Engine power question???

In article .com,
wrote:

On Oct 10, 9:17 pm, "Kyle Boatright" wrote:


Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of thrust
because of gearing, disc area, etc? But, that thrust is only effective in a
narrow (vertical) speed range. The same engine, combined with an RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

That Soob had the same diameter of prop and ran at the
same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why
the results were so startling to me. The 150s performance was much
better with the Soob, confirming its output. So either the Soob
produced more power than claimed, or the O-200 was really sick. Yet
the guy said that the O-200 was OK and the 150's performance with it
was typical.

Dan

I have a friend who put a Soob in a homebuilt, with "help" from the Soob
conversion people. I told him that I was not impressed with some of the
design (especially the cooling installation) and to be sure to make a
lot of test flights.

Well, it lasted to just short of Oshkosh and then from Oshkosh to just
short of Dayton. Fortunately, the plane was relatively undamaged; my
friend's ego was his sole injury.

In short, tread carefully when going with someone's conversion.

On Wed, 10 Oct 2007 19:10:18 -0400, "J.Kahn"
wrote:


Actually, I'm starting to look for a 150 to play around with and for the
kids to learn in next spring. They fly about as well as most
airplanes, with a really good useful load for that size. The 150 does a
lot of things reasonably well and are becoming dirt cheap as the big
flight schools unload them. Where else can you get a 600 lb useful
load, electrics, really powerful fowler flaps, etc all for 20k.
Everybody else hates them, but I like the '64/65 straight tails. If
you block out the front half of the airplane in a picture, it looks like
an A-26.

Apparently aileron gap seals make the ailerons much lighter and
snappier, probably the biggest complaint in handling.

John

Here is one you can play around with a lot.
http://saltlakecity.craigslist.org/rvs/440160765.html

Would all this work qualify as a homebuilt?

--Andy Asberry--
------Texas-----

wrote in message
oups.com...
On Oct 10, 9:17 pm, "Kyle Boatright" wrote:


Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of
thrust
because of gearing, disc area, etc? But, that thrust is only effective
in a
narrow (vertical) speed range. The same engine, combined with an
RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

That Soob had the same diameter of prop and ran at the
same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why
the results were so startling to me. The 150s performance was much
better with the Soob, confirming its output. So either the Soob
produced more power than claimed, or the O-200 was really sick. Yet
the guy said that the O-200 was OK and the 150's performance with it
was typical.

Dan

I still think it is important to have the *exact same* prop, not just the
same diameter. Depending on prop pitch, chord, etc. you could get
significantly different amounts of thrust from props with the exact same
diameter.

On Oct 11, 8:44 pm, "Kyle Boatright" wrote:
wrote in message

oups.com...



On Oct 10, 9:17 pm, "Kyle Boatright" wrote:

Don't confuse thrust with HP unless you're using the exact same prop and
prop RPM. An 0-360 powered Robinson R-22 generates what, 1500 lbs of
thrust
because of gearing, disc area, etc? But, that thrust is only effective
in a
narrow (vertical) speed range. The same engine, combined with an
RV-style
cruise prop, would only generate (WAG coming) 250 lbs of static thrust.

That Soob had the same diameter of prop and ran at the
same RPM. I'm aware of the diameter/RPM/pitch effects, and that's why
the results were so startling to me. The 150s performance was much
better with the Soob, confirming its output. So either the Soob
produced more power than claimed, or the O-200 was really sick. Yet
the guy said that the O-200 was OK and the 150's performance with it
was typical.

Dan

I still think it is important to have the *exact same* prop, not just the
same diameter. Depending on prop pitch, chord, etc. you could get
significantly different amounts of thrust from props with the exact same
diameter.

Not so much. Efficiencies are typically in the range of
85-90% unless the prop is a real dog, and I don't think Cessna would
have continued using the prop they did on the 150 if it was a poor
performer.
We had an Ivoprop on a 135 hp Soob in a Glastar. Didn't trust
that prop, and had problems getting it to run smoothly. We eventually
put a Warp drive on it, three Blades instead of two, but the
performance was nearly identical even though there were big
differences in chord and planform.
The guy who put the Soob in the 150 may have used the same
prop, but I can't remember. Some of those Soob conversions used the
Lycoming bolt circle instead of the Continental, and the Cont's prop
wouldn't fit, of course.
As you mentioned, a larger, slower-turning prop is far more
efficient, so a redrive is better than direct drive, especially where
an auto engine is used. The airplane that became the Helio Courier was
a much-modified Piper Super Cruiser, IIRC, with a 125 hp Lyc driving a
big, slow prop through a redrive using several V-belts. Very rapid
acceleration and spectacular climb, aided by slats and flaps and the
usual STOL wizardry.

Dan

Andy Asberry wrote:
On Wed, 10 Oct 2007 19:10:18 -0400, "J.Kahn"
wrote:

Actually, I'm starting to look for a 150 to play around with and for the
kids to learn in next spring. They fly about as well as most
airplanes, with a really good useful load for that size. The 150 does a
lot of things reasonably well and are becoming dirt cheap as the big
flight schools unload them. Where else can you get a 600 lb useful
load, electrics, really powerful fowler flaps, etc all for 20k.
Everybody else hates them, but I like the '64/65 straight tails. If
you block out the front half of the airplane in a picture, it looks like
an A-26.

Apparently aileron gap seals make the ailerons much lighter and
snappier, probably the biggest complaint in handling.

John

Here is one you can play around with a lot.
http://saltlakecity.craigslist.org/rvs/440160765.html

Would all this work qualify as a homebuilt?

--Andy Asberry--
------Texas-----

Yikes too much work....

You could license it as a homebuilt if you did something like build up
the wings from parts so you could squeeze past the 51 percent rule for
the primary structure. You would have to be able to show that you were
at least equivalent to a "quick build" kit.

Here in Canada there is a category called "Owner Maintenance" where you
can buy one that is in annual but is maybe a bit rough, and license it
as OM (it has to have a current CofA to start, then you put X's on all
the data plates) then you can maintain and repair it yourself and use
uncertified parts, like a homebuilt. The number of airplanes converted
to date is limited, probably less than 100, mainly because the FAA
refuses to acknowledge the category so OM airplanes can't travel or be
sold to the US. If they treated OM the same as second owner homebuilts,
a major impediment would be removed and a LOT of older airplanes would
be converted. On an airplane that is airworthy but ratty and therefore
cheap to buy, it's still attractive even if you can't go south.

John