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How to fix acoustic interference on gyros in jets?

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How to fix acoustic interference on gyros in jets?

Old 03-19-2022, 10:34 AM
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authomassen
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Default How to fix acoustic interference on gyros in jets?

I've just converted an e-flite 90mm viper to K-45G3 power. I'm using a jeti assist receiver, and I'm experiencing what I believe is acoustic interference causing the stabilised surfaces to jitter mildly when the turbine is close to and at full power. As soon as I turn off the gyro, the jittering goes away.

I've read some advice to fix the acoustic interference causing jittering:
  • Mount the RX/gyro using the double sided tape and nothing else (how I have done it).
  • Cover the RX/gyro with the soft side of velcro/hook and loop.
  • Insulate the RX/gyro with neoprene or some sort of dense foam
  • Move the RX/gyro farther away from the turbine
I've done several searches on google, youtube, RCG and here at RCU, but I have not found any other solutions or reports that the above advice actually have worked.

So, what do you guys suggest to be the best fix to acoustic interference on gyros in jets?
Old 03-19-2022, 10:57 AM
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Bob_B
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Make a sound hood from foam rubber

https://www.michaels.com/12x18-foam-...609_color=Gray
Old 03-19-2022, 11:43 AM
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arizcowboy
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Go with a cortex . Never had any problems and I run Jeti
Old 03-20-2022, 03:43 AM
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I use Dynamat. Seems to work well to eliminate these jitters for all my cortex pro's. The foam box is another option but I have not tried it.
Old 03-20-2022, 07:22 AM
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DHON
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Originally Posted by GULDUKAT View Post
I use Dynamat. Seems to work well to eliminate these jitters for all my cortex pro's. The foam box is another option but I have not tried it.
how did you apply the dynamat to your gyro? Or in my case, using it on Jeti assist receiver, should I just wrap around it? How about the expose sidewhere the servo connection goes.

I found this on amazon. Is it good enough
?

Amazon Amazon
Old 03-20-2022, 08:55 AM
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Dansy
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My cortex pro don’t do that…..
Old 03-20-2022, 01:21 PM
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Springbok Flyer
 
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I don't use Jeti, or own any EDF jet turbine conversions.

Apart from all the gyro mounting suggestions, which I'm sure could help - how about turning down the gyro sensitivity and see if that helps.

JanR
Old 03-20-2022, 02:28 PM
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authomassen
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Thank you guys for your suggestions.

Originally Posted by DHON View Post
how did you apply the dynamat to your gyro? Or in my case, using it on Jeti assist receiver, should I just wrap around it? How about the expose sidewhere the servo connection goes.
I'd like t know this as well.

Originally Posted by Bob_B View Post
Make a sound hood from foam rubber
Same goes for this, could you please elaborate with more details? Thanks!

Originally Posted by Springbok Flyer View Post
I don't use Jeti, or own any EDF jet turbine conversions.

Apart from all the gyro mounting suggestions, which I'm sure could help - how about turning down the gyro sensitivity and see if that helps.

JanR
I tried that, but it didn't help very much. I had to turn down the gain so much that gyro is more or less turned off for the jittering to go away.

Originally Posted by Dansy View Post
My cortex pro don’t do that…..
Not any more, but they used to. Bavarian even made their own acoustic suppression hood for it.

I guess the cortex comments are ment to be helpful, but the point of the tread is trying to gather info on how other have fixed problems with acoustic interference, without changing out the gyro to something else. I know the cortex pro is great, and I have it in my bigger jets, but in the smaller and less expensive stuff it would be great to have the assist working without interference.
Old 03-20-2022, 04:07 PM
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Bob_B
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First off contrary to what some may say every gyro is prone to this issue.

Cut the suggested foam to create a tight fitting cover around the rx. Design it so the servo plugs are covered.

Test by setting the gyro gain to high value and then start and run the turbine through its entire range while watching the surfaces for jitters.

sometimes its just one particular RPM the creates noise that makes the sensor go crazy.

i hope this helps.

Old 03-20-2022, 06:25 PM
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I had this same problem with my Rebel Classic and could see and feel the control surface bump in flight. The fuse is very light but basically a hollow tube without formers from the turbine up to the front landing gear mount. I tried the foam box thing and it did not help much. I even sent the turbine back in for rebalancing and it was the same issue. I ended up making my own former and place it mid fuse right under the gyro. Problem solved.
Thanks,
Tone
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Old 03-20-2022, 10:44 PM
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GULDUKAT
 
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Originally Posted by DHON View Post
how did you apply the dynamat to your gyro? Or in my case, using it on Jeti assist receiver, should I just wrap around it? How about the expose sidewhere the servo connection goes.

