skyfox wings 21 through 25N

[foxworker]

If I can be of any assistance to anyone with respect to skyfox wings, repairs, rebuilding etc. feel free to ask me any questions. I built pretty much all of the Gazelle wings, updated and re-wrote the specs. for them, and know them inside out. Also have access to the covering process and the fellow who did the covering in the factory. Repairing 'fox wings including hangar brackets, trailing edge sections, epoxy joints, drag braces etc. isn't rocket science however if you're going to do it yourself and you're not an L2, you need the correct info. and the correct proceedures on how to go about it. I've read some pretty disturbing comments written by people fixing their wings obviously not really knowing what they're doing. I am happy to help anyone who is prepared to listen and do it properly. cheers.

 

 

[Guest Maj Millard]

Foxworker, A few years back I sent a couple of Gazelle wings to an organization in Gympie for repairs, after a landing accident. Although the wings were not actually damaged in the accident, one of the ailerons had completely fallen off the wing after all five hangars had failed cleanly through the wood grain where they exit the wing, due to the vertical impact. There was no evidence of any wood rot leading to the failure, and the aircraft was in good shape otherwise. I requested the back-up mod to the hangars, using alum plates.

 

After recieving both wings back,I noted that only one wing had been modified. What was the use of this when the other aileron could just as easily fall off ?!..I insisted th other wing be done, and it was.

 

It is my belief that all Skyfoxes, Gazzelles and applicable Kitfoxes should be grounded until all with wood hangars are modified. I am aware of at least three fatal accidents in this country caused by aileron failure on the above aircraft. I think two of them were double fatalities.

 

What is your view on this ??.......................................................................................................Maj...

 

 

[foxworker]

Where are you located mate,cheers Mat

Hi Mat,

 

I'm in Brisbane, northside.

 

 

[foxworker]

Foxworker, A few years back I sent a couple of Gazelle wings to an organization in Gympie for repairs, after a landing accident. Although the wings were not actually damaged in the accident, one of the ailerons had completely fallen off the wing after all five hangars had failed cleanly through the wood grain where they exit the wing, due to the vertical impact. There was no evidence of any wood rot leading to the failure, and the aircraft was in good shape otherwise. I requested the back-up mod to the hangars, using alum plates.After recieving both wings back,I noted that only one wing had been modified. What was the use of this when the other aileron could just as easily fall off ?!..I insisted th other wing be done, and it was.

 

It is my belief that all Skyfoxes, Gazzelles and applicable Kitfoxes should be grounded until all with wood hangars are modified. I am aware of at least three fatal accidents in this country caused by aileron failure on the above aircraft. I think two of them were double fatalities.

 

What is your view on this ??.......................................................................................................Maj...

Hi Maj.

 

I believe ther are over 5000 Kitfox's flying with much the same set-up (excluding the spars), and I believe (from their website) there have not been any inflight structural failures. As I've pointed out to Mr Bell from RAA, I do not believe the design is the problem. You've stated that there was no evidence of wood rot, and that the hangars broke on impact which is not surprising. If you were to have the same landing and impacted with the same force or greater having had the al. hangars installed, the damage may be more substantial, as the aluminium hangars will withstand the force, but somthing else has to give. I have a friend whose 'fox has had one outboard hangar replaced with the al. type and he is concerned that if for any reason the wooden hangars were to snap landing or in flight, he would be left with the aileron hanging on at one point only which would have disasterous results. It is my opinion that earlier models 21. 22. 22a, may need inspections carried out on the junction at the hanger brackets/trailing edges to check the epoxy glue joint. This glue joint (either side of the hangar) needs to be formed into a gusset shape and faired into the rib and trailing edge so that water cannot get between the epoxy and the timber. The whole joint has to be sealed after that with a 2-pak polyurethane sealer, at least 2 coats. Personally I believe that the wooden hangars are fine if they are maintained properly and inspected regularly (more so if they are not undercover). I'd like to know about the accidents you speak of as I'm not sure they were all caused by aileron failure. One was caused by lift strut failure, not sure about the other two. I do not believe that all foxes should be grounded and and have the hangar mod carried out, I don't believe there is justification to do so and I think it would be a huge expense to owners of these aircraft. The approved timber repair is fine as long as it is carried out properly. Thanks for your response and for asking for my opinion, appreciated. paul

 

 

[Guest Maj Millard]

Thanks for your reply Paul,

 

Agreed that my instance was the result of vertical crash forces which also damaged the main landing gear. The pilot in question pulled up to avoid wallabies on the runway, stalled the aircraft, and dropped in from an altitude higher than he should have.

