Any interest in a "Jupiter Giant"? - Page 3 - RC Groups
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Aug 22, 2017, 12:52 PM
I Look, Listen, and Learn
Timbo383's Avatar
My motor knowledge is very limited and the 15-16 inch prop sounded a little small to me, but a higher kv motor on a 4s or 5s battery would probably work with that prop. I just think it would not look right... "propositional"... with that plane. I think you are right to go with the 20 to 22 incher. Hopefully you'll get some help somewhere with that.
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Aug 22, 2017, 01:07 PM
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Quote:
Originally Posted by Timbo383
My motor knowledge is very limited and the 15-16 inch prop sounded a little small to me, but a higher kv motor on a 4s or 5s battery would probably work with that prop. I just think it would not look right... "propositional"... with that plane. I think you are right to go with the 20 to 22 incher. Hopefully you'll get some help somewhere with that.
I agree completely.

The Bipe using a low pitch prop threw me off as well as the prop calculator calling for 16"

These calculators and "rules of thumb" are not meant for slow flying cartoon planes lol

I think I need large diameter (20-22"), medium pitch (6-8") and low kV (<700).

So far lots of lookers, but no suggestions....No hurry though
Aug 22, 2017, 01:47 PM
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I 'tried' a turnigy sk3 350kv on 3S swinging a 24x12 prop in ecalc, got around 3500g of static thrust @ ~50A IIRC. That's the sort of setup I would use if I built something like this. What weight are you expecting for the airframe without gear?
Aug 22, 2017, 03:02 PM
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Quote:
Originally Posted by IridiA
I 'tried' a turnigy sk3 350kv on 3S swinging a 24x12 prop in ecalc, got around 3500g of static thrust @ ~50A IIRC. That's the sort of setup I would use if I built something like this. What weight are you expecting for the airframe without gear?
Thanks for the reply, I haven't come across that motor in my search for low kV and that is a lot more thrust than my calculations say I need (is that a good thing?).

The 4 x 8 sheets of foam weight 2.7 lbs each and I will use about 3 sheets including waste.

so if we conservatively say only 10% waste that gets us to 6.75 lbs.

With glue, and hardware, let's call it about 7 lbs. without gear.
Aug 22, 2017, 03:44 PM
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I have a (much smaller) quadruplane with that sort of thrust to weight ratio, and because it's so draggy (which I guess yours will be too!) and pitch speed is marginal it does not feel overpowered at all.
Aug 22, 2017, 04:01 PM
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Quote:
Originally Posted by IridiA
I have a (much smaller) quadruplane with that sort of thrust to weight ratio, and because it's so draggy (which I guess yours will be too!) and pitch speed is marginal it does not feel overpowered at all.
Oh yeah, she is going to have some drag, but she should also make some lift, so I am hoping to be able to slow her way down at times.

Off the shelf, I am only finding a 24 x 10 (in the antique prop type I want to use) - what did you use? Is that a problem?

Did you use the Turnigy prop adapter kit? I cannot find the specs on it, the 24 x 10 has a 10mm hole, but I think they will custom drill one if I need something different.
Aug 22, 2017, 11:14 PM
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My plane is much smaller scale, only draggyness of airframe, wing loading, pitch speed and thrust/weight is very similar to the hypothetical setup I posted, so can't give advice on prop adapter for you.

But FWIW my setup is ~700g turning an 11x7 prop on a ~900kv sk3 @ 2S, so same pitch speed as a 12" pitch on 350kv @ 3S. For 10" pitch I would go with a slightly higher kv to compensate.

I do see why you'd want a Xoar scimitar prop though, I have pondered getting one myself but they are hard to come by without steep shipping fee in Sweden.
Aug 23, 2017, 06:39 AM
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Good point

The next one up is 410kV

It doesn't match pitch speed as well as your example, but gets close
Aug 23, 2017, 09:37 AM
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FYI the push for a motor selection is because one of the dimensional issues with just making the plans larger is the firewall location.

the other dimensional issue is making sure I have prop clearance with the floats and with the water.

Now that it looks like I have a motor/prop combo, I would assume I should mount the firewall so that the end of the motor (not the end of the shaft) is even with the front of the fuse?

EDIT: the dimensions I see do not include the motor mount, should I plan on 1/2", 3/4"?
Last edited by Scott in NH; Aug 23, 2017 at 09:49 AM.
Aug 23, 2017, 09:42 AM
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The other dimensional issue is with the height of the fuse with thicker top and bottom decking

What I did was cut one side of the fuse to the drawing, then I compared the foam thickness to the relief found in the front where the hatch goes on

Doing so revealed that about another 3/16" needed to be removed (only on the areas that get decking)

I then taped a pen to a piece of foam so that as I dragged the foam down the side it made a new line 3/16" in

Once cut I traced that side onto the foam to cut the other side

I think this was easier than trying to fix the drawing YMMV

So I now have both sides of the fuse and the top and bottom wing cut
Aug 23, 2017, 10:18 AM
Registered User
Sorry for all the questions, this is the first model I have built that didn't already have recommendations

for me learning this stuff is part of the point in building it

Soooo - what should I get for batteries that aren't too expensive?

Do they have to be sized to continuously handle the max amp draw of 55A?

EDIT: also is a 55A ESC sufficient or should i go with the 60A for about $15 -$20 more?
Last edited by Scott in NH; Aug 23, 2017 at 10:36 AM.
Aug 23, 2017, 12:36 PM
Registered User
I would wait until I had the motor with mount physically available for measurements if I were aiming for a clean install

Regarding esc, these get good reviews
https://m.banggood.com/Hobbywing-Sky...l?rmmds=search
but I don't have first-hand experience with them yet (I have a pair that will be used in an upcoming giant twin bipe)
Aug 23, 2017, 01:15 PM
Registered User
I'm spoiled and don't have the patience to wait for BangGood shipping lol
Are you saying I need an 80A ESC?
FYI on my motor thread in the motor forum, I am being steered toward a 23 x 8 prop with the 410kV motor
Aug 23, 2017, 01:26 PM
Ken's CAD Models
dz1sfb's Avatar
Watching with interest.

Ken
Latest blog entry: Ken's CAD Models new web site
Aug 23, 2017, 01:30 PM
I Look, Listen, and Learn
Timbo383's Avatar
Don't forget that the esc is also for the servos, allow a little bit extra for those. They don't use much, but every little bit adds up.


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