Discussion in 'Starduster' started by smizo, Feb 24, 2018.
Put the discussion here please......
Good idea. Let’s have at it. Lol. I would like to keep my build thread on a positive note, but if there is still energy to discuss this would be a good place to do that.
I'd like to start over but it doesn't matter. I simply don't think we are seeing the forest for the trees? Maybe?
Me, I started last night by looking at the NTSB report on the Gold Duster accident. Here is what I think is interesting.
From the full report,
"According to an Internet posting dated December 29, 2002, by a person using the name of the accident pilot, he reported that while, “…practicing vertical torque rolls. On the fifth one I had a monster, rolling tail-slide and violent flop back toward the ground. After which I noticed that the stick was unusually stiff in roll and the aircraft was now out of trim in roll. I carefully returned to the airport and found that with the stick centered the aileron was in the proper position and the aileron was deflected [approximately] 3 inches up.” The individual reported that inspection of the aileron system revealed the left bellcrank inside the fuselage and an AN-5 bolt that secures the bellcrank were bent.
The pilot’s father reported that following the December 2002 event, new bellcranks were manufactured and installed. The maintenance records did not reveal an entry related to this maintenance. At that time, his son questioned whether the replacement bellcranks needed to be stronger, but concluded that if they strengthened the bellcranks, the failure would show up somewhere else in the system. Additionally, at that time his son noted that wood aileron stop blocks were installed on the aft side of the main spar of both lower wings. He also reported that his son had performed numerous aerobatic maneuvers since the 2002 event."
TESTS AND RESEARCH
"Review of postaccident photographs of the forward spar of both lower wings, provided by the pilot’s father, revealed one wooden block attached to the aft side of the main spar of both lower wings. Each block was nearly perpendicular to the main spar and was supported on both sides at the base by a triangular shaped wedge. Further inspection of each block revealed parallel crush lines consistent by contact made with the upper and lower portions of each aileron outer bellcrank. Additionally, scrape damage to a drag truss associated with the left and right wing outer aileron bellcranks was noted in both lower wings. Another photograph provided by the pilot’s father revealed both inboard aileron bellcranks were bent slightly up.
Review of the builder’s guide revealed a note indicating that, in tail slides, it is quite easy to lose control of the stick and have the ailerons go violently stop to stop as the airplane slides backwards. In order to keep these high shock loads from traveling thru the entire control system, put blocks of wood on the front spar, placed so the aileron bell cranks will hit the wood stops at, or a fraction of an inch before, the stick hits the stops in the fuselage.” The illustration of the guide indicates a wood wedge attached to the aft side of the main spar; the shape of the wedge is parallel with the shape of the bellcrank at the point the bellcrank would contact the wedge. The illustration does not provide dimensions of the wedge; however, it clearly shows that both sides of the wedge are different thicknesses. The installed aileron stop blocks were not consistent with the shape or design of the wedge depicted in the builder’s guide."
Back to me.
While we have been discussing the possibility that pilot effort caused the control jamming I see no evidence that was the case. Even if it was, what would have been the reason he had to exert so much force? Something unusual had to have been happening.
Also, the NTSB(FAA) said,
" The installed aileron stop blocks were not consistent with the shape or design of the wedge depicted in the builder’s guide."
Well, the fact that they had crush marks would seem to suggest they were doing their job.
I think we are missing something?
When I get time I'll go to my airplane with a couple friends and brainstorm the system for what it's worth.
Whatever. It would certainly seem that strengthened bell cranks and reversers are a good idea. But frankly I don't know why? The only thing I can think of is that the torque tube stops were not set in tune with the stops in the wings...maybe?
But again, where did the force come from that either damaged the control system and/or caused the pilot to make inputs hard enough to do the damage?
Also. While the parts were bent the report does NOT say they would have been jammed. Again the report says they were only "slightly" bent!
Maybe the pilot "simply" lost control?
Oh, the other thing that jumps out at me is that 3500' is probably not high enough with 2 people in the airplane although I suppose in retrospect that's obvious.
The answer to this is quite simple, but I’ll need some time so I’ll put this here to hold my place until I get back.
I’ll try to be concise.
I believe the gold duster suffered from a multipoint failure. This is just speculation and maybe The answer is buried in the documents. My point is it doesn’t really matter because it is a probability as designed. My point with my improvements is to reduce or eliminate the probability of a failure at any single point or worse yet in multiple points.
The recommendations made to install the up stop on the wing spar is the first essential improvement. A good idea in theory but in practice they are hard set and unadjustable making them hard to impossible to rig properly, especially on already flying aircraft.
