Tail strength

[hammed]

Great post Dan! Nice to hear from the designer in such detail.

[bagarre]

Thanks Dan, that was exactly the type of information I was looking for. You answered all of my questions and concerns.

At this point, I don't do any aerobatics as I currently own a Cessna 170. I've done some in a Citabria/Decahalon/S2B to know that this is something I'd like to get into (thus looking for a second plane).

[danweseman]

HI Guys, I'm still trying to get a handle on the forums...As a general note ,emailing me directly dan@flywithspa.com is the best way to get a quick reply.Also I typically answer tech questions first, I want to provide good service to those building. If the question seems appropriate I may ask that you post it here for others to see.I will see if Rachel can spread the word.
Ok Tail strength. First we do hammer heads, and snaps rolls on almost every flight. The Panther LS doesn't snap or spin as cleanly as many would like due to its good stability and low wing low wing loading.it has a small entry airspeed window ,and you must make it enter with g load and full rudder. It doesn't retain energy in the snap very long (light wing loading) .To snap/spin you must stall one wing,so stall strips properly placed would likely improve stall/ snaps for the purist.
Next I have heard the accidental tail slide and locked control stuff before and also the no hammer head or tail slide with out tail brace wires. Both are totally unfounded .Many aerobatic aircraft designed in the past 20-30 years do NOT have tail brace wires. think Extra,Yak ,Sukoi,Zlin,Chipmunk,Giles etc. But many do , if you are using steel tube stabs, and control surfaces which are not as common in current design ,you have to have them. adding tail brace wires to a Panther would do nothing but add weight ,drag, complexity, and false piece of mind! You would just shift the load into the fuselage ,with a unknown and likely poor load path! Also consider the fuse has the same torsional margins as the tail was designed for,so if you don't feel the tail is strong enough ... the tail cone isn't either! If you added brace wires,you would falsely think you have made it "stronger", and "safer" but wouldn't have .
As for jamming controls in tail slide (regardless of how it was entered) it is not a real concern. if you freak out and go into the fetal position and leave controls to flop and did this repeatably you may have stress cracking and damage etc. But if cannot keep pressure on rudder pedals and a firm hold of stick ,you have absolutely no business doing any acro ,in ANY aircraft! Also consider that the Panther LS has a VA of128 mph (maneuvering speed). Below this the aircraft will stall before doing structural airframe damage. If Sean D Tucker tried to get the Panther to tail slide he couldn't even get close to this speed while "backing up". Watch Him do tail slide on you tube, his controls are constantly moving trying to force the aircraft into "Rutan" mode! How could he do this if the controls "JAM" in a tail slide? The Panther has a good tail volume (length VS area) and will aggressively resist becoming a canard! In respect to botched hammer head (which we all do) the Panther dose just fine and quickly, but some time uncomfortably for your stomach, points it self in the correct direction again. The engine sometime quits do to the "whip" but it fires right back up.
In regard to hinge design ask any engineer (Paul) if he would rather have 2 points to gather loads across a stab /control surface, or the load spread evenly across entire structure! When we load test the Cougar tail I will include a hinge loading case and then repeat this with a Harmon rocket horizontal I have on the shelf (2 hinge points for each elevator 270 MPH vne and a 300 hp engine beating it to death, hmmm) and will have some interesting data to show ! also the Panther has good stops on the controls also.
Two more points this brings me to, tail slide /whip stall can produce very high loads on other components , mostly the engine mount and its attach points. this is a serious concern on heavier engines.
Another concern is the "pounding" from the engines. This is a big reason we do not design for constant speed ,or metal props. Watch a RV-x with a wood prop, then a metal, or constant speed prop crank up or shut down, and notice how the tail shakes ! The pounding and vibration from the high inertia props combined with the larger (0-320) 4 cylinder engines ,On the low mass Panther Airframe will effect the service life (this is true for any aircraft)
Last Point , Anytime frequent "hard" aerobatics are preformed , the inspection and maintenance program need to be adjusted. All parts of airframe need post flight inspections and frequent "heavy" inspections on all attach points etc!
The Panther will satisfy the aerobatic itch of most pilots , but if aggressive high energy snaps, tumbles ,and outside maneuvers are needed ,then you should consider one of the many unlimited choices (pitts one desighn etc)
Thanks Dan

[Tony Spicer]

I'm not trying to make a Panther compete with a Pitts or One Design, don't get me wrong.
But I'm sure there are ways to make the plane stronger where needed if you're willing to compromise more in that direction.
Speed is not my concern, stress cracks are. So, could my Panther benefit from wire bracing the tail and possibly re-thinking the rudder hinge?

Are the SPA folks open to discussing things like this? I know the Sonex folks simply wont discuss any deviation from the plans but that sorta takes the Experimental out of Experimental Aircraft (imo)

-David

My opinion is that Dan won't make anything available that he has not flight tested, so best to not hold your breath waiting on the changes you would like to see. You, as the manufacturer, would be free to make whatever mods you would like.

What is your experience flying aerobatics?

Tony

[bagarre]

I completely forgot about Oshkosh and traveling back and forth.

I'm not trying to make a Panther compete with a Pitts or One Design, don't get me wrong.
But I'm sure there are ways to make the plane stronger where needed if you're willing to compromise more in that direction.
Speed is not my concern, stress cracks are. So, could my Panther benefit from wire bracing the tail and possibly re-thinking the rudder hinge?

Are the SPA folks open to discussing things like this? I know the Sonex folks simply wont discuss any deviation from the plans but that sorta takes the Experimental out of Experimental Aircraft (imo)

-David

[Tony Spicer]

Not the most active of forums

Dan's only been back from Oshkosh for 3 days. I suspect he's frying bigger fish. Like parts for me

I've watched Dan do snaps and suspect it will not be a prohibited maneuver.

Tony

[Adam Wright]

Personally I think you are encroaching into Pitts territory David. I would be cautious about regularly doing snaps in anything less than a well known and dedicated aerobatic machine. The Panther is a fine sport aircraft however so I think anything in the primary or sportsman level IAC routines would be a great match. To my knowledge snap rolls are only in intermediate and higher level sequences.

[bagarre]

Not the most active of forums

[bagarre]

Are there any issues with doing frequent snap rolls with the panther?
Without any bracing, I'm concerned about cracking.

Also, how strong are the hinges on the elevator and rudder? Worried about an accidental tail slide in a botched hammer head jamming the controls over and breaking something.

As you might have noticed, I'm interested in doing sportsman aerobatics in the Panther but want to make sure it can hold up to it. I don't expect it to be an Extra 300 but I'd like to know if it will hold up if I snap it too fast or screw up a maneuver a few times.

thanks!