CARF Skygate Hawk in the house !
08-17-2015, 11:13 PM
#1051
Hi David,
Interesting thoughts. Mine is a later kit and the elevator bearings are free moving without being sloppy. No doubt they will firm up with heating but I wouldn't think they could cause a problem in my case.
Re matching servos - at the urging of the LMA I've modified the elevator servo linkages like this: (yet to be inspected!)
As a minimum it should deal with any slight servo mismatch though, of course, I will still match the servos. Be interested in anyone's thoughts on this approach particularly if you spot a potential problem. There will be lots of testing before maiden but it wont be truly tested until it flies.
I'm very sorry for everyone's losses. I hadn't realized that so many were going down. On balance, I'd prefer not to add to the statistics!
Bob
Interesting thoughts. Mine is a later kit and the elevator bearings are free moving without being sloppy. No doubt they will firm up with heating but I wouldn't think they could cause a problem in my case.
Re matching servos - at the urging of the LMA I've modified the elevator servo linkages like this: (yet to be inspected!)
As a minimum it should deal with any slight servo mismatch though, of course, I will still match the servos. Be interested in anyone's thoughts on this approach particularly if you spot a potential problem. There will be lots of testing before maiden but it wont be truly tested until it flies.
I'm very sorry for everyone's losses. I hadn't realized that so many were going down. On balance, I'd prefer not to add to the statistics!
Bob
08-18-2015, 02:12 AM
#1052
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David,
interesting indeed! Actually never thought of possible heat related elevator bearing issue. I can check this because I still have the crashed fuselage. And good luck on the JWM in Leutkirch - I will visit there for a couple of days, arriving on Sunday. See you there!
interesting indeed! Actually never thought of possible heat related elevator bearing issue. I can check this because I still have the crashed fuselage. And good luck on the JWM in Leutkirch - I will visit there for a couple of days, arriving on Sunday. See you there!
Last edited by jseppanen; 08-18-2015 at 03:11 AM.
08-18-2015, 02:56 AM
#1053
Thanks, Jan, I look forward to seeing you there and discussing this issue. I like the rear servo installation too, particularly as my model needed weight in the tail. Any chance you can bring the bearings ?
If Darryl Tarr is at Leutkirch or Jet Power, I will also discuss the issue with him as he has two SG Hawks, and is using the original setup.
I know of at least three AW Hawks lost with pitch failure and I am convinced these were the result of servo burnout due mismatch, or bearing seizure, they can be under very heavy load, and I discovered one of mine had become very stiff due lubrication drying out.
David.
If Darryl Tarr is at Leutkirch or Jet Power, I will also discuss the issue with him as he has two SG Hawks, and is using the original setup.
I know of at least three AW Hawks lost with pitch failure and I am convinced these were the result of servo burnout due mismatch, or bearing seizure, they can be under very heavy load, and I discovered one of mine had become very stiff due lubrication drying out.
David.
Last edited by David Gladwin; 08-18-2015 at 03:01 AM.
08-18-2015, 03:51 AM
#1055
Further lunchtime thoughts.
I have just looked at mine again, they seem to be steel balls in the aluminium frame. The pipe below is single wall and there is nowhere for the heat from it to escape in that area so the bearing unit will receive some, perhaps a lot, of warming. Over time it may be that any lube has dried out and that is assuming that the unit was adequately, if at all, lubed on assembly. As the ball is quite a tight fit, external oiling may not allow much oil to reach the ball itself.
I am going to disassemble mine, thoroughly oil before reassembly and I am going to drill a hole through the frame to the ball so I can run oil down that hole onto the ball.
I will also install the balsa sheet screen lined with heat reflector above the tailpipe, as I have done on other models with tail mounted servos. to keep the bearings as cool as possible.
Of course its possible that none of these is the cure but they can't do any harm !
Also just oiled the bearings on my AW Hawk for germany, they looked quite dry !
Looking forward to hearing any other suggestions or theories before I fly mine.
David.
