stunthanger.com
General control line discussion => Open Forum => Topic started by: Chris_Rud on September 13, 2015, 05:46:17 PM
-
It has been a hard season for me and this years season was cut short due to another control system failure. I'm posting this so that other people will know what happened since I would absolutely hate to hear of another person having this issue. About a month ago I was flying with Billy and when I had him fly my orange Typhoon he said that it was not wanting to fly level. We checked the controls and there was slop from the bellcrank to the flaps. We cut the top off and looked inside and found that the ball link had worn the hole in the aluminum and the 4-40 bolt from the balllink was rocking. I took off the ball link and laminated the top and bottom with phenolic and JB welded it all back together (you can see this in the picture). It worked great for another 50 flights when on the bottom of an hourglass the aluminum delaminated from the balsa and buckled. It looks like it only buckled about a half inch but when you are turning at the bottom of the hourglass you don't have a lot of room to loose when you don't have full control movement. Like I said earlier I'm posting just to let other people know that they can wear out. I was recommended this style of crank but from now on I will stick with phenolic bellcranks.
So after 670 flights this year I'm going to have to pass on the team trials and get back to the workbench. I don't have the energy to do another 2 week build like before this years NATS. I wish everyone luck and happy flying!
-
It has been a hard season for me and this years season was cut short due to another control system failure. I'm posting this so that other people will know what happened since I would absolutely hate to hear of another person having this issue. About a month ago I was flying with Billy and when I had him fly my orange Typhoon he said that it was not wanting to fly level. We checked the controls and there was slop from the bellcrank to the flaps. We cut the top off and looked inside and found that the ball link had worn the hole in the aluminum and the 4-40 bolt from the balllink was rocking. I took off the ball link and laminated the top and bottom with phenolic and JB welded it all back together (you can see this in the picture). It worked great for another 50 flights when on the bottom of an hourglass the aluminum delaminated from the balsa and buckled. It looks like it only buckled about a half inch but when you are turning at the bottom of the hourglass you don't have a lot of room to loose when you don't have full control movement. Like I said earlier I'm posting just to let other people know that they can wear out. I was recommended this style of crank but from now on I will stick with phenolic bellcranks.
So after 670 flights this year I'm going to have to pass on the team trials and get back to the workbench. I don't have the energy to do another 2 week build like before this years NATS. I wish everyone luck and happy flying!
I am very sorry to hear about that. Where did you get that? To be clear, I *did not* make this bellcrank. I want to know because I want to talk to them.
The grain appears to go the wrong way. It's supposed to be end grain balsa. With it flat and with no compression fitting I can see how the ball would work loose. Also, when I tested the prototype to destruction, it took a tremendous amount of force to cause that sort of buckling, even after I intentionally delaminated by prying on the forked end. I wonder of the facing material is the specified 6061-T6 aluminum, or (more likely) something much softer.
Brett
I blew this picture up and note that the aluminum peeled away very cleanly from the balsa, suggesting that the glue bond was not correct, either.
I would add that the buckling in my test part was similar but I had to pick myself all the way off the ground and then bounce to get it to fail that way.
-
Sorry to see that happen Chris. I'll miss seeing you at the TT!
-
That counts as a splat. Man, that it horrible. Sorry to hear about the failure.
-
I'm wondering if it came from Stunt Hangar Hobbies?
http://stunthanger.com/hobby/product_info.php?cPath=24_29&products_id=54
-
Very sorry to hear about that Chris, that was a good flying plane.
-
I'm wondering if it came from Stunt Hangar Hobbies?
http://stunthanger.com/hobby/product_info.php?cPath=24_29&products_id=54
Yes I got it from Stunt Hangar Hobby. I believe Tom Morris makes it. Tom makes great products and I'm surprised that it failed.
-Chris
-
My condolences -- it's a ratty thing to have happen.
+1 on all the mechanical details of what Brett said. I don't use a Brett-style bellcrank because I'm too lazy and because it's easy to whack a decent bellcrank out of phenolic, not because I don't think it's at least a little bit better than phenolic.
On top of what Brett said:
Even assuming that you were using exactly the right epoxy, I'm not sure that gluing the wood in side-grain wouldn't contribute to the delamination: at one point my dad did a lot of experimenting with gluing wood to fiberglass, and basically no matter what he did, eventually the glue joint breaks. Usually it breaks right at the glue-wood interface, leaving a thin layer of wood behind on the glue (in other words, it's the wood that fails, not the glue). It can seem strong as houses, then one day it just falls off with barely a "pop". Our theory was that because of differential expansion between wood and glass, both due to temperature and due to humidity, the joint is continually stressed. Then because wood is not strong in shear, particularly shear in parallel with the grain. So, eventually, the joint just lets go.
If the wood-aluminum joint was made with CA -- well, CA is noted for being very weak in shear, and brittle to boot.
Brett's method of gluing the wood end-grain not only gives you compression strength at the bolt-holes but also, in my humble opinion, isn't going to come unglued as readily. Both the conclusion and the opinion stem from wood being strong in compression in end-grain, but very compliant in both compression and tension across the grain. The compression strength across the bolt-holes is obvious. The lack of delamination is (again in my opinion) because the wood is so compliant across the grain that as the aluminum grows and shrinks with temperature it just carries the wood with it -- the wood just doesn't have enough fight in it to put any stress on the glue joint.
Brett, assuming I ever get up the gumption to make a Brett bellcrank, do you use any old goo from the hobby shop to glue things together, or do you use JB weld, or do you use something even fancier than that?
-
Sorry Chris.... I feel your pain.
Derek
-
Brett, assuming I ever get up the gumption to make a Brett bellcrank, do you use any old goo from the hobby shop to glue things together, or do you use JB weld, or do you use something even fancier than that?
Not fancier, I use West Systems 2-hour epoxy I got from Jim Aron, who got it from Aerospace composites. It is much tougher than the usual finishing epoxy. Another issue is the potential use of a conversion coating on the aluminum to ensure you aren't gluing to oxidised metal. I apply the glue and then sand it with 240 wet/dry so the bare metal is not exposed to air. If you don't then some sort of conversion coating is a good idea.
Brett
-
Did the motor survive?
-
Did the motor survive?
It's crazy but the prop survived. It hit straight in. I think the case is ok and it will turn over but there's ruff spots. Not going to do anything but send it to randy and have him fix it up. I think it will live to fight another day.
-chris
-
I am very sorry to hear about that. Where did you get that? To be clear, I *did not* make this bellcrank. I want to know because I want to talk to them.
The grain appears to go the wrong way. It's supposed to be end grain balsa. With it flat and with no compression fitting I can see how the ball would work loose. Also, when I tested the prototype to destruction, it took a tremendous amount of force to cause that sort of buckling, even after I intentionally delaminated by prying on the forked end. I wonder of the facing material is the specified 6061-T6 aluminum, or (more likely) something much softer.
Brett
I blew this picture up and note that the aluminum peeled away very cleanly from the balsa, suggesting that the glue bond was not correct, either.
I would add that the buckling in my test part was similar but I had to pick myself all the way off the ground and then bounce to get it to fail that way.
