Laser vibration issue..

[David Martin 2]

I hope someone can shed some light on the vibration issue I have found myself with having just ground run my new Laser 120 in my YT Spitfire.

 When I first turned it over with the starter, I could see the backplate of the 4 1/2" Ali spinner wasn't running true per revolution, probably only by about 1/2mm, but enough to notice.

The engine started but the level of vibration running through the model wasn't what I've experienced in 25 years of this hobby, but I've only had engines up to 10cc before as well..

I had the backplate checked and trued up on a lathe (the keying groves on the backplate that mesh with the prop driver were off, causing the b'plate to not sit square to the prop shaft and make the centre brass bush to be slightly distorted). This improved things quite a bit, but still quite a level of vibration was shaking the model.

 I removed the complete spinner assy and ran a different 15x8 Graupner prop on it's own (that balances perfectly), only to find that the vibration is still there..bent prop shaft on a new out of the box Laser..?...I wouldn't think so, would you..?

 What level of vibration do you think is acceptable on a 72" model..? In all my years, I've held quite high standards towards this kind of thing for safety sake and a long model life. The whole engine mount and model visibly vibrates as I go through the rev range.

This is the first Laser I've ever owned and only my 2nd 4 stroke, I was expecting smooth as silk somehow. Should I expect a little more movement from a 20cc Laser than say my OS 55 AX 2 stroke..? It is pushing through quite a volume of air I suppose but it isn't a 'torque' kind of movement, more a vibration. 

 I don't appear to have had any detrimental effects on the model so far, all nuts and screws have had loctight carefully applied as usual.

I would add a picture but I always get an error message saying the images I try to upload are of zero size..!

 Any comments would be appreciated, thanks...David

[Tim Mackey]

I would give Neil a ring, he is very helpful. The only Laser I ever had many years ago did run beautifully, and I expect something is amiss. I take it you have checked obvious things like mounting fixings, prop hole centred,  and so on? They are all test run before dispatch, so it is odd.

Tel: 01525 210596

[David Martin 2]

Thanks Timbo I appreciate your help but I'll ring Neil as a last resort though I think, I'm sure it's got to be the spinner causing a majority of the vibration somehow, I tried again today and I could see the tip of the spinner as a moving blur by a good 1+ mm.

I think I'll take spinner and backplate joined back to my mates lathe. A bit miffed at this hassle as it cost £27..!

The Graupner grey props have been the smoothest and quietest I've ever used and very rarely had any balance issues with them. I have them fitted in all different sizes to all my models now. I'll check the centre hole though as you say, but I've tried two now..

I'm pleased with the mounting and seems as solid as I would expect from the supplied kits nylon mount. I have (very securely) added my lead ballast to the mount as well...14oz...I wonder if there could be any form of resonance going on..? I'll illiminate the spinner first I think then move on from there..

Cheers.

[Ernie]

Hi David, I'd be really suprised if one of Neil Tidey's little gems was not in perfect nick out of the box. Why not eliminate all of the problems, mount the engine out of the airframe, no spinner, no ballast, no periphal problems, I'll bet it is perfect. and if it  isn't,  come out to France, and I'll stand you a cognac. Also, I agree with Timbo, Neil Tidey shouldn't be a last resort, he is one of the most helpful people on planet aviaton.

Ernie

[David Martin 2]

Hello Ernie...I can't believe the engine is at fault Ernie, I've treated it like a kitten since I unpacked it and like Timbo said, Neil runs every one before despatch and would have picked up on vibration I'm sure.

I feel like I should eliminate all other avenues before ringing Neil though as I'm sure he'll suggest all that you've just said as well and I'll feel a bit

 Maybe you could PM me your address Ernie, sounds like a tempting offer with the cognac, I could always fib and just say it's the prop shaft like a cork screw to get there...

[The real Ron Truth]

Without any desire to be flammed, I do know of a friend who runs a laser 150 in his cm pro kittyhawk and suffers vibration problems. The engine vibrates forward every flight and hes lost for reasons. He said it may be due to overheating causing the bolt holes to swell.