 

What scared me was that all five wood aileron hangers sheared cleanly right where they exited the trailing edge of the wing. The wood grain runs vertically, not horizontally, and the failure was cleanly vertically along the grain, and identical on all five hangers. I can guarantee you there was no wood decradation, and the paint cover was in good shape, and as I said before the aircraft generally was in good shape for it's age. I may have one of the severed hangers around some where, I'll see if I can dig it up.

 

Any chain is only as strong as it's weakest link, and this is obviously a weak link here. I personally won't fly this type aircraft without the modified hangers, as I don't believe they would be up to handling severe turbulance, and could easily lose an aileron . As a comparison I regulary fly my GR 912 lightwing into Shute harbour, often in severere turbulance which can often be expected in that area. I would certainly not want to do that approach in that turbulance with unmodified hangers.

 

One aileron failure accident was in the Darwin area, there was evidence of wood degradation on that one. There was one in the Cabulture area, where the female pilot threw a prop blade, and the resulting vibration shook one of the ailerons off the aircraft. She did not survive that encounter. The aircraft in question was rebuilt and I saw it about a year ago at South Grafton airport. There was one other involving an aileron failure, which was also a double fatality, I believe possibly in Victoria somewhere.

 

The one in central Qld, also a double fatality, was probabily the strut failure you mention. I read the accident report closely, and they basically blamed a failure of the jury strut, leading to wing separation.

 

I disagreed totally with their report summation, and some who saw the accident said they thought the aileron on the failure wing, fluttered badly before separating. This was the aircraft that was kept beside the Dingo roadhouse in central Qld for many years. I also believe that the RAA tech manager at the time, imposed a max speed limitation of 80 kts. on similiar types, because of that accident.

 

As you know the Skyfox/Gazelle line of aircraft in this country are certified and CASA approved as trainers. It is hard for somebody to say these aircraft have a potential fatal flaw, as because it would lead to a redesign of the wing/aileron hangers, or yet another CASA AD on the aircraft requiring the hanger back-up mod. The CASA AD requiring the wing-strut carry-thru mod was also the rusult of several failures in the early wing-strut carry-thru tubes.

 

I am currently involved in major repairs to a Karatoo J6 wood wing that was damaged recently in Cyclone Yasi. the aircraft was picked up, pivoted on it's left wing tip which destroyed the wing outer bay completly. The aileron and aileron hangers which are welded steel brackets were completely undamaged. Luck, yes no doubt, but also a great demonstration of a well designed structure which is up to the job............................................Maj...

 

 

 

[foxworker]

Thanks for your reply Maj.,

 

I must correct you on one point. The wood grain does not only run vertically, that would be impossible as it is 11 ply. I'm not going to argue about the hangars; the ply ones are fine in my opinion as long as they have the correct gusset joint and have been properly sealed. I am here to help people with advice and possibly help with re-pairing or refurbishing their 'fox wings, not including the ailerons. I have the only existing set of specs. for the wings as I wrote them and I also know the whereabouts of all the wing and associated components drawings, the originals. The biggest problem faced by 'fox owners is that in the case of an accident the spars are damaged, obtaining new ones is pretty much impossible and to get someone to reproduce them is very unlikey being that they're for certified aircraft. My best advice to owners is be very carefull when landing (especially the 'draggers), hangars and all other parts are replacable, the spars are not. cheers paul

 

 

[Guest Maj Millard]

Your offer of experienced help in properly maintaining these aircraft is appreciated, and I'm sure those in need of it will be happy to use it..............................................Cheers Ross

 

 

[carlsnilsson]

"One aileron failure accident was in the Darwin area, there was evidence of wood degradation on that one. There was one in the Cabulture area, where the female pilot threw a prop blade, and the resulting vibration shook one of the ailerons off the aircraft. She did not survive that encounter. The aircraft in question was rebuilt and I saw it about a year ago at South Grafton airport. There was one other involving an aileron failure, which was also a double fatality, I believe possibly in Victoria somewhere.The one in central Qld, also a double fatality, was probabily the strut failure you mention. I read the accident report closely, and they basically blamed a failure of the jury strut, leading to wing separation.

I disagreed totally with their report summation, and some...

I'm a CA22 Skyfox owner and have been for 15 years. I have also followed accidents involving Skyfox wings and ailerons reasonably closely, having disagreed with the AUF's Technical Manager Mr Hewitt-Cook over the incident in Qld in or about the year 2000 which a Skyfox lost one aileron and landed safely. That resulted in an AN 2-2000 which required the chrome moly insert to the aileron torque tube OR an X-ray inspection of that tube and it's junction with the aileron crank. At the time I wrote (to AUFCHAT) " it is likely the root hanger broke first - but the real question is why did they (or at least one) break? Both Bill Whitney and Daffyd Llewellyn (Reg 35 Engineers) believe flutter is the likely cause - most probably due to an out-of-balance aileron....". Now, those two CAR35 engineers are two of the most knowledgeable and respected Reg 35's in the country and Daffyd Llewelyn hada lot to do with testing the Skyfox wing and aileron - of which he is not particularly fond. Out of balance ailerons will flutter and that will likely tear off an aileron regardless of whether it is attached with Al or aircraft quality plywood. In this particular instance it was and still is my view that Mr Hewitt-Cook incorrectly attributed the initiating cause as torque tube attachment failure when that failure was subsequent to a hangar failure due to flutter - due to an out-of-balance aileron probably due to water ingress. Two good things came from this, however: firstly, further checking revealed a lot of out-of-balance ailerons and more attention was paid to having proper drain holes in each wing panel and each aileron segment.

