HobbyKing.com New Products Flash Sale
Reply
Thread Tools
Old Sep 12, 2012, 03:54 PM
Learn to build with wood.
Tucci's Avatar
United States, NC, Newport
Joined Sep 2012
824 Posts
Discussion
First build, point me in the right direction

Hi all,

New to the group. I am currently building my first plane. 38" span low wing balsa plane. 3 channel park flyer. I just completed the air frame. without covering and control rods it weighs 2.3 oz. I'm trying to figure what battery/prop/esc/motor combo to use in this thing. I have read MANY of the posts/threads on here, and though they're full of very useful information, I'm still pretty confused. In order to select the proper motor and prop, I need to know the ready to fly weight of the plane. I cannot know that without knowing the battery(ies) and ESC I will need to run the motor safely. Do I just guess? That's gonna be difficult.

Also. I read one thread that put a lot of stock in the whole watts/pound thing, then another that just basically throws that in the trash with real world examples.

So, I'm basically looking for help.

How much does the average 38" low wing weigh fully dressed?

I don't just want to buy some foamy thing. The only way to learn is to do it from the ground up.
Tucci is online now Find More Posts by Tucci
Reply With Quote
Sign up now
to remove ads between posts
Old Sep 12, 2012, 06:04 PM
I think I'm inverted. Maybe.
acetech09's Avatar
United States, CA, Pacifica
Joined Apr 2012
1,505 Posts
There's a 'Power systems' subforum that might be a bit more fruitful, but here's some help anyway. Instead of me just handing you a salmon, be prepared to learn how to fish. It'll help you in the long run.

So... to determine the power system, you gotta know two things. Wing loading and weight. Wing loading is how well the weight of your plane is spread across your wings. Think 'Weight-to-wing' ratio. Lower wing loading means more wing less plane, so it has more lift and flies slower, etc.

Wing loading can be done through some online calculators. You need to enter your model's weight, wing chord, and wing span.

That brings me to determining your model's weight. I've found that the most reliable way of predicting how much a model will weigh is to

1) weigh the parts you're putting into it, even before it's assembled. Has been scarily accurate on a few of my builds. If you don't know what all you'll be using, then move on to plan 2:

2) See how much somebody else's plane weighs...
http://www.horizonhobby.com/products...480-EFL3000#t1
That aircraft's flying weight is 2.44 pounds. It's a few inches longer than yours, but you can count on the first build being a bit on the heavy side.

Determining the power system is normally in watts per pound. There's a general rule of thumb for the 'watts per pound rule':
http://www.rc-airplane-world.com/watts-per-pound.html

The recommended motor for that plane is a park 480, which is a ~310 watt motor. Using 120 watts per pound, that's nearly spot on for moderate level sport plane.

So it sounds like you'll want a 350 watt motor. I recommend a Suppo from Altitude hobbies. Cheap as HK but one-on-one support from the owner, and great motors:

http://www.altitudehobbies.com/brush...v-suppo-2814-8

Will also need a ~40A esc... get the ZTW ESCs there from altitude.




Well, there ya go. You wanted to learn from the ground up, and you got an education ... plus a recommendation.
acetech09 is offline Find More Posts by acetech09
Reply With Quote
Old Sep 12, 2012, 06:42 PM
Suspended Account
Switzerland
Joined Aug 2012
173 Posts
Tucci-do you know what manufacture and model the plane is? I could post some links that will also help allot.

Just remember don't fly on a windy day. That is how most beginners break their airoplanes.
mikhail tupulov is offline Find More Posts by mikhail tupulov
Reply With Quote  (Disabled)
Old Sep 12, 2012, 06:55 PM
Learn to build with wood.
Tucci's Avatar
United States, NC, Newport
Joined Sep 2012
824 Posts
thanks for the prompt replies. I spent some time in the power systems forums. That's kind of what led me to post.

Thanks for the recommendation on motor size.

The plane I built is not from any manufacturer, It is scratch built from some plans I found online.

Do you think its better to over power the thing from the start? I mean as far as ESC and battery go.

I'm thinking that if I go that route, I'll be able to step up the motor and prop for more speed/handling next year.

I'm ready to corkscrew this thing into the ground right now!