Id consider upgrading to SC.... ( Runs and hides)

[Allan Jordan]

 Hi David, Take Timbo's advice and contact Neil Tidey, he must surely be the one person to help you with this problem! Best of luck, Allan J...

[David Ovenden]

Hello,

A friend of mine had SERIOUS vibration problems with a Laser 150 in a 77" Hangar9 Mustang. In the end it turned out to be mostly caused by a hugely out of balance ali spinner. I reckon this could well be the cause of a lot of your problem. £27 is a lot to pay for an item if you have to completely re-work it. My friend ended up throwing his spinner in the bin after extensive dynamic balancing failed to sort it out. Hope this helps a bit.

[Tim Mackey]

I agree that the spinner is the most likely culprit, but ( wrongly apparantley) thought you mentioned earlier in the thread that DM2 had run it up without the spinner and it was still naff ?

 "I removed the complete spinner assy and ran a different 15x8 Graupner prop on it's own (that balances perfectly), only to find that the vibration is still there..bent prop shaft on a new out of the box Laser..?...I wouldn't think so, would you..?"

[David Martin 2]

Thanks for your response gents.

As Timbo rightly says, last Wednesday I removed the spinner/backplate completely and tried a different Graupner 15x8 prop only for a level of vibration to still exist, it was an improvement (sorry for any confusion) but still not as good as I would like and get from my only other 4 stroke..an OS.

The main problem appears to be the grooves on both sides of the backplate are engraved as a spiral that to my knowledge won't mesh with any prop driver or prop I've ever owned..! The two mating surfaces (prop driver/backplate back and prop/backplate front) sit proud on the teeth or sink into one another in uneven places causing the backplate to not sit square on the shaft. The outer edge of the 4 1/2" spinner only needs to be 1mm out per revolution for the model to shake unbelievably, the point of the spinner is the obvious place to see the discrepancy.

I have persevered in turning the backplate/retightening/measuring until I got it seated as good as I could get and the level of vibration has now reduced to that what I experience with my other models and I would concider useable. Lets hope I don't need to remove the spinner backplate at the field one day..! (30 miles from home.) I have keyed it's position with a marker but I probably can't rely on that too much.

Not an entirely satisfactory conclusion but operational. I would really like to have the backplate's spiral grooves completely smoothed off in the lathe and have it engraved to match my prop driver and prop but how can I do that..??

The plane looks doomed at the moment as for some stange reason I have bad glitching now on the ailerons..only..! Never been present before and too bad to fly. Still the same indoors to where I tested it earlier in the day...Oh for the squirt and go of the Acrowot..!

My main thoughts are towards the extension leads causing voltage drop or noise pickup from somewhere. I'm careful to illiminate any metal to metal contact during any builds so this is a little frustrating after the vibration issue to say the least..!

Thanks for your input chaps.....David

[Tim Mackey]

David. Removing the serrations on the spinner backplate shoul

d be possible, or alternatively could you fill them in with isopon or similar, and then have the surface turned down smooth? I could do that for you if you need.

However, if you have tried removing the entire spinner assembly including backplate, and run her up with JUST the prop attached and still have an issue...then there is still a problem huh.

As to you glitchy ailerons, IF this problem has only just appeared, and all was consistently fine before, them something has changed. Even slight repositioning of components, or leads should be investigated. If you believe that lead length is the cause, then either try ferrite rings ( I have a bunch of them here going free if you email your address, as I dont use any of this sort of stuff since I went 2.4Ghz ) or if you feel your model is worth it and it probably is, then use a powerbox style device.

[Doug Ireland]

Sounds to me like the spinner/backplate may indeed have bent the crankshaft. It would only need to be a few thou out to make it run like a bag of nails. If David has access to a lathe (as he said he has) then why not take the crankshaft out and put a clock-guage on it?

[David Martin 2]

I'm going back to the field tomorrow Timbo and have another look..I've tried so many little adjustments and variations that I need to go back to basics I feel. This has been going on for a while now...but...