It appears the grain is the wrong way, and there's no adhesion to the wood that I can see. The wood surface looks untouched. Cleanliness and good surface prep is key to good bonds. I prefer Hysol 9309 for this application. It's used in high strength titanium/composite rotor blade repairs and, if prepped, mixed and used correctly, withstands stresses far greater then you'll see in this bellcrank application. Also, 6061T6 is significantly stronger then 6061T4.
-
Sorry to see that. I didn't want to say anything but, I would never have a sandwich bellcrank in one of my planes. Maybe you can make it less likely to delaminate with special glue or whatever but why risk it, a solid piece will never peal apart like that.
MM
-
Very sorry to see that Chris! That plane flew great at the NATS.
-
I think there was a previous use of this type of construction. Weren't the cabin floors of most airliners made of a composite sandwich of aluminum and balsa, with the balsa grain running vertical between the aluminum? The construction method is sound but needs to be executed properly.
Sorry about the loss of the model.
Type at you later,
Dan McEntee
-
I don't have the energy to do another 2 week build like before this years NATS. I wish everyone luck and happy flying!
You don't need to build one for this contest just borrow one.
-
Holy Crap :'(
-
Sorry for your loss Chris. Everything seemed to be working quite well for you on Saturday. I'm confident you will be back next season with something even better. One thing is for certain, the worlds are going to miss one world class competitor.
-
I think there was a previous use of this type of construction. Weren't the cabin floors of most airliners made of a composite sandwich of aluminum and balsa, with the balsa grain running vertical between the aluminum? The construction method is sound but needs to be executed properly.
Sorry about the loss of the model.
Type at you later,
Dan McEntee
It's quite common, Dan, going back a long time, and still is. You are exactly right on the grain orientation for floors. Now we use honeycomb in between the skin layers. That method was also used on helicopter rotor blades aft of the spar.
As I said, the key is surface prep. On the aluminum, Brett referred to a conversion coating. That is typically alodine which is a corrosion preventive measure normally used on 2024 and 7075 aluminum, both of which tend to corrode much easier then 6061. On the other hand, prior to alodine, the aluminum is typically acid etched with a material called AlumiPrep 33. After etching, the aluminum takes the alodine (or adhesive) much better.
Sufficient surface etching can easily be achieved by using a maroon (medium grade) ScotchBrite 7447 pad. No green pads! Those usually have a cleaning agent in them for pots and pans which is corrosive to aluminum. ScotchBrite 7447s have aluminum oxide as the cutting agent. After scarfing up the surface to a dull finish, clean with alcohol. In critical applications, you then do a "water break". Spray water over the surface and it should sheet out over the piece evenly. Any beading up and the surface is not completely clean. Once it's clean and dry, it's ready for assembly. Don't worry about exposure to air. It takes at least a week or so for aluminum oxide to form on 2024, a couple days for 7075, and will not typically occur for years on bare 6061 if ever. in fact, 6061 is used with no coatings on secondary engine exhaust components because of it's corrosion resistance.
P.S. Post revised per advice of Bill Byles. Incorrect etching solution called out initially.
-
What Robert S. said!
Doug
-
I think Bill has nailed it. It looks as though there was no adhesion between the balsa and the aluminum. Surface prep is everything!!
-
I don't anything about this, but have a question. What is wrong with the old Fox or Perfect solid aluminum bellcrank with the bronze bushing? Are they not strong enough?
Not strong enough, wear out, but the real reason in this case is to make a better way for the leadouts to go to the bellcrank. All the methods that loop the leadout through the hole are notoriously prone to failure. including bushing the leadout with tubing. And they tend to tilt on the shaft when used with ball links.
The two bellcranks I tested to destruction took nearly my entire considerable weight to cause any damage. I cannot conceive of the failure that happened to Chris under the ~10-12 lb load that it sees in flight, or under occasional 45-ish lb pull tests.
Brett
-
Not strong enough, wear out, but the real reason in this case is to make a better way for the leadouts to go to the bellcrank. All the methods that loop the leadout through the hole are notoriously prone to failure.
Have mercy! :o Y'all must be flying bricks!! I've yet to have one fail me in all my years of "planting trees". As I write this, I have a bird with 510 documented flights on it, 90% of which have been witnessed by my flying buddies over the years) and although it has made a number of dents in the earth I can honestly say not one has been due to the failure of the bellcrank :). Nearly every one of mine (especially the older ones) has either a Fox or Perfect bellcrank in it. Other old birds in my "squadron" have 136, 107 and 72 flights respectively, all with either Fox or Perfect bellcranks (I may have to step back because the one with 107 might have been replaced with a Brodak bellcrank, I just don't remember and I can't see inside). Am I doing something wrong? ??? Am I missing something something? ??? Just askin' ;)
-
Have mercy! :o Y'all must be flying bricks!! I've yet to have one fail me in all my years of "planting trees". As I write this, I have a bird with 510 documented flights on it, 90% of which have been witnessed by my flying buddies over the years) and although it has made a number of dents in the earth I can honestly say not one has been due to the failure of the bellcrank :). Nearly every one of mine (especially the older ones) has either a Fox or Perfect bellcrank in it. Other old birds in my "squadron" have 136, 107 and 72 flights respectively, all with either Fox or Perfect bellcranks (I may have to step back because the one with 107 might have been replaced with a Brodak bellcrank, I just don't remember and I can't see inside). Am I doing something wrong? ??? Am I missing something something? ??? Just askin' ;)
The difference between flying competitive corners and sizes in all sorts of conditions, with large models, for maybe thousands of flights, is a bit different story. The flat aluminum cranks will not stand up to that, nor will the leadouts, for long.
I don't know what exactly caused this failure. But just imagine the kind of force required to buckle a piece of 6061T6 through that kind of angle over the space of 1". In fact, you probably can't bend a single sheet like that without clamping it into a vise and pounding on it with a hammer.
Brett
-
Chris,
Sorry for your loss.
An easy fix for the buckling problem would be to wrap the outside with kevlar thread and epoxy/cyano. We do it routinely in our wing spars that have similar construction principle. Except that carbon is used on surfaces, not aluminium. Of course, the top view of bellcranc has to be such that the thread does not slide when wrapping. Maybe a small step every 1/4" or so.
I have my doubts that you can ever trust just the balsa core/aluminium skin adhesion in this case, some wrapping would secure it 100%.
Also, maybe a simple aluminium rivet in the critical place would secure the skins in place.
Vertical grain core is of course nice, but personally I think it's not absolutely necessary as the up/down bending forces are quite small. If I used horizontal grain balsa I would, after spreading the glue, stick the wood full of pin holes to spread the glue and shear stresses deeper into the wood.
Lauri
-
I think there was a previous use of this type of construction. Weren't the cabin floors of most airliners made of a composite sandwich of aluminum and balsa, with the balsa grain running vertical between the aluminum? The construction method is sound but needs to be executed properly.
Sorry about the loss of the model.
Type at you later,
Dan McEntee
That balsa wood end grain thing, it's done this way with the construction of some boats for sub-flooring also.
-
I don't know what exactly caused this failure. But just imagine the kind of force required to buckle a piece of 6061T6 through that kind of angle over the space of 1". In fact, you probably can't bend a single sheet like that without clamping it into a vise and pounding on it with a hammer.
