Push-Pull propeller combinations.

[Eunometic]

Several aircraft have been built with both a pull (or tractor)
propeller and a push (or rear) propeller aligned with each other.

Supposedly the arrangment is inefficient, yet the some of the Dornier
aircraft were record breakers.

Given that some aircraft were ruined or delayed by the problem of
combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
the B-29 with its backup V-3420) it looks like an attractive
proposition.

What's going on here?

List of such aircraft:

Cessna 337 Skymaster
Rutan Model 76 Vogager
Adam A500

Dornier Wal
Dornier Do X
Dornier Do 18 Seaplane, the German PPY Catalina.
Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
built.
Dornier Do 335 Pfeil (arrow) perhaps one of the fastest piston
engined aircraft ever built.
Dornier Seawings Seastar, modern Seaplane of composites.

Savoia-Marchetti S.55
LeO H-242

[Daryl Hunt[_2_]]

On 9/2/2010 8:08 AM, Eunometic wrote:
> Several aircraft have been built with both a pull (or tractor)
> propeller and a push (or rear) propeller aligned with each other.
>
> Supposedly the arrangment is inefficient, yet the some of the Dornier
> aircraft were record breakers.
>
> Given that some aircraft were ruined or delayed by the problem of
> combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> the B-29 with its backup V-3420) it looks like an attractive
> proposition.
>
> What's going on here?
>
> List of such aircraft:
>
> Cessna 337 Skymaster

I built a flying scale model of the Skymaster. Trust me, it
needed an Engineer rather than an AC Mechanic model builder. The
initial flight saw a yawing affect. I lengthened the boom a bit,
increased the horizontal stab and tightened everything up. It
flew fine after that. But, danged, was it fast. The Engines
didn't need to be sinced but it would have definately helped. I
made the mistake on the first one of putting both the same in
relationship with the body. Bad mistake. One needs to be
slightly higher. The next model had the rear elevated in
relationship to the front motor. All of a sudden, it turned into
a piece of cake to fly and danged, it got faster. I used two
different motors. The gear box idea I doubt if it would have
made much difference between a single prop and a front and rear
prop. If you have that much motor, use a heavier cutting prop.
If you don't have the power up front, add another motor in the
rear.



> Rutan Model 76 Vogager
> Adam A500
>
> Dornier Wal
> Dornier Do X
> Dornier Do 18 Seaplane, the German PPY Catalina.
> Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> built.
> Dornier Do 335 Pfeil (arrow) perhaps one of the fastest piston
> engined aircraft ever built.
> Dornier Seawings Seastar, modern Seaplane of composites.
>
> Savoia-Marchetti S.55
> LeO H-242
>
>
>

[Starshiy[_3_]]

Hello
Another one, a rarity
http://www.aviastar.org/air/france/moynet_jupiter.php
Regards

[Peter Twydell]

In message
>,
Eunometic > writes
>Several aircraft have been built with both a pull (or tractor)
>propeller and a push (or rear) propeller aligned with each other.
>
>Supposedly the arrangment is inefficient, yet the some of the Dornier
>aircraft were record breakers.
>
>Given that some aircraft were ruined or delayed by the problem of
>combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
>the B-29 with its backup V-3420) it looks like an attractive
>proposition.
>
>What's going on here?
>
>List of such aircraft:
>
>Cessna 337 Skymaster
>Rutan Model 76 Vogager
>Adam A500
>
>Dornier Wal
>Dornier Do X
>Dornier Do 18 Seaplane, the German PPY Catalina.
>Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
>built.
>Dornier Do 335 Pfeil (arrow) perhaps one of the fastest piston
>engined aircraft ever built.
>Dornier Seawings Seastar, modern Seaplane of composites.
>
>Savoia-Marchetti S.55
>LeO H-242
>
>
>
And the Fokker D.XXIII, of course.
http://www.aviastar.org/air/holland/fokker_d-23.php
--
Peter

Ying tong iddle-i po!

