Go Back  RCU Forums > RC Airplanes > Scratch Building, Aircraft Design, 3D/CAD
Reload this Page >

How to estimate finished weight?

Notices
Scratch Building, Aircraft Design, 3D/CAD If you are starting/building a project from scratch or want to discuss design, CAD or even share 3D design images this is the place. Q&A's.

How to estimate finished weight?

Old 01-23-2006, 07:33 PM
  #1  
strawtarget
Member
Thread Starter
 
Join Date: Jan 2006
Location: , TX
Posts: 39
Likes: 0
Received 0 Likes on 0 Posts
Default How to estimate finished weight?

I'm scratch building a plane from a set of 3-views. I have absolutely no clue what the finished weight might be. The best I've been able to do is guess based on similarly sized planes. For example, a HOB 1/12 Mustang (36" span, 216 sq. in.) is supposed to come out between 22 and 28 ounces. A Global Tequila Sunrise 25 ARF (36" span, 288 sq. in.) is supposed to come out at 52 ounces.

My plane is a similar size (38" span, 261 sq. in.). It is a scale subject, so goal #1 is "scale" looks. Goal #2 is "speed". I want a fast airplane. Maybe not as fast as a pure speed plane, but I want it as fast as I can build it without compromising goal #1 too much. As such, I'm trying to build a strong airplane so that it doesn't fold up while turning. I'm a n00b, though, and I don't know quite how strong it will really be.

It isn't a light weight airframe, but it isn't unnecessarily heavy either. I don't think. I'm using top and bottom 3/16" square basswood main spars with 1/16" shear webs root to tip. Wing thickness as the root is 1.6", and 0.5" at the tip. A 1/4" balsa rear spar goes through the top of the ribs (and serves as a the hinge location for the barn-door ailerons). The leading edge material is extremely lightweight... basically the sheeting forms the leading edge. The wing will be sheeted from the leading edge to the main spars, and then 1" from the trailing edge (there is no "trailing edge material" other than the rib tips and sheeting). The unsheeted areas of the wings will have cap strips. Most ribs (spaced 1.5" apart) are 1/16" balsa with no lightening holes. Some ribs are 3/32". It has retractable landing gear (2" lightweight foam wheels, 3/32" bent wire gear legs, one Bluebird 380MAX servo driving the retraction). I'm using 4 E-Flite S-75 servos for control, despite a strong gut feeling that they're not enough for an overpowered speed plane and I should use a normal Micro servo like an HS-81... at least for the elevator. I'm using a JR UL 6 channel RX since I hear good things about them and they're small/lightweight. Fuselage construction will be balsa formers with stringers, sheeted 100% with 1/16" balsa. Tail surfaces will be built up, truss-style out of 1/4" square balsa (with a 1/2" x 1/4" trailing edge) and not sheeted. The plane will be covered with ultracote, and is built using run of the mill balsa (not contest balsa).

Mostly, I'm trying to get a ballpark estimate so that I can decide which outrunner/esc/lipo battery configuration I want to use. I want to design the firewall and cowl around the motor selection.

I'm thinking it will lean more towards the "tequila sunrise" end of the weight spectrum, given that there will be 5 servos, a significant spar structure, and retractable landing gear. But 52 ounces still seems a bit high to me. Anyone with small-plane building experience care to weigh in on this matter? Where might it be between 22 and 52 ounces?

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.