F-84 handling characteristics

[Hoggardhigh]

Hi all,

I recently read at a forum on the FineScale Modeler website that the F-84 series aircraft had a tendency to roll during hard maneuvers when the inboard wing pylons weren't installed.

I have one question: was this particular problem addressed (or at least greatly alleviated) with the swept-wing F-/RF-84F models?

Any information about this would be greatly appreciated.

 

[FLYBOYJ]

Hi all,

I recently read at a forum on the FineScale Modeler website that the F-84 series aircraft had a tendency to roll during hard maneuvers when the inboard wing pylons weren't installed.

I have one question: was this particular problem addressed (or at least greatly alleviated) with the swept-wing F-/RF-84F models?

Any information about this would be greatly appreciated.

Tendency to roll? As compared to what? Is the roll adverse?

Unless the author of that article could come up with a source (like someone who actually flown the aircraft), any second hand info about flying an aircraft, especially something like an F-84 coming from a modeling magazine is just hearsay.

 

[Hoggardhigh]

Tendency to roll? As compared to what? Is the roll adverse?

Unless the author of that article could come up with a source (like someone who actually flown the aircraft), any second hand info about flying an aircraft, especially something like an F-84 coming from a modeling magazine is just hearsay.

Just FYI, here's the following text which I got from the forum in question:

"The F-84 series of aircraft had a tendency to roll during high 'G' turns. With the pylons in place, it prevented the aircraft trying to roll."

Does anyone have any evidence to back this up?

 

[Shortround6]

I am not an Aerodynamicist but I can't figure out such pylons would resist roll. Maybe they do but it would seem really strange.

 

[Hoggardhigh]

Perhaps FLYBOYJ or another user has something more informative to say about it?

 

[FLYBOYJ]

Perhaps FLYBOYJ or another user has something more informative to say about it?

I do - I read some on line info and briefly went into the -1 for the F-84 and saw NOTHING about a roll tendency if the aircraft flew without pylons. Like the F-80 or the T-33, there's a lot of inertial potential when you have tanks mounted on the wing tips. Like SR mentioned, I could see how those underwing pylons could reduce the roll rate, but then again I think any aircraft with a similar configuration would be in the same boat. I've flown in T-33s and L29s with and without wingtips and saw nothing that raised an eyebrow with regards to roll rate. Unless the originator could come up with some verifiable reference for that statement, I throw the BS flag!!!

 

[Hoggardhigh]

I do - I read some on line info and briefly went into the -1 for the F-84 and saw NOTHING about a roll tendency if the aircraft flew without pylons. Like the F-80 or the T-33, there's a lot of inertial potential when you have tanks mounted on the wing tips. Like SR mentioned, I could see how those underwing pylons could reduce the roll rate, but then again I think any aircraft with a similar configuration would be in the same boat. I've flown in T-33s and L29s with and without wingtips and saw nothing that raised an eyebrow with regards to roll rate. Unless the originator could come up with some verifiable reference for that statement, I throw the BS flag!!!

Did the document apply to the straight-wing models, the swept-wing F-/RF-84F series, or both?

 

[pbehn]

"The F-84 series of aircraft had a tendency to roll during high 'G' turns. With the pylons in place, it prevented the aircraft trying to roll."

I don't understand this statement. An aircraft shouldn't try to do anything it should follow pilot input. If it had a tendency to roll during high "G" turns and the wing pylons prevented it then that is a plus for the pylons isn't it?

 

[Shortround6]

I can understand wing tip tanks, or stores (like missiles) mounted on the wingtips affecting roll in a number of levels or ways. Due to inertia for one. Changing airflow over the wingtip and outer wing for another ( see Spitfires for major changes in roll with relatively minor changes in wing area).

Some aircraft had a tendency to tighten up turns after a certain point in high "G" turns but that is not rolling/banking ( I think?)
For an aircraft to either try to bank more or less than the pilot wants (inputs) there has to be some sort of asymmetrical force acting on the wings over and above the ailerons (or countering them?)
Perhaps on some aircraft there is some sort of asymmetrical airflow over the wings in a steep turn (High G maneuver?) that can be corrected with some sort of "fence" on the wing but wing fences are usually on the top of the wing and usually further out on the wing than the "inboard" pylons on an F-84.
Those inboard pylons are too close to the fuselage to affect much of the air flowing around (under) the wing and much too far away from the ailerons to affect them. Positively or negatively.

I can understand wing tip missile rails affecting things.

forget weight for now. The rails and missiles increase the area or plan form (shape) that you are trying to push through the air if you are rolling. You are trying to push them sideways to the line of flight. I know it is actually a tangent
Now perhaps such fittings add or subtract from the roll rate (I would suspect subtract) but the under wing pylons of the F-84 don't do a thing to add or subtract from either the "wing area" or change the plan form (shape) in anyway.

I am not saying it is totally impossible but it would be so far from what is "normal" that you really need some sort of documentation.

 

[FLYBOYJ]

Did the document apply to the straight-wing models, the swept-wing F-/RF-84F series, or both?