The outer bellcrank is smallish in design and the forces on it are tremendously high given the aileron sizes. The output rod end bolts ride with in less then a quarter inch of the inter wing brace. Although the off axis load of the output rod is small, it is there. A stiff bellcrank system is essential to reducing a failure point. Aluminum sheet as designed is insufficient to reduce this potential.
Reverser system. Enough has been stated about the needed improvements, but I want to reiterate that even with the heavier 5/16 pivot bolts, the potential to bend these bolts exists. These parts take the pilots inputs from the stick, about a 15” lever of mechanical force and poor all that energy into two little pieces of sheet aluminum. Just ten pounds of input energy is yielding multiple times the force into the reverser at an off axis angle. Unfair advantage? Absolutely. Here again two little sheets of aluminum are asked to do the job. Along with substitution of material for the reverser, I am working on a lower tie in bracket that is easy to fabric, and will give the needed support to the pivot point. My speculation is, and this seems to be proven in the real world, the pivot bolt is the first point of failure by bending the bolt.
Lastly, there is no aileron down stop. The force of the down traveling aileron transfers it’s stopping force Through the system to the other side. While a torque tube stop is the best solution here, it is AFTER traveling through ALL of the failure points. The only solution to this is to build a stout system that can endure the stress imposed on it. Even if the torque tube stop is relied upon to stop the down traveling aileron again the forces must travel through the system
Having worked on a large number of certified aircraft I can tell you that this system is underdeveloped in design and under built in materials. Ideally there are both control yoke stopes and control surface stops. The control stick stops protecting the airplane form the pilot and the control surface stops are there to protect the aircraft system from outside forces imposed on it.
Occasionally the FAA has to catch up too. Just recently issuing AD to the Cessna 150 fleet concerning rudder stops after two fatal incidents . Reed about that here
The point is in our certified world when an issue is found a solution is issued, we work to improve the aircraft we trust our lives too. I think a lot of folks in the experimental world scoffs at ADs but I know the system has vastly improved the safety of aviation. One of my former jobs was working freight operations. We had about 15 Barron’s. We actually moved several issues we had with our fleet from in house issues to airworthiness directives that spanned the whole type. One Case in point: The dreaded switch AD requires owners to retire old circuit breaker switches. We had multiple failures, and many in flight power shut downs until this issue was pin pointed and stopped. The pilot would report his feet were glowing orange from red hot wires under the panel. The world now benefits from this knowledge, like it or not. Luckily no one was hurt, and not one in flight fire. The failure point was eliminated before a loss of life.
Imagine now that our Stardusters and Acroduster were certified aircraft subject to the scrutiny of airworthiness directives. What would have the AD that was issued after the Gorman accident read like??? It’s a rhetorical question and each Acroduster owner must answer this for themselves.
You don’t have to be doing tail slides and monster aerobatic maneuvers to envision troubles with this system. Jets taxing by on a busy ramp can develop winds exceeding what any tail slide could produce. Even Mother Nature can dish out damaging micro bursts.
What’s that saying about aviation?
View attachment IMG_0374.jpg
...Guaranteeing you the luck to hit the only tree in a field.
Kendall there are two other things, one I am sure you are aware of, Kevin held a low altitude aerobatic waiver, so doing aerobatics at 3500' and with parachutes seems to me would be prudent and responsible. For the rest of us novice acro pilots a much higher altitude would be a better choice.
The other thing and is only speculation? I think Kevin recognizing a control problem told his passenger to jump, and was the right thing to do. But I think that he stayed with the airplane with the feeling he could regain control and save it, right up until impact, as there was no attempt on his part to jump. He had experienced control issues before and was able to land safely, and as such thought he could do it again. Just my view, and worth only that.
The above picture and comment speaks volumes to the point, that flying is fraught with risk when doing so straight and level in good weather, add low altitude aerobatics and doing so in amateur built aircraft can quickly become unforgiving. Dave
Kendall makes some great points, and to add to the concept that we need to fly safe, consider that to mean, do everything in flight, and not in flight, like when building/maintaining, with the question in mind, " will this cause undue risk?".
I used to hate government regs, homebuilding is great because we are allowed to decide for ourselves what to do/build. But as I get older and have seen some scary builds, the need for some regulation seems prudent. That regulation, I hope, can come from peer pressure/advice, not government. The control stop requirement is a case in point. In Canada it's mandatory to have stops in both directions on homebuilts, and on both ends of a control linkage, ie. at the torque tube and out at the aileron. This forum is a great resource, especially for those of us building "rare" aircraft, not covered by AD's. We should persuade all new builders to build in these control stops.
Jim Osborne was an aeronautical engineer, not a self taught builder doing so from prior experience like many of his peers. But several of the things he did/changed turned out not to be such a good idea especially in retrospect. As Kendall commented on, the ailerons on the Acroduster Too are very powerful, and as such with out an equally strong cabane strut design and installation was compromised, mostly from the bolt on cabane design IE: Roll tubes and eye bolts, once the roll tubes, fittings and rod ends were compromised aong with the powerful ailerons would allow the upper wing to move from side to side thus compromising the eye bolts.
