Light twins not using contra-rotating propellers

Newps schrieb:

I consider the effects of P-factor and torque to be design defects.

Christ your an idiot. Until you change the laws of physics you're stuck
with those 'design defects'.

Be extra careful before calling names! Even when you don't like the poster.

Of course the effects of the P-factor can be overcome by appropriate
design. The most simple solution would be the possibility to trim all
three axis. As this seems to be a pretty straight forward and cheap
solution, I've never understood why this isn't offered in all airplaes.
Sure would make flying a light single more enjoyably. Yes, I even agree
that this avoidance could be called a design defect.

On the more expensive level (much more expensive, I would guess), you
can overcome the P-factor effects by using two contra-rotating coaxial
propellors. This would not only overcome the effects of the P-factor,
but also those caused by torque. Kamov helicopters are an example of
such a design.

Contra-rotating coaxial propellors not only solve the P-factor and
torque, but they make the propellor more efficient, too. Probably too
little effect compared to the additional cost and complexity, so it has
been realized only rarely. Tupolev 114 is an example. (In marine
applications, you find contra-rotating coaxial propellors more often.)

Stefan

Stefan wrote:

Of course the effects of the P-factor can be overcome by appropriate
design. The most simple solution would be the possibility to trim all
three axis.

Yaw damping does wonders in the Pilatus. Of course your typical GA
aircraft doesn't have 1200hp - and doesn't cost $3.5M.

On the more expensive level (much more expensive, I would guess), you
can overcome the P-factor effects by using two contra-rotating coaxial
propellors. This would not only overcome the effects of the P-factor,
but also those caused by torque. Kamov helicopters are an example of
such a design.

Effective, yes, but very complex, heavy and expensive. I recall seeing
an ad for Breitling watches that had a P-51 with contra-rotating props.
I think it was a one-off aircraft with a RR Griffon engine?

Contra-rotating coaxial propellors not only solve the P-factor and
torque, but they make the propellor more efficient, too. Probably too
little effect compared to the additional cost and complexity, so it has
been realized only rarely. Tupolev 114 is an example.

IIRC Tu-95/114 was the fastest prop aircraft of its category. I think
the cruise speed was near 500mph? I think that was a combination of
high-shp Kuznetsov turboshafts and the efficiency of the contra props.
Pretty amazing aircraft IMO.

In article ,
T o d d P a t t i s t wrote:

"Kev" wrote:

You can't design out P-factor or torque,

Actually, if you really needed to, you probably could design
them out, or at least reduce them significantly. But only
if you wanted an aircraft that was so expensive no one could
afford to maintain or buy. As usual, the cost/benefit says
it isn't worth it and you'd probably add a host of other
problems. (Kill P-factor by sensing relative wind and
pivoting the engine to keep it aligned, kill torque effects
by contra-rotating props)

You could design out P-factor by using a prop with a cyclic pitch control,
like on a chopper. Wouldn't be worth doing, but it's possible.

That's the hard part of engineering. Not figuring out what's possible, but
differentiating between the possible and the useful.

Recently, Stefan posted:

Newps schrieb:

I consider the effects of P-factor and torque to be design defects.

Christ your an idiot. Until you change the laws of physics you're
stuck with those 'design defects'.

Be extra careful before calling names! Even when you don't like the
poster.

Of course the effects of the P-factor can be overcome by appropriate
design. The most simple solution would be the possibility to trim all
three axis. As this seems to be a pretty straight forward and cheap
solution, I've never understood why this isn't offered in all
airplaes. Sure would make flying a light single more enjoyably. Yes,
I even agree that this avoidance could be called a design defect.

I think it would be a good idea to distinguish between design defects and
design _trade-offs_ in this kind of discussion. Many GA planes have 3-axis
trim, but, as in other areas, this option comes at a cost. The question
becomes which options a buyer might find more attractive, for example
would you prefer 3-axis trim or better avionics and moving map GPS?

Neil

Neil Gould schrieb:

distinguish between design defects and design _trade-offs_

Agreed.

for example would you prefer 3-axis trim or better avionics and
moving map GPS?

Personally, I'd choose the trim without having to contemplate one
second. That's why I actually think that the lack of a three axis trim
is a defect. But then, I also think that an engine which has a
dispacement of 360 cubic inch and burns 10 US gallons per hour only to
produce a mere 180 hp (actually much less in cruse) should be called
defect in the 21th century. But I'm getting OT.

Stefan

"Mxsmanic" wrote in message
...
Neil Gould writes:

A design defect is a problem caused by some aspect of the design. I don't
know why you would consider the effects of propeller propulsion to be
"design defects". They are simply aspects of that type of propulsion.

An aspect of propulsion that constantly pulls the aircraft to one side
sounds like a defect to me.

--
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You could say the same thing about lift, it has a "defective" component
called drag. Why don't you simply design that out? Why would anyone deliver
a defective airplane that came with drag?

The answer, of course, is that we have all done what we could, with what we
have. All real world design is a result of compromises, we don't have a
registry where the drag can be turned off, the p-factor zeroed without other
side effects.

Al G

Recently, Stefan posted:

Neil Gould schrieb:

distinguish between design defects and design _trade-offs_

Agreed.

for example would you prefer 3-axis trim or better avionics and
moving map GPS?

Personally, I'd choose the trim without having to contemplate one
second. That's why I actually think that the lack of a three axis trim
is a defect. But then, I also think that an engine which has a
dispacement of 360 cubic inch and burns 10 US gallons per hour only to
produce a mere 180 hp (actually much less in cruse) should be called
defect in the 21th century. But I'm getting OT.

Then, I guess we disagree on the meaning of the term "defect". It may be a
defect if it is an unintentional outcome, but I fail to see how simply
being a different choice or priority qualifies under the definitions I
know of. For example:

Dictionary.com Unabridged (v 1.0.1) - Cite This Source
defect /n. Pronunciation Key - Show Spelled Pronunciation[n. dee-fekt,
di-fekt; v. di-fekt] Pronunciation Key - Show IPA Pronunciation
–noun
1. a shortcoming, fault, or imperfection: a defect in an argument; a
defect in a machine.
2. lack or want, esp. of something essential to perfection or
completeness; deficiency: a defect in hearing.
(rest snipped)
----------

#2 might seem closer to your usage, but if that is gauge, then all
manufactured items are defective, and the term becomes meaningless or at
least redundant.

Neil

Neil Gould writes:

It is a simple matter accounted for by Newtonian physics. Apparently, the
"designer" of that aspect of the real world doesn't see a problem with it,
as "real world version 2.0 has yet to be released, AFAIK.

It is more likely that nobody wants to pay to fix it.

BTW, pilots of propeller-driven aircraft don't see a problem with it either.

So if they had a choice between two otherwise identical aircraft, with
identical prices, they'd just flip a coin to choose between the one
with P-factor and torque and the one without?

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Al G writes:

You could say the same thing about lift, it has a "defective" component
called drag. Why don't you simply design that out?

Modern airfoils attempt to do exactly that, with varying amounts of
success.

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Neil Gould writes:

There is no violation at all. Such twins are designed to take advantage of
the laws of physics.

Then the design defect of propellers that rotate in the same direction
is not a violation of the laws of physics, QED.

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