I found this on amazon. Is it good enough
?

https://www.amazon.com/Dynamat-Xtrem...469739176&th=1

1 word - UGLY. Add it anywhere and everywhere possible. Cover as much as you can. You cannot overdo it. A nighmare to remove but atleast it fix's the issue. Make sure to put it under the gyro as well (very important - under you base plate - plywood/CF/etc.)

I add it in all my jets - I do not check to see if they have the issue or not.

The one of Amazon is ok. I got it from Amazon as well. Pablo @ EA told me this fix a few years back. Big thanks to Pablo.
Old 03-21-2022, 12:29 AM
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CARS II
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This is very interesting, I fly Jeti and have the assist receivers in all 3 of my jets, the acoustics that I can see on my radio screen when I run the engine on all 3 is minimal and that's with the gyro sensitivity turned up to max, been flying them for over a year now, I have not experienced any gyro problems so far.
Old 03-21-2022, 12:54 AM
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authomassen
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A big thank you to you all!

All the different replies about how to fix this had one thing in common, and that's to isolate the RX/gyro from the acoustic interference, using some sort of sound insulation.

I thought I'd give it a go with what I already had lying around. I started by covering the RX with the soft side of self adhesive velcro, and then I added the other side of the velcro to a semi dense foam I had laying around. I think the foam is a packing material from a small electrical appliance. I then covered the RX with the foam, and I also used some scrap foam to cover the open ends where the servo wires are. And what do you know, I could now turn the gain to max without any visible jittering, at any throttle setting! As I stated in the first post, I only had mild jittering, som I probably got away with less insulation than some might need.

I'l probably refine it in some way down the road using either a dynamt equivalent or some EVA foam board, but for now I'm happy with it as it is.

A before and after picture of the fix. And a family portrait.







Last edited by authomassen; 03-21-2022 at 12:58 AM.
Old 03-21-2022, 12:56 AM
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HarryC
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Originally Posted by CARS II View Post
This is very interesting, I fly Jeti and have the assist receivers in all 3 of my jets, the acoustics that I can see on my radio screen when I run the engine on all 3 is minimal and that's with the gyro sensitivity turned up to max, been flying them for over a year now, I have not experienced any gyro problems so far.
You are completely misunderstanding the nature of this problem. The Assist data on the Tx screen is low frequency mechanical vibration of the airframe, not acoustic. The acoustic interference is sound waves at very high frequencies. Also, gyro gain does not have any effect on the level of mechanical vibration recorded by the Assist.
Old 03-21-2022, 01:42 AM
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authomassen
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HarryC, since you're here.

I've found some comments from you regarding this topic in older post, back when Weatronic had similar problems.

Do you know exactly which sound is causing the problem? I've read somewhere that it's the sound of the turbine causing it, but elsewhere someone claimed that it's the sound of the airflow causing it.
Old 03-21-2022, 03:03 AM
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HarryC
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Originally Posted by authomassen View Post
HarryC, since you're here.

I've found some comments from you regarding this topic in older post, back when Weatronic had similar problems.

Do you know exactly which sound is causing the problem? I've read somewhere that it's the sound of the turbine causing it, but elsewhere someone claimed that it's the sound of the airflow causing it.
I have never seen an authoritative statement of the source. My suspicion is the air in the intake. Jets big and model emit a low rumble from the rear but a painful high pitch noise from the intake.
Old 03-21-2022, 09:21 AM
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Bob_B
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Good chance thats the issue Harry.
I have a Cortex Pro mounted between the inlets on my Flex Jet Pro. Never an issue in over a year of flying it.

There is an air inlet on the bottom of the fuse its there to cool an esc .

Old 03-22-2022, 06:51 AM
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RCISFUN
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Originally Posted by arizcowboy View Post
Go with a cortex . Never had any problems and I run Jeti
I am pretty sure that my Cortex connected to my Jeti was the cause of a violent wing wag with my X-45 powered Sebart mini Avanti at about 3/4 throttle and caused a crash, luckily I had power back right away and the crash was repairable.
I agree with Bob B, ALL gyros are prone...
Old 03-22-2022, 07:04 AM
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Originally Posted by Bob_B View Post
Good chance thats the issue Harry.
I have a Cortex Pro mounted between the inlets on my Flex Jet Pro. Never an issue in over a year of flying it.