 

Another result was that here in Tasmania one Skyfox owner tested a standard aileron section flying free (no restraining control) at about 7o kn and it was perfectly stable with no sign of flutter - as expected. Thus, if you lost one aileron and it broke free of the aircraft or the controlling torque tube snapped for some reason, you could adequately fly on one aileron, as happened in the incident in Queensland that gave rise to AN 2-2000. I would much prefer an aileron to depart entirely than hang on and inhibit the use of the other.

 

I am aware of the accident in the NT, in which a hangar broke due to wood rot and that was a fatality because the aileron hung on with the remaining hangars and the aircraft was uncontrollable. Note the common factor here - the aicraft were left out-of-doors in tropical climates and the hangars deteriorated due mainly, I believe, to inadequate drainage.

 

The awful fatality of father and son in central Queensland was not "probably" due to strut failure - it was certainly due to strut failure. Again, Daffyd Llewellyn was the engineer whom the ATSB had investigate and his investigation and report were both thorough and professional. The forward lift strut buckled under severe compression load caused by a strong turbulent downdraft (which pushed the jury struts into the wing) and then the following updraft snapped the weakened lift strut. There was some evidence, if I recall correctly, of excessive speed in the severe turbulence of the day. Quite frankly, to disagree with the expert report by a Reg 35 engineer of great experience who knew the Skyfox limitations intimately and had examined the broken aircraft and all other evidence, does not do you much credit. It is not widely appreciated that, above 70 kn IAS, the forward lift strut on a fox is not under tension, but rather under comprsssion. That is why it is of larger cross-section than the rear strut which actually carries most of the load. The front strut needs buckling strength. It is also why, when you are flying in turbulent conditions, you should SLOW DOWN! I'm talking about 60 - 65 kn - forget the maneuvering speed limitation of 80 kn.

 

I am not aware of any of the fatal accidents to which you refer due to wooden aileron hangar failure apart from the one in the NT. Rather than vague assertions of fatalities here, there and everywhere, I ask you to do a little research and list the history accurately. Certainly I may have missed one, but you have made these sweeping assertions, so please back them up with references.

 

Carl

 

 

[Blueadventures]

I'm a CA22 Skyfox owner and have been for 15 years. I have also followed accidents involving Skyfox wings and ailerons reasonably closely, having disagreed with the AUF's Technical Manager Mr Hewitt-Cook over the incident in Qld in or about the year 2000 which a Skyfox lost one aileron and landed safely. That resulted in an AN 2-2000 which required the chrome moly insert to the aileron torque tube OR an X-ray inspection of that tube and it's junction with the aileron crank. At the time I wrote (to AUFCHAT) " it is likely the root hanger broke first - but the real question is why did they (or at least one) break? Both Bill Whitney and Daffyd Llewellyn (Reg 35 Engineers) believe flutter is the likely cause - most probably due to an out-of-balance aileron....". Now, those two CAR35 engineers are two of the most knowledgeable and respected Reg 35's in the country and Daffyd Llewelyn hada lot to do with testing the Skyfox wing and aileron - of which he is not particularly fond. Out of balance ailerons will flutter and that will likely tear off an aileron regardless of whether it is attached with Al or aircraft quality plywood. In this particular instance it was and still is my view that Mr Hewitt-Cook incorrectly attributed the initiating cause as torque tube attachment failure when that failure was subsequent to a hangar failure due to flutter - due to an out-of-balance aileron probably due to water ingress. Two good things came from this, however: firstly, further checking revealed a lot of out-of-balance ailerons and more attention was paid to having proper drain holes in each wing panel and each aileron segment.Another result was that here in Tasmania one Skyfox owner tested a standard aileron section flying free (no restraining control) at about 7o kn and it was perfectly stable with no sign of flutter - as expected. Thus, if you lost one aileron and it broke free of the aircraft or the controlling torque tube snapped for some reason, you could adequately fly on one aileron, as happened in the incident in Queensland that gave rise to AN 2-2000. I would much prefer an aileron to depart entirely than hang on and inhibit the use of the other.