[John[_9_]]

On Sep 2, 10:08*am, Eunometic > wrote:
> Several aircraft have been built with both a pull (or tractor)
> propeller and a push (or rear) propeller aligned with each other.
>
> Supposedly the arrangment is inefficient, yet the some of the Dornier
> aircraft were record breakers.
>
> Given that some aircraft were ruined or delayed by the problem of
> combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> the B-29 with its backup V-3420) * it looks like an attractive
> proposition.
>
> What's going on here?
>
> List of such aircraft:
>
> Cessna 337 Skymaster
> Rutan Model 76 Vogager
> Adam A500
>
> Dornier Wal
> Dornier Do X
> Dornier Do 18 Seaplane, the German PPY Catalina.
> Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> built.
> Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
> engined aircraft ever built.
> Dornier Seawings Seastar, modern Seaplane of composites.
>
> Savoia-Marchetti S.55
> LeO H-242

I don't know about the others but my understanding is that the
Skymaster was an attempt to design a twin engined plane that would
have the same overall dimensions as a single engine aircraft and be
safer to fly since it would eliminate asymetric thrust during engine
failure. The ironic thing is that the Skymaster safety record is no
better than a conventional twin.

[Eunometic]

On Sep 3, 6:19*am, Peter Twydell > wrote:
> In message
> >,
> Eunometic > writes
>
>
>
> >Several aircraft have been built with both a pull (or tractor)
> >propeller and a push (or rear) propeller aligned with each other.
>
> >Supposedly the arrangment is inefficient, yet the some of the Dornier
> >aircraft were record breakers.
>
> >Given that some aircraft were ruined or delayed by the problem of
> >combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> >the B-29 with its backup V-3420) * it looks like an attractive
> >proposition.
>
> >What's going on here?
>
> >List of such aircraft:
>
> >Cessna 337 Skymaster
> >Rutan Model 76 Vogager
> >Adam A500
>
> >Dornier Wal
> >Dornier Do X
> >Dornier Do 18 Seaplane, the German PPY Catalina.
> >Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> >built.
> >Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
> >engined aircraft ever built.
> >Dornier Seawings Seastar, modern Seaplane of composites.
>
> >Savoia-Marchetti S.55
> >LeO H-242
>
> And the Fokker D.XXIII, of course.http://www.aviastar.org/air/holland/fokker_d-23.php
> --
> Peter
>

I like this aircraft, a 6500lb, 324mph speed one a pair of 520hp
engines means it matches aircraft of the same weighyt with the same
power in a larger single engine.

And the Hungarian Marton X/V looking like a sort of push pull Me 109.
http://www.whatifmodelers.com/index.php/topic,24457.0.html

[Eunometic]

On Sep 3, 12:41*am, Daryl Hunt > wrote:
> On 9/2/2010 8:08 AM, Eunometic wrote:
>
>
>
>
>
> > Several aircraft have been built with both a pull (or tractor)
> > propeller and a push (or rear) propeller aligned with each other.
>
> > Supposedly the arrangment is inefficient, yet the some of the Dornier
> > aircraft were record breakers.
>
> > Given that some aircraft were ruined or delayed by the problem of
> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> > the B-29 with its backup V-3420) * it looks like an attractive
> > proposition.
>
> > What's going on here?
>
> > List of such aircraft:
>
> > Cessna 337 Skymaster
>
> I built a flying scale model of the Skymaster. *Trust me, it
> needed an Engineer rather than an AC Mechanic model builder. *The
> initial flight saw a yawing affect. *I lengthened the boom a bit,
> increased the horizontal stab and tightened everything up. *It
> flew fine after that. *But, danged, was it fast. *The Engines
> didn't need to be sinced but it would have definately helped. *I
> made the mistake on the first one of putting both the same in
> relationship with the body. *Bad mistake. *One needs to be
> slightly higher. *The next model had the rear elevated in
> relationship to the front motor. *All of a sudden, it turned into
> a piece of cake to fly and danged, it got faster. *I used two
> different motors. *The gear box idea I doubt if it would have
> made much difference between a single prop and a front and rear
> prop. *If you have that much motor, use a heavier cutting prop.
> If you don't have the power up front, add another motor in the
> rear.
>

Sounds like there are a few 'tricks' in squeezing the best out of this
arrangment.