Brett
This buckling to me looks like impact damage. I am no reconstructive engineer but I can't see the force our planes fly at bending the aluminum. I can see the impact bending this in this direction. I use that bellcrank and will continue to do so. I'm not sure on the number of cranks sold you would have to ask Tom that question but this is the first I have seen do this.
-
Chris,
This sucks! I am sorry to see you lost your plane.
-
This buckling to me looks like impact damage. I am no reconstructive engineer but I can't see the force our planes fly at bending the aluminum. I can see the impact bending this in this direction. I use that bellcrank and will continue to do so. I'm not sure on the number of cranks sold you would have to ask Tom that question but this is the first I have seen do this.
I'm not trying to start a debate... I was simply posting a message about what happen to my plane. People can take it or leave it. I put a lot of flights on planes and it lasted for 300. My guess is that most people who use the crank don't fly that much. Maybe I'm wrong... I wore out a handle that everyone else hasn't had an issue with earlier in the year... Maybe I just fly to much :)
I have checked all other parts of the control system and everything else is in tact. Clearly something gave when I started that bottom corner. It has to be the culprit. And since the buckling is that exact same thing that happened when Brett was trying to make them fail it seems very clear that it was the reason for the failure.
-chris
-
Vertical grain core is of course nice, but personally I think it's not absolutely necessary as the up/down bending forces are quite small.
The purpose was more to prevent something like what happened here. In this case the glue joint failed somehow. If the glue joint doesn't fail, the next failure mode would be the buckling force splitting the wood horizontally along the grain. You cannot pull it apart with tension along the grain lines.
In any case, with the specified materials it easily beats the pull test *with no balsa at all*, just the two aluminum facing sheets and the standoffs and bolts.
An earlier version that Tom made also cut huge triangular lightening holes in the center. I recommended that they stop doing that, and also, that any existing bellcranks be wrapped with kevlar thread and glue along the inner arms.
If anyone is concerned with the solid version, I suggest a series of 1/16" holes about 3/16 from the inner edge, and about 3/32 apart, into which you lace Kevlar and epoxy, keeping substantial tension on the string until the glue dries. Sullivan Tuff-strand lines, for example.
Again, I tested two of the cranks I made to destruction and it had no issue with this, and I also intentionally peeled the facing sheets apart, and that was also with great difficulty.
There seems to be a fundamental misunderstanding of the purpose of the design. It was to get a forked end to keep the leadouts alive, and to be stronger/stiffer than the typical 1/4" Delrin/GRP/phenolic. It was never intended to save any weight as weight doesn't matter any more, within reason, and 10 extra grams is worth it to keep the leadouts together. It actually did come out reasonably light but that's just a coincidence.
Brett
-
I don't know what exactly caused this failure. But just imagine the kind of force required to buckle a piece of 6061T6 through that kind of angle over the space of 1". In fact, you probably can't bend a single sheet like that without clamping it into a vise and pounding on it with a hammer.
Brett
Yep, and if this indeed happened in flight then we know the system is seeing a lot more pressure than just 10-12 lbs pull in flight.
I know on Friday morning at the nats during the first round I had to walk towards my plane several times to ease up the pull/pressure. The pull was at least 2x if not more than I normally see in flight. During the round loops I feared it was going to fold. I know Chris flew during that time as well, the stress point could have started there, who knows...
There are times in flight where the model is seeing severe pressure from all different angles. In flight our planes are in a constant state of "tension" across the entire frame. The pressure will find the weak spot and beat on it until it lets go. Normal CL fliers might fly a plane 50-75 times a year, this plane would have lasted 4-6 years with those numbers. Long enough to move to another plane. But Chris is still in his early "IronMan" days of his stunt career and still beating his models to death day in and day out. There is no telling where it all started on this one.
I think it was Bob Barron that said something to the effect of he would build the model using simple techniques, CA, and 5 minute epoxy and expect it to last one year, if you get more than that its a bonus.
CLPA is hard on models. It may not look like it on the outside because they are so pretty. But if you open up an old stunter and get a look inside there is typically lots of wear and tear....at least that's what I have seen...
-
I have checked all other parts of the control system and everything else is in tact. Clearly something gave when I started that bottom corner. It has to be the culprit. And since the buckling is that exact same thing that happened when Brett was trying to make them fail it seems very clear that it was the reason for the failure.
Yes, but that was at something around 200 lbs of force. That's why I think the one you got has some issues different from mine.
There's no problem posting your results. It makes me very upset to see this happen with something associated with me and that should have a factor of about of 20 margin over normal flying loads. I didn't cause this and the design is still sound as far as I know. I feel indirectly responsible because I let the design out of my direct control and I had concerns over some of what I saw.
I would be interested in whether or not the ball came loose due to compression of the wood (i.e lacked a standoff between the sheets where the bolt goes through) or from the face sheet wearing. I can see also sorts of black stuff around the ball. and once the wood compresses a little, the ball will come loose, then pound out the hole.
Also, when you installed the standoffs for the leadouts, did you have to force them?
I ask because based on the degree of buckling shown I suspect that the face sheets are not actually 6061T6 but something much softer, and that the spacing was likely not correct, causing a peeling force to be applied. Until I found the electronic standoffs that were machined to a consistent dimension, I spent hours and hours getting standoffs to fit correctly.
Brett
-
It really is as simple as a bond failure. Boeing, Airbus, Douglas, McDonnell-Douglas, Bell, Eurocopter, etc, etc ALL use bonded composites for applications just like this. No threads, no rivet, screws, etc. It's just a matter of proper surface prep and an appropriate adhesive. Carbon fiber is no different. You cannot take carbon fiber laminates straight out of a box/bag with shiney smooth surfaces and expect a reliable bond. Knowing how to bond composites is the key and it's not that difficult to do properly.
-
How about a picture of the bell crank out in the open. The picture I see does not look like a typical bell crank failure.
-
How about a picture of the bell crank out in the open. The picture I see does not look like a typical bell crank failure.
It may not be a typical bell crank failure, but then it's not a typical bellcrank construction. Given the way that the plates are loaded, the way the aluminum bent is exactly what I would expect to see from line tension that exceeded the material's ability to stand up. I'm not saying anything about whether 6061-T6 would stand up here, 'cause Brett already has.
-
Have mercy! :o Y'all must be flying bricks!! I've yet to have one fail me in all my years of "planting trees". As I write this, I have a bird with 510 documented flights on it, 90% of which have been witnessed by my flying buddies over the years) and although it has made a number of dents in the earth I can honestly say not one has been due to the failure of the bellcrank :). Nearly every one of mine (especially the older ones) has either a Fox or Perfect bellcrank in it. Other old birds in my "squadron" have 136, 107 and 72 flights respectively, all with either Fox or Perfect bellcranks (I may have to step back because the one with 107 might have been replaced with a Brodak bellcrank, I just don't remember and I can't see inside). Am I doing something wrong? ??? Am I missing something something? ??? Just askin' ;)
I know Brett already mentioned something about this but I'm going to anyway to emphasize the fact!
