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Author Topic: Shorter nose or longer tail or both when using the two-motors-in-tandem contra  (Read 815 times)

Offline Matt Piatkowski

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Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« on: June 30, 2020, 02:33:23 PM »
Hello,
Using two-motors-in-tandem contra (TMT contra), changes the nose and tail moments in the stunt plane.
Two motors of the TMT contra must have two ESC and also additional cabling/harness.
These parts weight between 80 to 120 grams ( 2.8-4.23 oz.)
Two ESCs must be mounted as close as possible to the motors to avoid electromagnetic cables interference, suffered by the system with long ( 10-15 cm.) leads from the motors to the ESCs.

All this means that the nose lengths of the stunt plane must be made shorter to maintain the C.G of the RTF plane where it supposes to be, having in mind the wings airfoil.

This also means, that to keep the C.G of the RTF plane in the proper place ( having in mind the wings airfoil), the tail part of the fuselage must be made longer.

What is better from the pattern's quality point of view: shorter nose or longer tail?

Your comments are, as always, appreciated if they stay on the topic.

Thank you,
M


 
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Offline TDM

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #1 on: June 30, 2020, 05:33:49 PM »
I go for longer tail moving the stab back.
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Online Tim Wescott

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #2 on: June 30, 2020, 06:35:58 PM »
Quote from: Matt Piatkowski on June 30, 2020, 02:33:23 PM
Hello,
Using two-motors-in-tandem contra (TMT contra), changes the nose and tail moments in the stunt plane.

The proper scientific & engineering term is moment arm.  Only stunt pilots shorten this to "moment".  A "moment" in proper scientific & engineering terms is a torque (or, if you're talking to your spouse then you say "just a moment" when you mean "go away for at least an hour, let me work").

Quote from: Matt Piatkowski on June 30, 2020, 02:33:23 PM
Two motors of the TMT contra must have two ESC and also additional cabling/harness.
These parts weight between 80 to 120 grams ( 2.8-4.23 oz.)
Two ESCs must be mounted as close as possible to the motors to avoid electromagnetic cables interference, suffered by the system with long ( 10-15 cm.) leads from the motors to the ESCs.

Interference with what?  Running long motor wires is fairly benign, even when you've got a radio in the mix.  Unless someone's come up with a timer with a magnetometer.

Quote from: Matt Piatkowski on June 30, 2020, 02:33:23 PM
All this means that the nose lengths of the stunt plane must be made shorter to maintain the C.G of the RTF plane where it supposes to be, having in mind the wings airfoil.

This also means, that to keep the C.G of the RTF plane in the proper place ( having in mind the wings airfoil), the tail part of the fuselage must be made longer.

What is better from the pattern's quality point of view: shorter nose or longer tail?

Your comments are, as always, appreciated if they stay on the topic.

Thank you,
M

Put the nose where the nose needs to be for aerodynamics, the tail where the tail needs to be for aerodynamics, keep the ESCs close to the batteries so the battery leads can be short, and put the batteries where the batteries need to be for balance.  Then make the motor leads as long as they need to be to reach, and if you feel there'll be a problem with EMI, braid them or twist them.

If you feel you must change the structure to balance the plane, shorten the nose -- but you'll be going against the grain of what at least one world champion (Igor Burger) is (or was -- I haven't kept track) doing.
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Offline Matt Piatkowski

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #3 on: July 01, 2020, 12:52:07 PM »
Hi Tim,
The C/L stunt/F2B community uses both terms interchangeably and it really does not matter as long as the person using the term knows the meaning of it.
You are probably aware that many people belonging to one professional / hobby group use the truncated versions of different definitions or terms simply for the ease of speaking.
This is how professional / hobby slang or lingo or jargon is created.

Nobody says "2x4 wooden beam made of spruce cut along its grains" - almost everybody says "hey, Joe!...give me this 2x4".

Igor's Max Bee II indeed has a rather long nose. The term "rather long" is rather vague but I do have this particular plane (it was called Big Red) and I aim to shorten the nose by 0.50".

The entire story leading to this 0.5" is very difficult to explain, even using the most strict and formal scientific language.

If I succeed, Big Red will make very tight pivoting corners without the tendency to stall and will fly with almost constant velocity in maneuvers.

Hi TDM,
The hinge-to-hinge distance in many well flying, modern stunt planes is slowly growing: 18.50" (typical in Yatsenko's F2B planes) is becoming 18.75, 19, and even more.
I am still searching for a convincing explanation of this change from the pattern quality point of view.


Best Regards,
M

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Online Tim Wescott

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #4 on: July 01, 2020, 12:55:43 PM »
Quote from: Matt Piatkowski on July 01, 2020, 12:52:07 PM

Hi TDM,
The hinge-to-hinge distance in many well flying, modern stunt planes is slowly growing: 18.50" (typical in Yatsenko's F2B planes) is becoming 18.75, 19, and even more.
I am still searching for a convincing explanation of this change from the pattern quality point of view.

Someone really needs to make an ugly plane with an adjustable fuselage length, for experimentation.

It'd take a lot of work, but basically, start at ridiculously long and test-fly at increments down to ridiculously short.  With proper trimming at each size, and variations in the tail plane size, it should only take a few years.
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Offline Matt Piatkowski

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #5 on: July 01, 2020, 01:28:22 PM »
Hi again Tim,
What matters the most is the judges' scores.

I know the guy who is the top fifteen in the world and he flies something having the hinge-to-hinge distance 20.27" (!!).
Of course, the surface area of the horizontal stabilizer and elevator is larger than for the models with hinge-to-hinge distance 18 -19" and I hope you know why.

This "fuselage tail extension" allows moving the RTF model C.G AFT without adding lead to the tail in the models with hinge-to-hinge distance 18 -19" - a common problem with the full-size stunt planes.

The stunt/F2B RTF top models C.G is slowly creeping AFT because top people fly better and more aggressive corners each year and the wings and empennage aerodynamics allows for this change.
Stay Safe and Fly Safely,
M
 
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Offline TDM

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #6 on: July 02, 2020, 11:27:44 PM »
My plane has a hinge to hinge about 22in. The model has corner to spare, in fact I have to slow the corner because I can't keep up with it. The logic to longer tails is, that you have greater torque on the wing forcing the change in AOA, which in turn created the necessary lift to pitch the plane. Another advantage of longer tails is better tracking easier to fly rounds and the option of an further aft CG. If you watched the videos I put in this forum you would see what I am talking about.
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Online Ken Culbertson

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Re: Shorter nose or longer tail or both when using the two-motors-in-tandem contra
« Reply #7 on: July 03, 2020, 12:13:51 AM »
Quote from: Tim Wescott on July 01, 2020, 12:55:43 PM
Someone really needs to make an ugly plane with an adjustable fuselage length, for experimentation.

It'd take a lot of work, but basically, start at ridiculously long and test-fly at increments down to ridiculously short.  With proper trimming at each size, and variations in the tail plane size, it should only take a few years.
It can be done.  Box in box like an adjustable table.  It certainly would look like crap.

Ken
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