Two vertical stabilizers on the F-22 Raptor angled

[Danger]

Anyone here ever fly a T-bone? I haven't, but I'd like to see how it handles. I can't say as I find it aesthetically pleasing, but it certainly is distinctive and a true classic. The 'V' tail in this instance had nothing to do with radar, since it was strictly a civilian aviation design. The first prototype flight was in 1945, and it hit the market a couple of years later. They dropped the 'V' tail in '82, but the Bonanza itself is still in production.

 

[Cyrus]

Another hijacking of this thread:

NASA's Lessons Learned from the SR-71 program. This paper has TONS of really good information. It does have a blurb on page 36 about meeting the customer's requirements for RCS reduction, but it doesn't really go into detail.

http://www.scribd.com/doc/18029452/NASA-SR71-Blackbird-Challenges-and-Lessons-Learned-2009

sweeeet, this is turning out to be an A+ thread guys!

 

[mugaliens]

Why are the two "vertical" stabilizers on the F-22 Raptor angled sort of like a V-Tail as opposed to being completely vertical?

Right angles form what's known as a http://en.wikipedia.org/wiki/Corner_reflector" .

 

[Cyrus]

The link above that I gave directly states that they were canted in for reduction in RCS. Whether the aircraft was stealthy or not is a moot point (which I disagree with). They were canted because they were thinking about making the aircraft smaller on radar.

http://books.google.com/books?id=fVQRmQo-bfUC&pg=PA17&lpg=PA17&dq=kelly+johnson,+canted+vertical+tails&source=bl&ots=eUPlC_78Qq&sig=WOYbMSciQuyGYzaqH686TVnHObU&hl=en&ei=5C4gS4qtO5XSMo78ucUC&sa=X&oi=book_result&ct=result&resnum=3&ved=0CAsQ6AEwAg#v=onepage&q=kelly%20johnson%2C%20canted%20vertical%20tails&f=false

Turn to page 17:

Ultimately, the low-RCS technology on the A-12 proved less useful than expected. By 1962, U.S. intelligence had detected the Soviet Union's massive P-14 early-warning radar, code named Tall King, and its computer based control and display system. The P-14s performance undermined the blip-scan theory. The level of RC reduction achieved on the A-12 would not prevent an adversary from detecting it.

In other words, nice try, but no cigar.

Side: I got the book in yesterday from Amazon for only $15 bucks. It has lots of full page images - very nice.

 

[FredGarvin]

I think I still have the cigar: Whether they worked or not is not the issue (I do concede that argument). The sources shown all stated Lockheed said the intent of the inward can't was for stealth. OK, it didn't work but there is nothing saying any other intent. Your wind tunnel source mentioned nothing about the SR-71. Do we know that that reasoning applies, especially since the SR was a delta wing operating in a much different regime?

So we still have no directly stated source stating the contrary to the stealth argument.

 

[FredGarvin]

I had to laugh when I found this:

Stealth

There were a number of features in the SR-71 that were designed to reduce its radar signature. The first studies in radar stealth seemed to indicate that a shape with flattened, tapering sides would reflect most radar away from the place where the radar beams originated. To this end the radar engineers suggested adding chines (see below) to the design and canting the vertical control surfaces inward. The plane also used special radar-absorbing materials which were incorporated into sawtooth shaped sections of the skin of the aircraft, as well as caesium-based fuel additives to reduce the exhaust plumes' visibility on radar. The overall effectiveness of these designs is still debated, but since the aircraft did not include other elements of today's stealth technologies, it was still easy to track by radar (and had a huge infrared signature when cruising at Mach 3+).

http://www.aircraftguru.com/aircraft/aircraft-information.php?craftid=80

 

[Cyrus]

I think I still have the cigar: Whether they worked or not is not the issue (I do concede that argument). The sources shown all stated Lockheed said the intent of the inward can't was for stealth. OK, it didn't work but there is nothing saying any other intent. Your wind tunnel source mentioned nothing about the SR-71. Do we know that that reasoning applies, especially since the SR was a delta wing operating in a much different regime?

So we still have no directly stated source stating the contrary to the stealth argument.

