Sadler make Vampire two seater

[fly_tornado]

its has to be very wide to accommodate a large prop

 

your control cables and pulleys have to travel a long way, out the wings, then down the booms.

 

you have to coordinate 2 rudders

 

the wings need to support the tail

 

From a manufacturing stand point you are building a lot more stuff into your airframe without a lot of benefit.

 

Lot of little inefficiencies add up after a while. The conventional lower boom with T tail is a lot less engineering.

 

 

[flyvulcan]

Generally fair points FT. Again, pros and cons. The examples that you have given relate to design or manufacturing whereas the ones I have given relate to aerodynamics and handling. One set of examples is relevant to designers/maintainers and one to pilots.

 

At the end of the day, the designers/maintainers may have a preference for the single boom as being the "best" configuration (due to designability/maintainability) while the pilots may have a preference for the twin boom configuration (due to performance and handling characteristics).

 

I was simply questioning the validity of your statement that "The best pushers are single boom with the prop above the boom" . Perhaps your statement should have been predicated with "In my opinion,..." in order to differentiate opinion from fact.

 

 

 

[pylon500]

its has to be very wide to accommodate a large prop[/color=black]

 

Generally your tailplane would be between the booms, and most tails are wider than your typical prop diameter.[/color=red]

 

your control cables and pulleys have to travel a long way, out the wings, then down the booms.[/color=black]

 

Only a couple of extra turns, usually not much more than going down a single tube.[/color=red]

 

you have to coordinate 2 rudders[/color=black]

 

If your rudders are run by cables, it's a closed loop requiring an just extra cable to join the two, or a slave pushrod from the driven one to the other.[/color=red]

 

the wings need to support the tail[/color=black]

 

Hopefully, the wings are usually pretty strong, an offset is that usually twin booms associate with a centre section which should fairly stiff, and generally has outboard wing panels which, if un-strutted, have a lower attach point load.[/color=red]

 

From a manufacturing stand point you are building a lot more stuff into your airframe without a lot of benefit.[/color=black]

 

On the Vampire, the twin boom concept allowed a more rigid, self supporting jig system, just by adding one more tube, the tailplane could be built lighter as it was not so much of a cantilever structure, AND you get all the aerodynamic benefits of bigger prop, better thrust line arrangement, less torsional problems than a single boom, and finally a public protected prop![/color=red]

 

Lot of little inefficiencies add up after a while. The conventional lower boom with T tail is a lot less engineering.[/color=black]

 

[/color=red]Much as I like the Aeroprakt products, the A20 had torsional stiffness problems with the T tail on a single boom.[/color=red]

 

I think the ION tail system is more for show than any real practical reason, I guess it stops it being called a Vampire?[/color=blue]

 

I was simply questioning the validity of your statement that "The best pushers are single boom with the prop above the boom" . Perhaps your statement should have been predicated with "In my opinion,..." in order to differentiate opinion from fact.

Here, here.(that means I agree)[/color=blue]

? OK, don't know what's happening here, all the HTML coding is going strange?

 

 

[fly_tornado]

I would think you could reinforce a boom based off a single tube without too much difficulty. I think the A20 was limitted by its design being held to 450kgs and a tail dragger. get rid of the tail wheel and one cause of flex is gone.