Hey fighter guys!

I'm new to RV flying and have a pure civilian background.

As I read up on acro it seems like "corner speed" may have a similar meaning as "maneuver speed"

Pull 6 Gs in an RV below Va and you will experience an accelerated stall. Pull 6 Gs faster than Va and you may damage the aircraft.

Heavier aircraft (more inertia) = faster Va.

Can this mean the same as "corner speed"?

Thanks in advance

Not quite.

Corner velocity (speed) is that minimum speed that your aircraft can pull maximum G, but you will almost certainly also lose energy while doing so. At corner speed, you will achieve your maximum turn rate.

Corner velocity is also the speed at which, if slightly exceeded, one can over-g the aircraft (if not artificially limited by a flight control system).

As an extension to the first paragraph, any maximum G turns at speeds in excess of corner speed will result in a lower turn rate per second, and an increased turn radius.

Ok. So could one say that in an RV if one was to fly at Va and introduce the max (6G as an example) than that would yield the corner speed or max efficient speed per unit G?

Asked another way. Would the corner speed of a fighter change with aircraft weight?

https://en.wikipedia.org/wiki/Maneuvering_speed

"In the context of air combat maneuvering (ACM), the maneuvering speed is also known as corner speed or cornering speed.[2]"

I'm curious from an academic point of view / civilian teaching in my RV.

Not a fighter guy but former IAC acro type in Pitts. Anyone, feel free to throw darts, this is just ballpark testing that worked for me in an RV-6 at 1350 pounds, standard day, PA of 3000 feet.

Cornering velocity gives maximum turn RATE. It may be pulling the g imit at maneuvering speed, but it won't be maintained long without descending to use gravity.

The are two ways to look at it, then many permutations. Level flight, high bank angle, max power but NOT high speed- what constant speed and g can you attain the fastest turn rate? Power is fighting a lot of induced drag in level (edit to add "turning") flight.

Second- saving hitting the ground, pointed straight down, at low speed- what speed do you attain and maintain with g and power yielding the fastest return to level flight, minimzing altitude loss is the goal. Gravity is adding to your engine's accelleration pointed straight down. You may need a rapid power reduction to not exceed your target speed on attained.

Stay coordinated stick and rudder at all times in both.

Neither may look like an IAC scorable aerobatic figure- level turn or a scoreable quarter loop.

Remember the stall speed to g squareroot math- at 4g, you double your 1g wings level stall speed.

If you stall at 50 knots wings level, stall is about 4g at 100 knots. You may not have the smallest radius at level cornering velocity, but flying slower for a smaller radius may yield a decreased RATE of turn.

Honor your symmetrical g limits and maneuvering speed. Stall speed stays pretty close to the same indicated speed at high altitude, but in the RV, we honor the TAS, too as the same limiting number.

Have not seen this actual performance curves for a typical RV, but 105 knots (RV-6 Va 134mph or 115 knots blue tickmark ) and 3.3 ish g is a decent starting point for cornering leaving margin and not full elevator deflection. That's about 15% over stall speed and I can feel a bit of buffet. Every plane will talk to you differently.

Turbulence, both wake and atmospheric can significantly raise the loading.

Third use, "winning" a tail chase...

The easy question first...yes, corner velocity changes with respect to weight. An overall energy diagram will indicate that as weight goes up, altitude increases, or drag increases, overall energy loss per second increases.

See this link for a Energy Management chart (Ps, for short) for the MiG 21. Forgive the Chinese message board it came from!

http://www.acewings.com/cobrachen/forum/topic.asp?TOPIC_ID=8197&whichpage=2

Now, you ask

So could one say that in an RV if one was to fly at Va and introduce the max (6G as an example) than that would yield the corner speed or max efficient speed per unit G?

Click to expand...

Yes, by definition Va is the maximum speed at which full deflection of any single flight control surface (and ONLY one deflection...no reversals or doublets) allows for maximum G without the chance of structural damage.

But...your question about "max efficient speed per unit G" is a bit of a puzzler. Va allows for the maximum G available, and as such the greatest (and instantaneous) turn rate in degrees of turn/second.

It does not equate, however, to the minimum turn radius, which is defined (practically speaking) by only two things: speed and G pulled. In level flight, that equates to speed and angle of bank...remember that at 180 knots and 30 degrees of bank, an RV-8 and a 787 have the same turn radius.