[Eunometic]

On Sep 3, 3:40*am, Starshiy > wrote:
> Hello
> Another one, a rarityhttp://www.aviastar.org/air/france/moynet_jupiter.php
> Regards

Pity this attempt a safer light plane wasn't a commercial success

[Eunometic]

On Sep 3, 10:48*am, John > wrote:
> On Sep 2, 10:08*am, Eunometic > wrote:
>
>
>
>
>
> > Several aircraft have been built with both a pull (or tractor)
> > propeller and a push (or rear) propeller aligned with each other.
>
> > Supposedly the arrangment is inefficient, yet the some of the Dornier
> > aircraft were record breakers.
>
> > Given that some aircraft were ruined or delayed by the problem of
> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> > the B-29 with its backup V-3420) * it looks like an attractive
> > proposition.
>
> > What's going on here?
>
> > List of such aircraft:
>
> > Cessna 337 Skymaster
> > Rutan Model 76 Vogager
> > Adam A500
>
> > Dornier Wal
> > Dornier Do X
> > Dornier Do 18 Seaplane, the German PPY Catalina.
> > Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> > built.
> > Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
> > engined aircraft ever built.
> > Dornier Seawings Seastar, modern Seaplane of composites.
>
> > Savoia-Marchetti S.55
> > LeO H-242
>
> I don't know about the others but my understanding is that the
> Skymaster was an attempt to design a twin engined plane that would
> have the same overall dimensions as a single engine aircraft and be
> safer to fly since it would eliminate asymetric thrust during engine
> failure. *The ironic thing is that the Skymaster safety record is no
> better than a conventional twin.- Hide quoted text -
>
> - Show quoted text -

Possibly psychological "a single engined failure isn't dangerous so I
won't maintain the aircraft factor" and ofcourse perhaps engine
failure isn't the major cause of light plane crashes.

A single engined turbo prop is safer than a twin engine piston and
possibly even safer than a twin turbo since the pilots inabiility to
handle asymetrical thrust may be worse than his abillity to handle a
glide/crash landing.

Famously some singles have crashed and smashed through brick walls
and the pilot walked free unscathed, the engine acting as a battering
ram and protection.

[Bill Kambic[_2_]]

On Thu, 2 Sep 2010 17:48:37 -0700 (PDT), John >
wrote:

>I don't know about the others but my understanding is that the
>Skymaster was an attempt to design a twin engined plane that would
>have the same overall dimensions as a single engine aircraft and be
>safer to fly since it would eliminate asymetric thrust during engine
>failure. The ironic thing is that the Skymaster safety record is no
>better than a conventional twin.

I flew a Skymaster once. It was the pressurized version. I was
unimpressed by the single engine performance. While there was no
asymetric thrust there was a distince lack of climb capability, too
(with either front or rear out).

Your understanding is correct on the reasoning for the arrangement.
But sometimes there's no substitute for horsepower. ;-)

[David E. Powell]