I have just looked at mine again, they seem to be steel balls in the aluminium frame. The pipe below is single wall and there is nowhere for the heat from it to escape in that area so the bearing unit will receive some, perhaps a lot, of warming. Over time it may be that any lube has dried out and that is assuming that the unit was adequately, if at all, lubed on assembly. As the ball is quite a tight fit, external oiling may not allow much oil to reach the ball itself.
I am going to disassemble mine, thoroughly oil before reassembly and I am going to drill a hole through the frame to the ball so I can run oil down that hole onto the ball.
I will also install the balsa sheet screen lined with heat reflector above the tailpipe, as I have done on other models with tail mounted servos. to keep the bearings as cool as possible.
Of course its possible that none of these is the cure but they can't do any harm !
Also just oiled the bearings on my AW Hawk for germany, they looked quite dry !
Looking forward to hearing any other suggestions or theories before I fly mine.
David.
08-18-2015, 04:23 AM
#1056
Hi David,
Interesting thoughts. Mine is a later kit and the elevator bearings are free moving without being sloppy. No doubt they will firm up with heating but I wouldn't think they could cause a problem in my case.
Re matching servos - at the urging of the LMA I've modified the elevator servo linkages like this: (yet to be inspected!)
As a minimum it should deal with any slight servo mismatch though, of course, I will still match the servos. Be interested in anyone's thoughts on this approach particularly if you spot a potential problem. There will be lots of testing before maiden but it wont be truly tested until it flies.
I'm very sorry for everyone's losses. I hadn't realized that so many were going down. On balance, I'd prefer not to add to the statistics!
Bob
Interesting thoughts. Mine is a later kit and the elevator bearings are free moving without being sloppy. No doubt they will firm up with heating but I wouldn't think they could cause a problem in my case.
Re matching servos - at the urging of the LMA I've modified the elevator servo linkages like this: (yet to be inspected!)
As a minimum it should deal with any slight servo mismatch though, of course, I will still match the servos. Be interested in anyone's thoughts on this approach particularly if you spot a potential problem. There will be lots of testing before maiden but it wont be truly tested until it flies.
I'm very sorry for everyone's losses. I hadn't realized that so many were going down. On balance, I'd prefer not to add to the statistics!
Bob
This is simular to the seesaw that is used it the front mounting of the servos. The only problem I have with this is if one servo be inoperative becuase of power or if the gear strips and the arm is allow to move then you will loose most if not all controll. When the good servo pushes it will simply move the other direction allowing the stab to stay in flying position. IMO this is only good if the servo locks in center position.
I would rather have 400oz working against a dead servo that might still move instead of this. Plus with the pivot of the arm you are creating another failure point.
08-18-2015, 07:23 AM
#1057
I have no doubt that you have more experience than I have when it comes to building jets. I don't want to say anything to create an argument but the one thing that bothers me about your set up that I have read about is that you were using the Powerbox. I have not used one and I no where near an expert but I have seen a number of jets go in with loss of control and they were using Powerbox units.
I use the K.I.S. method of building. "Keep it simple" The less you have to use the less chances of a failure.
I have to ask was the elevator mix done in radio or the Powerbox? I do know there is not a issue with this design of the elevator.
I have way to many fights to prove that. I have let at least 10 different people fly mine. I would still have if not for a festo filter. Yes after so many wonderful flights I added one after I was told I should always have between the pump and turbine..I would rather have a flame out and have to send my turbine back for repair instead of having to sit there and watch it burn to the ground.
if you have a festo filter in your jet rip it out!
I just got my new one today and can't wait to get back up in the air.
lets us know what you find out.
Again, Sorry for your loss I know how you feel and I hope you find a reason to build another one.
I use the K.I.S. method of building. "Keep it simple" The less you have to use the less chances of a failure.
I have to ask was the elevator mix done in radio or the Powerbox? I do know there is not a issue with this design of the elevator.
I have way to many fights to prove that. I have let at least 10 different people fly mine. I would still have if not for a festo filter. Yes after so many wonderful flights I added one after I was told I should always have between the pump and turbine..I would rather have a flame out and have to send my turbine back for repair instead of having to sit there and watch it burn to the ground.
if you have a festo filter in your jet rip it out!
