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Old Apr 04, 2005, 12:57 PM
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Belle Mead NJ
Joined Mar 2005
71 Posts
HF DG-600 servo choice help.

I just ordered a HF DG-600 (2.7-3.3 m) from John at EMM (excellent service) and should receive it in few weeks.
It gives me time to think about servos to use. I already have 2 Futaba S3102 (51.4 oz/in @4.8V and 0.7 oz weight) that I plan to use for ruder and elevator. These are micro servos, somewhat powerful but not that fast: 0.26sec/60deg (can’t have everything…) but probably fast enough for smooth flying.
I was thinking of something even lighter for the ailerons, what do you consider to be the torque lowest limit? Any other advice, tips etc on building issues, settings etc are welcome.

Thanks all,

Fabrice
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Old Apr 10, 2005, 05:35 AM
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Zürich
Joined Feb 2003
166 Posts
Servos

Hello Fabrice

I used the Hitec 81 mg in the wings of my DG, they are strong, have very little play in the gears and are very reasonably priced. Two tips: 1. check the incidence angle before you fly, my DG had more than 3° which will make it almost unflyable with the CG as per instructions. The incidence should be around 1.5° or slightly less. 2. This model wants to be flown and any dawdling will see the tail overtaking the nose without any warning and you suddenly won't be having fun anymore.
It is a beautiful model and flies well when it is correctly set up. Are going to fly it on a slope or in the flatland?

Regards fron Zurich

Daniel
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Last edited by Daniel Gut; Apr 10, 2005 at 07:37 AM.
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Old Apr 10, 2005, 12:39 PM
That Freeking Laird Guy
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United States, CA, Riverside
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Put the 3102s in the wing too. There is no use risking an expensive scale model by trying to save $10 on a servo. The HS-81 servos have a terrible reputation (well deserved). They have a nasty tendency to not center after a few months of use. The case is also not very strong and if you jar them hard enough you can elongate the hole in the case that the gear shaft goes into. I have had both these problems with the 81s. You can do a search here in RC groups and you will find multiple threads about those servos. The HS-85s are better but they are about the same cost as the Futaba servo and the futaba is a better quality servo.

TFLG
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Old Apr 10, 2005, 01:07 PM
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Zürich
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Hs 81 Mg

In defense of the HS 81 MG, mine have behaved excellently for years and I have never had a reason to doubt them, the HS 85 that I had in my ORGANIC for the flaps on the other hand was miserable (not metal gear). The HS 85 MG has also been reliable.

Regards

Daniel
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Old Apr 11, 2005, 09:02 AM
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Belle Mead NJ
Joined Mar 2005
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Thank you all,
I'll check the Hitec servos. My goal is to save weight, no so much money and I agree that safer servos make a lot of sense.
The S3102 (51oz/In) weights about 0.7 oz but everything else I could find that is lighter has significantly less torque (~17oz/In i.e. 50% of the HS85…) and I was wondering if it would be too weak.
I’ll fly this DG-600 mostly on flat land (histart) since slopes are a bit far away. Therefore I’m really looking to improve the minimum sinking rate and I want to keep it light. I’ll add ballast if I found a decent slope…
Does the wing extensions vs winglets configuration changes the flying characteristics or just the look?

Fabrice
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Old Apr 11, 2005, 09:23 AM
That Freeking Laird Guy
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17 oz seems pretty wimpy. I need over 40 on my small 48" span PSS slopers. I calc'd out how much I needed for my DG-1000 and came up with about 30oz as a worst case number. You DG-600 is probably about the same. I always like to have a little extra as you never know what's gonna happen once you get the plane up.

You can use this servo torque calculator.

http://www.csd.net/~cgadd/eflight/calcs_servo.htm

You input the numbers and it calculates how much torque will be required. Make sure you put in a nice high number for the speed as the planes can really scoot when shoved into a steep dive.

TFLG
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Old Apr 11, 2005, 10:17 AM
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Zürich
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Weight

Hello Fabrice

The few grams that you will save on servos will have very little effect of the DG. The correct setup is going to be a far more important factor. The sink rate is good when you allow it to fly a little faster with a good setup.
The DG is very scale and thus the tailplane is really small, this makes highstarting a bit more tricky and it takes a little getting used to. On letting go the nose goes vertical before the plane can build up any speed (hook on the bottom of the fuselage and small surface area of the tail plane) It is in this initial phase that it is stalled for a split second before the tail pushes the nose back down and the airflow can become laminar. If the flow on one side becomes laminar before the other the dg will will want to break out to the side. Having said that, I never did any damage to mine, but it did go pear shaped a few times and it got quite close to the ground. It might be worth considering two hooks on either side of the fuselage just under the wings to reduce the initial asymetrical pull of the elastic. Here is a video that has been edited to cut out that first phase, but you will see at about 21 sec. that it is just coming out of its nose up position before it bites in and starts to climb http://www.lenger.de/cgi-bin/neu_web...=7517362_14715
The most noticable difference with winglets vs extentions is the roll rate, I flew mine mostly with the shorter span.

regards

Daniel
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Old Apr 11, 2005, 01:08 PM
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Belle Mead NJ
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Winch Hooks

Hi Daniel,
Indeed I also thinking of adding flaps on the DG at some point. I’ll probably not do it right away but that was an other reason to save weight. I’ve read threads on this forum about adding flaps on the DG-505 it seem to work very well, but the 505 has a different airfoil (HQ3/15). Have you done or heard about such modifications?
What is true for most scale sailplane applies certainly for the small DG-600: winch/histart launch is safer with a bridle and hooks both side of the fuselage. (see ISSA ).


Fabrice
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Old Apr 11, 2005, 03:02 PM
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Zürich
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Flaps

Hello Fabrice

The DG has a S3010 going into an S3021, these are fairly thin profiles and have a straight underside which is not really suited for flaps, in theory that is. (I think these were originaly HLG profiles). I did not add any to my DG. The biggest advantage you would gain by adding them in my opinion would be the possibility of using them in a butterfly configuration for landing, but if you have ordered the arf version it already has spoilers and they work well. As you can see the HQ 3/15 is very different and has a very rounded underside, it is an excellent flap profile.

Regards

Daniel
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Old Apr 11, 2005, 03:24 PM
That Freeking Laird Guy
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I added flaps to my MPX DG-600. I fly primarily on the slope and the flaps are fantastic in the butterfly mode to slow the plane and control the decent. I doubt I would use this mode while flat-land flying though as it might slow the plane too much leading to a nasty stall. On the slope we usually have a nice headwind which helps keep the airspeed up.

TFLG
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Old Apr 12, 2005, 10:29 AM
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Belle Mead NJ
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Thank you

Hi,
Thank you all for these tips. I ordered the DG-600 with sheeted foam wings and it’s not supposed to have spoilers (at least according to descriptions I could find on the web) but if it comes with it, that would be a very good freebie!!!
I wasn’t thinking about flaps for the butterfly capability (although it’s a good idea, not really scale-spirit but that could save critical landings) but rather as cambers to improve thermal properties by improving sinking rate to the detriment of L/D. I feel that for these rather small sailplanes sinking rate is more important than max L/D since we can not fly that far to try to catch thermals and need to exploit rather wimpy ones as long as we can. On the slope the story is a bit diferent since we are flying mostly at maximum LD.
But Daniel has a very good point; the thin S3010-3021 airfoil is probably not the best option for flaps anyway. I’m eager to fly this plane since beautiful days are finally back here in New Jersey.

Fabrice
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