On Sep 2, 9:15*pm, Eunometic > wrote:
> On Sep 3, 6:19*am, Peter Twydell > wrote:
>
>
>
>
>
> > In message
> > >,
> > Eunometic > writes
>
> > >Several aircraft have been built with both a pull (or tractor)
> > >propeller and a push (or rear) propeller aligned with each other.
>
> > >Supposedly the arrangment is inefficient, yet the some of the Dornier
> > >aircraft were record breakers.
>
> > >Given that some aircraft were ruined or delayed by the problem of
> > >combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> > >the B-29 with its backup V-3420) * it looks like an attractive
> > >proposition.
>
> > >What's going on here?
>
> > >List of such aircraft:
>
> > >Cessna 337 Skymaster
> > >Rutan Model 76 Vogager
> > >Adam A500
>
> > >Dornier Wal
> > >Dornier Do X
> > >Dornier Do 18 Seaplane, the German PPY Catalina.
> > >Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> > >built.
> > >Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
> > >engined aircraft ever built.
> > >Dornier Seawings Seastar, modern Seaplane of composites.
>
> > >Savoia-Marchetti S.55
> > >LeO H-242
>
> > And the Fokker D.XXIII, of course.http://www.aviastar.org/air/holland/fokker_d-23.php
> > --
> > Peter
>
> I like this aircraft, a 6500lb, 324mph speed one a pair of 520hp
> engines means it matches aircraft of the same weighyt with the same
> power in a larger single engine.
>
> And the Hungarian Marton X/V looking like a sort of push pull Me 109.http://www.whatifmodelers.com/index.php/topic,24457.0.html

That just looks like a Speed machine. Maybe some video game like
Crimson Skies will use it someday.

[Ken S. Tucker]

On Sep 2, 7:08 am, Eunometic > wrote:
> Several aircraft have been built with both a pull (or tractor)
> propeller and a push (or rear) propeller aligned with each other.
>
> Supposedly the arrangment is inefficient, yet the some of the Dornier
> aircraft were record breakers.
>
> Given that some aircraft were ruined or delayed by the problem of
> combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> the B-29 with its backup V-3420) it looks like an attractive
> proposition.
>
> What's going on here?

Overall the Puller-Pusher is complicated.
1) the Pusher needs serious clearance for landing and takeoff.
2) if it's a twin engine, a strong structure is required to connect
the engines, (wing based twins use the existing spar).
3) a single engine P-P needs a long horizontal shaft.
4) the inertial moment is greater if a passenger bay is between
the engines.
5) there is an unpredictable airstream for the Pusher.
....and more.
Ken

> List of such aircraft:
>
> Cessna 337 Skymaster
> Rutan Model 76 Vogager
> Adam A500
>
> Dornier Wal
> Dornier Do X
> Dornier Do 18 Seaplane, the German PPY Catalina.
> Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> built.
> Dornier Do 335 Pfeil (arrow) perhaps one of the fastest piston
> engined aircraft ever built.
> Dornier Seawings Seastar, modern Seaplane of composites.
>
> Savoia-Marchetti S.55
> LeO H-242

[Peter Skelton]

On Thu, 2 Sep 2010 18:22:49 -0700 (PDT), Eunometic
> wrote:

>On Sep 3, 10:48*am, John > wrote:
>> On Sep 2, 10:08*am, Eunometic > wrote:
>>
>>
>>
>>
>>
>> > Several aircraft have been built with both a pull (or tractor)
>> > propeller and a push (or rear) propeller aligned with each other.
>>
>> > Supposedly the arrangment is inefficient, yet the some of the Dornier
>> > aircraft were record breakers.
>>
>> > Given that some aircraft were ruined or delayed by the problem of
>> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
>> > the B-29 with its backup V-3420) * it looks like an attractive
>> > proposition.
>>
>> > What's going on here?
>>
>> > List of such aircraft:
>>
>> > Cessna 337 Skymaster
>> > Rutan Model 76 Vogager
>> > Adam A500
>>
>> > Dornier Wal
>> > Dornier Do X
>> > Dornier Do 18 Seaplane, the German PPY Catalina.
>> > Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
>> > built.
>> > Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
>> > engined aircraft ever built.
>> > Dornier Seawings Seastar, modern Seaplane of composites.
>>
>> > Savoia-Marchetti S.55
>> > LeO H-242
>>
>> I don't know about the others but my understanding is that the
>> Skymaster was an attempt to design a twin engined plane that would
>> have the same overall dimensions as a single engine aircraft and be
>> safer to fly since it would eliminate asymetric thrust during engine
>> failure. *The ironic thing is that the Skymaster safety record is no
>> better than a conventional twin.- Hide quoted text -
>>
>> - Show quoted text -
>
>Possibly psychological "a single engined failure isn't dangerous so I
>won't maintain the aircraft factor" and ofcourse perhaps engine
>failure isn't the major cause of light plane crashes.
>
>A single engined turbo prop is safer than a twin engine piston and
>possibly even safer than a twin turbo since the pilots inabiility to
>handle asymetrical thrust may be worse than his abillity to handle a
>glide/crash landing.
>
>Famously some singles have crashed and smashed through brick walls
>and the pilot walked free unscathed, the engine acting as a battering
>ram and protection.
>
That a single piston is safer than a twin is a classic of
probability theory, taugh in junior high around here (not back in
the day though).

