Inward V-tail, Good or bad?

[Wing Zero]

I'm curious to know what effects a plan would have with Inward canted tail surfaces, almost like a upside down V-tail. The YF-23 used butterfly, or a wide V-shape tail configuration... If the surfaces faced inwards instead of outward, what would be the difference in stability, control, etc... Would the area of the surfaces, angles, or width apart change anything? Thanks. I did try searching several times, but didn't find anything answering my questions. Perhaps I used wrong terms... any help would be nice. :)

[ciurpita]

http://www.rcgroups.com/forums/showthread.php?t=808506

[Wing Zero]

Thanks for the help... I'm not sure I completely follow them. I don't know why my search didn't turn this up, but atleast I have it now. I'm not certain an invert V would end be the case judging from what I read. I might have to look further into it, it would use small canards up front for pitch control, along with slight thrust vectoring. The tails are probly at 60 degrees, canted inward, but wide apart...

[BMatthews]

There was a twin boom glider from a few years ago that used a canted in ^ style shape. No issues at all with it. The elevator function works the same with both angling up or down equally. The rudder function worked the same as well with both moving to the "right" or "left" equally.

The mounting off the twin booms makes for a natural way to mount the inverted V with the joint up high and in the middle. But there's other examples of inverted V tails mounted to the fuselage directly. The Predator UAV used by the military has one and there was a pusher prop Reno air racer.

The biggest issue is damage at landing. The twin boom glider took care of that by mounting it high and the booms acting as skids.

Now if you're talking about using inward canted tail surfaces on a YF23 style jet design that's different. Now you'll have a big flat, wide fuselage closing the lower gap. Airflow through the triangle will be confused and turbulet and there will be interactions with the flat rear fuselage area.

But if it will be a center mounted jet motor with the area under the tail surfaces open like the Lynx shown below that's different. A model with this sort of planform could easily be adapted to a ^ style inverted V setup and fly just fine.

Now if you are talking about a planform like the Lynx below but just want to cant in the fins up to maybe 15 to 20 degrees from vertical and keep the flat horizontal stabilizer and elevator then there's no need for us as modelers to mix the rudder function with the elevators.

On the full sized F18 Hornet the canting of the fins adds some small amount of drag during high rotational pitching speed maneuvers. To compensate for this when you see an F18 pull hard back the rudders actually turn inwards very slightly to alter the camber of the fins so that they minimise the drag due to their horizontal component. Similarly when the pilot pushes hard forward the rudders turn outwards slightly. This is for drag reduction only although there would be some very slight elevator effect as well. But on our models we are flying for fun and getting that fancy just isn't required.

[ciurpita]

of course there's the predator UAV. flies itself, long duration flights, ...

http://www.uavcenter.com/english/wwuavs/north_america/images/31_predator_01.jpg

[Wing Zero]

In the design I am looking at, there is almost no flat area between the engine nacelles , which the fins come off of. The forward fuse comes into the wing and tappers off just past the wing. The wing, has two engine nacelles pushed outwards like the YF-23. Thse inward slopes up the side of the engines, have the fins. The wing is foward swept and the the front fuse has canards...

[Brandano]

I remember a twin boomed HLG that had the two halves of the inverted V-tails separated and spread apart. The inverted V with this kind of setup had more roll coupling (since the control surfaces where further apart) but this was mitigated by the fact that the booms would tend to twist the wing the opposite way. the inverted V should have a better roll coupling compared to a conventional V, but I am not sure how noticeable this would be.

[Gannet AME]

I did try searching several times, but didn't find anything answering my questions. Perhaps I used wrong terms... any help would be nice. :)

Attached is what I have on V-tails both Upright and Inverted. I was going to send a link to the largest one but I cannot find it on the internet anymore, luckily I copied it in its entirety.

Enjoy

[admodesi]

The term A-tail is used to describe an inverted V-tail. The Aerosonde UAV and the Have Blue are other designs that come to mind.