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Servos for my jet. Confused

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Servos for my jet. Confused

Old 11-26-2020, 08:49 AM
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Default Servos for my jet. Confused

Hi guys

I bought an f18 1/8 scale turbine jet. Itís the jet legend f18 or BVM F18 1/8th scale.

the model currently has JR DS171 servos on the ailerons and rudders. I was told these are more than enough by fellow pilots.

Flaps have savox Sc-0251 which are rated at 16kg torque.

my concern is whatís the best choice servo for my elevators. I need two servos and want to ensure I put the right servo with more than enough torque.

i currently have sets of MKS HV665 servos and at 6v, I will get 13kg per servo for each side of my elevator.

Is this enough or do I need more torque?

also, has anyone used Savox servos in Jets? How reliable are they if u did use them? I can get savox SC1256tg servos that deliver 20kg of torque for a good price. But not familiar with these in terms of reliability.

thanks

Last edited by [email protected]; 11-26-2020 at 08:56 AM.
Old 11-26-2020, 09:08 AM
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Len Todd
 
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Just a note: My two BVM planes came set up for High Voltage (i.e. 2S LiPo).

Point being: I am not sure if you want to base your servo decision on just 6 volts. ??
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Old 11-26-2020, 09:11 AM
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Originally Posted by Len Todd View Post
Just a note: My two BVM planes came set up for High Voltage (i.e. 2S LiPo).

Point being: I am not sure if you want to base your servo decision on just 6 volts. ??
hi, yes, I know. Would like to move towards HV servos but I know guys have been flying turbine jets on 6v setups for centuries.. most of my colleagues are so used to using older servos that the opinions Iím getting are super varied. For now, I would like to know what the minimum torque requirements are for the elevators. Thatís crucial for me to make a better decision. None of these manuals Iíve seen even discuss this..

thansk for replying.

Old 11-26-2020, 09:15 AM
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You might want to consider giving Rob a call at BVM.
Old 11-26-2020, 09:43 AM
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If you stay with 6V servos I highly the recommend the Savox 1256TG.
Ive used them for several years on various jets.
Old 11-26-2020, 11:14 AM
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Been using Savox in most of my planes. Great servos no issues.
Old 11-26-2020, 01:40 PM
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400 oz-in is a safe minimum for full moving stabs on a jet that size.
Old 11-26-2020, 01:46 PM
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On a full moving stab, I would definitely get the best servo you feel comfortable ($) with. I know it can get costly when all of this starts to add up, but you don't need the highest torque, "best servo" out there either.

I would compromise on the rudder and nose gear if required, but try and get good servos for the flying surfaces (ail, ele & flaps)

Last edited by skunkwurk; 11-26-2020 at 01:49 PM.
Old 11-26-2020, 08:58 PM
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Thanks everyone! Exactly what I wanted to hear.. years of experience counts and glad to know guys using the savox say they extremely reliable.

so far I have had many jet guys saying people are just over killing with servo specs.. (30kg/HV etc). When servos like the savox at even 13kg on this particular jet would be fine on my elevators.

ive been flying 3D helis and planes where torque was everything so just getting used to the jet guys saying a ď13kg servo would be just fineĒ.

The jet already has savox sc1256tgs on the elevator and itís been flying with it just like that.. so will stick with it..

Old 11-26-2020, 09:13 PM
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Originally Posted by [email protected] View Post
Thanks everyone! Exactly what I wanted to hear.. years of experience counts and glad to know guys using the savox say they extremely reliable.

so far I have had many jet guys saying people are just over killing with servo specs.. (30kg/HV etc). When servos like the savox at even 13kg on this particular jet would be fine on my elevators.

ive been flying 3D helis and planes where torque was everything so just getting used to the jet guys saying a “13kg servo would be just fine”.

The jet already has savox sc1256tgs on the elevator and it’s been flying with it just like that.. so will stick with it..
I'd opt for something with more torque than 13kg-cm (180oz-in), especially on a fully flying elevator. You can still obtain 6v servos that have 350oz-in which would be a much better choice. You don't want to encounter flutter at 200mph and have an out of control airplane.
Old 11-26-2020, 09:17 PM
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Originally Posted by FlyJ View Post
I'd opt for something with more torque than 13kg-cm (180oz-in), especially on a fully flying elevator. You can still obtain 6v servos that have 350oz-in which would be a much better choice. You don't want to encounter flutter at 200mph and have an out of control airplane.
hi, Iím sing servos that have 20kg-cm. That should be ok?
Old 11-26-2020, 09:21 PM
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Make the conversion man, 400 oz is safe. I’d bet 350 oz is fine too.

You’d be crazy with 180 oz servos on a full flying stab on a jet that size.
Old 11-26-2020, 09:35 PM
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Originally Posted by [email protected] View Post
hi, Iím sing servos that have 20kg-cm. That should be ok?
I'd step it up to to 25kg-cm at a minimum, but 30kg-cm would be better. The issue with a fully flying stab isn't the power required to move it, but instead the power required to hold it still and resist flutter. You could use 20kg-cm on the ailerons since they're quite small on the F-18. The flaps need 25+kg-cm as well since they're quite large on the F-18.
Old 11-26-2020, 09:40 PM
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Its all about linkage setup ,not servo specs...

1256tg is enough.
Old 11-26-2020, 11:20 PM
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Genlemen, let us keep in mind that for example Philipp Avonds used a Futaba S9202 on the F-15 tailerons in the year 1988 to become World Champion. This servo had roughly 400ounces/inch. Okay, the linkage ration was 2:1, makes it 800ounces/inch. But anyway, it was an analog Servo, and RC batteries could not deliver high peak amps. It is all about the linkage, no play, meaningful arm rations..
Old 11-27-2020, 04:34 PM
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I use MKS DS 1220. Analog LiFe servos. 422oz at 6.6v. Batteries are dual Electrodynamics A123s thru a Jeti CB200. I never have to remove batts for charging, charge in 10 minutes or so and the servos are great. I have never had a single issue using this combo.

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