Feb 04, 2014, 09:53 AM
Registered User
Joined Feb 2014
6 Posts
Help!
Motor Torque, Directional and Lateral stability

Hello Everyone,

My team has almost fabricated an r/c aircraft as per the specifications given below for a project, The model is scheduled to be tested for its flight this weekend.

Wing span - 2.4 Meter
Wing Chord - .25 Meter
Wing Planform - Rectangular, High Wing, No Dihedral
Total Fuselage length - 1.8 Meter
Horizontal and Vertical tail arm ( Lht and Lvt) = 1.2 Meter
Horizontal Tail Area = 0.45(Span) * 0.16(Chord) Meter^2
Vertical Tail Area = 0.5 * Horizontal Tail Area
Wing Airfoil - Positively Cambered High lift Airfoil
Tail Airfoil - Flat Plate ( 3.33% t/c)
Tail Planform - Conventional Tail
Operational Cl value of Aircraft = 0.84

Estimated Empty Weight ( Airframe and electronics) = 1.5 Kg
Total Weight = 4.5 Kg
Center of Gravity at 35% of Wing chord.

Propulsion :
Motor - Emax 4030-08 (353Kv)
Prop - 17" * 8" APC E
ESC - 60 A
Battery - 6 cell 2450mAh 30c
Expected Static Thrust - 4 kg

Mission : To Hand Launch the aircraft >> Gain Altitude >> Cruise >> Moderate Banking for turns >> Glide and Bell Landing. Also, to carry 4.5kg weight with ease.

*Structural analysis have been efficiently carried out to handle the expected loads during hand launch and belly landing*

Critical Parameters :
Stall Velocity : 12 m/s for 4.5kg Lift
Estimated Drag at 15m/s : Approximately 1 Kg

Questions:
1. What would be your opinion on the overall performance of the aircraft ?
2. Based on your practical experience, With Hand Launch, Would it be able to achieve stall speed of 12m/s i.e, carry a weight of 4.5kg ? Considering Thrust to Drag Ratio = 4:1 and Thrust to Weight ratio = 0.88
3. Can the Aircraft stabilize on roll and yaw axis considering the torque produced by huge 17" Prop diameter ? ( I am asking this question, because i had witnessed a crashed of a model which was using an oversized prop, As soon it was handlaunched, the motor torque induced 180 degree roll of the aircraft and it crashed within a fraction of seconds).

P.S. : I am using the above Motor,esc,prop and battery combination because that is the only combination available in the local hobby store which gives a thrust of 4kg. The project is subjected to time and budget constraints.

# Images

 Feb 04, 2014, 10:08 AM Registered User Joined Oct 2007 5,763 Posts You will quickly run out of battery with that setup! for an example : the EFlite 50 type motor used in the Splendor, utilizes a 6 cell pack rated at 3300ma-which gives about 5 mins max in typical use prop used a 14x7. your prop load is far far higher Your total weight of about 10 lbs is too much for the power setup you describe. make a simple thrust stand and couple your power setup to the battery, thru a WHATT meter - to read volts amps and watts - unless you get this squared away - the rest of the exercise won't work.
 Feb 04, 2014, 01:27 PM Registered User Joined Oct 2007 5,763 Posts I am afraid I disagree with Richard about it being too much for the power setup. 4Kg thrust (assuming you get it) That was my point - as described , the power arrangement won't fly. Project models are a great idea - the problems I have seen in the past are the lack of information provided to the students regarding structural integrity The instructor gets caught up in theoretical airfoils etc., which are really meaningless unless the power and load and flight parameters are resolved
 Feb 04, 2014, 02:04 PM An itch?. Scratch build. South Wales U.K. Joined Mar 2003 12,269 Posts It should fly and with the payload, based on models of a similar size and weight that I fly, with a near identical motor, (E-Power 4030 385kv) on 6s, and turning a 14x7, or 15x8, or 16x10, (all tried). Hope you get some good weather for the first flight.
Feb 04, 2014, 02:52 PM
I bail out, anywhere, anytime
The Netherlands, OV, Almelo
Joined Nov 2010
2,510 Posts
Quote:
 Originally Posted by abhishek. Hello Everyone, My team has almost fabricated an r/c aircraft as per the specifications given below for a project, The model is scheduled to be tested for its flight this weekend. Wing span - 2.4 Meter Wing Chord - .25 Meter Wing Planform - Rectangular, High Wing, No Dihedral Total Fuselage length - 1.8 Meter Horizontal and Vertical tail arm ( Lht and Lvt) = 1.2 Meter Horizontal Tail Area = 0.45(Span) * 0.16(Chord) Meter^2 Vertical Tail Area = 0.5 * Horizontal Tail Area Wing Airfoil - Positively Cambered High lift Airfoil Tail Airfoil - Flat Plate ( 3.33% t/c) Tail Planform - Conventional Tail Operational Cl value of Aircraft = 0.84 Estimated Empty Weight ( Airframe and electronics) = 1.5 Kg Expected Payload = 3 Kg Total Weight = 4.5 Kg Center of Gravity at 35% of Wing chord. Propulsion : Motor - Emax 4030-08 (353Kv) Prop - 17" * 8" APC E ESC - 60 A Battery - 6 cell 2450mAh 30c Expected Static Thrust - 4 kg Mission : To Hand Launch the aircraft >> Gain Altitude >> Cruise >> Moderate Banking for turns >> Glide and Bell Landing. Also, to carry 4.5kg weight with ease. *Structural analysis have been efficiently carried out to handle the expected loads during hand launch and belly landing* Critical Parameters : Stall Velocity : 12 m/s for 4.5kg Lift Estimated Drag at 15m/s : Approximately 1 Kg Questions: 1. What would be your opinion on the overall performance of the aircraft ? 2. Based on your practical experience, With Hand Launch, Would it be able to achieve stall speed of 12m/s i.e, carry a weight of 4.5kg ? Considering Thrust to Drag Ratio = 4:1 and Thrust to Weight ratio = 0.88 3. Can the Aircraft stabilize on roll and yaw axis considering the torque produced by huge 17" Prop diameter ? ( I am asking this question, because i had witnessed a crashed of a model which was using an oversized prop, As soon it was handlaunched, the motor torque induced 180 degree roll of the aircraft and it crashed within a fraction of seconds). P.S. : I am using the above Motor,esc,prop and battery combination because that is the only combination available in the local hobby store which gives a thrust of 4kg. The project is subjected to time and budget constraints. Thank you and i appreciate your kind help in answering these questions in advance.
abhishek, who designed this plane?
60 dm^2 wings and 7,6 dm^2 stab.
A flat stab of 12,6 % is a little bit small for a "Positively Cambered High lift Airfoil" winged airplane!

