Annoying Rattles...

[Joe Yau]

Ever since I replaced the ol' ST C.35 (ran at 8000rpm) on my Flite Streak with an OS FP-20 / APC 9x4 set up.  I've been getting a vibration or a resonating rattle at approx 11.5K rpm.. (maybe higher) sometimes 3/4 way into the flight, It usually starts at around between the verticle eight and the hourglas to the end of flight.  Just wondering if anyone has encounter this similar issue?   The Flite Streak has a solid 1/2" balsa fuselage with the 1/8" plywood doublers, and the engine are mountd on 3/32 aluminum pads.   I've replaced pretty much all the parts that has potential to rattle, but so far still no luck..

[Mark Scarborough]

Pushrods, rattle, wheels rattle, sometimes its just the resonant frequency that comes in due to the reduced mass of fuel burn. It can also be a monokote rattle, I have heard it make some very convincing rattle sounds

[Ron Hopping]

could be the engine the fp is non ball bearing.i have had several os engines from the fp line and had vibration trouble,not bad but noticeable vibration.

[Crist Rigotti]

Could be the wheels making noises.

[Joe Yau]

Thanks for all the replies.      

I think the fuel tank does have something to do it.. like damping the vibration when its full. I have replaced the bellcrank with the Sig ones (much tighter tolerance), and checked the wheels, pushrod ends, ball links etc.  I think its coming from the Monocoat, as the wing resonates.   maybe I should try a CF or wood prop, or maybe a 3 blader and see..  

[John Witt]

Joe,

If you think it's the Monokote, try putting a couple of spanwise strips of masking tape on the wings to dampen the Monokote a little and see if the noise reduces or goes away. Flite Streaks have a pretty narrow section (ie; not too stiff) where the profile front end meets the wing and it may be that as the fuel burns down the vibrating mass of the nose raises its natural frequency enough to cause something else to resonate with it.

John Witt

[Richard Grogan]

Could it be your tip weight? I've had that happen before...

[Air Ministry .]

 Detonation ? nother head gasket .

[Joe Yau]

it may be that as the fuel burns down the vibrating mass of the nose raises its natural frequency enough to cause something else to resonate with it.

John Witt

Yes, I believe that's what it was doing. 

Could it be your tip weight? I've had that happen before...

I have check it and it seems fine.   

Detonation ? nother head gasket .

Ya know, I think Matthew Spencer hit the nail n the head. I have two OS .40-LA-s that do that and it was from too high compression. Sounded like detonation when I first heard it. As the engines neared the end of the flight, they were hotter and the rattle started. Being a mechanic, that's what it sounded like, so sure enough it was. Might try a thin head gasket added to the existing one of about .003". 

Hmmm, I guess wouldn't hurt to give it a try..  thanks 

[Terry Bolin]

you could put some foam behind the tank to soften the contact.

[Joe Yau]

Thanks again for all the replies..... 

Well,  I tried lowering the compression and a few other things, but the noise still didn't go away..      So I put back the ST C.35 engine, and it is fine now  .  But I do sort of missed the run I had tho..  ohwell. 

[Dick Fowler]

You mention that the ST launched at 8K and the FP at 11.3K. Could be a resonate vibrate at the higher frequency. Try needling the FP way down and fly level laps.... no tricks ... and see if the vibration is still present.

[Joe Yau]

You mention that the ST launched at 8K and the FP at 11.3K. Could be a resonate vibrate at the higher frequency. Try needling the FP way down and fly level laps.... no tricks ... and see if the vibration is still present.

I've tried running at other rpms (down to around 10K-10.5K etc), But the APC 9x4 needs to spin at around 11.5K to produce adequate power for the Flite Streak to go through the pattern. Also,the noise was still there.. as it comes and goes depends on the load.

[john e. holliday]

Just load it up and bring it and yourself down to Shawnee Kansas and we will figure it out.  Have you tried a 10-4 prop on it.  The diameter will give more pull and the pitch will slow it down.   DOC Holliday

[Joe Yau]

Just load it up and bring it and yourself down to Shawnee Kansas and we will figure it out.  Have you tried a 10-4 prop on it.  The diameter will give more pull and the pitch will slow it down.   DOC Holliday

Hi John,

Thanks for the offer..    but I don't think its worth it.  Its just my stunt trainer/bad weather plane.  I havn't tried the APC 10x4 on the FP.20 though.  Would I still get the same type of run? (as I get with the 9x4) I think the rpm will be too low for the 2030 muffler to regulate speed properly,  and probably need to use a longer pipe.. 

[john e. holliday]

Joe, I think you will get better pull because of the diameter.  Maybe lose a couple hundred rpm.  By the way APC props are heavy.  Might try a wood prop sometime.   I use them to balance airplanes.  DOC Holliday

[dirty dan]

Ever since I replaced the ol' ST C.35 (ran at 8000rpm) on my Flite Streak with an OS FP-20 / APC 9x4 set up.  I've been getting a vibration or a resonating rattle at approx 11.5K rpm.. (maybe higher) sometimes 3/4 way into the flight, It usually starts at around between the verticle eight and the hourglas to the end of flight.  Just wondering if anyone has encounter this similar issue?   The Flite Streak has a solid 1/2" balsa fuselage with the 1/8" plywood doublers, and the engine are mountd on 3/32 aluminum pads.   I've replaced pretty much all the parts that has potential to rattle, but so far still no luck..

Joe,

What you are hearing is called "pipe rattle." When most people hear this rattle coming from a dedicated and piped PA motor, everybody nods in affirmation of a proper tune-up. When these same people hear this sound from a bottom-feeder 20FP--fitted with a muffler for God's sake!--it seems to confuse them.

I have no idea why you would change the head clearance on a 20FP, especially to eliminate pipe rattle. Further, I have not a clue as to why you would give up a clearly superior stunt run from the 20FP in going back to the ST motor.

My best,

Dan

[Joe Yau]

Joe,

What you are hearing is called "pipe rattle." When most people hear this rattle coming from a dedicated and piped PA motor, everybody nods in affirmation of a proper tune-up. When these same people hear this sound from a bottom-feeder 20FP--fitted with a muffler for God's sake!--it seems to confuse them.

Hi Dan,

Not sure if that is the noise..  as the vibration was felt through the lines. and it has snaped a cupples of Dubro socket heads 4/40 engine bolts already.