Peter Skelton

[David E. Powell]

On Sep 3, 8:24*am, Peter Skelton > wrote:
> On Thu, 2 Sep 2010 18:22:49 -0700 (PDT), Eunometic
>
>
>
>
>
> > wrote:
> >On Sep 3, 10:48*am, John > wrote:
> >> On Sep 2, 10:08*am, Eunometic > wrote:
>
> >> > Several aircraft have been built with both a pull (or tractor)
> >> > propeller and a push (or rear) propeller aligned with each other.
>
> >> > Supposedly the arrangment is inefficient, yet the some of the Dornier
> >> > aircraft were record breakers.
>
> >> > Given that some aircraft were ruined or delayed by the problem of
> >> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> >> > the B-29 with its backup V-3420) * it looks like an attractive
> >> > proposition.
>
> >> > What's going on here?
>
> >> > List of such aircraft:
>
> >> > Cessna 337 Skymaster
> >> > Rutan Model 76 Vogager
> >> > Adam A500
>
> >> > Dornier Wal
> >> > Dornier Do X
> >> > Dornier Do 18 Seaplane, the German PPY Catalina.
> >> > Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
> >> > built.
> >> > Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
> >> > engined aircraft ever built.
> >> > Dornier Seawings Seastar, modern Seaplane of composites.
>
> >> > Savoia-Marchetti S.55
> >> > LeO H-242
>
> >> I don't know about the others but my understanding is that the
> >> Skymaster was an attempt to design a twin engined plane that would
> >> have the same overall dimensions as a single engine aircraft and be
> >> safer to fly since it would eliminate asymetric thrust during engine
> >> failure. *The ironic thing is that the Skymaster safety record is no
> >> better than a conventional twin.- Hide quoted text -
>
> >> - Show quoted text -
>
> >Possibly psychological "a single engined failure isn't dangerous so I
> >won't maintain the aircraft factor" and ofcourse perhaps engine
> >failure isn't the major cause of light plane crashes.
>
> >A single engined turbo prop is safer than a twin engine piston and
> >possibly even safer than a twin turbo since the pilots inabiility to
> >handle asymetrical thrust may be worse than his abillity to handle a
> >glide/crash landing.
>
> >Famously some singles *have crashed and smashed through brick walls
> >and the pilot walked free unscathed, the engine acting as a battering
> >ram and protection.
>
> That a single piston is safer than a twin is a classic of
> probability theory, taugh in junior high around here (not back in
> the day though).
>
> Peter Skelton

Twice the number of things to go wrong?

