Which gear ratio? - RCCanada - Canada Radio Controlled Hobby Forum
RCCanada - Canada's Radio Control Hobby Forum
Electric Flight Discuss Electric Flight in Canada

Closed Thread
Thread Tools Display Modes
Old 02-18-2005, 08:57 AM   #1
RCC Contributor
I am: Glen M
Join Date: Aug 2003
Location: Middle Sackville NOVA SCOTIA

Feedback: 14 / 100%
Posts: 352
Total Props: 0
Which gear ratio?

       Remove this ad - become a site supporter!
Hi, I was wondering if anybody would have an idea what gear ratio I should use, I'm going to build a 71" lancaster and I want to use GWS geared 400's and swing 4 bladed props ( like the gws mustang ). They have several different gear ratio's available so I don't know which ones to order. Which one is in the mustang ?
CRAZYFAST is offline   Quick reply to this message.

Sponsored Links - Subscribe to remove this ad.
Old 02-18-2005, 06:47 PM   #2
RCC Expert Contributor
NorseHammer's Avatar
I am: Moe N.
Join Date: Mar 2004
Location: Terrace B.C.

Feedback: 0 / 0%
Posts: 766
Total Props: 0

Well, Let's assume a weight of 5 lbs without motor, esc, or batteries and an estimated wing area of 800 square inches. This is a bomber so trainer style flying is probably also desired, we can assume a semi symetrical wing and plug this into Motocalc. The selected prop, a 10 X 8 four blade as used on the GWS Mustang is not the optimum for a slow flying bomber.

Motocalc's first choice would have been what's listed at the bottom

Motor: GWS EM400; 2785rpm/V; 1.3A no-load; 0.235 Ohms.
Battery: Sanyo 2300SCE; 24 cells; 2300mAh @ 1.2V; 0.0055 Ohms/cell.
Speed Control: Generic High Rate ESC; 0.003 Ohms; High rate.
Drive System: Graupner Speed Gear 400 4:1 Gearbox; 4 motors (2 series by 2 parallel); 10x8 4-bladed (Pconst=1.31; Tconst=0.95) geared 4:1 (Eff=95%).
Airframe: Lancaster; 800sq.in; 141.2oz; 25.4oz/sq.ft; Cd=0.057; Cl=0.5; Clopt=0.64; Clmax=1.11.
Stats: 77 W/lb in; 34 W/lb out; 25mph stall; 32mph opt @ 59% (21:10, 112F); 37mph level @ 65% (18:09, 118F); 681ft/min @ 13.8; -310ft/min @ -6.2.

MotOpinion - Untitled
Sea Level, 29.92inHg, 59F

Motor: Graupner Speed 400 7.2V #1794 (cat); 2332rpm/V; 0.5A no-load; 0.338 Ohms.
Battery: Sanyo CP-1700SCR; 12 cells; 1700mAh @ 1.2V; 0.0055 Ohms/cell.
Speed Control: Generic High Rate ESC; 0.003 Ohms; High rate.
Drive System: Generic 9x9in Prop w/4:1 Gearbox; 4 motors (parallel); 9x9 (Pconst=1.25; Tconst=0.956) geared 4:1 (Eff=95%).
Airframe: Lancaster; 800sq.in; 110.7oz; 19.9oz/sq.ft; Cd=0.057; Cl=0.5; Clopt=0.64; Clmax=1.11.
Stats: 48 W/lb in; 33 W/lb out; 22mph stall; 29mph opt @ 62% (12:57, 83F); 33mph level @ 67% (11:01, 87F); 515ft/min @ 11.8; -275ft/min @ -6.2.

Possible Power System Problems:

The estimated steady-state still-air battery temperature at the hands-off cruise airspeed and throttle setting (approximately 140F) is higher than the suggested maximum temperature for this cell type (140F). This could result in battery pack damage unless adequate cooling airflow is provided and/or run times are kept short. A lower current would also decrease the battery temperature.
Current can be decreased by using fewer cells, a smaller diameter or lower pitched propeller, a higher gear ratio, or some combination of these methods.