I am aware of the accident in the NT, in which a hangar broke due to wood rot and that was a fatality because the aileron hung on with the remaining hangars and the aircraft was uncontrollable. Note the common factor here - the aicraft were left out-of-doors in tropical climates and the hangars deteriorated due mainly, I believe, to inadequate drainage.

 

The awful fatality of father and son in central Queensland was not "probably" due to strut failure - it was certainly due to strut failure. Again, Daffyd Llewellyn was the engineer whom the ATSB had investigate and his investigation and report were both thorough and professional. The forward lift strut buckled under severe compression load caused by a strong turbulent downdraft (which pushed the jury struts into the wing) and then the following updraft snapped the weakened lift strut. There was some evidence, if I recall correctly, of excessive speed in the severe turbulence of the day. Quite frankly, to disagree with the expert report by a Reg 35 engineer of great experience who knew the Skyfox limitations intimately and had examined the broken aircraft and all other evidence, does not do you much credit. It is not widely appreciated that, above 70 kn IAS, the forward lift strut on a fox is not under tension, but rather under comprsssion. That is why it is of larger cross-section than the rear strut which actually carries most of the load. The front strut needs buckling strength. It is also why, when you are flying in turbulent conditions, you should SLOW DOWN! I'm talking about 60 - 65 kn - forget the maneuvering speed limitation of 80 kn.

 

I am not aware of any of the fatal accidents to which you refer due to wooden aileron hangar failure apart from the one in the NT. Rather than vague assertions of fatalities here, there and everywhere, I ask you to do a little research and list the history accurately. Certainly I may have missed one, but you have made these sweeping assertions, so please back them up with references.

 

Carl

Hi Carl

 

I'm new to RAA and learning on a CA21 with a 912UL that I bought late 2010. With all the rain up in Mackay the airfields have been wet, so not many landings occuring. The skyfox (55-0606 - ca21-037) has the ply hangers. I have read as much as I can find about the hangers. Checking mine and getting a number of opioions from L2's and a L4 all appers good condition. I did purchase one alloy hanger kit from Gympie for the hanger at the strut to see whats involved in fitting the alloy hangers.

 

My present plan being considered is that if I ever decided or had to reskin the wings i'll replace all the hangers. Also I have a thought that it could be a plan to mod two hangers on each wing (4 in total) the inboard ones and the ones at the strut. (THIS IS ONLY AN IDEA THAT I WOULD GET EXPERT OPION ON BEFORE DOING.)

 

I am keen to learn of pre flight procedures to assess the sufficiency of the hangers. Presently I have a good close look at them, including at the attachment to the trailing edge area and then I apply pressure up and down and side ways slightly to judge the firmness including the press test on the sides to check for softness (rot) of the ply.

 

Cheers

 

Mike

 

 

[Blueadventures]

If I can be of any assistance to anyone with respect to skyfox wings, repairs, rebuilding etc. feel free to ask me any questions. I built pretty much all of the Gazelle wings, updated and re-wrote the specs. for them, and know them inside out. Also have access to the covering process and the fellow who did the covering in the factory. Repairing 'fox wings including hangar brackets, trailing edge sections, epoxy joints, drag braces etc. isn't rocket science however if you're going to do it yourself and you're not an L2, you need the correct info. and the correct proceedures on how to go about it. I've read some pretty disturbing comments written by people fixing their wings obviously not really knowing what they're doing. I am happy to help anyone who is prepared to listen and do it properly. cheers.

Hi Paul

 

Thanks for this information.

 

I have recently been flying Ca21-037 -- 55-0606.

 

I would be keen to get intouch about wing matters.

 

Thanks

 

Mike

 

 

[djpacro]

...... the spars are damaged, obtaining new ones is pretty much impossible and to get someone to reproduce them is very unlikey being that they're for certified aircraft.

I still wouldn't discard the thought of getting new spars built if some-one really wanted to rebuild a set of wings. Of course, more hoops to jump through and some costs associated with it. I'd also like to encourage people to keep these flying.

[carlsnilsson]

I'd like to design a wing with a friese aileron and flaps' date=' or maybe adapt the highlander wings , they look pretty good [/quote']Go for it. However, remember that the Skyfox is a certified aircraft and, unless you have half a million dollars or something of that order, you won't get your wings certified! As a comment, I would say that I've never really felt the need for flaps on the Fox - it sideslips pretty well and you can safely carry that slip close to the ground. Pilots of this type - or most types for that matter - should go to a safe altitude and then try stalling with backstick in a heavy sideslip. In other words, real crossed controls. See what the aircraft does. My Fox is benign - it simply wallows down. Some aircraft are real nasty, can flip and/or go into a spin. It pays to know your type. So, in the Fox, you can carry or initiate a good sideslip right down to the flare. Just straighten up! Flaps would give you a lower landing speed, but I don't know by how much. The wing is already somewhat inefficient with the undersurface cambered.