[Peter Skelton]

On Fri, 3 Sep 2010 12:05:31 -0700 (PDT), "David E. Powell"
> wrote:

>On Sep 3, 8:24*am, Peter Skelton > wrote:
>> On Thu, 2 Sep 2010 18:22:49 -0700 (PDT), Eunometic
>>
>>
>>
>>
>>
>> > wrote:
>> >On Sep 3, 10:48*am, John > wrote:
>> >> On Sep 2, 10:08*am, Eunometic > wrote:
>>
>> >> > Several aircraft have been built with both a pull (or tractor)
>> >> > propeller and a push (or rear) propeller aligned with each other.
>>
>> >> > Supposedly the arrangment is inefficient, yet the some of the Dornier
>> >> > aircraft were record breakers.
>>
>> >> > Given that some aircraft were ruined or delayed by the problem of
>> >> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
>> >> > the B-29 with its backup V-3420) * it looks like an attractive
>> >> > proposition.
>>
>> >> > What's going on here?
>>
>> >> > List of such aircraft:
>>
>> >> > Cessna 337 Skymaster
>> >> > Rutan Model 76 Vogager
>> >> > Adam A500
>>
>> >> > Dornier Wal
>> >> > Dornier Do X
>> >> > Dornier Do 18 Seaplane, the German PPY Catalina.
>> >> > Dornier Do 26K Seaplane, possibly the longer ranged seaplane ever
>> >> > built.
>> >> > Dornier Do 335 Pfeil (arrow) *perhaps one of the fastest piston
>> >> > engined aircraft ever built.
>> >> > Dornier Seawings Seastar, modern Seaplane of composites.
>>
>> >> > Savoia-Marchetti S.55
>> >> > LeO H-242
>>
>> >> I don't know about the others but my understanding is that the
>> >> Skymaster was an attempt to design a twin engined plane that would
>> >> have the same overall dimensions as a single engine aircraft and be
>> >> safer to fly since it would eliminate asymetric thrust during engine
>> >> failure. *The ironic thing is that the Skymaster safety record is no
>> >> better than a conventional twin.- Hide quoted text -
>>
>> >> - Show quoted text -
>>
>> >Possibly psychological "a single engined failure isn't dangerous so I
>> >won't maintain the aircraft factor" and ofcourse perhaps engine
>> >failure isn't the major cause of light plane crashes.
>>
>> >A single engined turbo prop is safer than a twin engine piston and
>> >possibly even safer than a twin turbo since the pilots inabiility to
>> >handle asymetrical thrust may be worse than his abillity to handle a
>> >glide/crash landing.
>>
>> >Famously some singles *have crashed and smashed through brick walls
>> >and the pilot walked free unscathed, the engine acting as a battering
>> >ram and protection.
>>
>> That a single piston is safer than a twin is a classic of
>> probability theory, taugh in junior high around here (not back in
>> the day though).
>>
>> Peter Skelton
>
>Twice the number of things to go wrong?

That and a non zero probability of crash as the result of a
single failure. The number was worked out sometime around the end
or WWII, aircraft with higher power reserves might show different
results.


Peter Skelton

[vaughn[_3_]]

"Peter Skelton" > wrote in message
...
>>> >> I don't know about the others but my understanding is that the
>>> >> Skymaster was an attempt to design a twin engined plane that would
>>> >> have the same overall dimensions as a single engine aircraft and be
>>> >> safer to fly since it would eliminate asymetric thrust during engine
>>> >> failure. The ironic thing is that the Skymaster safety record is no
>>> >> better than a conventional twin.- Hide quoted text -

Yes. One of the classic crash modes of the Skymaster is when the pilot attempts
a takeoff after failing to notice that the rear prop is not turning. The
procedure developed to detect that simple condition is to lead with the rear
engine throttle. If you push in the throttle and the noise level remains
unchanges, it is time to abort the takeoff and investigate!

>>Twice the number of things to go wrong?
>
> That and a non zero probability of crash as the result of a
> single failure. The number was worked out sometime around the end
> or WWII, aircraft with higher power reserves might show different
> results.

Of course, the biggest danger is loss of an engine on takeoff, but even a
single-engine *landing* can come to grief in various ways. We had a twin
fatally crash into our neighborhood from exactly that event.