There is an air inlet on the bottom of the fuse its there to cool an esc .
I think Harry means the inlet of the engine and compressor noise and not the Inlets of the Fuselage
Old 03-22-2022, 07:26 AM
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Authomassen:
since it is small foam model, with air inlets from outside fuselage...
You can try to isolate front section under canopy completely from the noisy turbine part.

Tank blocks almost 95% of connecting site, so only some small pieces of isolation is needed in small spaces around it.

I have jeti assist, foam avanti fw and also k45, seen some rocking and will try to block it around tank first, so rx can stay 'free', tucked between batteries and pump.

Wil report if it works.
Great you solved yours, at least we now have some hint what to do.

Did you try to play with notch filter in jeti assist settings?

Last edited by dr.tom; 03-22-2022 at 08:40 AM.
Old 03-22-2022, 09:04 AM
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authomassen
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Originally Posted by dr.tom View Post
Authomassen:
since it is small foam model, with air inlets from outside fuselage...
You can try to isolate front section under canopy completely from the noisy turbine part.

Tank blocks almost 95% of connecting site, so only some small pieces of isolation is needed in small spaces around it.

I have jeti assist, foam avanti fw and also k45, seen some rocking and will try to block it around tank first, so rx can stay 'free', tucked between batteries and pump.

Wil report if it works.
Great you solved yours, at least we now have some hint what to do.

Did you try to play with notch filter in jeti assist settings?
Good idea, I can try that idea later.

I did not play with the filter, as I understand it the filter is meant to filter out vibration from piston engines?
Old 03-22-2022, 09:46 AM
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Bob_B
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Originally Posted by causeitflies View Post
I think Harry means the inlet of the engine and compressor noise and not the Inlets of the Fuselage
I should have said having ducting shields the gyro from the turbine inlet noise.
Old 03-27-2022, 12:59 AM
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Authomassen:
I observed similar acoustic interference of my Jeti Assist receiver in my Xcalibur-Plus during engine run tests.
Glitches were visible on ailerons and elevators at various engine speeds (RPMs).
When later I tried to show this to another modeller, it was NOT visible with the top cover removed (note: the top cover is long and covers the electronics, fuel tank and engine).

Obviously with the top cover installed, the hollow space enabled some kind of amplification, resonance or a standing wave.
This is typical for most RC gyro's and after some research on the fora, this was solved by:
  • encompassing the receiver with a little box made of medium dense foam (wall thickness about 1 cm or 3/8", but no bottom), and
  • by placing a soft foam "bulkhead" just behind the fuel tank (approximately halfway in the fuselage) which blocks all open areas to prevent resonance/standing waves. The foam bulkhead has a rounded top which fits inside the top cover and is slightly lager to enable proper fitting.
After this, no more glitches were noticable at any givven engine RPM.
Hope this helps.


Last edited by Remco45; 03-27-2022 at 01:03 AM.
Old 03-27-2022, 09:57 AM
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There is a thread somewhere where this particular problem occurs with Jeti Assist rxs.

My su27 was so bad that it was all over the sky during approach... the spool up and low rpms during final approach caused tailerons to snap around...
Old 03-27-2022, 10:05 AM
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David Gladwin
 
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Originally Posted by RCISFUN View Post
I
I agree with Bob B, ALL gyros are prone...
No, they are not !
My zero problem experience :
Weatronics Gizmos with 3 axes gyros, in three Hawks, 2 AW, 1 SkyGate. 1 CARF Mig 29.
Weatronics 12 ch . Gyro 3, in two BobCats and PST Reaction., BVM F4 , F86.
Powerbox.I Gyro 1s. I. BVM F4., PST Reaction and Revision.
Powerbox I gyro SAT in Rotkoski Sabre, PST Reaction ,BobCat. AW Sea Fury.
This is a brilliant gyro with uncanny accuracy in attitude hold.
Plus several other electronic gyros in various model s !
Not a single problem and having used electronic gyros, inc those by JR and Fuzzy since their introduction.
So, no, not all gyros have the problem.

Last edited by David Gladwin; 03-27-2022 at 11:30 PM.

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