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Vibrations Log - SAB Kraken 700 Tri-Blade


andythilo
(@andythilo)
Active Member Customer
Joined: 2 months ago
Posts: 7
Topic starter  

Hi

Did my first maiden yesterday, well short maiden as it was really windy. During hover I noticed some vibrations in the landing gear so downloaded the log this morning. Screenshot shows the highest peaks which I presume are well within spec? Does this look acceptable? Headspeed was still quite low while I'm doing my initial flights.

I know it's dangerous to look at too much information and just fly the thing lol but I do like to know it's mechanically good.

Also the Kraken KSE is the tri-blade and as such I believe I should run a much lower cyclic gain? I've put it in the software as >2 blade and 670-806mm and cyclic gains are all auto set to 12. Anyone else with a Tri-blade know if this is ok?

Thanks

Andy

Flight 77 Vibrations

 


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BrainDev
(@customercare)
Member Admin
Joined: 3 years ago
Posts: 672
 

The vibrations seem to be acceptable even though there are harmonics present at both the main and tail rotor rotational frequencies that would indicate incorrect tracking of both the main and tail rotor blades. However the harmonics have acceptable amplitudes as well.

The RPM (1534), even with a three-blade, is a bit low compared to the 1800 RPM recommended in the manual when using the "D" "full rigid" derlin dampers supplied as standard and therefore designed for high RPM. Landing gear vibrations could almost certainly be caused by this.

Before changing the dampers to softer "C" dampers suitable for lower RPM values (in this case please read the manual advice about tail authority and longer tail blades flying at RPMs below 1800), you might try to use different RPM values, higher or even lower. The currently used RPMs might correspond to a resonant frequency of the model.

Reminder: if in addition to the single screenshots you all always send also the .csv file of the flight, the configuration file and the event file (as explained in the support stiky), we will be able to analyze the entire flight from takeoff to landing, the configuration values and provide you all more information and more support.


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andythilo
(@andythilo)
Active Member Customer
Joined: 2 months ago
Posts: 7
Topic starter  
Posted by: @customercare

The vibrations seem to be acceptable even though there are harmonics present at both the main and tail rotor rotational frequencies that would indicate incorrect tracking of both the main and tail rotor blades. However the harmonics have acceptable amplitudes as well.

The RPM (1534), even with a three-blade, is a bit low compared to the 1800 RPM recommended in the manual when using the "D" "full rigid" derlin dampers supplied as standard and therefore designed for high RPM. Landing gear vibrations could almost certainly be caused by this.

Before changing the dampers to softer "C" dampers suitable for lower RPM values (in this case please read the manual advice about tail authority and longer tail blades flying at RPMs below 1800), you might try to use different RPM values, higher or even lower. The currently used RPMs might correspond to a resonant frequency of the model.

Reminder: if in addition to the single screenshots you all always send also the .csv file of the flight, the configuration file and the event file (as explained in the support stiky), we will be able to analyze the entire flight from takeoff to landing, the configuration values and provide you all more information and more support.

Thankyou for the response. I'll swap out the D dampers for the C and see how she is. I'm certainly not (capable) into Hard3D :). I'll look into the longer tail blades as well.


BrainDev liked
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