So if your concept of "max efficient speed per unit G" means turning the tightest, maneuvering at Va does not do the job. It will however allow you to create the greatest number of degrees per second in turn rate.

The next big issue: energy loss. Turns at Corner Velocity are generally energy wasters, meaning that the wonderful instantaneous turn rate will soon degrade to lower values as the aircraft's speed diminishes. The aircraft's capability to attain maximum G is similarly quickly reduced as speed is ground away by the turn.

That is why fighter pilots who take their aircraft to the merge (passing close aboard a potential enemy) will do so at a far higher speed than corner velocity. Every model of fighter is different, and differing weapons, altitudes, drag indexes, and weights play a factor into what speed they will actually fly.

Thanks guys. This was fun to read through. I always enjoy expanding what I have already learned about aviation.

Anyone have a good recommendation on a book that covers this and aerobatics?

Thanks

Mike

http://www.acewings.com/cobrachen/fo...97&whichpage=2

Don't know about the rest of you guys, but when I clicked on this (From post 5), I got an option to translate the chinese into english. So if I'm reading this correctly, I'm seeing what "they" thought of our F 104's, 105's, 102's, etc. Very chilling.

I got a 404 error: Not found. Is the link correct?

Try Aerodynamics For Naval Aviators, a few years old now but the aerodynamics are still good---it's something of a classic in aerodynamics circles.

"Corner speed" is the lowest indicated/calibrated speed at which an aircraft has sufficient velocity to be able to generate (pull) its maximum permissible structural "g". In dogfighting it is useful to engage at corner velocity or higher in order to have the "sanctuary" of maximum "g" available for initial offensive or defensive moves/counter-moves. In the USN/USMC, non-slatted version of the F4-J, that speed was 445 kcas if memory serves. In recognition of that corner speed, we typically patrolled and flew to and from engagement and target areas at 450 kcas or above in order to be able to pull the full 6.5 "g" limit on the aircraft in case we got jumped. At about 10 degrees nose low (or less if you were light) an F4-J in afterburner would hold 6.5 g all the way to the ground (but the pilot and RIO couldn't)---a full 360 turn at a continuous 6.5 "g" is a pretty rough ride, let alone several in a row.

The F-18A Block 7's that I flew later had a lower corner velocity at around only 375 knots IIRC, but that was at 7.5 "g". Oddly, I could never get one to hold that as well as the Phantom would (probably my over exuberance). A full 360 at 375 knots/7.5 g is, however, a much tighter turn than the F-4 could pull.

Corner speed is a useful speed to know in combat maneuvers but has little application in more normal general aviation flying. I would guess (purely a guess, understand), that the 6 "g" corner speed in my F1 Rocket is somewhere around 160-170 knots indicated. Below that, you can't pull 6 and above it, you need to be aware of where you are and careful with the stick. You would still have some structural "overhead" to work with I suppose, but you'd be qualified to wear a "test pilot" patch when you got down if you got too carried away.

Regards,


Lee...

Maneuvering Speed = Corner Velocity

Va = corner velocity. The expression comes from the "corner" of the Vn diagram where the G limit crosses the aerodynamic limit. Since turn rate and radius are based purely on TAS and G, at corner, the airplane achieves maximum instantaneous turn rate at minimum turn radius without exceeding structural or aerodynamic limits. It does (almost always) bleed energy significantly at this condition (-Ps or specific energy), hence it's referred to as maximum "instantaneous" rate and is generally approached from a higher airspeed as Lee mentioned above. Maximum sustained turn performance occurs at a 0Ps (neutral specific energy) condition and is a higher IAS and lower AOA than corner. This can be depicted in a turn rate/radius diagram for any airplane. A rate/radius diagram is a "snapshot in time," but is an easy method to visualize relative turn performance at different airspeeds. A rate/radius diagram for an RV-4 is on page 349 of the transition training manual:

https://drive.google.com/file/d/1heUX0aynnoJtlimDwi-s578tGBO0o15I/view?usp=sharing

Va/Corner = the square root of the G limit x IAS for stall and assumes a symmetric pull (i.e., maneuvering about a single axis) which for a dumb*** fighter pilot like me means "unload, roll, set and pull;" i.e., unload to 1G or less, roll the airplane to place the lift vector where you want it, and pull to desired G at an appropriate aerodynamic onset rate (airframe dependent, but about 2G's per second for an RV). If I'm rudder maneuvering or maneuvering about two-axis simultaneously (rolling and pulling at the same time), G allowable is lower (assumed to be 4G's [33% less than maximum allowable symmetric G for civilian airplanes designed IAW FAR 23] in the case of an RV, although Van doesn't specify asymmetric G limits) meaning that corner is lower than for a single axis pull. Since the technical definition of maneuvering speed is "the maximum speed at which you can apply maximum control input about one axis, one time," these concepts marry up nicely.