Power System Notes:

The full-throttle motor current at the best lift-to-drag ratio airspeed (6.8A) falls between the motor's maximum efficiency current (4A) and its current at theoretical maximum output (16A), thus making effective use of the motor.
The voltage (12.6V) exceeds 12V. Be sure the speed control is rated for at least the number of cells specified above.

Possible Aerodynamic Problems:

The static pitch speed (50mph) is less than 2.5 times the stall speed (22mph), which may result in reduced performance at typical flying speeds and a low maximum speed. This situation is usually acceptable for an electric sailplane or other slow-flying model.
Pitch speed can be increased by using a higher pitched and/or smaller diameter propeller, a lower gear ratio, a higher cell count, or some combination of these methods.
The diameter (9.0in) to pitch (9.0in) ratio is less than 1.5:1, which will result in reduced propeller efficiency at low speeds (the propeller is stalled). Although this is not likely to affect flying characteristics, it may make take-off or hand launching difficult.

Aerodynamic Notes:

With a wing loading of 19.9oz/sq.ft, a model of this size will have trainer-like flying characteristics. It would make an ideal trainer, for use in calm to light wind conditions.
The static thrust (46.8oz) to weight (110.7oz) ratio is 0.42:1, which will result in medium length take-off runs, and no difficulty taking off from grass surfaces (assuming sufficiently large wheels).
At the best lift-to-drag ratio airspeed, the excess-thrust (24oz) to weight (110.7oz) ratio is 0.22:1, which will give good climbs and acceleration. This is a good in-flight thrust to weight ratio for a basic trainer.

General Notes:

This analysis is based on calculations that take motor heating effects into account.
Salutations from the Pacific North WET!

S.P.A.D.s, Fibreglas & Balsa EDF's, Foamies, Brushless powered and nitro balsa planes, they're all in my hanger, just don't explain what it all means to the mrs, eh?
NorseHammer is offline   Quick reply to this message.
Old 02-21-2005, 06:42 AM   #3
RCC Contributor
I am: Glen M
Join Date: Aug 2003
Location: Middle Sackville NOVA SCOTIA

Feedback: 14 / 100%
Posts: 352
Total Props: 0

Thanks norsehammer for the info, I really appreciate it, that will help lots making power plant decisions.
CRAZYFAST is offline   Quick reply to this message.
Closed Thread

Quick Reply

Register Now

In order to be able to post messages on the RCCanada - Canada Radio Controlled Hobby Forum forums, you must first register.
Please enter your desired user name, your email address and other required details in the form below.

Member names may only be composed of alpha-numeric characters. (A-Z and 0-9)

!!ATTENTION ADVERTISERS!! If you intend on advertising anything on this forum, whatsoever, you are required to first contact us here . Additionally, we do NOT allow BUSINESS NAMES unless you are an Authorized Vendor. If you own a business, and want to do sales on this site via posting or private message, you will need to follow the rules. Shops, Stores, Distributors, Group Buys without being authorized will see your account terminated.
User Name:
Please enter a password for your user account. Note that passwords are case-sensitive.
Confirm Password:
Email Address
Please enter a valid email address for yourself.
Email Address:
Your Name
Your first name and last initial is required if you plan on using the forum.
Which city & province you live in. This is mandatory for classified listings.
Radio of choice?
Which radio is your current favorite to use?
Number of RC Vehicles?
How many boats, cars, planes do you own?


Human Verification

In order to verify that you are a human and not a spam bot, please enter the answer into the following box below based on the instructions contained in the graphic.

Currently Active Users Viewing This Thread: 1 (0 members and 1 guests)
vBulletin Message

Thread Tools
Display Modes

Forum Jump

All times are GMT -5. The time now is 05:16 PM.

vBulletin Security provided by vBSecurity v2.2.2 (Pro) - vBulletin Mods & Addons Copyright © 2016 DragonByte Technologies Ltd.