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SC 120FS - will it pull the larger Black Horse Chipmunk

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Peter Eve07/07/2011 11:03:44
77 forum posts
16 photos
I have an SC120FS lyinh idle as a result of my incompetence! I fancy a Chipmunk but the smaller BH model would appear not to need such a large engine. The 45cc petrol version is only a few inches bigger than the RM276 plan version which seems to take a 90.
has anyone any suggestions, please?
Martin Harris07/07/2011 11:58:49
7564 forum posts
188 photos
It does seem a bit OTT - certainly if you're looking for reasonable scale performance. I wonder whether the tail has been built heavy to counteract the engine weight or if the battery is designed to go quite far back? If the latter is the case then I would imagine that with the 120 you should end up with a lighter overall package which probably is no bad thing.
My Airsail Chipmunk:
(quite a bit smaller at 1/6 scale - 69" span but not particularly light at 8 1/2 pounds with on-board glow etc.) is adequately powered by an OS 52 - although many people overpower these models with 70s and even 90s. I use not much more than 1/3 throttle for take-off to avoid it getting off in a couple of lengths, which looks most un-scale like. The designer told me that the prototype flew on a "well used OS40FS" and I can easily believe him.

Edited By Martin Harris on 07/07/2011 12:05:16

Lee Wilson07/07/2011 16:08:49
452 forum posts
258 photos
Saw one at the field over the weekend with a 26cc petrol in it and that had plenty of power. Reckon if you put in the recommended engine size you could prop hang it
Biggles' Elder Brother - Moderator07/07/2011 16:50:53
15228 forum posts
1407 photos
I have a OS91FS in the smaller BH Chipmunk and although the extra power is fun, it is, in my opinion, overpowered. The full "scale-like" flight envelop can be done on 1/2 to 2/3 throttle.
In my view a 70FS would be fine in the smaller one. Given that, I can't see a 120 failing to deliver the goods for the larger Chippy - especially if you are a fan of scale-like flying performance.
Danny Fenton07/07/2011 18:39:46
8489 forum posts
3443 photos
I have a fairly small electric motor in my big Black Horse Chippy and its fine if you are happy with scale aeros. I have to enter a loop from a shallow dive, but to me that's fine.
Andy Glover has been campaigning one of these Chipmunks in flying only at scale comps all over the UK, with great success. The motor he uses.... an SC120

Mine weighs around 11lbs and is a great flyer. Ditch the pilots though they weigh nearly a pound.

Alan Cantwell07/07/2011 18:40:25
3039 forum posts
my 88" span miles sparrohawk is fitted with one of the original OS 120 four strokes, it easily well powered, a 1/4scale all laser cut out with big holes everywhere chipmunk would should be easily powered by one of the modern 120s, should do the simple aeros the full size was cabable of in the hands of a cadet,
Peter Eve07/07/2011 18:58:03
77 forum posts
16 photos
Thanks, chaps, that was a swift response, I think i take that as a "go for it"
Happy landings
Redex18/11/2013 10:11:20
143 forum posts

Hi Danny, I know that this is an old thread, but I too am interested in an electric BH Chippy - so just wondered if you can recall what your power train setup was and roughly any flight times.

Many Thanks.

Danny Fenton18/11/2013 10:45:46
8489 forum posts
3443 photos

Hi Redex, my Chippy is still going strong. The motor is quite small, it being a Turnigy SK4260 x 500 developing around 1300 watts on a 15 x 10 at full throttle. The cells are Turnigy 2 x 5S 5000mAh in parallel to give 5S2P the flight times are between 20 and 30 minutes depending on how much you throw it around. But over 40 flights an average flight is 7 minutes and uses around 2300 mAh.

I noticed the new version has a different method for mounting the oleos, hopefully it will be a bit stronger. I managed to knock a leg out sideways by landing in too strong a crosswind. I have subsequently fitted some Unitracts oleos, they make the ground handling so much nicer.

If you need any further info just shout wink 2



Danny Fenton18/11/2013 10:55:46
8489 forum posts
3443 photos

Hi Redex just thought, you may not know there was a build blog on this forum for my leccy Chippy .



Redex18/11/2013 12:20:35
143 forum posts

Hi Danny,

Many thanks for you response - sorry should have searched first, but a great build log and with the suggestion of A123 usage, which also interests me.

Danny Fenton18/11/2013 12:45:58
8489 forum posts
3443 photos

Hi Redex, I never used A123 in this one in the end, I have a few 5000 lipo packs, so always have used them. I have also subsequently made some lith leg fairings which are much more scale in appearance. I was a bit surprised that I haven't shown pics. I will correct that when it is next out flying thumbs up



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