Just a few notes for the bigger picture.
Ventral Fin was standard on the F-15 and was chosen for overall greater aircraft stability (AoA and Mach) but their contribution to F-15 stability was found to be problematic and inadequate, so F-15 designers increased the area of the vertical tail surfaces and the stability problem was solved.
The MiG 29 had ventral fin very early on, perhaps from the beginning, it was later removed, on the other hand, the Su 27 did not have ventral fin from the beginning it was added later for better stability, probably to solve the stability problem.
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I don’t think the RWR covers on the sides of the intake ducts on the Su 27 had much effect on vortex formation, so they were soon removed. But I don’t know for sure. I won’t argue, I’ve never read about the benefit of these covers to the aerodynamics of the Su 27.
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pretty cool did not know this.
One drawing of a future F-15, probably 1968-1969
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They don’t affect anything.They were not even taken into account in the main aerodynamic model
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Yeah, could definitely be a reason. Definitely was placed in the flat shape for a reason in the exact position they have used Vortex Generators in prior designs…
Especially knowing the aircrafts most highlighted abilities. Flying really really well at very high angles of attack.
Making it flat with that specific tapering tip will increase drag in its most capable regime.
Thats pretty cool & very interesting. I am impressed you immediately knew the relevancy of the ventral fins
Ventral fin was part of the F-15 until 1971.
Removing them and increasing the vertical surfaces solved stability problems, plus reduced drag and weight.
EDITING :
Sorry, I thought you were responding to the F-15. Are you referring to the RVR covers on the sides of the intakes or the ventral fin on the Su 27?
As a point of interest, here are the failed F-15 designs from North American and Fairchild Hiller, they ended up behind today’s F-15.
McAir came in first with their 199B - today’s F-15, Fairchild second and NA third. The competition ended in December 1969.
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They sure did love the hell out of those ventral fins too huh. Artist did not definitely captures that lol.
The drawing reminds me of a B1 lancer
They were probably so jealous when the saw the Su-27 for the first time & that is has the massive LERX that actually extend to the canopy like the sculpture.
lol are they sure we did not get the real F-15?
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Every aircraft is about finding a compromise, there is always some advantage which brings some disadvantage.
Of course, the combination of expensive - big, and cheap - small like the F-15 and F-16 was very strong in its time.
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I’d probably guess the first use of LERX would be on the F-5, then the F-18 and F-16.
The “LERX” on the F-15 isn’t exactly a LERX, although it also makes a vortex.
F-15 Small? have you seen one irl?
They are given the nickname flying tennis court first. Not the Tomcat.
Comprise?
That was not the mindset of the United States whatsoever during the Cold War.
The Mig-25 put utter terror in the hearts & minds of the Americans.
The F-15 was developed under a sense of existential threat they perceived the Mig-25 was. Everything the United States produced was under driven by one objective, to prepare for imminent war with the Soviet Union. The Soviets produced & prepared likewise but operated under a Communist ideology.
There was actually no such thing as compromise or a program “budget” in the days of the Cold War.
It was simply, prepare for war with the Soviet Union.
There will never be another era in aviation quite like the Cold War where Lockheed & others were completely free of budgets constraints in developing top of the line technology.
For perspective, The US had 24 hour, 364 days a year nuclear Armed B-52s circling the entire Soviet Union nonstop from 1961-1968.
That was the mindset of the US in the cold war. “Cost” or “compromise” was just not in the cards.
Cheap- small - is F-16…
You don’t understand, everyone, really everyone who has designed aircraft knows it’s one big compromise. Su 27 too.
That’s not F-15 thread
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No, you actually do not understand. The Cold War was a whole other animal. The United States & Soviet Union operated completely differently. the RuF operates completely differently. China does not operate like the US & Soviet Union did.
I guarantee you, In the Soviet Union they did not order their nuclear physicist, rocket scientist & other aerospace engineers to develop a weapon system in preparation for imminent war with the United States, but at the same time “try to keep it within the budget.”
This did not happen in the United States Either. The Cold War was a period of time where the DOD, CIA, Pentagon, Navy, Army, & Airforce had countless black projects & R&D programs.
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RWR covers on the Su-27
I have a similar view
I actually meant strake or LERX. Please forgive me that English is not my first language (or even my second language), and I don’t have a good grasp of English terminology.
The Su-27 does have a very clever aerodynamic design. But this little antenna is obviously not one of them. It is treated as a wing shape more to reduce surface drag. For non-delta wing aircraft, the vortex generating device should at least be parallel to its main lifting body so that the airflow covers it. Some aircraft will place it at a positive mounting angle.
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Su-27s are already somewhat unstable in Simulation Battle. When exceeding 24 degrees AOA, lateral instability begins to occur, similar to other aircraft in SB.
Instability in reality is mainly manifested in sluggishness on the roll axis and uncontrollable pitch coupling, which will affect flight safety, so ASC override control is prohibited most of the time. For early FBW aircraft, it was common to limit the available angle of attack to ensure that the aircraft was in a safe flight range, usually around 24-26 AOA. Over time, FBW aircraft such as the F-18 adopted different control rates to ensure sufficient maneuverability when flying at high AOA, thus relaxing this restriction.
The following two figures compare the control rates of the flight control systems of the Su-27 and Su-27M (Su-37, white 711). On the Su-37, the AOA-G load limiter has been integrated into the flight control and uses proportional integral control, which can achieve a fixed stick amount corresponding to a fixed G load or AOA. The flight control system’s AOA/G load selector determines whether it is G load command or AOA command based on the speed.
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