Wich aileron and rudder servo for 6V in a Skymaster/Fei Bao Hawk?
This should be a mini (not a usual wing-) servo, digital, and the highest possible holding strength.

JR 3421`s will work fine.

I have jr 3421's on ailerons and 3301 on rudder

Hello.

I use the JR DS3301 on rudder as well.

I got it from Al's Hobbies. http://www.alshobbiesstore.com/acata...gregor_93.html

Graupner has the same servo. It's called DS3328. I've used them for years with great succes.
http://shop.graupner.de/webuerp/servlet/AI?ARTN=5157

Torque is 4 kg, holding power is 9 kg.

[X(] Hey guys, I do not wish to be the harbinger of doom but the 3301 is suspect in my opinion. This is a servo made by Hitec for glider wings. We had a guy loose a SM Hawk earlier this year due to one of these servos failing. The gearbox stripped. Now I don't know if they put a better gear set in for JR but the gears in this Hitec servo appeared to be aluminium. The servo being stripped caused the rudder to flutter so violently that the fin integrity was lost and with no directional stability, the model was lost. My club has now banned this servo for jet control surfaces. BTW this was the Hawks 1st flight and built by a guy who builds real aeroplanes, his installation was excellent. It was also scrutinised by two other pilots as is our club protocol and it was found to be fine, so we are sure that the servo was the cause, not the effect.
We are now using the Multiplex slimstar servo in very slim space applications. The output arm on this servo needs beefing up as it is flimsy but with that done it works well and we have a couple of Hawks flying with this arrangment. This servo has Brass gears.
Regards,

John.

I`ve used the white, strange and flat MPX servo for some years, but want to try something else.
Thanks everybody.

JR 8411 would work great

Thanks! I`ll take a look at the spec`s.

Maybe this should go to another forum but banning a specific mfgr's model of servo? That's a pretty serious position for a club to undertake.

Mike

Yep it is a pretty serious position to take. But this jet crashed 100 metres from the boundary to an the local air museum, full of families enjoying their Sunday afternoon. There was no one where it actually crashed, but on a different day there would have been a fair, again with families having a good time. To make it clear, this crash position was about a mile away from the flying area, well beyond the normal flying boundary because without a fin the model was out of control. The pilot was complimented for struggling to avoid crashing within the boundary of the air museum.
Serious! I'll tell you what serious is. Serious is standing in a coroner's court explaning to greiving relatives why their loved ones were killed by a model jet. That's about as serious as it gets Mike.
In comparison, banning our members from using a perfectly good servo (I use them in gliders myself) in a situation that the manufacurers never designed it for, and for which we have evidence it is not suitable for, does not really compare now does it?
Members are quite free to use this servo in non jet applications where we do not anticipate problems.

Did you ban the 8611A too???

What about it?
I use them alot...

I get the seriousness of the situation and the objective intent of the club.

My understanding now is that the club has adopted - let's say - an "application engineering oversight" posture that resulted in this case with a specific servo being banned from one application. In exercising this rigorous posture of due diligence over its members and how they construct their airframes, is there going to be a problem for the club if it fails to prevent a future application failure? I'm not criticizing here but I'm curious about potential blow back from a well-intended approach . . .

Mike

I appreciate your warnings..

According to Horizons site, the 3301 appears to have an all nylon geartrain. I've been looking at the 3301 and 3421 for an F-15's aileron and rudders. I dismissed using the 3301 on a flight surface because it is not a metal geared servo. JMO

Marty

Hi,

I have lost my Hawk at an Airshow this weekend due to 3301 servo's on ailerons! I have been flying the Hawk many times with these servo's but on a high speed upwind pass both ailerons flutter and parted with wing. With no directional control heading for crowd i had to pull vertical going into loop. Crashed it down wind far from spectators.

Lesson learned!

Regards

Morne

Hi John,

I think the 3301 is a JR product only . Could you possibly mean the DS 168 as seen here ......http://www.jrradios.com/Products/Def...ProdID=JRPS168

Marc

what about futaba s9650

Use the JR 9411 on the ailerons, you will have to do some work here, but they fit and the JR 3421 for the Rudder, again, you will have to do some work here, but it fits and for the flaps use a standard JR servo like the JR 8411, JR 8611, something with about 100 oz of torque at 6Vs or more.

This set up is very solid.

Morne..... Rudder cant be used for directional control???? [sm=50_50.gif]

I guess that's why rudders are mandatory in USA.... Sorry for your loss Morne.

Alejandro

John - I agree that the club has the right to do whatever it deems necessary to protect not only the club site, but most importantly the lives of anyone nearby.

I am, however, a bit puzzled by the above. Maybe there are salient facts missing, but given what I've read so far, my take on the would have been somewhat different than banning a given servo...

So, the model crashed a mile away from the flying area, with the pilot struggling with the aircraft the whole time, right ? Why was he fighting to keep the aircraft flying ? Once flutter occurred, surely the first thing that should have been done is retard the throttle to idle, or even kill ... at this reduced speed it would not cover the ground as fast, giving more time for the pilot to realise that he should plant it before it got to be a whole mile away.

I know hindsight is always 20/20, and I know that we may be missing some important details here, but I just wonder whether the corrective action by the club should have been not to ban a given servo, but to require you to all use spotters who in situations like this remind the pilot ASAP about the need to make any "sacrifice the aircraft" call sooner rather than later ... and if necessary, for the spotter to be authorised to reach over and shut down the engine if the pilot gets tunnel vision.

Gordon

Yes Gordon,
Quite a lot of facts missing actually. You cannot know the layout of our field or the special problems that it poses. The idea that we should have spotters is hardly an original thought. It is a club rule that everyone has a "qualified" spotter for evry flight.
The reason that the pilot had to fight the model is not that he needed to be given advice; he started his approach as soon as he knew about the problem. Base leg is parrallel to the museum boundary. So far,so good. As the model slowed down the reduced fin area caused the model to depart normal flight. Before he could blink the model was over the museum airspace. Whatever happened the model must not crash in the museum, so the pilot throttled up again and managed to get the model away from the museum.
The fact remains that the cause of the failure was the use of an innaproprite servo, not a bad servo, just not the right one for that purpose in our opinion. People may think we are being heavy handed and they have a right to their opinion but we have done as we see fit to protect our club. Period!

Morne..

Just a question.
Why blame the servos if there were flutter in the ailerons?
I do not think you could find any servo thet will survive flutter in the ailerons.

Maybe the weight of the aileron is to high and possitioned in the wrong place?

I am no fan of small servos, but to blame the function of it because of to heavy loads is not fair.

Regards and a Merry christmas and a happy new year.

Anders Wikman

May be I have lost the plot, but I just don't get WHY so many of you guys continue to use marginal servos when, with just a few extra dollars/ pounds you could use a servo that is more than powerful/suitable enough to meet the requirements of the aircraft in question. Time and time and time again, I hear of servos suffering from control surface flutter, being unable to cope with jet speeds etc and yet perfectly good, powerful servos with metal gears are readily available at little extra cost . I got it in the neck from some of the BVM police when I questioned the original Bobcat servo spec., (its the ONLY thing Bob got wrong on this otherwise superb machine) they had to eat their words when 3301s and 3421s proved, in some cases, as I had predicted, to be inadequate and failed.

Funny thing is, I have yet to hear of ANYONE reporting the loss of a jet model because the servos were too powerful for the control surface. If there is ANY doubt about the power/suitability of the servo, there is NO doubt, use a more powerful one, hardly rocket science !

Merry christmas !

David Gladwin.