My guess would be that you don't have a problem because you don't fly hard corners with 60+ oz airplanes in windy conditions...very windy conditions sometimes. The loads go up very significantly when you're flying in a 15 mph wind doing square eights downwind. Or for that matter even in a 8-10 mph wind like nearly all contests!!
Randy Cuberly
-
Wrapping the bell crank with "Kevlar" is a waste of time and energy.
I say this for the following reason: Several years ago Dr. Bayard (Now deceased) a SBSS (south bay soaring society) did an extensive study on wing spars to see if he could come up with a strong/light system to with stand the "ZOOM" launch with out folding the 100" + wings.
The spar system was: Spruce/balsa end grain web/spruce.
Several were used (Stressed to the breaking point) with different reinforcements being used.
The one with "Kevlar" was an abysmal failure. When load tested the 1/8" X 3/8" spruce spar simple "CUT" right through it like it wasn't even there!
The spar that was the strongest was the one with CF tow & slow cure CA with the spar over it (Top spar) to prevent "oil" canning and CF on the outside of the bottom spar. I don't recommend CA for anything other than liquid pins.
These statements can be verified by SBSS if you can find them. (I've been out of it for 20 or so years)
Cheers, Jerry
-
<snip>
<snip> On the other hand, prior to alodine, the aluminum is typically acid etched with a material called Prep Sol. <snip
<snip
Hi Bill,
"Prep-sol" is a naphtha-based paint surface cleaner that was made by Du Pont for use in automotive refinish applications to clean the surface to be painted just prior to painting. I used it for years in my full-scale aircraft restoration/painting business and it is a very mild solvent based cleaner and not acid-based. There may be another product with a similar name that is used to etching aluminum but for that purpose I use acid-based brightener followed by alodine.
-
Wrapping the bell crank with "Kevlar" is a waste of time and energy.
No, it isn't. The threading of Kevlar around the inner edge directly addresses the issue you see with buckling of the material, by applying the strength of the kevlar (primarily strong in tension) in direct opposition to the forces trying to buckle the aluminum. I can't say whether the spar application is similar or not, but I suspect the issue with the spar is that the strength and toughness of the material is not used in the correct way. For example, if you just wrap it around the spar, of course it's not going to do anything useful. I guess the spar fails in tension or compression, so you need to run it spanwise, and the wrap, in this case, would do nothing.
I still imagine that if the face sheets are not as specified, it might just give you a failure in a different spot. Again, I will make up another test piece soon using *no filler material at all* and verify my prior results. I knew I could make it even tougher, but it just didn't seem necessary as it was already gross overkill. Mine have been working for 10 years+ and many more than 300 flights and dozens of pull tests with no detectable degradation at all. I am dumbfounded at Chris' failure as the load necessary to break my version would destroy the rest of the airplane first.
Brett
-
[quote author=Gerald Arana
I say this for the following reason: Several years ago Dr. Bayard (Now deceased) a SBSS (south bay soaring society) did an extensive study on wing spars to see if he could come up with a strong/light system to with stand the "ZOOM" launch with out folding the 100" + wings.
The spar system was: Spruce/balsa end grain web/spruce.
Several were used (Stressed to the breaking point) with different reinforcements being used...
[/quote]
Yes, maybe several years (decades?) ago with wood spars but not anymore. I understand you're talking about free flight wings?
In time of zoom launches, the max. line tension at release was maybe 10kp. Today the towhook does not even open with such small force. I'd guestimate that the force at moment of line release is between 30 and 50kp. That makes kevlar wrapping absolutely crusial. L
-
Looks like something soft maybe "0". T6 if bent in that manner would probably crack depending on the grain.
-
Chris what did it feel like when it failed? When my first Dreadnought had the flap horn fail in the reverse wing over pullout, it felt like a bomb went off in the plane and I instantly knew something had broken and I was doomed. I'm curious if you felt a bang or if it suddenly just would not turn....
-
You can also see the delam, the balsa stuck to the lower piece in the pic. The top appears to be a clean separation. And judging from the impact damage to the surronding structure, that may be what buckled the aluminum.
-
My new stunt plane weighed 74 oz at the NATs, and is powered by the ROJett 76. From early indications, it is a supergood flyer, I'd hate to lose it to a mechanical. It has the Brett Buck style bellcrank purchased from Tom Morris. I don't fly nearly as often as a lot of us, 200 flights a year would be my average, usually in pretty substantial wind conditions. I'm wondering if this is an isolated case or can we expect this to be a real threat? Tough question, I know. Maybe Tom can post something to help make the decision on whether or not to perform pre-emptive surgery....
Tough break, Chris. I've got an Impcat and a Mule at your disposal,
dale g
-
No, it isn't. The threading of Kevlar around the inner edge directly addresses the issue you see with buckling of the material, by applying the strength of the kevlar (primarily strong in tension) in direct opposition to the forces trying to buckle the aluminum. I can't say whether the spar application is similar or not, but I suspect the issue with the spar is that the strength and toughness of the material is not used in the correct way. For example, if you just wrap it around the spar, of course it's not going to do anything useful. I guess the spar fails in tension or compression, so you need to run it spanwise, and the wrap, in this case, would do nothing.
I still imagine that if the face sheets are not as specified, it might just give you a failure in a different spot. Again, I will make up another test piece soon using *no filler material at all* and verify my prior results. I knew I could make it even tougher, but it just didn't seem necessary as it was already gross overkill. Mine have been working for 10 years+ and many more than 300 flights and dozens of pull tests with no detectable degradation at all. I am dumbfounded at Chris' failure as the load necessary to break my version would destroy the rest of the airplane first.
Brett
Yes, Brett. It was wrapped "around" the spar. And was totally useless. Dr. Bayard didn't use it span wise. The failures were in compression since that's the way most gliders are stressed.
Kind of like pulling a rope or pushing one! Ever try pushing a rope? LL~ LL~ LL~
Jerry
-
Yes, maybe several years (decades?) ago with wood spars but not anymore. I understand you're talking about free flight wings?
In time of zoom launches, the max. line tension at release was maybe 10kp. Today the towhook does not even open with such small force. I'd guestimate that the force at moment of line release is between 30 and 50kp. That makes kevlar wrapping absolutely crusial. L
[/quote]
Are you kidding me!? My 100" glider could break a 200 LB tow easily in the wind. (that is; if I were towing in the wind) Also I was the only guy I ever saw dive from a few 1000 feet and do a snap roll. That's right! Let me see you do it with your ship!
OBTW, I didn't use the spar system mentioned...........
It was my "Chameleon" that I used in competition for several years.
Cheers, Jerry
Chris, Very sorry about your ship. I didn't mean to hi jack this thread.
-
Back to the 50's and 3 inch BC's...There was a reason Fox and Veco Aluminum BC's cost 5 bucks and Perfect BC's cost 80 cents! NEVER use any perfect BC's. NEVER!
Fast forward to the millenium...Windy and Hunt sold thousands of bellcranks. What were the odds of failure with them? Bet most of the failures were improper
lead outs, not bellcranks.
Yes, and toward the end Windy was splitting the ends of his 5/16 in. thick BC's.
And...The more complex the machine, the greater the odds of failure.
Therefore the more parts, the more parts to break.
Nothing can gowrong, gowrong, gowrong....
Just an old phart thinking out loud.
