The ride quality is nothing else than the gust response of an aircraft. The vertical load factor (when we consider vertical axis only) changes with the airspeed flucturations (and angle of attack, but lets consider a purely hotizontal gust).
The function is:
n ~ CL ~ IAS² * WingArea * Lift Curve Slope * Angle of Attack

Canards only help in controlling the aircraft, the gust response is largely similar. The discomfort of low level flight is due to gusty conditions with high dynamic pressure. The pilot also needs to control the flight path, which may cause high workload (lots of disturbance, probably resonance with aircraft modes).
For a gust load allevation it is rather necessary to use wing trailing and leading edge devices, which normally have insufficient reaction time. The canards on the B-1B were necessary so that the flight control system could control pitch, the elevators were not fast enough.

Thanks i like this definition, i want to ask you this i am not an aerodynamist, do you think the Su-34 has good controlability at level flight at sea level and Mach 1.1 because for what you are saying the Su-34 has several control devices and must be able to use them properly to stay controllable, and do you think the general aerodynamic configuration does play a part in controlability?

The response of aircraft to stochastic atmospheric turbulence plays an important role in aircraft-design (load calculations), Flight Control System (FCS) design and flight-simulation (handling qualities research and pilot training). In order to simulate these aircraft responses, an accurate mathematical model is required. Two classical models will be discussed in this thesis, that is the Delft University of Technology (DUT) model and the Four Point Aircraft (FPA) model. Although they are well estabilished, their fidelity remains obscure. The cause lies in one of the requirements for system identification; it has always been necessary to relate inputs to outputs to determine, or identify, system dynamic characteristics. From experiments, using both the measured input and the measured output, a mathematical model of any system can be obtained. When considering an input-output system such as an aircraft subjected to stochastic atmospheric turbulence, a major problem emerges. During flighttests, no practical difficulty arises measuring the aircraft motion (the output), such as the angle-of-attack, the pitch-angle, the roll-angle, etc.. However, a huge problem arises when the input to the aircraft-system is considered; this input is stochastic atmospheric turbulence in this thesis. Currently, during flight tests it still remains extremely difficult to identify the entire flowfield around an aircraft geometry subjected to a turbulent field of flow; an infinite amount of sensors would be required to identify the atmospheric turbulence velocity component’s distribution (the input) over the vehicle geometry..In an attempt to shed some more light on solving the problem of the response of aircraft to atmospheric turbulence, the subject of this thesis, it depends on the formulation of two distinct models: one of the atmospheric turbulence itself (the atmospheric turbulence model), and the other of the aircraft response to it (the mathematical aircraft model). As concerns atmospheric turbulence, stochastic, stationary, homogeneous, isotropic atmospheric turbulence is considered in this thesis as input to the aircraft model. Models of atmospheric turbulence are well established. As for mathematical aircraft models, many of them have been proposed before. However, verifying these models has always been extremely difficult due to the identification problem indicated above. As part of the mathematical aircraft model, (parametric) aerodynamic models often make use of (quasi-) steady aerodynamic results, that is all steady aerodynamic parameters are estimated using either results obtained from windtunnel experiments, handbook methods, Computational Aerodynamics (CA) which comprises Linearized Potential Flow (LPF) methods, or Computational Fluid Dynamics (CFD) which comprises Full-Potential, Euler and Navier-Stokes methods. In this thesis the simplest form of fluid-flow modeling is used to calculate the time-dependent aerodynamic forces and moments acting on a vehicle: that is unsteady Linearized Potential Flow (LPF). The fluid-flow model will result in a so called “unsteady panel-method” which will be used as a virtual windtunnel (or virtual flighttest facility) for the example discretized aircraft geometry, also referred to as the “aircraft grid

sourcehttp://www.darenet.nl/nl/page/repository.item/show?saharaIdentifier=tuddare:oai:tudelft.nl:078317

Thanks for the lesson. I’d have never guessed that the primary axis of rotation for an aircraft are pitch, yaw, and roll. :rolleyes: :rolleyes: :rolleyes:

probably you need this lession too

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-008-DFRC.html
The second aircraft made its first flight on Jan. 19, 1991, with Deutsche Aerospace chief test pilot Dietrich Seeck at the controls. Despite the fact that the number one and two aircraft had identical external dimensions, X-31 number two experienced stronger yaw asymmetries than aircraft number one. For this reason, X-31 team members began to refer to aircraft number two as the “evil twin.” The team tested aircraft number two with varying lengths of extended nose strakes and found that it could get the two aircraft to fly identically with 8 1/2 inches of strake length on the second X-31, making it an evil twin no longer.