The reason for the bolt on adjustable cabanes was to fold, one to allow the the airplane to be rolled in and out of a two car garage with its wheels on and the adjustable eye bolts allowed a builder the luxury of wing adjustment, as opposed to the non adjustable weld on cabanes like the Starduster Too.
This and the control reverser under the floor, also was done to get the aileron push pull tube under the floor,and keep one from stepping on them while entering and exiting the rear cock pit. Both were done with good intentions, but resulted in unintended problematic consequences. Just my take. Dave
Thanks to both Kendall and Dave.
Dave, I take your point about the 3500'. With Kevin's experience it does seem reasonable. My comment about it was for mostly me.
Kendall. I also saw the reverser bolt as a weak point. Won't break but bending may be enough?
In all considering my initial opinion of your mods. I think maybe I suffered from tunnel vision so to speak. I look at my new airplane which is flown easy and am blinded to the loads put on a heavily flown airplane and also what happens as many hours are put on it. Even flown lightly @ 25 hours I needed to take up play that developed on both the reverser and bell crank bolts.
I've never liked the aileron push rods on the floor but they are sure better than that $#$# reverser.
Anyway I'm all for Kendall's new modifications. They are relatively easy to do and go far to make a somewhat problematic aircraft much better.
Just one other small point. Kendall said,
"Lastly, there is no aileron down stop. The force of the down traveling aileron transfers it’s stopping force Through the system to the other side. While a torque tube stop is the best solution here, it is AFTER traveling through ALL of the failure points. The only solution to this is to build a stout system that can endure the stress imposed on it. Even if the torque tube stop is relied upon to stop the down traveling aileron again the forces must travel through the system"
I'm not sure it's really an issue, at least not in my airplane. Let's say the right side aileron bell crank hits the stop. The way my stops are set, on the left side bell crank it will be a straight shot from the aileron to the bell crank/through the bell crank bolt. It can't go over center and the force is NOT therefore transfered to the other side. That said, making it stronger can't be bad.
Small point. Not sure it makes a difference if for some? reason the stick is banging back and forth from stop to stop.....?
Bottom line is that the system with the reversers is not the best and anything done to make it stiffer/stronger should be better.
Anyone have a picture of this “build Guide”? In report it stated the Gold Duster stops on he spar were not shaped like in the “build guide”. I have the Gold Duster book and will take a pic of the stops tonight. I’m curious how the shape is different and what guide they speak of?
No idea. I have a lot of info, but not a build guide.
You might ask yourself as to whether you intend to do torque rolls. Flying backwards puts loads into the control system that the original designer likely did not consider. If you are always flying forwards the pilot is loading the control system. This is self limiting. Flying backwards, Mother Nature gets to apply loads through the control surfaces, multiplied by the lever ratios of the pivot arms. If you position the control stick so that one aileron is against the stop, then you run into the situation described above where the loads are transferred all of the way to the other side of the airplane. And that situation is why you need two stops, limiting motion both directions, at both control surfaces. For a biplane with 4 ailerons that means on both top and bottom wings. With both up and down stops on each aileron, your will just rip off maybe one aileron if you screw up, and hopefully be able to still fly the airplane with what is left.
Torque rolls are for pilots with advanced skills and strong airplanes. Our friend Rob Holland was almost killed by a torque roll gone bad that broke the rudder and elevators. He has since improved his technique, but the incident remains a cautionary tale for those of us who would fly one.
Improving the control system might be a great idea. But if you never intend to venture into unlimited level aerobatics, you might just put a placard on the panel "Torque Rolls Prohibited".
Best of luck,
Wes. I agree. I’ll s not a machine for unlimited maneuvers but it needs to be strong enough to not be unintentionally damaged. That’s the whole point. Go have fun and don’t worry about the airplane because it will take good care of you. That’s my only intent.
It seems we have gone full circle.
"....... it needs to be strong enough to not be unintentionally damaged......"
I certainly agree but strong enough is relative. I believe my airplane is strong enough already. I prefer the placard.
which is exactly how the FAA has handled the Cessna 150 fleet.
You can A: Placard the panel "spins prohibited", or B: fix the airplane, by installing the rudder stop kit. Either way enhances safety.
Good point Kendall. I'd put the stops on the 150 but for my purposes will hold off on "my' AD2.
OTOH if I should up engine the airplane I'll reconsider it. Also I'm still operating it single place. If I were to start doing even moderate aerobatics 2-up knowing what we now know thanks to You I think your mods almost mandatory if only for piece of mind.
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