I just got my new one today and can't wait to get back up in the air.
lets us know what you find out.
Again, Sorry for your loss I know how you feel and I hope you find a reason to build another one.
Behzad
08-18-2015, 07:46 AM
#1058
I am thinking now about the heat issues that Dave is dicussing. Maybe the reason for mine not have the problem was the thermal blanket and the double wall pipe(tams).
Did you have the Carf Pipe? I was told there are single wall. Not sure becuase I have not seen one.
As far as movement I have a video of the elevator moving during flight post on my Youtube from Ky jets. You will see the elevator does't move very much. Most of the movement is on take off and flairing for landing.
https://www.youtube.com/watch?v=nPuig_i-Lxg
Did you have the Carf Pipe? I was told there are single wall. Not sure becuase I have not seen one.
As far as movement I have a video of the elevator moving during flight post on my Youtube from Ky jets. You will see the elevator does't move very much. Most of the movement is on take off and flairing for landing.
https://www.youtube.com/watch?v=nPuig_i-Lxg
Last edited by jws_aces; 08-18-2015 at 07:48 AM.
08-18-2015, 07:57 AM
#1059
Hi Jeff, I am supposed to be working!��
Carf pipe, it gets doubled after that spot. Heat shielded the stab and under the servos. Don't you think that if we had that much heat there, it would be at lest making the thin cover part fiberglass showing it. I was trying to form a little piece and it showed all the fiber weaves as soon as I got the heat gun in low to it. It was barely warm.
Behzad
Carf pipe, it gets doubled after that spot. Heat shielded the stab and under the servos. Don't you think that if we had that much heat there, it would be at lest making the thin cover part fiberglass showing it. I was trying to form a little piece and it showed all the fiber weaves as soon as I got the heat gun in low to it. It was barely warm.
Behzad
08-18-2015, 08:15 AM
#1060
I remebered touching mine after the first flights and it never appeared to be warm at all on the cover. Let us know how the testing of the electronics go.
I plan on recreating exactly the same set up in the new one. I hope I don't have any issues.
Thanks for talking about it. I know it is hard. I keep kicking myself on a crash of a F4 I bought off of a friend and used evrything he had except receiver. I lost it about half way around the first lap.
I am pretty sure in hind site I had the rudder Gyro backwards. I kick myself becuase I didn't have the gyro on a on-off for the first couple of flights.
Hard lesson learned.
I plan on recreating exactly the same set up in the new one. I hope I don't have any issues.
Thanks for talking about it. I know it is hard. I keep kicking myself on a crash of a F4 I bought off of a friend and used evrything he had except receiver. I lost it about half way around the first lap.
I am pretty sure in hind site I had the rudder Gyro backwards. I kick myself becuase I didn't have the gyro on a on-off for the first couple of flights.
Hard lesson learned.
08-18-2015, 10:37 PM
#1062
Bob,
"This is simular to the seesaw that is used it the front mounting of the servos. The only problem I have with this is if one servo be inoperative becuase of power or if the gear strips and the arm is allow to move then you will loose most if not all controll. When the good servo pushes it will simply move the other direction allowing the stab to stay in flying position. IMO this is only good if the servo locks in center position.
I would rather have 400oz working against a dead servo that might still move instead of this. Plus with the pivot of the arm you are creating another failure point."
Hi Jeff,
Thanks for your thoughts. I agree that it does not help in the case where one servo fails and is free to move but that, of course, is true of the original Skygate setup. The UK's Large Model Association wont let me use the 'direct' approach as indicated by Carf so I have to find another solution. This is the best I could come up with. If there's a better way I'm keen to hear it!
Bob
"This is simular to the seesaw that is used it the front mounting of the servos. The only problem I have with this is if one servo be inoperative becuase of power or if the gear strips and the arm is allow to move then you will loose most if not all controll. When the good servo pushes it will simply move the other direction allowing the stab to stay in flying position. IMO this is only good if the servo locks in center position.
I would rather have 400oz working against a dead servo that might still move instead of this. Plus with the pivot of the arm you are creating another failure point."