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-009-DFRC.html

Significant yawing moment asymmetries were encountered during the high angle-of-attack envelope expansion of two X-31 aircraf These asymmetries caused position saturations of the thrust-vectoring vanes and trailing-edge flaps during some stability-axis rolling maneuvers at high angles of attack. The two test aircraft had different asymmetry characteristics, and ship 2 has asymmetries that vary as a function of Reynolds number. Several aerodynamic modifications have been made to the X-31 forebody with the goal of minimizing the asymmetry. These modifications include adding transition strips on the forebody and noseboom, using two different length strakes, and increasing nose bluntness. Ultimately, a combination of forebody strakes, nose blunting, and noseboom transition strips reduced the yawing moment asymmetry enough to fully expand the high angle-of-attack envelope. . Analysis of the X-31 flight data is reviewed and compared to wind tunnel and water tunnel measurements. Several lessons learned are outlined regarding high angle-of-attack configuration design and ground testing. (23 refs.)
http://stinet.dtic.mil/oai/oai?verb=getRecord&metadataPrefix=html&identifier=ADA419040

Now tell me why the Su-34 has a blunt nose?
read here http://www.bihrle.com/site/pdfs/aiaa2000-4104.pdf

AbstractA full-scale F-15 forebody wind tunnel test was
conducted at the Langley Full Scale Tunnel. The goal of this program was to assess the impact of radome imperfections on the aerodynamic characteristics at high angles of attack. The results would support the possible revision of fleet F-15 radome maintenance requirements to prevent future high angle of attack departures associated with forebody side force and yawing moment asymmetry.The force and moment data as well as the surface pressure measurement obtained in the wind tunnel indicated that a high angle of attack aerodynamic offset could be triggered by minute forebody surface anomalies.Small imperfections near the apex of the radome caused significant forebody flow asymmetry while gross repair patches and ridges further aft on the forebody had minimal effects. Specifically, the direction and magnitude of the aerodynamic offset were very sensitive to minute geometric anomalies on or near the radome nose cap. Further aft from the radome apex, significantly larger imperfections were required to produce the same offset.These data clearly demonstrated the development of forebody aerodynamic asymmetry is primarily a function of the imperfection’s proximity to the apex of theforebody.Introduction Sub-scale high-angle-of-attack wind-tunnel testing on aircraft configurations with slender circular ogive forebodies have consistently revealed significant yawing moment and side force offsets at zero sideslip inthe 50° to 70°α region (e.g., Ref. 1,through 4). Research efforts on sub-scale forebody flow characteristics at high angles of attack have demonstrated the aerodynamic sensitivity to small geometric conditions on the forebody(Ref. 5). More specifically, the sub-scale F-15 wind tunneldata collected for the Air Force’s Keep Eagle Program in 1993 also indicated the F-15’s tendency to exhibit directional bias at high angles of attack (Ref. 6). These results were confirmed in subsequent high angle of attack flight tests (Ref. 7). While these and other tests have been empirically correlated to results observed in flight, questions relative to the applicability of sub-scale test results to full-scale aircraft have persisted; i.e., if offsets are observed in subscale laminar flow conditions, will they be reproduced at full scale Reynolds numbers where fully turbulent flow conditions exist?In 1995, a nose-slice departure following an abrupt full aft-stick input for a symmetrically loaded F-15C was reported at Nellis AFB. Observed irregular radome conditions were suspected to be the cause of the aerodynamic anomaly that led to the incident. Following the replacement of the radome, the aircraft demonstrated acceptable high angle of attack behavior. This prompted an investigation into the F-15’s high angle of attack forebody aerodynamic characteristics at the Langley FullScale Tunnel using the actual full-scale radomes.Prior to the wind tunnel entry, McDonnell Douglas had conducted a survey on the F-15 forebody conditions to identify surface imperfections sustained by the radomes in their operational environment. With such information, the wind tunnel test program was to assess the forebody imperfections’ impact on the F-15’s highangle of attack aerodynamic characteristics. These activities supported the formulation of radome/forebody maintenance requirements to minimize future occurrence of departure associated with forebody aerodynamic asymmetry.Nomenclature The units of physical quantities used herein are represented in U.S.