W.
-
Several planes, 1000s of flights, no failures. One of mine has 4000 flights over 5 years. I often fly in 15 mph wind, like today.
Will continue to use as is from Tom Morris.
RO
-
Has anybody notified Tom?
-
Has anybody notified Tom?
I am going to try to contact him tonight, probably. If there is an issue with a particular batch, he might be able to track it down. It's not like these things are made in the thousands.
Brett
-
I am going to try to contact him tonight, probably. If there is an issue with a particular batch, he might be able to track it down. It's not like these things are made in the thousands.
Brett
Yup, they should be rated FC1. Serialized and traced! He should know what mine they were dug from, and the exact alloy and temper.
;D
-
Is that the up line or the down line? Its a little unusual to have the pushrod off the bottom of the bellcrank. Is (was) the flap horn pointing down or up?
-
Would someone be willing to bench check one of these bellcranks as is and see how many pounds it takes to get this to delaminate and buckle like it did here. This will be a concern for all of us.
-
Looking at the buckeling I wonder if the actual buckling was caused on impact and the actual cause of the crash was maybe just the glue joints shearing. And the major bending resulted during the impact ?
-
Several planes, 1000s of flights, no failures. One of mine has 4000 flights over 5 years. I often fly in 15 mph wind, like today.
Will continue to use as is from Tom Morris.
Would someone be willing to bench check one of these bellcranks as is and see how many pounds it takes to get this to delaminate and buckle like it did here.
You both seem to assume that they are all the same. That may not be something one would want to assume.
-
I've been using this system for the last ten years on many airplanes and never had one fail. I make my own per Brett. I bought one from CLC that was manufactured by aforementioned vendor and tossed it out because of low quality. The lead outs were crimped instead of wrapped, as advertised and the hole was off center in the bushing. The bushing was also too short. At first I was going to just change the lead out cable to what I wanted and install a new bushing but the whole assemble began to separate. This is not a bash on the vendor, there are plenty of satisfied customers with no issues. Instead I just made a new bellcrank.
Just sayin.
Best to check fabrication against design specs. Maybe I just spent to much time in manufacturing.
Really sorry to hear about your loss Chris.
-
Hi Chris
Really sorry to hear about your loss. It certainly was a good flying airplane.
I use Brett's bellcrank's in my model's as well, but built to Brett's specificifations and using high grade aircraft aluminum. One of my bellcrank's was the victim of an "incident" in an aircraft with 100 flights on it. That bellcrank now resides in last year's model with near 600 flights, and still going strong. I can not imagine it failing, but hey, crap sometimes happens.
I can understand why you do not wish to use this type of bellcrank again, so rather than trying to talk you into something you are not comfortable with, thought I would suggest using the bellcrank system I believe Paul Walker is still using. Paul uses the old Windy nylon (Delrin?) 4" bellcrank. Paul slots the ends for the leadout loops and uses a 4-40 bolt with a nyloc nut, same as you did on your failed bellcrank. I used the same setup for many years with no issues. I could send you a picture if my less than stellar description isn't working for you.
I'll look forward to seeing you at the Nat's again next year with a shiny new airplane.
Chris
-
I still wonder if this isn't an artifact of the crash. Chris, was this indeed the "up" line? Coming downhill in the hourglass, the controls are neutral, pulling from a neutral position, so we are saying that the "Netzeband wall" (hinge moment) is what did this? We're talking about a 12 to 15 lb. pull, 20 at most. I'm not convinced that this was the failure.
-
Clearly it should not have failed and Frank makes some excellent points. I have trouble thinking it is impact damage when the photo shows the balsa core of the bellcrank is not smashed or caved in, only the tip of the balsa core is missing.
If as Brett points out the materials were too soft, though, maybe it is possible it yielded at 1/10th the load of Brett's test article.
It would be interesting to come up with a way to test the remaining arm of the crash bellcrank and see what measurements could be obtained.
-
Hi Everyone,
Wow I never thought we would open an FAA investigation. :)
I have enjoyed reading everyones comments and possible causes of the failure. When I got home I took a few pictures of the crank. See below.
A few observations:
1. I have flown that plane a lot and it was my 7 flight that day and the 302 flight of its life. I document all flights on my phone. It was very clear to me that something failed in the inside turn of the hourglass. And no other parts of the control system had been damage.
2. The damage was caused inflight and not from impact. I know this since there is no scrape marks on the end of the crank, it was bent slightly toward the handle and as Steve pointed out the balsa was intact. (see photo)
3. The glue joint was faulty. There was no adhesion on one side and minimal adhesion on the other. (see picture)
The crash felt as though the plane started to turn and then stopped. I felt as the controls had locked up. My first thought was the leadout clips had stuck or something but I couldn't believe that after 300 flights with the leadouts in the exact same spot that this was the cause. When I looked at the bell crank I new that was the issue. At first I thought it was the up line and the buckling alone had been the culprit causing it not to complete the turn. But as some have pointed out it was not the up line. I know believe that the culprit is the fact that the buckling caused the bellcrank to go from being just over 1/8 think to 1 3/8 thick and the bell crank caught on something and stopped it from turning (the wing is only 2 inches thick on the outside.) Though I can't say exactly what it caught on (best guess is the epoxy hardened foam on the center joint) because there wasn't much left in the center section and I burned the wood parts after the crash...
In the end I think its safe to say its not the design of the crank and an issue with the construction of this one. Whether there are others like it I don't know...
-Chris
-
Wow I never thought we would open an FAA investigation. :)
Well, this is serious stuff! I mean -- burning 777's in Los Vegas is just daily news, but a crashed stunt plane is important.
I just can't believe that's 6061-T6 aluminum. AFAIK, 6061-T6 would have cracked at the tight bends, and that surface finish looks more like soft aluminum to me at any rate.
If you have some soft aluminum to compare it to please do so, or toss the thing in your flight kit and show it to Brett at the team trials (assuming that someone manages to push a satisfactory airplane into your hands).
-
Is there no one available that can test the hardness of that damaged aluminum? Certainly not me, but it shouldn't be such a big deal...
W.
-
Is there no one available that can test the hardness of that damaged aluminum? Certainly not me, but it shouldn't be such a big deal...
That's why I suggested Brett. Anyone who's been around a few different alloys could do it, but I don't know who's close to Chris that has that experience.
If you can get it close to flat with your bare hands, that's a pretty good indication that it's soft, though.
-
That looks regrettably similar to one that I tossed out for poor quality. Notice the inside of the laminated aluminum is shiny, not dull like it should be if it was prepared.
It may be 6061-T6. It will usually bend sharply to 90 degrees once. When straightened it will probably break or at least crack. It may very well be some lesser heat treat. 70XX aluminum is stronger and probably way overkill and would probably have at least cracked before it bent that far.
Looks to me like bad surface prep and wrong adhesive.
I use a similar product to Brett's.
-
Surely, somebody has access to a Rockwell tester and maybe an Eddy Current tester? That would answer some questions, if not all. H^^ Steve
-
Steve is right. Most machine shops, even many small job shops would have a RC hardness tester.
-
Can this Eddy guy tell the difference between two alloys of aluminum? I guess there is some difference in resistivity between 6061 and 3003 (to pick two at random), but it's not a heck of a lot.
