The Pond Racer.....Rutan's Watergate

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

Ok Eric,

I figured something like that. My twin racer cannot have'em otherwise there is no flying tail.

I know a good engine out situation "safety" measure for a twin racer. In case the other engine seizes one has to quit the running engine too and make a feathered prop dead stick landing. Otherwise one has to cowboy himself with one engine.

That is how they do it with some Air Combat twin models.

rgds,

Juke / A4 WORKS


PS: Last nite in a half sleep state I figured an even better measure for engineout situation, which is a mechanical " gadget ", but I keep it a trade secret like the radiators on my twin design. I am not 100 % sure will it do the job, but definitely eaze it anyhow. It would enable the pilot to fly with one engine only and still have the small rudder and flying tail. Also squeezing the distance between nacelles a bit could make it better.

[AirDOGGe]

Re: The Pond Racer.....Rutan's Watergate

There is another reason for twin tails, at least as far as supersonic fighters go.....Inertial coupling.

This phenomenon occurs in high speed aircraft that have a large fuselage area to wing/tail area ratio. Something as simple as a roll can result in movement in pitch and yaw as well. The Douglas X-3 and the early F-100s suffered from this. The F-100 was fixed by increasing it's tail surface area. Modern aircraft from the 60's on have generous wing & tail area in comparison to earlier supersonic machines.

This is mentioned in "Exploring the Supersonic Frontier" by Richard P. Hallion (Center Historian of the Air Force Flight Test Center, Edwards AFB)

Inertial coupling, also called roll coupling or roll divergence, had first been predicted by William H. Phillips of Langley Laboratory in a classic theoretical study. [Ref 3-16] One important cure was to increase the wing area and, especially, the tail surface area of the aircraft....

...Generally speaking, the current-generation aircraft having twin vertical fins and generous wing areas plus other aerodynamic refinements are monuments to the lessons learned from the X-3 and its brethren.

Yet another advantage with twin tails on such aircraft is that during extreme maneuvers a single tail can be "blanked out" by airflow around the fuselage or wings. With 2 tails there's a better chance that at least one tail will be in the airstream.

Why the F-16 only has one tail, I cannot say. Since it was suppose to be a cheap, lightweight fighter perhaps an extra tail would have added too much weight or raise the manufacturing price higher than desired....I suspect the former.

.

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

Yup AD,

Undoubtably some advance did the twin verticals bring.



However Mossie and both Westlands Welkin and Whirlwind didn't have'em.

http://hsfeatures.com/images/welkintc_1.jpg

Whereas very potential FW187 "Falke" did loose to Me 110 in competition.
( It had engines that delivered together 400 less hp than the ones istalled in a Me 110.)

http://www.luftwaffepics.com/LCBW3/fw187-001.jpg

Food for ideas was brought to you by,

Juke

[51fixer]

Re: The Pond Racer.....Rutan's Watergate

Even at the risk of being labelled a moroon; how does this make a plane safer ? Was " Connie " the safest when it had three verticals ( like Pond Racer ) ?

The PR did not have 3 verticals. It had one. The stabilizers at the end of each boom were for safety reasons to give enhanced tail area. As flight testing progressed they were cut down and the final design was for these to be completely eleminated. They were cut down in stages and the thinking was that if some control probems were discovered then what had been removed at that stage could be added back on.

That was the one time that I worked on a composite airframe. It was amazing to watch how it could be damaged or reconfigured and then rebuilt. It had a history of being damaged by towing. If you went too fast (or sometimes not so fast) and stopped suddenly then the PR would slide out of its tow dolly and smash up the tail. (It was towed tail first) Another Rutan design. After this happened to Randy Scoville driving we redesigned the dolly. It needed a larger elevator trim tab anyway. Normally Jim Dale or myself would drive. Thank goodness it was the big cheese driving that time but we warned him not to go so fast. I think that happened a few times to the tail.

Rich P

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

The stabilizers at the end of each boom were for safety reasons to give enhanced tail area. As flight testing progressed they were cut down and the final design was for these to be completely eleminated.

Rich,

This is very interesting....I think we have learned more about the racer here in two weeks than in the previous 15 years.....at least I have. Thanks for the info.

rgds,

Juke

[First time Juke]

Re: The Pond Racer.....Rutan's Watergate

As far as EZ and eze spin performance, I do know the designs of his canard aircraft were intended to help prevent pilots from entering a spin in the first place compared to rear-elevator designs (by making it so difficult to stall and roll over). What happens if you somehow find a way to enter a spin in a varieze or long-ez, I can't say, but it must have taken some effort to get there.

There may be some grain of truth behind the comment about an inadequate forward wing design though. In the PDF file, a short-chord elevator was part of the early varieze design, and it was later recommended that owners stop flying until they replace it with an improved longer chord design (there's even a photo of a short-chord elevator modified into the longer unit).

Sorry Airdogge, I meant to say recovery from a stall ( not from a spin )...I am little bad with words sometimes. Please forgive me.

rgds,

Juke

[Blue Foam]

Re: The Pond Racer.....Rutan's Watergate

The PR did not have 3 verticals. It had one. The stabilizers at the end of each boom were for safety reasons to give enhanced tail area.

IMHO, this is a semantic distinction. Aerodynamically, the dual "stabilizers" had vertical projected area equal to the center vertical stabilizer, and therefore, had equal contribution to lateral stick-free stability. Whether they were intended to be "tails" or not, their effect was to improve Cnb (no greek letters on this board ).

The original statement derived from decades of trade studies stands: If these surfaces that were buried in prop wash had been equipped with rudders and the central tail removed, it would have resulted in higher controllability and lower drag than removing these surfaces and keeping the central tail. The point being that this was one of many areas where the design database clearly indicated a superior design direction that was not followed.