Stupid hp to thrust question

To quote Bill Clinton, "It depends on what your definition of what thrust
is"?

Damn, I've never read so much BS for a simple question.

Hi All, thanks for the responses, was not meant to be a trick question but
definately a newbie question. I was curious after reading about people using
mazda 13b engines for various homebuilts, and porting them, adding on
various components to boost the hp from 200 to 260+. Seems at a point that
it's overkill if the 200 hp engine is going to provide you with the needed
ponies and rpms to accomplish the same as the 260 hp engine. What would the
advantge be of having the extra horsepower ?

Thanks,

Mark


"Mark" wrote in message
...
Does a prop turning at 2300 rpm on a 150hp motor produce more thrust than
a
prop spinning 2300 rpm on a 100 hp motor ?

In article , "Mark" writes:


Hi All, thanks for the responses, was not meant to be a trick question but
definately a newbie question. I was curious after reading about people using
mazda 13b engines for various homebuilts, and porting them, adding on
various components to boost the hp from 200 to 260+. Seems at a point that
it's overkill if the 200 hp engine is going to provide you with the needed
ponies and rpms to accomplish the same as the 260 hp engine. What would the
advantge be of having the extra horsepower ?

Thanks,

Mark



NOW you have asked the question the right way and will see some good answers.
The advantage of more horsepower is the capability of increased thrust, which
is not a factor of just the RPM but of the ability to convert the horsepower to
usable thrust using a prop geared to the output of the engine. Thrust is
created by the prop and is determined by the RPM of the prop, the length of the
blades, the number of blades and the pitch of the blades along with a host of
other factors. Assuming for one example the same number of blades, the same
RPM, the same length of blades, and other conditions for two engines and two
props, the higher horsepower engine will be able to turn a larger pitch prop
than will the lower horsepower engine and will produce more thrust.

Think of it the same way as a race care. The higher the horsepower available
from the engine, the higher the gear ratio that can be used and the faster the
top end speed.

PS: This is a simple answer to your question but many factors are involved.
The effort to increase a 200 hp engine to 260 hp may or may not be worth the
effort and the 30% increase in hp wil not produce an equilivent increase in
thrust or speed. I don't remember the formula for calculating the increase but
it is far less than anticipated.




Bob Reed
www.kisbuild.r-a-reed-assoc.com (KIS Builders Site)
KIS Cruiser in progress...Slow but steady progress....

"Ladies and Gentlemen, take my advice,
pull down your pants and Slide on the Ice!"
(M.A.S.H. Sidney Freedman)

"RobertR237" wrote in message
...
PS: This is a simple answer to your question but many factors are
involved.
The effort to increase a 200 hp engine to 260 hp may or may not be worth
the
effort and the 30% increase in hp wil not produce an equilivent increase
in
thrust or speed. I don't remember the formula for calculating the
increase but
it is far less than anticipated.

Speed increases at about the cube root of the HP increase, so:

(260 / 200) ^ (1 / 3) = 1.091 or about 9% faster with 30% more HP

But other factors to consider are the increased weight of a larger engine,
the increased fuel burn, and the weight of that fuel.

Eric

In article ,
"Eric Miller" wrote:

"RobertR237" wrote in message
...
PS: This is a simple answer to your question but many factors are
involved.
The effort to increase a 200 hp engine to 260 hp may or may not be worth
the
effort and the 30% increase in hp wil not produce an equilivent increase
in
thrust or speed. I don't remember the formula for calculating the
increase but
it is far less than anticipated.

Speed increases at about the cube root of the HP increase, so:

(260 / 200) ^ (1 / 3) = 1.091 or about 9% faster with 30% more HP

But other factors to consider are the increased weight of a larger engine,
the increased fuel burn, and the weight of that fuel.

Eric



Extra horsepower converts directly into rate of climb, assuming the same
weight and airspeed. Fuel consumption rises approximately in proportion
to horsepower; stability decreases.

Other factors in boosting phenomenal horsepower out of small packages:

Increased thermal load
Increased stress on all parts of the engine
Some high RPM ranges may not yield usable thrust because the prop tips
are in the transonic range, where prop efficiency decreases greatly.

"Orval Fairbairn" wrote in message
news
In article ,
"Eric Miller" wrote:

"RobertR237" wrote in message
...
PS: This is a simple answer to your question but many factors are
involved.
The effort to increase a 200 hp engine to 260 hp may or may not be
worth
the
effort and the 30% increase in hp wil not produce an equilivent
increase
in
thrust or speed. I don't remember the formula for calculating the
increase but
it is far less than anticipated.

Speed increases at about the cube root of the HP increase, so:

(260 / 200) ^ (1 / 3) = 1.091 or about 9% faster with 30% more HP

But other factors to consider are the increased weight of a larger
engine,
the increased fuel burn, and the weight of that fuel.

Eric



Extra horsepower converts directly into rate of climb, assuming the same
weight and airspeed. Fuel consumption rises approximately in proportion
to horsepower; stability decreases.

Other factors in boosting phenomenal horsepower out of small packages:

Increased thermal load
Increased stress on all parts of the engine
Some high RPM ranges may not yield usable thrust because the prop tips
are in the transonic range, where prop efficiency decreases greatly.

And in the case of a rotary, you WILL be spinning the engine around 6000 or
so RPM. This means you must also use a PSRU to drop the RPM down to
something usable for the prop. The nice thing is, 6000 shaft RPM is only
2000 rotor RPM. The 13b can handle 6-8 grand with no problems.

Phillip

"Mark" wrote in message
...
Hi All, thanks for the responses, was not meant to be a trick question but
definately a newbie question. I was curious after reading about people
using
mazda 13b engines for various homebuilts, and porting them, adding on
various components to boost the hp from 200 to 260+. Seems at a point that
it's overkill if the 200 hp engine is going to provide you with the
needed
ponies and rpms to accomplish the same as the 260 hp engine. What would
the
advantge be of having the extra horsepower ?

Thanks,

Mark


"Mark" wrote in message
...
Does a prop turning at 2300 rpm on a 150hp motor produce more thrust
than
a
prop spinning 2300 rpm on a 100 hp motor ?




Mark,

A "typical" 13b (non-turbocharged) for aircraft is closer to 180-200 Hp.
A turbo will get you to that 250 hp mark, if you need it. Without the right
prop, the power is not usable.


Phillip