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BMFA F3F Nationals 2021 (Wales)


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Phil.Taylor
15 hours ago, oipigface said:

I tried to apply brakes, causing it to loop, so I applied the brakes very, very cautiously. It slowed down sufficiently that I felt I could land it safely, but was still gaining height, so I decided to trying steering it behind the slope where with any luck there would be less lift and I would be able to land it even though I wasn’t able to apply any further down elevator.

brakes caused it to loop...

Maybe... guessing... - CROW down elevator compensation is not properly set in one of the flight modes? - would cause the even more pitch up when applying CROW/brakes. The initial flight problem could then be simply that the CROW (throttle) stick was not fully set to off - knocked maybe - and some CROW = pitch up

Hope you track down the problem

Phil

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16 hours ago, oipigface said:

Another weekend another brace of crises! I know exactly what happened to the green one, and I have spent the afternoon so far replicating the various configurations of ballast in the red one and measuring the position of the CG for each. The red one you will recall behaved just as you would expect it to behave if the CG were too far rearwards. (Much too far!) On launch for R5, it pitched up and stalled, then continued to misbehave while I held in down elevator and fed in as much down trim as possible. 

Weird, can't see that a small CG shift would suddenly make the model barely controllable. If you're certain that the CG was within a couple of mm of the last successful flight, that might suggest a programming or a hardware issue. I would go through the programming with a fine tooth comb.

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What I dont get is that JT flew 2 rds with it fine ...then it was obviously wrong from the launch of rd4 ...unless John has different model memories for marginally differing conditions I dont see how it can go so seriously wrong  from rd to rd . I'm still thinking its a hardware failure in the Tx .

The lift was the best we had seen all day though ...so that may have also had a slight bearing on things ......😪

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oipigface
8 hours ago, Phil.Taylor said:

brakes caused it to loop...

Maybe... guessing... - CROW down elevator compensation is not properly set in one of the flight modes? - would cause the even more pitch up when applying CROW/brakes. The initial flight problem could then be simply that the CROW (throttle) stick was not fully set to off - knocked maybe - and some CROW = pitch up

Hope you track down the problem

Phil

I programmed the CROW carefully during its maiden session, and the compensation worked perfectly adequately in R2-4. I have three flight modes, only one - Landing - has CROW enabled. I try not to launch in Landing mode, and I am fairly certain that I didn’t for R5 on Saturday. The other point I would repeat is that it wasn’t just an ‘initial flight problem’. It was present throughout the flight and was improved by application of every micron of down elevator available to me. 

 

8 hours ago, rc-soar said:

Weird, can't see that a small CG shift would suddenly make the model barely controllable. If you're certain that the CG was within a couple of mm of the last successful flight, that might suggest a programming or a hardware issue. I would go through the programming with a fine tooth comb.

Weird is right. I am not convinced by your idea that it’s a programming issue. Once every little bit of down was applied - trim and stick and butterfly compensation, it floated around quite stably and could be controlled in every direction bar down! That suggests to me that the problem was with the physical configuration of the plane - either CG, wing or tail incidence or wing or tail camber. I’ve found no evidence since it landed that supports any of these possibilities.

6 hours ago, Andy_B said:

What I dont get is that JT flew 2 rds with it fine ...then it was obviously wrong from the launch of rd4 ...unless John has different model memories for marginally differing conditions I dont see how it can go so seriously wrong  from rd to rd . I'm still thinking its a hardware failure in the Tx .

The lift was the best we had seen all day though ...so that may have also had a slight bearing on things ......😪

The only thing I knowingly changed between R4 and R5 was to add two slugs of brass ballast to the front wing ballast tube. It was good lift, but plane wouldn’t have known about that unless Les threw it into a violent vertical shear! It was certainly on the same model memory, and I think I would have noticed a bunch of up trim before launch. 
I’m still thoroughly mystified.

Thanks for all your comments. I’ll continue to think about it, and investigate. If anything new occurs to any of you, I’d like to hear about it.

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Could it be that the ball link arms that enter the control surfaces tailplane, are slipping, causing the odd trims? 

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isoaritfirst

Elevator was set right when the model landed, but at that time you had put in loafs of down trim. 

Conclusion would be it was uptrimmed at launch. 

Cause of up trim could be,

Knocked trim tabs.

Slipped control rod ends, perhaps caught elevators  on landing and pulled the rods partly out of the clevises. 

Servo tray moved backwards. As this would effect both surfaces equally it would give the result you had. 

Transmitter pots breaking down. I've had this on a few occasions and it can give intermittent results or cause centres to move. Once in a transmitter just 3 months old.

 

Hope you can find the cause soon John, nothing worse than loosing confidence in your equipment.