Hi Jeff,
Thanks for your thoughts. I agree that it does not help in the case where one servo fails and is free to move but that, of course, is true of the original Skygate setup. The UK's Large Model Association wont let me use the 'direct' approach as indicated by Carf so I have to find another solution. This is the best I could come up with. If there's a better way I'm keen to hear it!
Bob
08-19-2015, 04:26 AM
#1063
So if I understand you correctly you can not use 2 servos directly to on moving surface. That is 2 mounted in the rear and each servo has a arm going directly to the control horn of the elevator. If that is the case how does the UK's LMA treat 2 servos on the alerons or any other large moving surface?
I guess I would find a large hi torque singe servo. I know on the 1.5 hawk I had one that only had a single servo on the elevator and never gave me any problems. I logged 100+ flights on it. The previous owner/bulder commented to me when I bought it he was tired of replacing a servos that would die in the dual setup so he opted for a single high torque. I know the LMA may require 2 servos on it on the larger surface. I sure there is a fomula for what is required. Here in the US the LMA requirement is what the manufacture recommends for models that weight in at 55+ pound flying weight.
I guess I would find a large hi torque singe servo. I know on the 1.5 hawk I had one that only had a single servo on the elevator and never gave me any problems. I logged 100+ flights on it. The previous owner/bulder commented to me when I bought it he was tired of replacing a servos that would die in the dual setup so he opted for a single high torque. I know the LMA may require 2 servos on it on the larger surface. I sure there is a fomula for what is required. Here in the US the LMA requirement is what the manufacture recommends for models that weight in at 55+ pound flying weight.
08-19-2015, 04:47 AM
#1064
Could you maybe explain this. What is the difference between that and having 2 or three servos on an aileron (widely done on all Large Scale aircraft), and what do the LMA suggest?
08-19-2015, 05:00 AM
#1065
So if I understand you correctly you can not use 2 servos directly to on moving surface. That is 2 mounted in the rear and each servo has a arm going directly to the control horn of the elevator. If that is the case how does the UK's LMA treat 2 servos on the alerons or any other large moving surface?
I guess I would find a large hi torque singe servo. I know on the 1.5 hawk I had one that only had a single servo on the elevator and never gave me any problems. I logged 100+ flights on it. The previous owner/bulder commented to me when I bought it he was tired of replacing a servos that would die in the dual setup so he opted for a single high torque. I know the LMA may require 2 servos on it on the larger surface. I sure there is a fomula for what is required. Here in the US the LMA requirement is what the manufacture recommends for models that weight in at 55+ pound flying weight.
I guess I would find a large hi torque singe servo. I know on the 1.5 hawk I had one that only had a single servo on the elevator and never gave me any problems. I logged 100+ flights on it. The previous owner/bulder commented to me when I bought it he was tired of replacing a servos that would die in the dual setup so he opted for a single high torque. I know the LMA may require 2 servos on it on the larger surface. I sure there is a fomula for what is required. Here in the US the LMA requirement is what the manufacture recommends for models that weight in at 55+ pound flying weight.
I'm not sure about other surfaces - this is my first encounter with the LMA. They are quite specific though in terms of the elevator and I think they will need 2 servos since this is all about 'redundancy'. I've yet to see a 'sliding link' that works for both circumstances i.e. when a servo fails 'hard' and 'soft'. They seem to acknowledge that it only works when the servo fails' hard' but "this is better than no redundancy at all".
I'm not sufficiently expert in this field - or in the workings of the LMA - to debate it with them. I'm hoping that real experts will chime in. It would be good if a way could be found to provide true redundancy that would deal with both types of failure - I'm just not smart enough to figure it out for myself.
Bob
08-19-2015, 05:02 AM
#1066
I don't know! See my post 1064. I can see the logic of what they're striving for - just not sure the full solution is available yet!
Bob
Last edited by Blancr; 08-19-2015 at 05:16 AM.
08-19-2015, 05:20 AM
#1067
Thanks Bob,
Sorry it seems I asked exactly what Jeff did as well.
I will have the same setup as CARF recommend, and as I currently have in the Skymaster big Hawk (2 servos direct to surface). I see no problem with it at all, with properly matched servos of course.