Documents? The only thing you're going to find "IF" an adverse roll condition existed would be in the -1 (POH) or within pilot reports.

 

[chuter]

It would seem to me to make more sense for an uncommanded hi-Alpha roll to be associated with the swept wing rather the straight wing. Designers back then were still coming to terms with the new swept wing. As previously noted the information given is vague and incomplete.

 

[Hoggardhigh]

It would seem to me to make more sense for an uncommanded hi-Alpha roll to be associated with the swept wing rather the straight wing. Designers back then were still coming to terms with the new swept wing. As previously noted the information given is vague and incomplete.

Do you think that applied to the F-84F?

 

[PStickney]

Hi all,

I recently read at a forum on the FineScale Modeler website that the F-84 series aircraft had a tendency to roll during hard maneuvers when the inboard wing pylons weren't installed.

I have one question: was this particular problem addressed (or at least greatly alleviated) with the swept-wing F-/RF-84F models?

Any information about this would be greatly appreciated.

Well, I'm a bit too young to have flown either the planl-wing F-84s (A,B,C,D,E,G) or the swept wings (F Models) of the ground hogs,
but I do have -1s for all models, and know people who flew them, and none of them mention any roll behavior that was particularly untoward or annoying. One of the straight-wing F-84's positives was its excellence as a gun platform, tracking smoothly and steadily under all conditions. It did have a strong pitch-up if pushed past its Mach Limits (Placard Limit Mach 0.82, pitchup at around Mach 0.84), but that's about it.
One characteristic of the straight-wing F-84s was a variable boost in the aileron controls. The pilot could dial in the amount of assist that the hydraulics could apply to the ailerons, allowing the balance between sensitivity and smoothness to be adjusted.

The swept wings could pitch up when stalled pulling high Gs - but given the weight and (lack of) thrust in the F-84F, youo were usually bleeding off speed so fast that you couldn't sustain a lot of G.
There was one characteristic of the F-84Fs that might be conflated into that report is that at relatively high Indicated Air Speeds (IAS) - say above about 325 KIAS, with the inboard pylons and the big 450 US Gallon tanks installed, the airflow between the tanks could get a bit chaotic, and the airplane would hunt directionally.

If you're of a more technical bent, you will find
http://www.dtic.mil/get-tr-doc/pdf?AD=ADB971840
"Letter Report on Relative Aerial Combat of the F-84E Versus the F-86A capability" really informative.

 

[chuter]

Do you think that applied to the F-84F?

Yeah, that's my guess based solely on this thread. lol

 

[Hoggardhigh]

Well, I'm a bit too young to have flown either the planl-wing F-84s (A,B,C,D,E,G) or the swept wings (F Models) of the ground hogs,
but I do have -1s for all models, and know people who flew them, and none of them mention any roll behavior that was particularly untoward or annoying. One of the straight-wing F-84's positives was its excellence as a gun platform, tracking smoothly and steadily under all conditions. It did have a strong pitch-up if pushed past its Mach Limits (Placard Limit Mach 0.82, pitchup at around Mach 0.84), but that's about it.
One characteristic of the straight-wing F-84s was a variable boost in the aileron controls. The pilot could dial in the amount of assist that the hydraulics could apply to the ailerons, allowing the balance between sensitivity and smoothness to be adjusted.

The swept wings could pitch up when stalled pulling high Gs - but given the weight and (lack of) thrust in the F-84F, youo were usually bleeding off speed so fast that you couldn't sustain a lot of G.
There was one characteristic of the F-84Fs that might be conflated into that report is that at relatively high Indicated Air Speeds (IAS) - say above about 325 KIAS, with the inboard pylons and the big 450 US Gallon tanks installed, the airflow between the tanks could get a bit chaotic, and the airplane would hunt directionally.

If you're of a more technical bent, you will find
http://www.dtic.mil/get-tr-doc/pdf?AD=ADB971840
"Letter Report on Relative Aerial Combat of the F-84E Versus the F-86A capability" really informative.

Do you think the F-84Fs flying characteristics may have been any better WITHOUT the inboard pylons, let alone the big underwing tanks?

 

[PStickney]

Do you think the F-84Fs flying characteristics may have been any better WITHOUT the inboard pylons, let alone the big underwing tanks?

Slightly less drag, for bare pylons, but otherwise not much change. I happen to have an F-84F Dash-1 (Pilot's Flight Operating Handbook - you never know, I might find one in a barn or something) and I've just reviewed it - Other than some notes about assymetric loading (Say, a full tank or 2,000# bomb on one side, an a bare pylon on the other) there isn't any mention of unusual behavior with pylons on vs. off.
Generally. the more you can concentrate weight and drag near the centerline of the aircraft, the less effect there is on the handling.
Consider that one of the main tasks of the Thunderstreak was Tactical Nuclear Strike - Toss Bombing Mk 7 bombs, if the need arose.
The Mk 7 was, as the first A-Bomb cabale of being carried by a fighter-sized aircraft, pretty large. (An F-86 couldn't carry one, for example).