Also, Acetech: the motor you linked to was what I was considering after the research I have done on this forum.
Tucci is online now Find More Posts by Tucci
Last edited by Tucci; Sep 12, 2012 at 07:00 PM. Reason: Followed link
Reply With Quote
Old Sep 12, 2012, 07:20 PM
Suspended Account
Switzerland
Joined Aug 2012
173 Posts
Have you thought about buying a Slow Stick and trying to learn how to fly first?
mikhail tupulov is offline Find More Posts by mikhail tupulov
Reply With Quote  (Disabled)
Old Sep 12, 2012, 08:38 PM
I think I'm inverted. Maybe.
acetech09's Avatar
United States, CA, Pacifica
Joined Apr 2012
1,505 Posts
Slow stick is a meh trainer imho... some people like it while some people say it ain't a trainer.

Either way, my first plane was a scratchbuild. I believe that it was one of the reasons I am where I am today. Knowing how everything works inside what you fly before you put it up in the air, is, in my opinion, one of the most valuable things you can do when getting started.

I did spend about 200 hours on a simulator before flying... nearly mastered every plane, and tested myself by doing some pattern routines in every plane the simulator had... that allowed me to be able to fly the plane I built.

And in response to Tucci:

I think you should give it a 480 from the start. Trim down the throttle a bit if you feel it has too much power, but chances are you should keep the power just in case you want to pull out from a bad situation.

Get a few lighter batteries to make the thing as slow and floaty as you can... it's better to have 5 minute flights on a light plane than 10 minute flights on a heavy plane, especially when you're learning how to fly.
acetech09 is offline Find More Posts by acetech09
Last edited by acetech09; Sep 12, 2012 at 08:44 PM.
Reply With Quote
Old Sep 12, 2012, 08:48 PM
Learn to build with wood.
Tucci's Avatar
United States, NC, Newport
Joined Sep 2012
824 Posts
@ Mikhail: No.
Tucci is online now Find More Posts by Tucci
Reply With Quote
Old Sep 13, 2012, 01:27 AM
The original Flying Pigs Sqd.
Up&Away's Avatar
Netanya, Israel
Joined Aug 2002
9,946 Posts
OK, some questions first:
Are you building from a kit or plan? Usually there are power recommendations with the instructions.
You say you are new to the group, are you also new to flying RC?
Up&Away is offline Find More Posts by Up&Away
Reply With Quote
Old Sep 13, 2012, 08:03 AM
Learn to build with wood.
Tucci's Avatar
United States, NC, Newport
Joined Sep 2012
824 Posts
Scratch built from plans. Plans call for Atlas 2308 and what appears to be 6x6 or 8x6 slowflyer prop. can't make it out, I'm pretty sure it's 8x6

Also says the RTF weight will be 10 oz, which seems low to me. Unless the electronics and battery weigh less than I think.

Looking at that motor, it'll be spinning that prop (8x6) at maybe 7k rpm on a 3s and probably drawing 15 amps or so.

maybe I'm wrong.

I just want to make sure it can stay in the air.

Also, I am completely new to this hobby, with the exception of a couple of hours on a sim. The sim seems too easy though. Phoenix.
Tucci is online now Find More Posts by Tucci
Reply With Quote
Old Sep 13, 2012, 08:46 AM
Registered User
United States, IA, Keosauqua
Joined Sep 2010
276 Posts
Don't know if it helps any, but my first 2 scratch-built planes were a 33" wingspan BluBaby and a 42" wingspan Divinity flying wing. Both weigh between 12-14 Oz. Auw powered with 24g/70 watt "blue wonder" motors and 800mah 3s batteries. They both fly fine and will go vertical, just not unlimited with 9050 DD GWS props.

Bob
Bob A is offline Find More Posts by Bob A
Reply With Quote
Old Sep 13, 2012, 08:47 AM
The original Flying Pigs Sqd.
Up&Away's Avatar
Netanya, Israel
Joined Aug 2002
9,946 Posts
FWIW, get an instructor!

Learning to fly RC on your own is a definite possibility (I did), but only with something close to unbreakable (i.e. a foamy. I started on an EPP Unicorn flying wing).
To learn to fly, you need a model that has proven airworthiness, or you will always be doubting whether you made the mistake, or the model wasn't flying properly.

If you do want to fly your scratch build, at least let an experienced pilot do the maiden flight, and let him "wring it out". That way, at least you'll know your work was done properly.

Do you have a link to the plan?
Up&Away is offline Find More Posts by Up&Away
Reply With Quote
Old Sep 13, 2012, 09:00 AM
buyer of the farm
United States, FL, DeLand
Joined Mar 2009
3,939 Posts
What's your experience? Have you built free flight planes and so know how a flyable plane differs from an unflyable one (example: a rock)? If you have free flight experience, including a scratch build or two, under your belt you are on a fruitful course.

