Turning rates

[Romani]

I have searched the archive but I haven't found anything on this topic, so maybe some of you gentlemen can enligthen me.

Forgive me if I am saying in the following post obvious things like "water is wet", lacking a flying background I am deliberately explaining in detail every concept to make sure I understand what they mean (or maybe not) and for the benefit of other readers that may be as technically challenged as myself.

A small turning radius is an important advantage for a fighter, at least defensively.

If I have the facts right, turning radius is dependent on speed. Supposed the same banking angle, the advantage goes to the airplane that goes slower.

The more pronounced the banking angle, the less lift generated by the wings, same thing happens with speed. Therefore, a plane slowing and banking hard to do a tighter run risks stalling or losing altitude.

The airplane with the lower wing load, this is weight of the craft divided by wing area, has the advantage in turning because it has more excess lift and can afford to bank more or go slower, resulting in a tighter turn.

Please note I am purposefully excluding from the discussion, at least for the time being, roll rates (the speed with wich an airplane can rotate around its longitudinal axis, or how fast it banks), responsiveness (or lack of it) of controls and the torque of rotary engines.

WWI fighter had turning radius of between 100 meters/yards (high speed turn at 180 kph (110 mph) or as little as 40-50 meters , wich I assume is a low speed turn at a speed of 80 kph (50 mph) or even less and restricted to such planes as the Sopwith Camel and Fokker Dr I.


Now, let's make a halt here. I suspect that the stamentes that the Camel or the DrI could make "a turn in its own length" wich would be a turn radius of 10 meters, are hiperbole. Unless they could spin around like a car performing a bootlegger turn , I take that is more likely the smallest turning radius was 40 meters, moving let's say at 70 kph (20m/s) they would complete a 180 degree turn in 6 seconds. (Since a 180 turn is a half circle, the total distance traversed would be pi * R = 120 meter)


Now we get to the main question. What exactly does turning rate mean? I understand that it means something along the lines of how fast a turn is completed. So turning radius is not the only thing to be taken into account, a faster airplane with a bigger turning radius has to traverse a longer distance than a slower airplane making a tighter turn, but if the faster airplane can make the turn fast enough, it can complete the turn before.

For example, could a Fokker DVII do a 180 degree turn , with a turning radius of 100 meters at a speed of 180 kph (110 mph)?

That's an arc of about 300 meters and at that speed of 50 meters/sec it can complete it in 6 seconds. I ask if such a turn could be performed, because I am aware of banking limitations and the Gs pulled on the frame and pilot. I am aware that most commonly turns are measured in Gs, rather than in speed and turning radius, but is late at night and can't find my old physics handbook to check the formulas.

I ask if that movement is reasonable, unlikely or ludicrous, just to have a base for comparison.

So are any figures available for WWI aircraft, either from original tests or modern replicas? Is my understanding that turn rate is measured by counting the time it takes for an airplane to invert the direction of flight (ie, making a 180 degree turn) but I don't know if I read it somewhere or I just made it up

[jumpinjan]

"What exactly does turning rate mean?"
Its angular velocity; (Omega) =V(velocity)/r(turning radius)
There was a paper published on the same questions in WWI Aero, #182 Nov 2003, Titled, "Airfoils & The Turning Ability of WWI fighters", written by Scott Campbell, Brownsburg, IN
Look it up, its very interesting.

[Taz]

Romani- Turn rate is expressed in degrees per second and is a function of "g"s and velocity. Bank angle has an effect on turn rate if you are trying to maintain level flight, but you can generate turn rate with no bank angle which would eventually put you in a loop. Turn rate can be generated in any plane to the horizon, including spiralling ascents and descents. It takes "g"s to maintain level flight in a turn. 30 degs is approximately 1.13 "g"s, 60 degs is 2-3 "g"s, 90 degs is infinite "g"s. How many "g"s you can pull is a function of engine power (actually entry velocity), wing loading, and placard "g" (aircraft strength) capability. There are photos of a Sopwith Triplane pulling 6 "g"s, but it could only do that for 4-5 seconds before it rapidly decelerated as it ran out of energy. Entry velocity, wing loading, and aircraft strength determined how many "g"s an aircraft could pull initially, and power and wing loading determined how long it could hold that "g" level and subsequent turn rate. In most WW-I aircraft, velocity slowed rapidly in a turn. As they slowed, their turn radius decreased, as did their "g" capability, so turn rate varied throughout a turn. Altitude could be traded for velocity and descending turns were normal. Read any description of a WW-I engagement and you will see a description of how the fight rapidly decreased in altitude as all players tried to keep their energy (airspeed) up.

The reason the Fokker D.VIIF and Siemens-Schuckert D.IV were such formidable opponents was that their engines actually gained power at altitude because they were overcompressed (for sea level operations). The additional power meant they could match their opponent's turn rate while not losing as much altitude or as much airspeed as he was losing. That gave you closure, and both an altitude and airspeed advantage. If the opponent's wing loading was lower, he might be able to turn a tighter turn radius than you, but you could just climb to slow and make your turn circle tighter, and then turn the altitude into airspeed and turn rate (high yo yo).

Do not know if this answered all your questions, but it is the best I can do without using formulas. There was an excellent piece in WW-1 Aero (I think) a while back which actually tried to quantify most of the WW-I fighters by climb rate, sustained turn rate, altitude capability, maximum speed and other criteria. If I remember correctly, the D.VIIF was king of the hill by a large margin.

Taz
Terry Phillips

[FlyXwire]

Romani,

You might enjoy reading this online report on the subject (in Adobe PDF format):

http://www.aa.washington.edu/faculty...202005-119.pdf

One thing that my personal research into the subject has led me to believe, is that "contollability" has nearly as much to do with aircraft handling in WWI, as did the aircraft's inherent aerodynamic potential. The Fokker D.VII fought well because it's aerodynamic potential was easy to achieve from a piloting viewpoint.

Other online reports related to the matter (or just for general interest.....all PDFs):

http://naca.larc.nasa.gov/digidoc/re...ACA-TR-153.PDF

http://naca.larc.nasa.gov/digidoc/re...ACA-TR-112.PDF

http://naca.larc.nasa.gov/reports/19...report-120.pdf

http://naca.larc.nasa.gov/digidoc/re...ACA-TR-155.PDF

http://naca.larc.nasa.gov/digidoc/re...ACA-TR-154.PDF

http://naca.larc.nasa.gov/digidoc/re...ACA-TR-249.PDF

[Barrett]

Excellent sources FlyXWire. Also, Taz properly injected altitude into the equation but I would add that turn radius (as with all performance parameters) is affected by altitude. That's why, ferinstance, the combat spread flown by WW2 USN squadrons varied with altitude and airspeed. The "Thach Weave" was flown within approx. two radii of each plane in the section: more up high and less lower down. If one a/c had to "drag" a bandit, it would present the partner with a 90-degree deflection shot more or less within boresight range.

However, note that pure turn performance is not the whole shebang. Agility also counts for a great deal--the ability to change directions rapidly. Consequently, aileron effectiveness (the roll axis) figured into the equation as well.

As Taz said, any sustained turn "bleeds" energy, which is why dogfights usually became descending spirals until well into the jet age. Afterburning engines finally permitted fighting with the nose above the horizon. But WWI fighters could and did make use of "boom & zoom" tactics, recovering from a steep dive to regain altitude and position for a reattack.

[Taz]

Barrett- You are absolutely right; "q" (air density) decreases, caused mostly by altitude, directly affect "g" capability and result in larger turn radii. Should have added an altitude factor in there.

Taz
Terry Phillips