My ex Rolls Royce lathe mate has kindly offered to mill the back of the spinner flat for me (luckily the serrations are proud of the backplate so can be milled off), and if I let him have the prop driver, he will kindly mill a matching pattern on the plate for me.

What do others do..? I was thinking of asking him to let me try it when the serrations have been milled off to a smooth finish but I should think I would need some form of grip surely..? Maybe the soft ali plate could be marked sufficiently when tightened up against it driver..? Thanks for your kind offers Timbo.

The only time that I connected up the electrics in the wing before was to set up the throws and directions of the aileron and flap servos, about 6 weeks ago. All seemed ok then.

When I done the first engine test, I just bolted the wing on and my time has been taken up with the vibration issue. I connected the wing electrics again on Friday, when at my Father's place to run the engine and see whether my tinkering had improved things but the ailerons were constantly glitching, engine on or off, all the time badly. Even as I moved the aileron stick through full deflection they still done it.

When back in my house, they were still doing it so I leant the wing to the side of the model with it still chattering away and touched a few of the leads. As soon as I slide the aerial from down the body, all stopped. For the rest of the weekend it worked perfectly after rerouting the aerial, so feeling it was very strange to only effect the ailerons, I excepted some kind of odd noise problem. Back up my Dad's to put another half tank through the Laser, switched on (full charge again - 4.8v JR pack) and ailerons and now flaps were going mad..!

Oddly, only one flap was sometimes glitching,  they go through a common Y lead to the Rx...so maybe I can suspect a lead problem..? All other channels were fine still except the wing. Back home it still done it again with no moving of any available lead improving things at all. I could have the aerial facing the moon and they still done the jitterbug....Then...an hour or so later...all was ok again...! I'm now suspecting maybe a temperature issue could be going on....I'm going to swap all 4 wing servos for my trusty old Futaba units and try again.

I've never had to use ferrite rings Timbo but I may take you up on your kind offer in future if need be.. My model has cost £850 to date so it's got to be right before I fly it.

Pity I can't seem to add pictures Timbo, all would be a lot clearer...honest..!

[David Martin 2]

Sorry Doug, I was adding my last message above when yours came through.

Yes, clocking it is a possibility, but the engine isn't that old and I'd probably contact Neil Tidey before dismantling if it came to it.

Cheers.

[Tim Mackey]

David. Posting pictures is not the easiest task on this site, but heres how. First post them to a picture hosting service such as IMAGESHACK. Then when on that site, find the picture you want to post, "copy" the "direct link" ( the picture will have several link types available ) and then come back to your post. On the red topbanner above, you see a picture of a tree? - click it, and then "paste" the link you have into the dialogue box which opened. Then "Insert" the picture, and presto!

Incidentally, how many servos are you running in this rather large model? A bog standard 4.8V receiver pack seems a little frugal to me, and you should really consider something better for your expensive pride and joy. This thread here is well worth a read right through.

http://www.modelflying.co.uk/forum/forummessages/mps/UTN/1787/URN/3/dt/1/srchdte/0/cp/1/v/1/sp/

HTH

PS email me via the site and I will send you the ferrites...it may just help. I know one thing for SURE, I would NOT commit this bird to flight until I was 100% sure that the radio system is spot on !! 

[Tim Mackey]

David. Having decided to try a larger diameter prop on my Spit, I was in the workshop this morning and after removing the old prop and spinner thought that it may well be the same spinner /backplate as yours! Upon removing it, I noticed a slight lateral movement of the backplate on the crankshaft, and have decided that the hole is slightly oversized. This has probably happened due to "wear and tear" but I decided to rectify it, especially as it looks as though the new prop choice of a Graupner 14 X 7 means I need to make a bush for that too - the hole is too big for the crankshaft!

It occured to me that this backplate bush may be your problem too ? That i, if indeed yours has one.

I have decidedto turn a new one in the lathe, and attach a picture of the backplate and old bush  - is it the same as yours ?? ( The picture is clickable to get full size) 

[David Martin 2]

Hello Timbo...you should have received a PM from me today hopefully regarding the ferrites, thanks very much.