Daffyd Llewellyn designed a new wing for the Fox, but the estimated cost was somewhere around $20,000 about a decade ago. The Eurofox has a completely redesigned wing, but I note that the two spars are about the same diameter as those in the Fox (61-62 mm), are made of heavier material (2 mm instead of about 1.6 mm), but don't have that marvellous central vertical web that gives the custom-drawn Fox spar greater stiffness and strength - and makes it so difficult to replicate or get a spare. Reputedy, after Skyfox folded, the spare spars went to Dubai and were (possibly) melted down. My guess is that there are one or two still squirreled away somewhere in the country by far-sighted owners.

 

To the best of my recollection, the Fox wing was static tested to above 7G - "'til it bent like a bow", I have heard. I know I have pulled 4G plus a bit with my earlier Fox, as recorded on a G-meter, without any ill effects. Don't recommend it as a normal practice, though, as all stress has cumulative effects.

 

Just making a few comments in response to your input. Treated right, the wing is fine, in my opinion. Two weeks ago I flew mine back to Hobart from a trip to Melbourne and Canberra through some most unpleasant turbulence in NE Tasmania. When between Flinders Is. and NE Tas., Melbourne Centre passed on a severe turbulence warning for NE Tas. just issued by BOM. Not much I could do about it! The wings and control were just fine and show no signs of over-stressing - more than can be said for the pilot!

 

Some of the older Fox wings were not built with quite enough attention to detail as regards the epoxy joints of metal to wood and wood to wood and the trailing edges were a bit inadequate - you will see some scalloping under the tension of the covering. Foxworker, who opened this thread, is the master here. He repaired my broken wing (replaced the front spar) and generally showed me some of the skills of a master tradesman regarding the refurbishment of these wings. When it comes to appreciating the behaviour of these wings in flight, I defer to (retired?) Reg. 35 Engineer Daffyd Llewellyn, who brought the wings and ailerons to certification for Skyfox - and who flew them beyond their certified limits. These are the people who know what they are talking about and not just posting wind! I will say more about this in a reply to Blueadventures.

 

Regards

[djpacro]

........ The Eurofox has a completely redesigned wing, but I note that the two spars are about the same diameter as those in the Fox (61-62 mm), are made of heavier material (2 mm instead of about 1.6 mm), but don't have that marvellous central vertical web that gives the custom-drawn Fox spar greater stiffness and strength - and makes it so difficult to replicate or get a spare. .........

Good info, some technical challenges there alright. Per my prior post, the approval of a replacement spar need not be a show stopper if some-one has the technical solution.

 

......... These are the people who know what they are talking about and not just posting wind! ....

......

[foxworker]

Hi PaulThanks for this information.

 

I have recently been flying Ca21-037 -- 55-0606.

 

I would be keen to get intouch about wing matters.

 

Thanks

 

Mike

Hi Blueadventures, good to hear from you. You can contact me on mobile 0402871771. Often I don't hear my phone during work hours due to the noise where I work, so please leave me an sms message with a contact number and I will call you back as soon as I am able. Look forward to talking 'fox wings. chers paul

 

 

[Guest Maj Millard]

I'm a CA22 Skyfox owner and have been for 15 years. I have also followed accidents involving Skyfox wings and ailerons reasonably closely, having disagreed with the AUF's Technical Manager Mr Hewitt-Cook over the incident in Qld in or about the year 2000 which a Skyfox lost one aileron and landed safely. That resulted in an AN 2-2000 which required the chrome moly insert to the aileron torque tube OR an X-ray inspection of that tube and it's junction with the aileron crank. At the time I wrote (to AUFCHAT) " it is likely the root hanger broke first - but the real question is why did they (or at least one) break? Both Bill Whitney and Daffyd Llewellyn (Reg 35 Engineers) believe flutter is the likely cause - most probably due to an out-of-balance aileron....". Now, those two CAR35 engineers are two of the most knowledgeable and respected Reg 35's in the country and Daffyd Llewelyn hada lot to do with testing the Skyfox wing and aileron - of which he is not particularly fond. Out of balance ailerons will flutter and that will likely tear off an aileron regardless of whether it is attached with Al or aircraft quality plywood. In this particular instance it was and still is my view that Mr Hewitt-Cook incorrectly attributed the initiating cause as torque tube attachment failure when that failure was subsequent to a hangar failure due to flutter - due to an out-of-balance aileron probably due to water ingress. Two good things came from this, however: firstly, further checking revealed a lot of out-of-balance ailerons and more attention was paid to having proper drain holes in each wing panel and each aileron segment.Another result was that here in Tasmania one Skyfox owner tested a standard aileron section flying free (no restraining control) at about 7o kn and it was perfectly stable with no sign of flutter - as expected. Thus, if you lost one aileron and it broke free of the aircraft or the controlling torque tube snapped for some reason, you could adequately fly on one aileron, as happened in the incident in Queensland that gave rise to AN 2-2000. I would much prefer an aileron to depart entirely than hang on and inhibit the use of the other.