Exactly and it’s due to wing loading. You could get around it with active ride control /gust alieviation / whatever-you-want-to-call-it on the F-15E if it had a few more surfaces. The F-15 ACTIVE with canards and TVC could be programmed with it if the canards can move quickly enough. That’s also why the SU-34 would have a smoother ride down low because it’s got that. Turn it off and the SU-34 would probably be bouncing more than an Eagle because of the loading issues, turn it back on and you could probably get it as smooth as a Fencer. I’m not sure why it’s so difficult for Mig-23MLD to wrap his head around the concept.

You’ll note those canards are angled down to give them authority in both pitch and yaw. They work in conjunction with the section of rudder below the horizontal stabilizer to smooth out the ride.

I think most of what you or me are doing is guessing, computers help aerodynamics some times in reacting quicker before the disadvantages of an aircraft configuration do appear, however the Su-34 very likely has more controllability than the F-15E.

Its canards, flattened nose radome, LERXes and computers must allow it to fly low and fast better than a Su-30M, the F-15E still has basic F-15A/C aerodynamics, yeah it has better and quicker reacting computers to allow it to fly smoother but it does not mean the aerodynamics of the F-15 were designed for a low altitude interdictor.

The Russians probably could had fielded the Su-30M as a Su-24 replacement in the same way the americans did with the F-15E when they replaced the F-111.

However the evidence shows the Su-34 was custome built to make it a low altitude interdictor and much of the airframe was modified.

the Su-33KUB also shows you that the Su-34`s flattened radome must have its design advantages in the area of stealth and aerodynamics and the bluntness of the Su-34`s radome seems to go along with yaw controlability, the canards only can be explained as in the Su-33 as low speed control devices since the Su-34 is basicly a bomber.

The times are gone, when a striker flew the whole mission at low level nearly.
There is no longer such a concentration of weaponary and coverage by sensors, like it was in former Central Europe.
Most of the mission profiles had shifted to medium heights. Just the defended areas around the intended target have to be penetrated at low level and max ~600 kt dash close to target. A Su-24 f.e. can cruise with ease at ~450kt low level all the time before dashing at 600 kt as long as fuel does allow, without bouncing the crew and the striker to pieces. A F-15E can not do something similar in general. To avoid too much bouncing at low level it has to reduce cruise speed there to ~300 kt+ related to loading. In a brief dash it can reach ~600 kt too, but it has to reduce that speed after a few minutes related to severe bouncing. Here the details do kick in. General claims do not help, because all does depend on the circumstances of every mission, which can differ considerably. Related to low level flying, the Su-24 faces less speed restrictions, except from the unfavourable fuel consumption of its engines compared to a F-15E. If the very low level cruise is >300 kt or >400 kt does not matter really, als long as the striker is not detected by the hostile defence. The main difference between VG, high-wing-load and other strikers is the practical time and speed envelope at very low level available. Even a MiG-29/F-16 can do a brief high speed dash at low level, but it will run into high buffeting will reduce its targeting capability or it has to reduce speed to regain that.
The big B-1B has VG and canards to give it “unlimited” high speed low level capability. The Su-34 is not in a similar way “unlimited”. It is better than the F-15E related to that, but not as good as the Su-24 f.e. All three will not differ in max dash speed, but will due in low level cruise speed or time to do so.

I agree the F-15E must have its advantages, it is a good fighter, has good warload carrying capacity and probably is cheaper to operate.

The mission also must have changed a bit and the attack tactics too.

There are two ways to smooth out the ride; 1. have a high wing loading or 2. use an active ride control. (Or like the B-1B you can have both.)

If you don’t have an active system then the quality of the ride is going to be largly based on wing loading. All the control surfaces in the world aren’t going to help if they’re not actively controlling the ride and will actually make things worse by increasing the area. Do you have any evidence that the Su-34 has active ride control? Yes or no. If it doesn’t then it’s back to wing loading which the F-15E likely has won.

Sferrin
Aircraft aerodynamics are more complex than just that, to have a smooth flight you have to have controlability in roll, pitch and yaw, asymetries in the flow create modifications in the flight path and can stall an aircraft, a computer which basicly all the modern aircraft have now aid the pilot to control the aircraft in fact any modern aircraft has computers to basicly translate the pilot`s intentions to the aerodynamic control surfaces, however aircraft are still ruled by physics, and they need to create a controllable flow over the aircraft surfaces.