One situation where twins are considered inherently safer is night IFR. The
classic advice for a forced landing at night is to maintain control of the
airplane; in particular maintain a safe airspeed. At 300 feet, turn on the
landing lights. If you don't like what you see, turn them off!

Vaughn

[Eunometic]

On Sep 3, 10:20*pm, "Ken S. Tucker" > wrote:
> On Sep 2, 7:08 am, Eunometic > wrote:
>
> > Several aircraft have been built with both a pull (or tractor)
> > propeller and a push (or rear) propeller aligned with each other.
>
> > Supposedly the arrangment is inefficient, yet the some of the Dornier
> > aircraft were record breakers.
>
> > Given that some aircraft were ruined or delayed by the problem of
> > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> > the B-29 with its backup V-3420) * it looks like an attractive
> > proposition.
>
> > What's going on here?
>
> Overall the Puller-Pusher is complicated.
> 1) the Pusher needs serious clearance for landing and takeoff.

Overall I agree with what you say, however the conventional arrangment
also has some problems.

Also in the case of only having a limited horsepower the push-pull
arrangment does have a record of outperforming the side by side wing
arrangment it seems to me.

Yes, but no so bad with a tricycle undercarriage.

> 2) if it's a twin engine, a strong structure is required to connect
> the engines, (wing based twins use the existing spar).

But the by mounting engines on the wing the spar exeperiences twist,
also a problem


> 3) a single engine P-P needs a long horizontal shaft.

Yes, but can be reduced with a snall engine.

> 4) the inertial moment is greater if a passenger bay is between
> the engines.

Definit stabillity issues but countered by the intrinsic contra
rotation and gyroscopic stabalistation of the props.

> 5) there is an unpredictable airstream for the Pusher.
> ...and more.

Pushers can be slightly more efficient IF the structure ahead of the
pusher is kept small and streamlined.

> Ken

I was thinking more along the lines of wing mounting of inline tandem
push-pull pairs in the fashion of this aircraft:
http://en.wikipedia.org/wiki/Dornier_Do_26
http://www.historicaircraft.org/Other-Country-Aircraft/pages/Dornier-26-2.html

An arrangment that had been used succesfully for decades on Dornier
aircraft and these aircraft seemed to give nothing away in terms of
speed or range.

At one point it looked like being transfered to land based:
http://www.luft46.com/prototyp/me264.html
(Right at the bottom, youy see an illustraion of an Me P.1075 )

[Bill Kambic[_2_]]

On Fri, 03 Sep 2010 08:24:47 -0400, Peter Skelton >
wrote:

>That a single piston is safer than a twin is a classic of
>probability theory, taugh in junior high around here (not back in
>the day though).
>
>Peter Skelton

As a general rule you put multiple engines on an aircraft 'cause you
want to haul a bigger load. The safety issue is more complex because
just how you add the additional engines can have significant
consequences if one (or more) fail.

There's also, however, a question of environment. Aircraft that
operate almost exclusively over land are going to have some different
considerations than those that operate almost exclusively over water.
There the that junior high principle might not be so clear. :-)

On my one flight in a Skymaster the "rear engine first" technique was
used. Of course if you watch the gauges you can also tell if the rear
engine is producing rated power.

One place that the push-pull system might just work out well is the
seaplane/amphibian. I note that Dornier says it's going to produce a
new one in Canada starting later this year (IIRC). It looks like an
interesting machine. We'll see how well it does in a very depressed
market.

[Ken S. Tucker]

Euno...
There are counterpoints to your counterpoints etc. especially true in
engineering, so I'll cut to the chase, more below...