I am aware of the accident in the NT, in which a hangar broke due to wood rot and that was a fatality because the aileron hung on with the remaining hangars and the aircraft was uncontrollable. Note the common factor here - the aicraft were left out-of-doors in tropical climates and the hangars deteriorated due mainly, I believe, to inadequate drainage.

 

The awful fatality of father and son in central Queensland was not "probably" due to strut failure - it was certainly due to strut failure. Again, Daffyd Llewellyn was the engineer whom the ATSB had investigate and his investigation and report were both thorough and professional. The forward lift strut buckled under severe compression load caused by a strong turbulent downdraft (which pushed the jury struts into the wing) and then the following updraft snapped the weakened lift strut. There was some evidence, if I recall correctly, of excessive speed in the severe turbulence of the day. Quite frankly, to disagree with the expert report by a Reg 35 engineer of great experience who knew the Skyfox limitations intimately and had examined the broken aircraft and all other evidence, does not do you much credit. It is not widely appreciated that, above 70 kn IAS, the forward lift strut on a fox is not under tension, but rather under comprsssion. That is why it is of larger cross-section than the rear strut which actually carries most of the load. The front strut needs buckling strength. It is also why, when you are flying in turbulent conditions, you should SLOW DOWN! I'm talking about 60 - 65 kn - forget the maneuvering speed limitation of 80 kn.

 

I am not aware of any of the fatal accidents to which you refer due to wooden aileron hangar failure apart from the one in the NT. Rather than vague assertions of fatalities here, there and everywhere, I ask you to do a little research and list the history accurately. Certainly I may have missed one, but you have made these sweeping assertions, so please back them up with references.

 

Maj replied :

 

Carl, I will be happy to reply with some facts and references, however I am currently away from home , so it may take a few days for me to post. Additionally I want to find that piece of broken hanger, as I am damn sure it wasn't 11 ply, and I'm certain it was a clean vertical break on all 5 x broken hangars................Maj...

 

Carl

[foxworker]

Good info, some technical challenges there alright. Per my prior post, the approval of a replacement spar need not be a show stopper if some-one has the technical solution.......

Dear djpacro,

 

Wish it were that simple. The original spars as far as I can remember, were extruded in the USA, (I remember there were often hold ups with delivery). I think there may of been a couple of suppliers because I remember at one stage, I think when we started producing the Gazelles, the extruders kept having problems when the die sets kept breaking. Here's the problem/s, 1) even if I were able to locate the extruders, equipment and dies, from the manufacturer in the USA, if they still exist, I expect there would be zilch chance of getting the equipment off them. 2) Manufacturing the equipment to produce the extruded section would be prohibitively expensive and therefore the spars would cost a fortune to produce/purchase. 3) It is not just a simple case of going and producing a part for a fully certified aircraft without having an APMA. I have a friend who is the holder of such an approval, and I tend to believe what he says. I believe the best thing to do is to have the spar life extended to 10000 hours. Note I say spars not the rest of the wings. All the parts for the wings can be reproduced easily, legally, and reasonably inexpensively. cheers paul

 

 

[foxworker]

I can guarantee you if it is a Skyfox Gazelle Ca25N, they will be 11 ply mahogany quality ply of 6mm thickness. As a minimum, the min ply spec is for GL2 birch. This information is on the C.A.R approved drawings. No designer in his right mind would use anything less than ply in such an application, where wood is the prefered material. I certainly did not put any other type of timber rib into any of the gazelle wings that I built or oversaw the construction of, and I was in charge of building every set of Gazelle wings.cheers paul

 

 

[djpacro]

Paul, no argument with your technical info. I don't know enough to comment further on that side of things.

 

Certainly, APMA (or a production certificate) is required if anyone was going to organise for a batch of spars to sell to people. However, there is provision for "manufacture of parts during course of maintenance" when an APMA is not required. An approved maintenance organisation having access to approved data etc could make spars as required when an individual aeroplane turned up requiring a replacement spar. That organisation could not make spars for stock or for sale. That organisation may subcontract the manufacture of spar(s) as required for the specified aircraft. Of course, some-one would need to have a stock of extrusions handy to make a spar when required.

 

 

[foxworker]

Paul, no argument with your technical info. I don't know enough to comment further on that side of things.Certainly, APMA (or a production certificate) is required if anyone was going to organise for a batch of spars to sell to people. However, there is provision for "manufacture of parts during course of maintenance" when an APMA is not required. An approved maintenance organisation having access to approved data etc could make spars as required when an individual aeroplane turned up requiring a replacement spar. That organisation could not make spars for stock or for sale. That organisation may subcontract the manufacture of spar(s) as required for the specified aircraft. Of course, some-one would need to have a stock of extrusions handy to make a spar when required.