The entire aircraft from radome to nozzle and wing tip to wing tip can create diferences in flow and air pressure to modify the flight path.

Radomes for example do create vortices and these vortices can help in controlability, the Su-34 has a flattened nose radome, contrary to the Su-33KUB, how can we explain that?


http://www.airwar.ru/enc/fighter/su33kub.html
The most logic explanation rests with their mission, in my opinion the Su-47 Berkut and Su-34 Fullback have blunt and flattened nose radomes to have controbaility at yaw, the F-15 also has a slightly blunt radome but it is not flat, if you have standed in front of an F-15 you can see the F-15`s radome is not sharp as a needle but blunt it basicly has a very blunt cap at the front part of the radome.

The X-29 also has a flattened nose radome to control vortices separation and have more controlability at yaw.


The MiG-29 also has flattened plates in the pitot tube, the Su-34 has LERXes and canads that suggest a more complex vortices control than the F-15E.

In my opinion the F-15E is a fighter but not a low speed striker in the league of the F-111 or Su-24

The Su-30M was a PVO project that had nothing to do with strike capability. It was developed as a fighter group leader that would use its superior radar to detect and designate targets for the cheaper less capable fighters operating with it. The west called it a mini AWACS, but it was more like getting the GCI officer out of the van and into the back seat of the Su-30M and to bring his radar with him and put it in the nose of the aircraft.

Frontal Aviation and Strategic Aviation weren’t interested in the Su-30M because they had the Su-34 model for the role.

It was the export or Su-30MK model that sparked international interest in being a fully combat capable two seater that lent itself to improved combat capability in intercept and ground attack through having two crew and a full sized radar. (unlike at the time the two seat Fulcrum…)

Except the Hornet can fly from carriers.

I remember reading something about the withdrawl of the Ravens hit the AF quite hard as the replacement was Naval… some version of the A-6 or something… can’t remember off the top of my head, but it was subsonic and had problems getting to where it was needed and moving with fast strike packages.

In the case of Russia it is true, the Su-34 made more sense so the Su-30M was not of interest, however China uses the Su-30 like the USAF flies the F-15E, if Russia wanted they could had opted like the USAF to replace the Su-24 with the Su-30M, however it seems the Su-34 is a more sophisticated machine and better suited to the Russian needs, so they will fly Su-34 instead of the Su-30M.

The F-111 probably had scored some success if the program had not nuked its own budget and schedule. Probably one related to the other: “There is no thing like free lunch”, as Milton Friedman knows, and the very capable F-111 proposal of the 1960s was probably not possible within that budget. The common problem, see F-35.
The F-15E was as far as I know basis for F-15 versions for Singapoor, Saudi Arabia, Korea and Israel (later deliveries in some cases). I don’t know about specific differences between F-15B/D and F-15E, but I guess the later has tougher structure and of course much more black boxes built in, it looks they didn’t even change the radar too much (no Terrain Following Radar).

I do not agree with that opinion too much Schorsch, i think limited budget depends in the nation, in the US limitations mean propesperity for another air forces.

Even compared to Europe or Russia, the USAF has very few limitations in what respects budget.

The Su-24 for example has not been replaced even despite Russia has Su-30M to replace it or Su-34s. In Europe that basicly has an economy as powerful as the US and even has signs of becoming even more powerful, the military budgets have more limits.

http://bvvaul-barnaul.narod.ru/11orap-4.htm
Only China seems to have a similar budget to the US where military programs can be more important than the economy and welfare of the whole nation.

In my opinion the F-111 was simply retired to continue the cycle of rearmament that characterizes the US military complex.

The F-111 probably even in 2008 can deal with the vast majority of threats the F-15E can defeat, with ASRAAMs, cruise missiles, AMRAAMs and new radars the F-111 very likely can remain a potent weapon for at least ten years more.

http://www.fas.org/man/dod-101/sys/ac/row/su-24.htm
http://www.ausairpower.net/APA-NOTAM-211107-1.html
http://bvvaul-barnaul.narod.ru/Mar-Su-24mr-3.htm
http://narod.yandex.ru/100.xhtml?bvvaul-barnaul.narod.ru/1976-6.files/1976Bes_056.jpg

http://www.ipmsnymburk.com/forum/viewtema.php?ID_tema=27592
The Russians do have a real limited budget and they chose to keep the Su-24 for at least 15 years more.