured out this payload problem before you bought the
Rebel) and trade up to a Super Rebel. Buy a 172 and stop watching your life go by
in the garage. I hope that you can appreciate the humor here Roger.
Good luck, you'll need it.
Rick D.
Rebel S/N 404R

rognal@dcsol.com wrote:

RJohnson-

This was one of the points I was trying to make. You have 672 lbs of useful
load. I want to carry two people (400#), and full fuel(264#). If I want to make
a flight to Oshkosh, I've got 8 lbs left for gear/luggage. Again, I do not
choose to exceed gross wt limits and I don't want to have to drain fuel to gain
payload.

Thanks for your comments.

Roger #687R
Eugene, OR USA



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Rick D.,

I considered the payload issue before I purchased the Rebel. I asked questions
of this list, I researched the archives, I bought the literature/video from
MAM, etc.

I guess I believed the Rebel would fly with an engine rated from 80 to 160 HP.
Certainly I knew that more HP would likely improve performance. I didn't
realize however, that it would not fly without an O-320....(humor).

Thanks for your comments. And thanks everybody else for your comments as well.

R Hoffman #687R
Eugene, OR USA

On 9/24/02 7:43 AM, RSDEC1@ISP01.NET wrote to MURPHY-REBEL:

Scrap the Rebel (you should have figured out this payload problem before you
bought the Rebel) and trade up to a Super Rebel.... I hope that you can
appreciate the humor here Roger.






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