You are correct and I understand the provision. The organisation would still have to make up the die and extrusion equipment and that is quite expensive itself; I vaguely recall a conversation with the owner of Skyfox/Hedaro ( pre the Abu Dhabi owners), who was telling me how expensive it was at the time. The cost of having replacement spars made up would be prohibitive to most owners, just the 6061 T6 aluminium stock would cost a small fortune; we're talking thousands not hundreds. However, if it were ever to happen, it would solve a potential dilema down the track, as even if the spars were lifed to 10000 hrs, after that the aircraft would basically be throw away. APMA :Australian Parts Manufacturing Approval. cheers paul

 

 

[barandbrew]

Hi Paul

 

From another Fox owner thank you for offering your expertise . I have a question is there a fix for the bushers on the hangers when they start to get play.

 

Thanks

 

John

 

 

[Guest Maj Millard]

Foxhunter, I don't doubt that they were plywood, but then the big question does beg to be answered !....why did all five shear vertically, clean as a whistle ??...............Tony Kerr at Gympie did the repair and installed the mod kit..check with him if you like..........................................................................................Maj...

 

 

[foxworker]

Hi PaulFrom another Fox owner thank you for offering your expertise . I have a question is there a fix for the bushers on the hangers when they start to get play.

Thanks

 

John

Hmm, this is an interesting question. I'm assuming your referring to the "plastic" bushes between the aileron spars and the 4130 steel tube sections which are welded to the two flat sections which in turn are bolted to the ply hangers. There are no bushes in the ply hangers themselves, just two AN bolts running through the 4130 flat metal sections and the ply. There will be slight movement side to side with the steel tube sections , but I don't believe there should be play in the bushes up and down or forward and backwards. What sort of play are you experiencing? The ailerons were built seperately to the wing structures by another fellow so I'm not positively sure about proceedures for replacing these bushes; from memory the bushes were inserted whilst the ailerons were being built and then the whole lot was glued and rivetted. I will endeavour to find out more about this and get back to you as soon as I have the correct info. Thanks for the question, cheers paul.

 

 

[carlsnilsson]

I'm new to RAA and learning on a CA21 with a 912UL that I bought late 2010. With all the rain up in Mackay the airfields have been wet, so not many landings occuring. The skyfox (55-0606 - ca21-037) has the ply hangers. I have read as much as I can find about the hangers. Checking mine and getting a number of opioions from L2's and a L4 all appers good condition. I did purchase one alloy hanger kit from Gympie for the hanger at the strut to see whats involved in fitting the alloy hangers.My present plan being considered is that if I ever decided or had to reskin the wings i'll replace all the hangers. Also I have a thought that it could be a plan to mod two hangers on each wing (4 in total) the inboard ones and the ones at the strut. (THIS IS ONLY AN IDEA THAT I WOULD GET EXPERT OPION ON BEFORE DOING.)

I am keen to learn of pre flight procedures to assess the sufficiency of the hangers. Presently I have a good close look at them, including at the attachment to the trailing edge area and then I apply pressure up and down and side ways slightly to judge the firmness including the press test on the sides to check for softness (rot) of the ply.

 

Cheers

G’day Mike:

Good luck to you learning on a CA21. I don’t know if you have previous experience with taildraggers, but learning on a CA21 is not the easiest way. I had a few hours solo on a Piper Cub back in 1968, but when I started again on a CA22 in 1996 at Penfield, Vic., I was classed as a slow learner. I had difficulty, to say the least, in landing! Eventually circumstances caused me to transfer to a Drifter on which I made better progress and eventually, much poorer in pocket, I got my certificate! I then hotfooted up to Caloundra and bought a much-used, much loved and sometimes-abused CA22, namely 55-747, which my friend Tony Curzon (instructor) and I flew back to Penfield. At the time, I was not aware of some of 747’s chequered history, but I have to say that I kept that aircraft on line at Penfield for many years and it never gave any significant trouble and helped a lot of students get their certificate. Since then I have bought two others and sold one, keeping 55-0688 for my own use sinceY2000. I could converse at some length on the joys and pitfalls of learning on a Fox, but maybe not on this thread.