One of the most important considerations for RV'ers is that maneuvering speed isn't a fixed number...it varies based on gross weight and whether you are maneuvering around one or more axis simultaneously. If you have a calibrated AOA system in the airplane and know where ONSPEED is (maximum power point for a straight-wing prop), that provides an optimum turn cue. In other words, there generally isn't any sense pulling any harder than optimum turn due to the high energy bleed. The exception to that is if you are pulling to the aerodynamic (stall) limit to either bring your nose to bear (shoot) or avoid the ground (emergency dive recovery). If you can listen to your AOA in the cockpit, this becomes really simple:

https://youtu.be/BphHzWHbOjo

The airplane is ONSPEED (achieving optimum turn performance) when the tone is steady. As the AOA increases (high pitched beeps), I adjust the back pressure on the stick to re-establish an optimum turn condition, and vice versa if fast (low pitched beeps). You can see the difference in turn rate by noting how the nose tracks along the horizon as I adjust pitch to control AOA.

Here's another example of what would be called a level break turn in an RV-4:

https://youtu.be/4tvrWWtBEbQ

Turn rate/radius management is integral to 1 v 1 air-to-air maneuvering.

Cheers,

Vac

Old, washed up USAF fighter weapons school instructor pilot

Thanks Vac. As I heard my prior service pilot friends talk about Corner Speed, I was thinking about how this may translate over to RV flying. Specifically an emergency pull up speed.


Say there's a botched roll that turns into a split S (with no aoa installed in said RV), I guess the pilot could pull to max G and hope to stay below Va. If over acro weight, pull as needed to avoid the ground and hope you didn't bend the plane.

I'm sure no one has ever had this happen...but nice to think about on the ground before one may be pulling out with no ejection seat and a canopy full of earth.

Hoody

Hoody,

Great question. Unfortunately folks have had that happen and pulled the tail off RV's; so kudos for thinking about it at zero knots and 1 G!

Emergency pull up speed reference airspeed is corner velocity: if you are faster than corner, then you have to modulate power and G/buffet (i.e., drag) to slow to corner; if you are slower than corner, then you want to accelerate to corner to achieve maximum instantaneous turn performance. Emergency Dive Recovery discussion is on page 368 of the transition training manual, so I won't reiterate that here.

If you fast forward to 9:33 in this video, there's an example of an inverted recovery/pull-through that highlights the acceleration characteristics of RV's when the nose is below the horizon:

https://youtu.be/-kbA6NxMpmQ

You'll notice in the video when I set up the demonstration, I'm careful to manage my entry parameters to control acceleration, and really only allow the airplane to accelerate in the last portion of the dive recovery on the back side of the split-S (pitch <90 degrees). That's because I know if that if I start the demonstration too fast (i.e., screw up my entry parameters), or get lazy with the pull in the first 90 degrees of pull-through, things will get ugly quick and it would be safer to revert to an unusual attitude recovery, as opposed to a pure split-S. If you get to the 90 degree nose-low point, however, you are now committed to the dive recovery.

Without a calibrated AOA system in your airplane, you can still recover based on CAS, G/buffet cues and lift vector management: which is just a fancy way of saying roll, pull and power. Understanding and using AOA as a reference makes maneuvering easier, more efficient and helps avoid loss of control--which is really helpful for a ham-fisted pilot like me. And the real key to avoid unintentionally split-s'ing out of a botched roll or recovery when you screw it up is good aerobatic flight instruction from a current and qualified instructor pilot; but I'm guessing you knew that already

The bottom line is that before any vertical maneuvering, I take a quick energy snapshot (IAS + nose position), and then make a decision where I have to place the lift vector (roll), throttle (power) what my target G and onset rate is going to be (how hard I pull). In the transition training manual I have a couple of conservative suggestions for airspeeds when you make this assessment before you go "over-the-top" or "pull-through," as well as discussion about throttle control and how hard to pull.

Good discussion, thanks for bringing up the topic!

Cheers,

Vac