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isoaritfirst

Two models both having what seemed like the same issue, would point to elevator transmitter pot issue.

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oipigface
On 09/06/2021 at 12:03, Mikeb52 said:

Could it be that the ball link arms that enter the control surfaces tailplane, are slipping, causing the odd trims? 

I don’t think there were any ‘odd trims’. I fed in 49 points of down trim during the flight. That was what was in it when it landed. Returned the trim to zero on the transmitter returned it to zero on the plane. 

 

On 09/06/2021 at 12:51, isoaritfirst said:

Elevator was set right when the model landed, but at that time you had put in loafs of down trim. 

Conclusion would be it was uptrimmed at launch. 

Cause of up trim could be,

Knocked trim tabs.

Slipped control rod ends, perhaps caught elevators  on landing and pulled the rods partly out of the clevises. 

Servo tray moved backwards. As this would effect both surfaces equally it would give the result you had. 

Transmitter pots breaking down. I've had this on a few occasions and it can give intermittent results or cause centres to move. Once in a transmitter just 3 months old.

 

Hope you can find the cause soon John, nothing worse than loosing confidence in your equipment.

No, Mike you’ve got it wrong. There were about 2mm of downtrim when the model landed. It is equivalent to the 49 point maximum that I fed in.

On 09/06/2021 at 12:52, isoaritfirst said:

Two models both having what seemed like the same issue, would point to elevator transmitter pot issue.

Wrong again, Mike! The green/ orange issue was that I chose the wrong version of the model on the Tx. The red issue wasn’t that. I’ve only got one program for it. 
 

Yesterday, Bruce Hudson spent the afternoon here. We checked the CG again. He looked over the mechanical condition of the model, and the electrical system, and I hope he will confirm that there is nothing loose, broken, displaced, unscrewed or otherwise unsatisfactory. The plane is what you would expect from a model that has had less than half a dozen flights since it was fitted out. (The installation was done at the Baudis factory.)

I’m open to the idea that there is something obscure in the programming that I am not aware of, and I’m going to check that now, by looking through all the program pages and doing another check of the effects of all the switches.

If this yields no result, I think I will try the nuclear option of chucking it off again to see what happens. After all, it has flown satisfactorily  5 times out of 6!

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oipigface

A little more evidence: Last Wednesday I took my refurbished Personal Best Pitbull to Whitesheet for its remaiden. Same transmitter. No problems.

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17 minutes ago, oipigface said:

A little more evidence: Last Wednesday I took my refurbished Personal Best Pitbull to Whitesheet for its remaiden. Same transmitter. No problems.

Still could be an intermittent problem with the transmitter John.

I think if it was me I'd send it of for service to see if they highlight any issues,at least then you remove any uncertainty you may have with it.

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rc-soar

Well this is a real teaser. Just to summarise my understanding of the possible causes: 

  1. CG shift due to ballast addition
  2. CG shift due to battery movement
  3. Change in elevator linkage geometry immediately after launch, magically restored to normal on landing
  4. Unexpected trim offset applied by the transmitter, due either to hardware issue or programming error, only during flight

It seems that 1-3 have all but been ruled out. Which leaves (4).  I'm wondering whether it's a trim offset thing. Most trannies have an option for trim offset to be FM-dependent. Maybe start by looking at the FM's, in particular how they're activated and their elevator trim settings. May be worth making a backup of the original setup before doing the forensics.

 

 

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oipigface
1 hour ago, rc-soar said:

Well this is a real teaser. Just to summarise my understanding of the possible causes: 

  1. CG shift due to ballast addition
  2. CG shift due to battery movement
  3. Change in elevator linkage geometry immediately after launch, magically restored to normal on landing
  4. Unexpected trim offset applied by the transmitter, due either to hardware issue or programming error, only during flight

It seems that 1-3 have all but been ruled out. Which leaves (4).  I'm wondering whether it's a trim offset thing. Most trannies have an option for trim offset to be FM-dependent. Maybe start by looking at the FM's, in particular how they're activated and their elevator trim settings. May be worth making a backup of the original setup before doing the forensics.

 

 

Mike, I’m very grateful for your suggestion, but sadly I don’t have a clue what is. What are FM’s? 
After having suffered from making a backup when I was working on the other plane, do you really think it’s a good idea to risk that route again?

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oipigface
9 hours ago, Les said:

Still could be an intermittent problem with the transmitter John.

I think if it was me I'd send it of for service to see if they highlight any issues,at least then you remove any uncertainty you may have with it.

Good suggestion, Les. I shan’t follow it before Tuesday. I’m hoping to maiden my Sea Duck tomorrow!

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