 

In my opinion, wooden or aluminium hangers is not too much of an issue with respect to Fox wings. Get hold of Skyfox Aviation’s Service Bulletin No. 24 or the equivalent issued by the (then) AUF – now RA-Aus. There was an AD or similar issued by CASA on the subject, as there were a number of VH-registered CA-22’s, not to mention all the Gazelles. Basically, SB 24 gives some guidelines on examining wooden hangers. As best you can, look for any signs of wood rot. You can’t really examine them properly unless you remove fabric. What you can and should do, is make sure every wing bay has a decent (>4 mm say) and clear drain hole close to a rib and as near to the trailing edge as possible. Ailerons should also have drain holes in each segment near the trailing edge. Also, there was an AN and AD (Airworthiness Notice and Airworthiness Directive) regarding the removal of the outermost bit of the outboard aileron (outside the last hanger). The aim was to prevent water ingress – which can also be achieved by application of a suitable filler material through the slot for the hanger bracket. Use your common sense – you are acting to prevent water getting into the aileron segments and providing a means of letting any water out.

 

Wood rot takes place when moisture is present around unsealed wood and there is lack of air circulation. Water inside wings is a pretty good starter for the fungus. That’s why foxworker stressed the sealing of all wood surfaces. Unfortunately, on some early wings (CA21 and CA22), some epoxy joints were not made with proper attention to smoothing out fillets with a sufficient amount of epoxy and blending to the wood , particularly around the trailing edges where they attach to the ribs. Any cavity, be it in your teeth or an epoxy joint to a rib inside the Skyfox wing, provides a nucleous for rot. This could well apply to the attachment of aluminium hangers to the wooden ribs, just as to the wooden ones.

 

Foxworker would advise you to take a look at your trailing edges. Are they even where they join each rib – that is, does one side sit higher than the other? Feel them between thumb and forefinger. If one is loose and co-joins a hanger, you have a potential site for water penetration. You seem to be doing this OK. Don't get too obsessed with this matter. If you read the ATSB report of the NT accident (No. 199800361) you will see that the rot was widespread and advanced and should have been very detectable.

 

It helps a lot if the aircraft is hangared (I’m spelling it correctly this time!) – a Fox is not a machine which should be left outside in the elements for months at a time. This is not to imply that it has to be cosseted and is particularly fragile – but a machine of wood and fabric is not designed for prolonged outdoor storage in the tropics.

 

To me, these are the issues that warrant attention – more than the question of wood vs aluminium hangers. The other matter to arise from the two occasions of which I am aware a hanger has broken in flight is the question of ensuring the ailerons are balanced – that is, the C of G of the ailerons has not moved aft either due to a weight coming loose or water ingress and retention. There is an AN on this and you have to remove the ailerons (not a big job) to check. As I said, if you get severe aileron flutter due to unbalanced or insufficiently supported ailerons, things will quickly tear apart regardless of whether the hangers are aluminium or wood. I would prefer the guilty aileron to depart swiftly from snapped hangers and broken aluminium torque tube and good luck to all who sail in her! I would watch it flutter to the ground as I flew home with one good aileron! But it won’t happen to me!!

 

Now you have me going on this forum, I want to write something about the behavior of the wing in turbulence – the easy guide to Daffyd Llewellyn’s enlightened report. Give me a couple of days.

 

Regards Carl

 

 

[barandbrew]

Hmm, this is an interesting question. I'm assuming your referring to the "plastic" bushes between the aileron spars and the 4130 steel tube sections which are welded to the two flat sections which in turn are bolted to the ply hangers. There are no bushes in the ply hangers themselves, just two AN bolts running through the 4130 flat metal sections and the ply. There will be slight movement side to side with the steel tube sections , but I don't believe there should be play in the bushes up and down or forward and backwards. What sort of play are you experiencing? The ailerons were built seperately to the wing structures by another fellow so I'm not positively sure about proceedures for replacing these bushes; from memory the bushes were inserted whilst the ailerons were being built and then the whole lot was glued and rivetted. I will endeavour to find out more about this and get back to you as soon as I have the correct info. Thanks for the question, cheers paul.

Thanks Paul

Yes the plastic bushes round the aileron tube it is only slight play but I would like to take it out if possible. I can see no way of doing this apart from taking the whole aileron apart.

 

Thanks John

 

 

[carlsnilsson]

Yes the plastic bushes round the aileron tube it is only slight play but I would like to take it out if possible. I can see no way of doing this apart from taking the whole aileron apart.

John: Remember, this is a flexible wing. The original ailerons before certification were one piece. When loaded in flight, the wing bends enough such that the original one-piece ailerons jammed solid. That's what Llewellyn was testing. That's why the ailerons are now segmented. The wings still bend in flight and so does the full length of aileron. Play when the wing is unloaded on the ground does not necessarily mean play in flight. I suspect that you need some degree of clearance in those bushes to prevent binding in flight. So long as the bushes are still in one piece, I don't think I would worry about it, unless the aileron as a whole rattles around. The wings can flex inches in flight. I think the one bush you should pay attention to is the one that constrains the torque tube where it emerges from the fuselage/turtle deck, based on the experience of my friend Tony Curzon who once suffered aileron flutter. I'm not an expert in this matter. Few people are. Llewellyn is.

 

Carl