twin tail questions

On Mon, 04 Aug 2003 18:13:25 +0000, Chris W wrote:

I got such a good answer on my question about flap design I thought I
would ask another design question. why would a plane that has two
engines have two vertical stabilizers. No in the case of the Aircoupe I
always thought the reason for the twin tail was so that the helical prop
wash wouldn't induce a yaw tendency from the prop wash hitting the
vertical stabilizer/rudder. It is my understanding that the Aircoupe
was designed so you wouldn't need rudder pedals, and the twin tail I
think would have helped that. But on a twin engine, what's the point?
having two vertical stabilizers and two rudders seems significantly more
complicated both structurally and mechanically so why do it if there
isn't some advantage? There must be one I don't know about.


--
Chris Woodhouse


Planes may have multiple vertical stabs for several different reasons.
Some (e.g. the Lockheed Constellation) may have them to facilitate fitting
them in existing hangars without hitting the top of the door opening.

Some multiple engine designs have multiple vertical tails so that one
portion is directly in the prop wash of the operating engine which may
help reduce the minimum control speed following an engine failure. At
least that is what Kelly Johnson says about the twin vertical tails of the
first Lockheed Electra (More Than My Share of it All, Kelly Johnson, pg.
24). And he says that they also acted as end plates on the horizontal
tail, which increased its effectiveness, and improved the static
longitudinal stability - same book, same page).

--
Kevin Horton RV-8 (finishing kit)
Ottawa, Canada
http://go.phpwebhosting.com/~khorton/rv8/

"Chris W" wrote in message
...
I got such a good answer on my question about flap design I thought I
would ask another design question. why would a plane that has two
engines have two vertical stabilizers. No in the case of the Aircoupe I
always thought the reason for the twin tail was so that the helical prop
wash wouldn't induce a yaw tendency from the prop wash hitting the
vertical stabilizer/rudder. It is my understanding that the Aircoupe
was designed so you wouldn't need rudder pedals, and the twin tail I
think would have helped that. But on a twin engine, what's the point?
having two vertical stabilizers and two rudders seems significantly more
complicated both structurally and mechanically so why do it if there
isn't some advantage? There must be one I don't know about.


--
Chris Woodhouse

There used to be an argument that, in the event of an engine failure, a
twin-tail twin would have one fin and rudder directly behind the operating
engine, in the prop wash, where it would be more effective.

The more likely reason that the '30s and '40's saw a number of twin and
triple tail aircraft had to do with the low vertical clearance of hangar
doors. A multi-vertical tail aircraft would more likely be able to pass
through the low door opening where a single tail would have to be much
higher and have to be left outside.

Bill Daniels

So why did the P-38 have a twin tail. I think it is a pretty cool
looking bird. I think the bird the "Doolittle Raiders" flew had a twin
tail too.

Fred

Chris W wrote:
I got such a good answer on my question about flap design I thought I
would ask another design question. why would a plane that has two
engines have two vertical stabilizers. No in the case of the Aircoupe I
always thought the reason for the twin tail was so that the helical prop
wash wouldn't induce a yaw tendency from the prop wash hitting the
vertical stabilizer/rudder. It is my understanding that the Aircoupe
was designed so you wouldn't need rudder pedals, and the twin tail I
think would have helped that. But on a twin engine, what's the point?
having two vertical stabilizers and two rudders seems significantly more
complicated both structurally and mechanically so why do it if there
isn't some advantage? There must be one I don't know about.


--
Chris Woodhouse
3147 SW 127th St.
Oklahoma City, OK 73170
405-691-5206

N35° 20.492'
W97° 34.342'

"They that can give up essential liberty
to obtain a little temporary safety
deserve neither liberty nor safety."
-- Benjamin Franklin, 1759 Historical Review of Pennsylvania

"Frederick Wilson" wrote in message
et...
So why did the P-38 have a twin tail. I think it is a pretty cool
looking bird. I think the bird the "Doolittle Raiders" flew had a twin
tail too.

Fred

The Doolittle raiders flew B-25's, and yes, they had twin tails.

I was not in the head of the designers of the P-38, but as it ended up,
there are a few reasons that they ended up with twin booms (different than
most other twin tails of the time).

In the P-38, everything went towards speed and low drag. They made as
skinny frontal profile as possible. To get lots of HP, thery also wanted it
turbo (or was it super) charged. They put the intercooler (and perhaps the
turbocharger) back behind the engine, and it made it so long, they must have
figured they were halfway back to the tailplane, so why not contine it, and
connect to the tail, and leave off the fuselage. Works for me! G
--
---Jim in NC---

On Mon, 04 Aug 2003 17:13:25 GMT, Chris W wrote:

I got such a good answer on my question about flap design I thought I
would ask another design question. why would a plane that has two
engines have two vertical stabilizers. No in the case of the Aircoupe I
always thought the reason for the twin tail was so that the helical prop
wash wouldn't induce a yaw tendency from the prop wash hitting the
vertical stabilizer/rudder. It is my understanding that the Aircoupe
was designed so you wouldn't need rudder pedals, and the twin tail I
think would have helped that. But on a twin engine, what's the point?
having two vertical stabilizers and two rudders seems significantly more
complicated both structurally and mechanically so why do it if there
isn't some advantage? There must be one I don't know about.
So many smart answers to averything but the question.
If the tail assembly is in the prop awsh, the low and no-speed
response is much greater. ie ground and taxi.
The tradeoff is the crosswind component induced by the spinning prop,
which the Ercoup didn't want, so the put the rudders outboard of the
prop and pu on a kickass main gear system to keep the thing straight.
Mr Knowital.

In the case of some Navy jets, the issue was one of space. The vertical
surface area desired on a plane like an F-14 would have required a single tail
too tall to fit inside the hangar deck. Or so I have heard it explained by the
"Aviator" types.

Harry "first effective rudder" Frey
Wright 1902 glider, etc.