On Sep 3, 10:04 pm, Eunometic > wrote:
> On Sep 3, 10:20 pm, "Ken S. Tucker" > wrote:
>
>
>
> > On Sep 2, 7:08 am, Eunometic > wrote:
>
> > > Several aircraft have been built with both a pull (or tractor)
> > > propeller and a push (or rear) propeller aligned with each other.
>
> > > Supposedly the arrangment is inefficient, yet the some of the Dornier
> > > aircraft were record breakers.
>
> > > Given that some aircraft were ruined or delayed by the problem of
> > > combining gearboxes (He 177, Northrop XB-35 and if it ever came to it
> > > the B-29 with its backup V-3420) it looks like an attractive
> > > proposition.
>
> > > What's going on here?
>
> > Overall the Puller-Pusher is complicated.
> > 1) the Pusher needs serious clearance for landing and takeoff.
>
> Overall I agree with what you say, however the conventional arrangment
> also has some problems.
>
> Also in the case of only having a limited horsepower the push-pull
> arrangment does have a record of outperforming the side by side wing
> arrangment it seems to me.
>
> Yes, but no so bad with a tricycle undercarriage.
>
> > 2) if it's a twin engine, a strong structure is required to connect
> > the engines, (wing based twins use the existing spar).
>
> But the by mounting engines on the wing the spar exeperiences twist,
> also a problem
>
> > 3) a single engine P-P needs a long horizontal shaft.
>
> Yes, but can be reduced with a snall engine.
>
> > 4) the inertial moment is greater if a passenger bay is between
> > the engines.
>
> Definit stabillity issues but countered by the intrinsic contra
> rotation and gyroscopic stabalistation of the props.
>
> > 5) there is an unpredictable airstream for the Pusher.
> > ...and more.
>
> Pushers can be slightly more efficient IF the structure ahead of the
> pusher is kept small and streamlined.
>
> > Ken
>
> I was thinking more along the lines of wing mounting of inline tandem
> push-pull pairs in the fashion of this aircraft:http://en.wikipedia.org/wiki/Dornier_Do_26http://www.historicaircraft.org/Other-Country-Aircraft/pages/Dornier-...
>
> An arrangment that had been used succesfully for decades on Dornier
> aircraft and these aircraft seemed to give nothing away in terms of
> speed or range.
>
> At one point it looked like being transfered to land based:http://www.luft46.com/prototyp/me264.html
> (Right at the bottom, youy see an illustraion of an Me P.1075 )

Nice pics, (me likes Do-26 too), I think the science of operating a
Pusher prop in the the prop wash of a Puller is difficult mainly at
slow speeds such as landing and take-off, that's beyond theory.
Additionally is the Pusher hub suction and cooling, given that one
can work those problems to near irrelevence then it looks like a
heck of good design to me.
Ken

[Ken S. Tucker]

On Sep 4, 4:36 am, Bill Kambic > wrote:
> On Fri, 03 Sep 2010 08:24:47 -0400, Peter Skelton >
> wrote:
>
> >That a single piston is safer than a twin is a classic of
> >probability theory, taugh in junior high around here (not back in
> >the day though).
>
> >Peter Skelton
>
> As a general rule you put multiple engines on an aircraft 'cause you
> want to haul a bigger load. The safety issue is more complex because
> just how you add the additional engines can have significant
> consequences if one (or more) fail.
>
> There's also, however, a question of environment. Aircraft that
> operate almost exclusively over land are going to have some different
> considerations than those that operate almost exclusively over water.
> There the that junior high principle might not be so clear. :-)
>
> On my one flight in a Skymaster the "rear engine first" technique was
> used. Of course if you watch the gauges you can also tell if the rear
> engine is producing rated power.
>
> One place that the push-pull system might just work out well is the
> seaplane/amphibian. I note that Dornier says it's going to produce a
> new one in Canada starting later this year (IIRC). It looks like an
> interesting machine. We'll see how well it does in a very depressed
> market.

Good, thanks for the notice...
http://en.wikipedia.org/wiki/Dornier_Seastar

The economy is always cyclic, canucks will need that type of thing
for commodity developement, of course the Twin Otter is a good deal,
we'll need to see the price.
Ken