-
I agree with Mr Bill Johnson,,,, if I want the best Epoxy I'd use Hysol... I think it's made by Weld Wood believe it or not. But I dout it was the epoxys fault.
John
-
Can this Eddy guy tell the difference between two alloys of aluminum? I guess there is some difference in resistivity between 6061 and 3003 (to pick two at random), but it's not a heck of a lot.
I think that's a little too subtle n1 .... <=
-
Since I would like to make my own bell cranks I am very interested in finding out what happened here. I do not want to repeat a mistake.
To me, a bellcrank can be viewed as a simply supported beam with a concentrated load at the center. Bending stresses, etc. can then be calculated.
However, even if the stresses in a beam are below critical limits at a given load, a beam can go unstable laterally if a span is too long and unsupported or there is not enough material to resist the tendency to buckle laterally. Could that be what happened here?
-
I have to agree with Frank .
-
I have a Brinell hardness tester in my tool box specifically made for testing aluminum after heat treatment. If you want, I'll test it and send you the results. Too easy.
-
I still wonder if this isn't an artifact of the crash. Chris, was this indeed the "up" line? Coming downhill in the hourglass, the controls are neutral, pulling from a neutral position, so we are saying that the "Netzeband wall" (hinge moment) is what did this? We're talking about a 12 to 15 lb. pull, 20 at most. I'm not convinced that this was the failure.
I really don't dispute his analysis, plus, what to we think it might have hit in the crash to cause this kind of damage? If it didn't buckle in-flight, then you have to find something that rammed into it, end-on, hard enough to cause this damage. If nothing else you might expect a big dent in something else and the forked end of the bell crank flattened out from the impact.
The only thing that suggests anything else is that the buckling was all the way across the arm. Mine failed by buckling (at very high loads compared to flight) but it left a "wedge" buckled up, as the inner edge (toward the load) buckled and the outer edge remained straight because it was in tension. I did the test at zero deflection, so the fore/aft component of force was essentially zero. Maybe with it deflected that was different.
Brett
-
Can this Eddy guy tell the difference between two alloys of aluminum? I guess there is some difference in resistivity between 6061 and 3003 (to pick two at random), but it's not a heck of a lot.
Eddy alone doesn't tell you the alloy or temper, but if you have Rc and Eddy tests, you can nail it. So there... :P Steve
-
Well, I hate to say this but, "Houston, we may have a problem".
I took a NIP bellcrank and applied just a little pressure between thumb and finger and .... oops it de-laminated very easily. The other three I have did also.
There also seemed, without too much wiggling, for the two aluminum sides to want to go in opposite directions.
In use I've always wrapped them with kevlar thread ....... I think I did them all.
-
Its hard to argue with an experiment like that! Thank you for sacrificing some bellcranks to shed light on the problem.
-
It has been said solid aluminum like Fox and Perfect are not strong enough, then how on earth can thinner aluminum and balsa be stronger? (that is adding the 2 thin sheets of aluminum do not add up to the thickness of a Fox or Perfect bellcrank)
https://en.wikipedia.org/wiki/Euler%E2%80%93Bernoulli_beam_theory
-
Solid piece. Notched and bushed.
Sent from my iPhone using Tapatalk
-
After seeing Franks post I think if I were to make these 1/16 holes could be drilled every 1/4 inch before lamination and let the epoxy ooze out in the clamp state. That would fix this issue.
-
I really didn't set out to sacrifice a bellcrank ....... just picked one up and gently applied a lateral load, one handed between thumb and forefinger.
I plan to redo these with 1/16 in holes along the edge , interlaced with kevlar line, and BVM epoxy. Everything else is good except for the de-lamination of skins.
-
After seeing Franks post I think if I were to make these 1/16 holes could be drilled every 1/4 inch before lamination and let the epoxy ooze out in the clamp state. That would fix this issue.
Sure, and be much heavier than need be. Use the right materials and make like the designer intended. Also a longer bushing to stop any rocking causing play in the controls. Franks observation is exactly why I tossed mine in the garbage.
Again, just sayin.
-
Very interesting and cool stuff Howard. I'm surprised you didn't call and wake me at mid-nite last night to tell me about it!
Oh yeah, the contest is over....
😇
-
Sure, and be much heavier than need be. Use the right materials and make like the designer intended. Also a longer bushing to stop any rocking causing play in the controls. Franks observation is exactly why I tossed mine in the garbage.
Again, just sayin.
Why not just send them back to Tom? This is a manufactures defect and I wouldn't lose $ for something I didn't do.
-
I don't understand all of this. If it needs to be stronger, then why not make a bellcrank out of steel?
Most of the metal in the middle has no useful effect in terms of stiffness, but just adds weight. The material on the outside gets more effective as you separate it further.
This makes me think of the guy that was collecting money to make perpetual motion machine all because he was a good salesman, not because the machine was even a possibility.
So now I am a scam artist and/or incompetent? Or Tom Morris and I are *both* scheming to cause people's airplane to crash for some reason? Even if there is a defect in the design, or in the manufacturing, it certainly wasn't intentional. I get exactly *zero* for this, and have provided the plans to whoever wanted them for free. Tom manufactures them and sells them but I am pretty sure it is not to get rich, and it is not intended to sabotage people. What motivation would I have to cause Chris's (or anyone else's) airplane to crash. Particularly since I use the prototype in my NATS-winning airplane for the last 10 years, and another one in my current project?
Listen, I feel bad enough about this already, but I certainly am not attempting to trick, sabotage, or scam anyone, and I resent the suggestion.
Brett
-
I'm here to learn from the best of the best. This has been a very interesting topic thus far. I've learned:
1) If its damaged - replace it. Any attempt at a repair is at your own risk (not the designers, the manufactures or the retailers)
2) An ideal installation would allow for inspection from time to time. Maybe via an inspection hole or even a camera if required.
3) If possible, design an installation that allows for the bellcrank removal without major surgery.
Paul
-
Brett, I apologize, I didn't intend for you to take it that way. Honestly, I don't see how you can use balsa and not expect to separate. I have seen many times on a rc plane where ply is laminated to balsa along the nose of the plane and when it separates, the balsa tears or pulls apart. The glue is not the weak point.
Anyway, my point in my comment was intended toward the thought that extreme lightness is not going to give extreme strength, like a machine that can run without an energy source. I don't know, maybe the comment is out of order, sorry.
I have really stayed out of this up to this point because Brett is not only a friend but a highly respected engineer and and in my opinion has designed a very effective bellcrank intended to, as he stated, provide better connection for the leadouts.
The design is sound in my opinion but does require careful assembly and has a couple of very process sensitive items involved in the construction. First end grain balsa is significantly stronger in shear and compression than normal grain wood. The endgrain balsa also would provide a significantly stronger bond of the epoxy due to it's more porous and rougher surface. This provides far more surface for the epoxy to bond to and at this thin section would probably become totally filled with epoxy making the section stronger.
