Re: Light twins not using contra-rotating propellers

[Jim Macklin]

The cost of manufacturing two versions of the engine and
recertification of the design is not worth the small
advantage. Most light twins were designed and certified
over 40 years ago.


"Mark Levin" > wrote in message
...
| Hello,
|
| As was pointed out to me the Beechcraft Baron does not use
contra-rotating
| propellers. A bit of research showed me that most U.S.
built light twins do
| not use them either.
|
| My question is why?
|
| It seems silly to me not to take advantage of having
various propeller
| effects cancel each other out unless there were overriding
engineering or
| cost issues.
|
| For single engine operations it seems that you would want
to match rotation
| to which side the engine is on so as to let propeller
caused turning
| tendencies to help offset the asymmetrical thrust. Though
I can imagine
| that asymmetrical thrust is so much greater than propeller
caused turning
| tendencies that this isn't really an issue.
|
| Are the added engineering/manufacturing/maintenance issues
for
| contra-rotating props that great?
|
| inquiring minds
| ml

[Capt. Geoffrey Thorpe]

"Jim Macklin" > wrote in message
...
> The cost of manufacturing two versions of the engine and
> recertification of the design is not worth the small
> advantage. Most light twins were designed and certified
> over 40 years ago.
>

What would be all the unique parts?

Camshaft has to be different.
Crankshaft probably is drilled differently for the oil passages.
Starter.
Oil pump.
Magnetos.
Vacuum pump, I assume?
Prop, obviously.

That should be about it?

--
Geoff
The Sea Hawk at Wow Way d0t Com
remove spaces and make the obvious substitutions to reply by mail
When immigration is outlawed, only outlaws will immigrate.

[Jim Macklin]

The only benefits are that the advertised and charted
performance is the same with either engine inop. Since
there ids no "critical" engine the Vmca number is a single
number and thus the take-off data can be based on the lower
Vmca and the performance looks a little better. But Vyse
will still be abut the same and that is a number that is
more critical than Vmca.

The cost of making the engine rotate in different directions
is spread over a small number of applications, yet those few
parts must be certified, cataloged, stocked, tracked and
shipped. That makes the airplane expensive. Since the CE
303 and BE 76, the DA42 is the first piston twin that I can
think of. The Baron hangs on, because of tradition and now
cost well over a million dollars.



"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com>
wrote in message
news:vZSdnVUBModXwfLYnZ2dnUVZ_rKdnZ2d@wideopenwest .com...
| "Jim Macklin" > wrote
in message
| ...
| > The cost of manufacturing two versions of the engine and
| > recertification of the design is not worth the small
| > advantage. Most light twins were designed and certified
| > over 40 years ago.
| >
|
| What would be all the unique parts?
|
| Camshaft has to be different.
| Crankshaft probably is drilled differently for the oil
passages.
| Starter.
| Oil pump.
| Magnetos.
| Vacuum pump, I assume?
| Prop, obviously.
|
| That should be about it?
|
| --
| Geoff
| The Sea Hawk at Wow Way d0t Com
| remove spaces and make the obvious substitutions to reply
by mail
| When immigration is outlawed, only outlaws will immigrate.
|
|

[karl gruber[_1_]]

It's the same prop. Just put it on backwards.

Karl
ATP CFI

"Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com> wrote in message
news:vZSdnVUBModXwfLYnZ2dnUVZ_rKdnZ2d@wideopenwest .com...
> "Jim Macklin" > wrote in message
> ...
>> The cost of manufacturing two versions of the engine and
>> recertification of the design is not worth the small
>> advantage. Most light twins were designed and certified
>> over 40 years ago.
>>
>
> What would be all the unique parts?
>
> Camshaft has to be different.
> Crankshaft probably is drilled differently for the oil passages.
> Starter.
> Oil pump.
> Magnetos.
> Vacuum pump, I assume?
> Prop, obviously.
>
> That should be about it?
>
> --
> Geoff
> The Sea Hawk at Wow Way d0t Com
> remove spaces and make the obvious substitutions to reply by mail
> When immigration is outlawed, only outlaws will immigrate.
>

[Jim Macklin]

No, it is different as are internal engine parts and the
accessories.


"karl gruber" > wrote in message
...
| It's the same prop. Just put it on backwards.
|
| Karl
| ATP CFI
|
| "Capt. Geoffrey Thorpe" <The Sea Hawk at wow way d0t com>
wrote in message
| news:vZSdnVUBModXwfLYnZ2dnUVZ_rKdnZ2d@wideopenwest .com...
| > "Jim Macklin" >
wrote in message
| > ...
| >> The cost of manufacturing two versions of the engine
and
| >> recertification of the design is not worth the small
| >> advantage. Most light twins were designed and
certified
| >> over 40 years ago.
| >>
| >
| > What would be all the unique parts?
| >
| > Camshaft has to be different.
| > Crankshaft probably is drilled differently for the oil
passages.
| > Starter.
| > Oil pump.
| > Magnetos.
| > Vacuum pump, I assume?
| > Prop, obviously.
| >
| > That should be about it?
| >
| > --
| > Geoff
| > The Sea Hawk at Wow Way d0t Com
| > remove spaces and make the obvious substitutions to
reply by mail
| > When immigration is outlawed, only outlaws will
immigrate.
| >
|
|

[Greg Farris]

In article >,
TheSeaHawkatwowwayd0tcom says...

>>
>
>What would be all the unique parts?
>
>Camshaft has to be different.
>Crankshaft probably is drilled differently for the oil passages.
>Starter.
>Oil pump.
>Magnetos.
>Vacuum pump, I assume?
>Prop, obviously.
>
>That should be about it?
>


That is interesting.
I think nevertheless it is not so much the number of parts variables, but
the fact that dual-inventory has to be established through the entire
supply and QC chain, all to support an infinitessimal minority that makes
it a poor choice. Or, let's say an infrequently adopted choice.

As stated above, the only performance difference is the elimination of
the concept of the "critical" engine. We are not talking about something
as radical as centerline thrust, which introduces net, single-engine
performance gains compared with off-center mounts.

GF

[Dave[_3_]]

Plus (possibly)

Pistons(different or installed differently)

Con rods (Weighted or balanced differently)

Dynamic balance weights

Balance dampners
Accessories..

maybe more...

Dave





On Thu, 30 Nov 2006 17:35:55 -0500, "Capt. Geoffrey Thorpe" <The Sea
Hawk at wow way d0t com> wrote:

>"Jim Macklin" > wrote in message
...
>> The cost of manufacturing two versions of the engine and
>> recertification of the design is not worth the small
>> advantage. Most light twins were designed and certified
>> over 40 years ago.
>>
>
>What would be all the unique parts?
>
>Camshaft has to be different.
>Crankshaft probably is drilled differently for the oil passages.
>Starter.
>Oil pump.
>Magnetos.
>Vacuum pump, I assume?
>Prop, obviously.
>
>That should be about it?