My model runs 6 JR 591's on the main functions (due to their 5kg rating) and standard JR servos for the retract valve and throttle, 8 in total..

The Powerbox thread makes interesting reading...this Spitfire could make the grand after all..! It's my first model in 25 years going 14lb and using the 2 switches on top of the Tx. My heli's, slopers, WWl Pup and Acrowot sized stuff seems to have just chugged along fine all these years, but this 72" model is giving me grief at the moment.

 My spinner has got a brass bush in the centre but thankfully is a tight fit on the Laser's 8mm shaft (being unflown so far). I got it from Inwood Models last year, the 4 1/2" Ali spinner in their range. All looks very good quality but has the wrong keying pattern to the prop driver. My lathe mate milled off the original grooves last night and added some new ones..! 51 teeth on a Laser 120 prop driver face, believe me, I counted them about 20 times..! I'll see how the vibration looks with that.

Tried the Spitfire ailerons indoors again last night and all 100% again. Could be a power issue in the cold I suppose. I'll get around to swapping the servos, one side of the wing at a time, then the extensions to see if anything happens. I'll definitely not fly the plane until I'm totally satisfied with it's operation.

Please read my PM to you regarding the photos..thanks.

[David Martin 2]

Just seen your photo of the backplate Timbo....yes that's the same as mine..

 I had the key pattern milled off mine last night..

[Ernie]

Hi, David,       You've gone very quiet     is it sorted?          That cognac is needing a home

ernie

[David Martin 2]

Hello Ernie...good news with the radio glitching...caused by a u/s servo spreading noise to the leads and upsetting the other wing servos. Tried the u/s one in place of some of the others and the glitching comes back. Replace that servo only and all ok.

 I've never been happy with the new 591's buzzing, even at rest, so I've dug them all out now and replaced the lot (6) with new Futaba 3010's. Bit of an investment but I'm happy now, all quiet and fast with plenty of torque.

I've also uprated the Rx battery now and switch.

Sorry, Timbo, the ferrite rings were beaten this time..maybe next time, I'll return them if you want them back mate, please PM me your address if necessary.

I'm still in the process of replacing the bits and bobs around the tank, but soon as I have, I'll try out the new spinner backplate...weather permitting..!

I'm sure it'll still be the same though Ernie, best get it ready...

TTFN

[Tim Mackey]

Ah glad you have it sussed - nothing scarier than an erratic radio problem! Keep the ferrites mate no problem

[David Martin 2]

         Good man...

[David Martin 2]

Managed to run up the laser again yesterday and the level of vibration is about on par with my other models now.

I put the milled backplate on and gave it a good old tighten up to the prop driver, this has keyed the driver's pattern nicely onto the backplate and seems to grip it ok. I could probably get the vibration better by balancing the spinner but I think I'll give the model a few flights and see if it actually goes..!

The radio glitching problem has been cured 100% and the voltspy monitor stayed in the top 2 green LED's throughout the 1 hour engine and radio testing, so hopefully the upgrade battery is just the ticket to run the 8 servos.

Looks like you'll have to drink the Cognac yourself now Ernie over Christmas...

 Thanks to all for your help and suggestions on this thread.

[David Martin 2]

Maidened the Spitfire yesterday and found it very solid in the air. Can't say the same for on the ground though..!..3 out of 5 take off runs ended up biting the dust. I need to learn the art of elevator control when I have a full tank up front I feel..

The landings all came to a stop on 3 wheels and were a piece of cake with the flaps deployed. A curved approach then 1/3rd throttle until the ground came up to meet it. When the speed had bled off a bit, I flicked up the flaps and held in full up elevator to keep the tail down until it stopped.

The vibration is acceptable now with the milled backplate and the radio all played ball. The Laser 120 needs to be leaned off a bit though to give more power, a lot of the flight was with full throttle and pretty rich, but made for a scale speed. Pretty economical too using 1/8th of a gallon of 10% Coolpower for 2 x 12 minute flights.

[Tim Mackey]

Great! We want pictures  we want pictures!