Now to the real problematic part of this assembly process. Brett mentioned that he applied epoxy to the aluminum surface and sanded it with the epoxy in place. This provided a non-active surface for the epoxy to bond to by ommiting air that would allow the aluminum surface to oxidize giving a firm bond brtween the aluminum and the balsa. In Aerospace applications only anodized or in some cases conversion coating such as alodine are specified for bonding aluminum surfaces. My educated guess in this case after looking at the pictures is that no conversion coating was provided on the aluminum surfaces and being active surfaces they continued to oxidize during the curing process so the epoxy bonded to the oxide which provides a very weak bond. It then delaminated, probably over a period of time and numerous stresses until the connection between the upper and lower aluminum sheets was non existent and the aluminum buckled under stress.
I also agree somewhat with what Chris said earlier that the buckling could have occurred over time untill it reached a point where the bellcrank snagged on something in the wing. I further think that the first failure with the pushrod connection was an indication that the delamination had already occurred and was likely a factor in that failure due to movement between the top and bottom plates of the bellcrank.
In closing I believe that this failure was caused by poor process control of the bonding and not really a factor of the design.
Randy Cuberly
-
It has been said solid aluminum like Fox and Perfect are not strong enough, then how on earth can thinner aluminum and balsa be stronger? (that is adding the 2 thin sheets of aluminum do not add up to the thickness of a Fox or Perfect bellcrank)
If a beam that's strong on the outside and light on the inside can't be strong overall, then how on earth does nearly every bridge and skyscraper in the world stay up? Not to mention every single full-size airplane and most flying models?
Please answer, because inquiring minds want to know.
-
I don't understand all of this. If it needs to be stronger, then why not make a bellcrank out of steel?
This makes me think of the guy that was collecting money to make perpetual motion machine all because he was a good salesman, not because the machine was even a possibility.
It has been said solid aluminum like Fox and Perfect are not strong enough, then how on earth can thinner aluminum and balsa be stronger? (that is adding the 2 thin sheets of aluminum do not add up to the thickness of a Fox or Perfect bellcrank)
Does the manufacturer of the aluminum / balsa bellcrank make good on things like this?
Rusty,
To be as strong as the laminated bellcrank, a solid bellcrank of the same material would have to be nearly as thick as the laminated one and hence would be much heavier and would not provide the convienent slots at the ends for the line attachment spools without some precision machining.
Simply put the failure mode here is not simple tension but a combination of stresses of tension and bending. The bending stresses cause compression on one side of the material and tension (or stretching) on the other side. The farther apart the two sides are the less stress they actually see. This of course does require the two sides to be firmly attached to each other. Hence the bonded light material in the center which actually sees very small stresses except at the joining surfaces...in this case the bond between the aluminum and balsa.
The actual failure mode shown in the photos is "Buckleing" or "folding" of the material on the outside of the laminations caused by these combined stresses because the laminations were not joined by the bonding material.
You can google "beam stress" for a technical description of how the stresses are distributed...unfortunately it's got a lot of that nasty old math in the description. LL~ LL~ But you can understand the principle if not the math!
Randy Cuberly
PS: Fox Bellcranks were made from 2024 T4 Aluminum and were fairly strong. The Perfect Bellcranks were made from 1100 Aluminum and were very weak.
-
I really didn't set out to sacrifice a bellcrank ....... just picked one up and gently applied a lateral load, one handed between thumb and forefinger.
I plan to redo these with 1/16 in holes along the edge , interlaced with kevlar line, and BVM epoxy. Everything else is good except for the de-lamination of skins.
Frank,
I would HIGHLY recommend that you NOT put any holes in it. That will raise the net stress in the aluminum making the buckling lever lower, not counting the support of the wrap. Simply wrap it with kevlar "string" and cover with a small amount of epoxy. This is a belt and suspenders approach to a good assembly, but if the interlaminar joint goes bad the kevlar takes over and does the job. As long as the edge doesn't budge, the center isn't going to buckle.
I had a plane with one of these bellcranks from Tom and I wrapped it in Kevlar and there were no issues......Until the bird hit it. Inside the wreckage, the bellcrank was just fine.
Please just wrap it with kevlar.
-
Did the kevlar help the bird?
Sorry to hear chris.
Weve ALL lost planes to control failure of some type.
-
Now to the real problematic part of this assembly process. Brett mentioned that he applied epoxy to the aluminum surface and sanded it with the epoxy in place. This provided a non-active surface for the epoxy to bond to by ommiting air that would allow the aluminum surface to oxidize giving a firm bond brtween the aluminum and the balsa. In Aerospace applications only anodized or in some cases conversion coating such as alodine are specified for bonding aluminum surfaces.
I used the process as described. I attempted to delaminate a test part and couldn't do it with my bare hand, and it bent the "fork" where it attached to the balsa. I did get it to come apart with a lot of effort using vice-grips.
But again, I got it to about 80 lbs with *no balsa at all*, just the pivot and the three screws, before it buckled as described. So I would expect that debonding itself, alone, would cause the problem Chris had. That bent a Top flite into a "u" shape, and pulled about 1/4" each side on a Sig. I also tried to bend it out of plane as Frank describes and could get it to deflect a bit, but not come apart, with the amount of strength I have in my hands.
There should be tremendous margin in the design, at least a factor of 10, so I am at a loss as to how it could give up so easily.
Brett
-
I used the process as described. I attempted to delaminate a test part and couldn't do it with my bare hand, and it bent the "fork" where it attached to the balsa. I did get it to come apart with a lot of effort using vice-grips.
But again, I got it to about 80 lbs with *no balsa at all*, just the pivot and the three screws, before it buckled as described. So I would expect that debonding itself, alone, would cause the problem Chris had. That bent a Top flite into a "u" shape, and pulled about 1/4" each side on a Sig. I also tried to bend it out of plane as Frank describes and could get it to deflect a bit, but not come apart, with the amount of strength I have in my hands.
There should be tremendous margin in the design, at least a factor of 10, so I am at a loss as to how it could give up so easily.
Brett
I would have to suspect that the aluminum material is not as specified (6061T6). 50series aluminum is only about half the tensile strength of that and common hardware store aluminum (1100series) is very soft and only about half of the 50 series (about 15,000psi if my memory serves...which it doesn't sometimes these days).
I'm relatively sure Tom would not knowlingly use any such material but aluminum looks like aluminum and mistakes can occur!
Randy Cuberly
-
Is it possible that the the aluminum was something like 6061-o by mistake ? o means annealed which is soft.
-
This thread has opened my eyes to many things I didn't know about bonding aluminium with epoxy. It just shows, you're never too old to learn something new. Thanks to all.
-
Is it possible that the the aluminum was something like 6061-o by mistake ? o means annealed which is soft.
Possibly -- but an important part of that bellcrank design is the end-grain balsa, and that was done wrong, too. It's certainly screamingly obvious to me that you can't substitute end-grain wood for balsa with the grain running the length of the crank. By extension, if someone uses end grain in an application like that where it's obviously so much harder to implement than "board grain" (what is that called?) then clearly the glue joint matters -- and the glue came undone where even well applied hobby shop epoxy would have ripped the wood apart.
IMHO whoever built Chris's bellcrank (back before 2015, remember this is an old old thread) just didn't understand the reasoning behind Brett's design, yet felt free to change things up. If that's the case, there'd be very little chance that the changes would be good.