TF
 Feb 04, 2014, 03:19 PM Registered User Joined Oct 2007 5,763 Posts Textbook design---
Feb 04, 2014, 07:20 PM
B for Bruce
Joined Oct 2002
10,694 Posts
Quote:
 Originally Posted by Taurus Flyer ....A flat stab of 12,6 % is a little bit small.....
Well spotted. I didn't get that deep into the numbers. But yeah, for that length fuselage a safer size would be more up around 17% or more for the stabilizer area.
 Feb 04, 2014, 10:30 PM Grad student in aeronautics United States, GA, Atlanta Joined Oct 2010 410 Posts To my fellow modeling scientists: Please let students figure out this stuff on their own.
 Feb 04, 2014, 11:10 PM B for Bruce The 'Wack, BC, Canada Joined Oct 2002 10,694 Posts Haven't you got the memo? Apparently WE are the new research library....
Feb 05, 2014, 01:38 AM
Registered User
United Kingdom, England, Southampton
Joined Oct 2013
1,053 Posts
Quote:
 Originally Posted by DPATE To my fellow modeling scientists: Please let students figure out this stuff on their own.
In principle you are right of course. But they don't, do they? They come here and ask. Often, though of course different students each time. It's like Wiki. I'm mildly interested in astronomy and cosmology. Read Wiki and I can know all there is to know. But it won't turn me into a proper scientist like Stephen Hawking - he figured it out for himself.

By asking us they don't really learn anything. Better for us not to pick faults in their efforts at all. If they have faith in their teachers and their own calculations they will learn from their crashes. Pay attention to us and it will fly fine first time. That's partially why I suggested they just go buy an ARTF trainer.

PS: Don't know about the USA, but here we have thousands of unemployed new science graduates. They come out of university clutching their brand new degrees and nobody wants them. Because they haven't done any 'research' at all. Nothing new, just a repeat of what thousands of them have done before. Like this. It's not their fault - it's because the universities want to show good educational 'numbers' to the gubment.
Last edited by Mark Powell; Feb 05, 2014 at 02:00 AM.
 Feb 05, 2014, 01:57 AM Registered User Joined Feb 2014 6 Posts lol :P Thank you for the suggestions, I have designed many gliders, They have all flown well, i know how to design a wing and tail. Also, yes for a 2.4 m wing, we do have struts, my only intention to post this here was to know if the torque produced by 17 * 8 will be a problem (Practically) ? Theoretically it should not. The tail area is certainly not less as we do something called as optimization, i am not here to do acrobatics with huge tail area, its just a heavy lifting glider. @eflightray : Thank you for you positive comments and reply regarding prop sizes. @Everyone else : Thank you for being over pessimistic and behaving like you are the gods of Aircraft design. Also, the hand launch is designed for a certain mission, even a kid knows that a landing gear can be put instead. I have learnt the designing in a very hard way, i have no aerospace department in my college, i went through the books, i learnt the theory, i fabricated it by myself and then flew it by myself, got to know what really happens in practical. My only intention was that there might be some veterans here who could give some valid inputs (based on their practical experience). But this forum seems to be filled up with aeromodellers and not aircraft designers who like their ARF's so much!!
 Feb 05, 2014, 02:24 AM Registered User United Kingdom, England, Southampton Joined Oct 2013 1,053 Posts We are the gods of aircraft design . Many of us (not me for long, no money in it) have gone on to become some of the worlds top full size aircraft designers. Maybe not even 'gone on' as that might give the idea that real ones are somehow 'better'. More often doing models and full size design simultaneously. We can do this stuff with our eyes closed. And we did our degrees in aeronautics too, you know. 17 x 8 should not give you a 'torque' problem. It is a good choice for a plane of that size, if you can drive it. Most propellors on models are too small. It's not actually torque at all, that only happens for a short time if you suddenly open or close the throttle, as you will find out if you fly a full size light aircraft. The nose will diverge slightly for a second or two and will then come back straight without you having to do anything, though some of us 'purists' like to make the momentary rudder correction. What so many wrongly call 'torque' is actually the spiral flow of air from the propellor over the tail surfaces. The only time real torque is significant is on takeoff with very high powered aircraft with very narrow undercarriages, such as the WW2 Spitfire and Me109. 'Acrobatics' with huge tail surfaces? Wrong. For aerobatics you want small tail surfaces. And a high proportion of that small tail being the elevator and rudder. It makes the plane near unstable so it does not want to resist changes. Last edited by Mark Powell; Feb 05, 2014 at 02:55 AM.
 Feb 05, 2014, 02:35 AM Registered User Joined Feb 2014 6 Posts Thank you Mark, I just wanted to know about prop. Am glad you answered it.