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Old Oct 06, 2012, 09:12 PM
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here is my jet that is ready to go minus the system please give me your opinion

http://www.nitroplanes.com/rcjetfo16076.html
http://www.hobbypartz.com/96m605-big...020-670kv.html
http://www.hobbypartz.com/96m607-big...325-295kv.html

The first link is my jet. I was going to put a turbine in it than changed my mind. Than i was looking at EDF options but cant fly it more than 3-5mins. SO now I decided to make it a pusher. I have found some motors that seem to work well. THIS is a big plane so I have many choices on battery size and set up. My goal is to keep it light because I will be flying off grass. My question to you experts here is what set up can i go with where it will fly pretty fast but be light. I have 6s packs at home and dont wish to purchase more packs. My first option is to do 1 6s 4000 60c pack with 670kv motor and the biggest prop i can possibly fit. THe second option is the bigger motor 295kv and go 12s. LET me know what you guys think.
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Old Oct 07, 2012, 07:57 AM
Jack
USA, ME, Ellsworth
Joined May 2008
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"..the biggest prop i can possibly fit..."

That is one of the key pieces to the puzzle here. That, and your battery voltage, will decide the Kv of the motor. And of course, the maximum safe RPM spec for the prop will enter into the equation too.

What is the distance between the booms?

One you have the prop choice you can get to the thrust and that will lead you some some of the other factors and deciding the practicality of things.

Jack
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Old Oct 07, 2012, 09:12 AM
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okay will measure the distance from the booms and get back to you

It would be awesome to do a light 6s set up and can fly about 7 mins. THE 12s would have much more power but the weight factor on landing in grass can start to tear apart things.
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Old Oct 07, 2012, 12:16 PM
Jack
USA, ME, Ellsworth
Joined May 2008
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RC Jet Formost 160 Specifications:
Wing Span : 76 in / 1930mm
Wing Area : 969 sq in / 62.5 sq dm
Flying Weight : 14.3 lb / 6500g
Fuselage Length : 71 in / 1800 mm

Looking at the above specs for that plane it has a very high wing loading with the intended power system. The 14.3 lb./6500g weight works out to a wing loading of 34 oz./sq. ft. or 103 grams/dm2. Typical wing loadings for various types of RC planes would be as follows:

Loading ---- Airplane Type
10 oz/sq.ft - Gliders
15 oz/sq.ft - Trainers
20 oz/sq.ft - Sport Planes
25 oz/sq.ft - Warbirds

So that does not mean that it is not practical but if it has to fly at that weight and loading, it will need a lot of speed to take off and land. And it will not be a plane that will be easily flown by an inexperienced RC pilot.

But I think EDF and turbine power systems may be heavier than a motor and prop system. So maybe you can get the wing loading down to a more reasonable number.

There are a bunch of other rules of thumb that can be used to give you some answers. For example, these are the electric power levels needed to fly various types of electric airplanes:

Approximate power requirements:

50-70 watts per pound; Minimum level of power for decent performance, park flyer/slow flyer models
70-90 watts per pound; Trainers and slow flying scale models
90-110 watts per pound; Sport aerobatic and fast flying scale models
110-130 watts per pound; Advanced aerobatic and high-speed models
130-150 watts per pound; Lightly loaded 3D models and ducted fans
150-200+ watts per pound; Unlimited performance 3D and aerobatic models

Again, at 14 lbs. and by the numbers above, if it would need 110-130 Watts per pounds to fly and that is 1540 to 1820 Watts. But again, we're not sure about the weight yet so maybe less will work.

Another consideration is thrust. You'll have to get your thrust from one propeller and there are some estimated thrust to weight requirements for model flight:

1 lb/3lbs = 0.33:1 - basic flying
1.5 lb/3lbs = 0.5:1 - advanced flying
1.71 lb/3lbs = 0.57:1 - aggressive flying

As an example, most 3D flyers want 1:1 to 2:1 thrust to weight. If you wanted to have 1:1 thrust to weight ratio you would need 14 lbs. of thrust.

But maybe something will work...

Note - I corrected all my bad number! The AUW is 14 lbs. not 34 lbs.

Jack
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Last edited by jackerbes; Oct 07, 2012 at 12:39 PM. Reason: Correct my mistaken numbers!
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Old Oct 07, 2012, 12:23 PM
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this is what they recommend

Engine Required :4c 1.80 or Turbine

Flying weight is 14lbs.

NOt sure how much power a 4 stroke 1.80 has but if i can get a electric motor that has the same power it should be good.
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Old Oct 07, 2012, 12:40 PM
Jack
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Thanks for pointing out my dumb mistake, Sherlock.

Yeah, 14 lbs. That sounds much more practical.
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Old Oct 07, 2012, 01:04 PM
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im thinking tacon 160 motor with 12s 4000 60c with a 16x8 prop

should be really good. 245kv
but will check the measurements. I have seen the edf version, seems to be too much work, I think its easier to make few mounts and just put a motor and prop and make it pusher.
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Old Oct 07, 2012, 02:06 PM
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It needs longer landing gear.
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Old Oct 07, 2012, 02:39 PM
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I have retracts, these are the ones I have for it.

here is link.

http://www.hobbyking.com/hobbyking/s...dProduct=18243


Might go for a smaller prop and higher kv than.
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Old Oct 07, 2012, 04:16 PM
Wake up, feel pulse, be happy!
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Once again...

I wouldn't suggest offering advice here given Sherlock's track record with safe flying decisions, such as flying large, powerful models in crowded public parks. Read this thread and do a little background reading on his antics before proceeding. Here's a screenshot from a video he posted on YouTube awhile back:

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Old Oct 07, 2012, 05:43 PM
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If you have a watt meter, you can watch your power go up as you increase throttle for the first time on the ground. If the amperage goes above the ESC or Motor maximum allowed, you know that the prop is too big.
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Old Oct 07, 2012, 05:53 PM
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yes I AGREE, i will make up my mind tomorrow

which way to go. I can go either EDF or prop, Im leaning more towards the prop.
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Old Oct 07, 2012, 05:53 PM
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HEY why dont you leave my threads alone

Quote:
Originally Posted by C₄H₁₀ View Post
Once again...

I wouldn't suggest offering advice here given Sherlock's track record with safe flying decisions, such as flying large, powerful models in crowded public parks. Read this thread and do a little background reading on his antics before proceeding. Here's a screenshot from a video he posted on YouTube awhile back:

GET a life and do something else other than bash my threads
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Old Oct 08, 2012, 08:58 AM
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It is not thread bashing when you flagrantly ignore safety protocol and endanger children's lives so that you can have fun. It would be easy to say it was a mistake that won't happen again. Speaking for my self I have done dumb things that went unrealized until someone pointed it out. Acknowledging the error and thanking the someone for pointing it out will usually gain people's respect. A little humility goes a long way
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Old Oct 08, 2012, 11:18 AM
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The plane was not flying where the kids were

There is two sides to this park, its no different than flying at our field where one side we have airplanes and the other side people play soccer. Its a foam plane, I am not going to fly this big 15lbs plane at a park.
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