I'm going to reiterate here, since the thread's coming alive again -- in my opinion Brett's original design (strong aluminum, end-grain balsa, strong glue joints) is an excellent of example of mixed-media structural design. I'm envious I didn't think of it. Unfortunately, if you don't understand structures, it'll be easy to make something that looks the same but doesn't hold together well.
-
I would have to suspect that the aluminum material is not as specified (6061T6). 50series aluminum is only about half the tensile strength of that and common hardware store aluminum (1100series) is very soft and only about half of the 50 series (about 15,000psi if my memory serves...which it doesn't sometimes these days).
I'm relatively sure Tom would not knowlingly use any such material but aluminum looks like aluminum and mistakes can occur!
Randy Cuberly
5083-H116 which is the standard aluminium for boat building is pretty close to 6061-T6.
5083 H116 - http://asm.matweb.com/search/SpecificMaterial.asp?bassnum=MA5083H116
6061 T6 - http://www.matweb.com/search/datasheet_print.aspx?matguid=1b8c06d0ca7c456694c7777d9e10be5b
-
For sure end grain balsa require a lot of epoxy because it soaks it up like a sive the guy I worked for in high school tried it as a replacement for foam to stiffen transoms, decks , etc in a boat. not enough presoak on the end grain & you have a dry layup. Which equals poor bond & delamenation. I'll bet a nickel some of the bent , collapsed aluminum is from the crash.
John L.
-
As previously noted, my prototypes, and the versions I made to test after this incident, would take the 80 lb pull test with no balsa at all, and I could lift myself off the ground with the complete design as specified. The failure mode of the "no balsa" types were as shown, buckling in the arm , but only at the inside edge, the outside edge was still straight, being under tension.
It does take a lot of glue - this design was never intended to save weight - and it certainly requires proper aluminum gluing techniques as previously described. My test parts could be delaminated only when I bent one side of the "fork" and clamped it in a vise, and grabbing the other side with vice-grips and heavily pulling on it, while also bending/curling it. Large chunks of balsa remained on the aluminum. Note Chris' picture, one side had a bit of wood/glue stuck to it, the other looks like it came out of the rolling mill minutes earlier- no bond whatsoever, and no apparent surface prep.
Of the premanufactured versions I subsequently acquired, I performed similar tests, but noted that just trying to assemble them with the hardware provided required forcing the spacers in which started delamination even before a load was applied. The grain ran parallel to the plates, not cross-grain, and they failed around 40 ish lbs much as shown. I also had a few of the early ones where there were large cutouts made to "lighten it up", those failed at very low tension. I didn't test the hardness, but the faces looked like aluminum strip flashing and was much softer and easier to bend.
Note that I also have one made of .020 titanium face sheets. Cutting that with tools I have in my bedroom closet was a fun afternoon, and provided nothing particularly useful over the 6061-T6 versions.
Again, I am sorry if anyone had problems with this, particularly Chris. I learned (actually reinforced) a very valuable lesson - *never, ever* cede control of a process or product that I am associated with in any way. The same thing happened with the Infinity plans, they got out against my better judgement, and now I have people building "Infinities" with Trivial Pursuit wings or with "better" features like flat pointy stabs, then complaining about them not flying properly, same with 20FPs - 'no power' - after they toss the muffler "to save weight" and put in ST spraybars. Same with another, er "activity" that got out of my control.
That's why I am *never* going to publish plans for the Infinity for real, too many people will "fix" it and then complain it doesn't work.
Brett
-
I built a bell crank as discussed & I pretty much figured mine is bullet proof. The design is sound providing it is assembled correctly. Different adhesives for different folks I hear some people say,,, when we rebuilt the Atlas Van Lines unlimited hydroplane that Bill Muncey crashed in in 1981 in Mexico anything structural such as sponsons, deck we used Hysol Epoxy no screws only clamps , weights & clecos . Layups such as fiberglass parts, fiberglass over the deck we used Systems 3 epoxy. These were not ideas dreamed up by me they were the calculated plan of Crew Chief Don Mock & original design genius by the name of Jim Lacero. This is a 5,200 pound boat with a 2000 plus cubic inch V12 Rolls Merlin pounding the water at 185 MPH .
I doubt sub standard adhesives would hold Brett's design together very long. I have maybe 75 flights on my bell crank.
-
Several years ago I ordered two of these from Tom. They arrived compromised in adhesion and were not centered. I sent them back and received two new ones that were slightly better. I won't use them. I like Brett's, as shown in forum pictures, and do not think that the outside manufactured ones measure up in quality. I hated to write this, but the defects were noticeable. - SK
-
Comisrations,
Theres a chance id be somewhat put out , were it me .
I relate Stunt Ships , if ' All Weather " planes , to say rally cars , or moto-X / Enduro motosickles . Somewhat bounced around and ' stressed ' .
Therefore ' Service Life ' , is related to durability . Envisage a FoMoCo like test cycle device , operating it thousands or millions of cycles . :(
" I still wonder if this isn't an artifact of the crash. Chris, was this indeed the "up" line? Coming downhill in the hourglass, the controls are neutral, pulling from a neutral position, so we are saying that the "Netzeband wall" (hinge moment) is what did this? We're talking about a 12 to 15 lb. pull, 20 at most. I'm not convinced that this was the failure. "
Flying in knew zeelund , whilst the Americas cup twits were chickening out , as their boats blow up if theres a chop & thirty knot winds ,
the two kilo Spitfire , G 51 , on a grass circle / center - would have you dragged on Std Shoes , downwind . If it was damp . As it sometimes is when it rains .
Thered be a pull of at least 50 POUNDS .
Golf Shoes ( studded ) Kicking ones heels into the ground , leaning back . Often both hands on handle .Twanging a line in Sq bottoms on .018 7 strand steel . >:(
Therefore if we do a 200 % operating load multi cycle test , And a destruction - cycling - test . We'd see how it ' GOES ' . :-\
-
I know this is a slightly older thread, but one thing bothers me about it..
300 flights is a very short time for failure, and I noticed Chris said
" I put a lot of flights on planes and it lasted for 300. My guess is that most people who use the crank don't fly that much. "
Well Ive used the Tom Morris / Brett Buck bellcrank on all my models since 1998, when I would purchase them off windy.
I never had one single failure, and flew this same bellcrank system on the Lancaster, which weighed 120oz.
On my regular competition ships I have had no problems with the bellcrank ever wearing out.
Now I as for total flights, I have my own circle and can fly as long as I like. 300 flights? Id do that in a week, no problems.
Im not going to comment on the failure beyond saying Ive installed the same purchased product for 20+ years, and have certainly pushed "number of flight" envelope beyond 3000 flights on more than 2 plan.
The last major failure of a control system I had was breaking a titanium 4.40 bolt. Due to a faulty manufacturing process.. so that CAN happen..
This is Bretts point, its hard to associate your name if you dont have 100% control over the finished product.
I personally started using the bellcrank because it was endorsed by a World class engineer and pilot, so yes I believe the products I have purchased and use have been nothing short of "exceptional" and a 100% success rate.
-
I have my own circle and can fly as long as I like. 300 flights? Id do that in a week, no problems.
#^ #^ #^