Oh, his discussion with me was not about stealth, it was purely about straight twin tails vs canted twin tails from an aerodynamics point of view. Interestingly enough, I saw a picture of the latest variant of the F-15 Silent Eagle. It now comes with canted vertical tails, probably for the exact reasons mentioned on vortex shedding.

http://themoderatevoice.com/wordpress-engine/wp-content/dr-e/f-15-silent-eagle-boeing.jpg

​

You are right that they were canted inward for stealth on the SR. That I don't argue.

 

[FredGarvin]

Oh, his discussion with me was not about stealth, it was purely about straight twin tails vs canted twin tails from an aerodynamics point of view. Interestingly enough, I saw a picture of the latest variant of the F-15E strike eagle. It now comes with canted vertical tails, probably for the exact reasons mentioned on vortex shedding.

You are right that they were canted inward for stealth on the SR. That I don't argue.

I thought the F-15 was a done deal. When did they come out with a canted tail version?

 

[Cyrus]

I thought the F-15 was a done deal. When did they come out with a canted tail version?

See my edit above.

Source:

[1] http://themoderatevoice.com/27219/b...5-silent-eagle-with-fifth-generation-add-ons/

 

[mugaliens]

I thought the F-15 was a done deal. When did they come out with a canted tail version?

"http://en.wikipedia.org/wiki/F-15_Silent_Eagle#Design_and_development"."

Canted in or out doesn't matter.

The F-15SE's vertical stabs are, as Cyrus mentioned, canted out to reduce vortex issues, as delta or pseudo-delta's tend to "sit" in slow flight, and inward-canted vert stabs exacerbate the problem. The '-71 experienced this issue with the 'Q during refueling, but it wasn't insurmountable.

 

[Cyrus]

"http://en.wikipedia.org/wiki/F-15_Silent_Eagle#Design_and_development"."

Canted in or out doesn't matter.

The F-15SE's vertical stabs are, as Cyrus mentioned, canted out to reduce vortex issues, as delta or pseudo-delta's tend to "sit" in slow flight, and inward-canted vert stabs exacerbate the problem. The '-71 experienced this issue with the 'Q during refueling, but it wasn't insurmountable.

I think the main lesson is, don't have them vertical: but can't them inward or outward depending on what the aerodynamics favors (for a similarly obtainably RCS in either configuration).

Edit: While I don't necessarily doubt the claim by Boeing that the angle decreases RCS, I also don't put it past them to lie and say this to boost sales of the aircraft. Without actual comparison of RCS of the E and SE models to actually show if the tail works - be skeptical.

 

[mugaliens]

I think the main lesson is, don't have them vertical: but can't them inward or outward depending on what the aerodynamics favors (for a similarly obtainably RCS in either configuration).

Edit: While I don't necessarily doubt the claim by Boeing that the angle decreases RCS, I also don't put it past them to lie and say this to boost sales of the aircraft. Without actual comparison of RCS of the E and SE models to actually show if the tail works - be skeptical.

It's not that they're vertical, but that they're not at 90 deg angles to the wings. That said, canting inward is better for deflection against ground-based radars, but worse for low-level operation against lookdown radars.

The SR-71 did not employ radar absorbant material, so canting was their only option given the high heat-resistant requirements, and given their high-altitude profile, canting inward was the better stealth choice, even if it resulted in slightly degraded slow flight performance (drivers said "it wallowed").

The F-15SE's operating environment is less heat-restrictive, allowing the use of far better radar-absorbing materials (though some are simply translucent or transparent to radar).

I agree Boeing is in the market, but given their engineering expertise, they have little need of stretching the truth. I think they're main goal is to sell it as a much lower-cost but nearly capable alternative to the far more expensive F-22 and F35.

Besides - we have lots of potential targets around the world that don't require "the best of the best of the best" in technology. Just look at how admirably Sandy's (A-1 variants) and similar aircraft performed in Vietnam. It was a 40's-era plane that kicked butt twenty years later!

Interestingly enough, the plethora of variants created somewhat of a maintenance nightmare. Fortunately, most of the versions involved ancillary equipment to the basic airframe and powerplant. Still, it was a lesson in how not to modify an aircraft into every conceivable role.