Maybe someone will come up with what the LMA want.
Sorry it seems I asked exactly what Jeff did as well.
I will have the same setup as CARF recommend, and as I currently have in the Skymaster big Hawk (2 servos direct to surface). I see no problem with it at all, with properly matched servos of course.
Maybe someone will come up with what the LMA want.
08-19-2015, 05:42 AM
#1068
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Bob, I would ask them how mine and others in the past have got through the LMA scheme with the original Skygate/Carf servo setup. Sounds like the usual ridiculous LMA rules that nobody can explain.....
08-19-2015, 06:14 AM
#1069
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By way of interest there was a UK builder flyer who scratch built a large T45 (Goshawk) and the rear elevator was worked by two servos which were mounted to the stab and the linkages were then connected to points fixed to the fuselage, now I would imagine in this scenario a soft dead servo would still allow the other to drive the surface albeit half the torque, issue this time is a lock up would possibly prevent the good servo from working - guess the gamble is what is more likely....
Either way it was a very clever system which seemed to work well, maybe those who know this jet can chime in as to who the pilot was (I should remember as I was on flightline duty at the NATs on both years this jet flew).
marcs
Either way it was a very clever system which seemed to work well, maybe those who know this jet can chime in as to who the pilot was (I should remember as I was on flightline duty at the NATs on both years this jet flew).
marcs
08-19-2015, 09:23 AM
#1072
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A small snippet of Paul's T45 and a much longer video...
https://www.youtube.com/watch?v=J6ICFAKfgd0
https://www.youtube.com/watch?v=YM1y0uSLOSI
And a beautiful still of the scratch built T-45
http://rc-cropduster.com/dutchjettea...ges/image8.htm
https://www.youtube.com/watch?v=J6ICFAKfgd0
https://www.youtube.com/watch?v=YM1y0uSLOSI
And a beautiful still of the scratch built T-45
http://rc-cropduster.com/dutchjettea...ges/image8.htm
Last edited by Hinckley Bill; 08-19-2015 at 09:39 AM.
08-19-2015, 09:31 AM
#1073
08-19-2015, 11:30 AM
#1074
[QUOTE=marc s;12086668]By way of interest there was a UK builder flyer who scratch built a large T45 (Goshawk) and the rear elevator was worked by two servos which were mounted to the stab and the linkages were then connected to points fixed to the fuselage, now I would imagine in this scenario a soft dead servo would still allow the other to drive the surface albeit half the torque, issue this time is a lock up would possibly prevent the good servo from working - guess the gamble is what is more likely....
Either way it was a very clever system which seemed to work well, maybe those who know this jet can chime in as to who the pilot was (I should remember as I was on flightline duty at the NATs on both years this jet flew).
Marc,
It's obviously possible to create these linkages in a number of different ways but the essential issue is to come up with a system that deals with both 'soft' and 'hard' failures. His approach sounds ingenious but still leaves us with the fundamental problem.
Actually, given the reliability of modern servos when correctly set up, I'm wondering just how much of a problem this actually is!
Bob
Either way it was a very clever system which seemed to work well, maybe those who know this jet can chime in as to who the pilot was (I should remember as I was on flightline duty at the NATs on both years this jet flew).
Marc,
It's obviously possible to create these linkages in a number of different ways but the essential issue is to come up with a system that deals with both 'soft' and 'hard' failures. His approach sounds ingenious but still leaves us with the fundamental problem.
Actually, given the reliability of modern servos when correctly set up, I'm wondering just how much of a problem this actually is!
Bob
08-19-2015, 12:20 PM
#1075
A small snippet of Paul's T45 and a much longer video...
https://www.youtube.com/watch?v=YM1y0uSLOSI
And a beautiful still of the scratch built T-45
http://rc-cropduster.com/dutchjettea...ges/image8.htm
https://www.youtube.com/watch?v=YM1y0uSLOSI
And a beautiful still of the scratch built T-45
http://rc-cropduster.com/dutchjettea...ges/image8.htm
Wow if you click thru there were a lot of big hawks at this event. I would think they are still flying I hope.