Your questions lead me to believe you might not be. Check out RTF planes of the same size and see what kind of power systems they use. Make sure it is a GOOD flying RTF, Flyzone Cubs need not apply. A bit of research on RC Groups in threads related to the plane will expose posts like "PLANE IS WAY UNDERPOWERED" or "Best flying plane ever." Pick a plane the everyone likes and copy what works there.

Copying success almost always works!
Rockin Robbins is offline Find More Posts by Rockin Robbins
Reply With Quote
Old Sep 13, 2012, 10:02 AM
Suspended Account
Switzerland
Joined Aug 2012
173 Posts
200 hours is over a week of flying.

Slow Stick? How much easier can you get? If you can't fly a slow stick after many tries something is wrong.

Get a Slow Stick it's the best trainer ever, and also fun. Guys I know still fly their Slow Sticks more than their 0.50 glow racers.

Quote:
Originally Posted by acetech09 View Post
Slow stick is a meh trainer imho... some people like it while some people say it ain't a trainer.

Either way, my first plane was a scratchbuild. I believe that it was one of the reasons I am where I am today. Knowing how everything works inside what you fly before you put it up in the air, is, in my opinion, one of the most valuable things you can do when getting started.

I did spend about 200 hours on a simulator before flying... nearly mastered every plane, and tested myself by doing some pattern routines in every plane the simulator had... that allowed me to be able to fly the plane I built.

And in response to Tucci:

I think you should give it a 480 from the start. Trim down the throttle a bit if you feel it has too much power, but chances are you should keep the power just in case you want to pull out from a bad situation.

Get a few lighter batteries to make the thing as slow and floaty as you can... it's better to have 5 minute flights on a light plane than 10 minute flights on a heavy plane, especially when you're learning how to fly.
mikhail tupulov is offline Find More Posts by mikhail tupulov
Reply With Quote  (Disabled)
Old Sep 13, 2012, 04:03 PM
Learn to build with wood.
Tucci's Avatar
United States, NC, Newport
Joined Sep 2012
824 Posts
Acetech,

You might be way out of line with that motor recommendation. Punching it into WebOcalc leads to some suprising results.

I think I better read that thread again. (Nevermind, i revisited the WebOcalc thread)

Also I think that while the 10 oz AUW in the plans is a little low, I think 2.4 lbs is on the high side. If this thing goes 16 oz, I'll be surprised.

link to plan: www.indoorflyingmodel.com/Documents/Snapper%20Plan-PDF.pdf

I do have an experienced instructor.....thank God.

Also Bob: What's the flight time on those 800mAh batteries? I'm thinking of going 800 or larger, just to keep it in the air longer that 3 minutes.
Tucci is online now Find More Posts by Tucci
Last edited by Tucci; Sep 13, 2012 at 05:18 PM.
Reply With Quote
Old Sep 13, 2012, 04:43 PM
Registered User
United States, CA, Oceanside
Joined Apr 2011
4,755 Posts
Quote:
Originally Posted by Tucci View Post
thanks for the prompt replies. I spent some time in the power systems forums. That's kind of what led me to post.

Thanks for the recommendation on motor size.

The plane I built is not from any manufacturer, It is scratch built from some plans I found online.

Do you think its better to over power the thing from the start? I mean as far as ESC and battery go.

I'm thinking that if I go that route, I'll be able to step up the motor and prop for more speed/handling next year.

I'm ready to corkscrew this thing into the ground right now!

Also, Acetech: the motor you linked to was what I was considering after the research I have done on this forum.
And you will too!! Not trying to be negative, but you may want to try out a small foamie like a Hobbyzone Champ before you put that plane in the air. I take it you have never flown an RC plane before. If that is the case...........good luck.
chucksolo69 is offline Find More Posts by chucksolo69
Reply With Quote
Reply


Thread Tools

Similar Threads
Category Thread Thread Starter Forum Replies Last Post
Question Reparing a Balsa Wing. Point me in the right direction! Tommy D Parkflyers 5 Apr 29, 2004 09:35 PM
Point me in the right direction tapeedit Foamies (Kits) 2 Dec 09, 2003 05:23 AM
point me in the right direction.... flowerpower Beginner Training Area (Aircraft-Electric) 6 May 05, 2003 10:06 PM
Anyone in NY, NY...point me in the right direction! saint152 Electric Sailplanes 3 Oct 15, 2002 10:44 AM
Help me pick a brushless motor or point me in the right direction. Mike Palko Sport Planes 15 Aug 15, 2002 08:30 PM