[NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED

Wed Dec 5 11:17:05 AKST 2012

There's an old thread on RCU starting on page 37 that discusses this in length
http://search.yahoo.com/r/_ylt=A0oG7hayqb9Q6XkA85dXNyoA;_ylu=X3oDMTE1MjF1cTg5BHNlYwNzcgRwb3MDMgRjb2xvA2FjMgR2dGlkA1NNRTE0NV8yMTU-/SIG=12i3ovjq4/EXP=1354766898/**http%3a//www.rcuniverse.com/forum/m_5004679/mpage_38/key_/tm.htm

I think it's a violent warble much like a shimmy in a loose front tire when you hit a certain speed (been there done that a long time ago in a 56 Ford station wagon) or a flutter in an aileron. Once the harmonic is set into action it's steps up in intensity exponentially.
 I've thought in the past that thin floopy long props contribute to the problem because they can go into a dynamic inbalance.. I think stiff props work better.
 But if you read the thread the smart people shot me down. 
 Bottom line...... support the rear of a front mount.
 M²

________________________________
From: Verne Koester <verne at twmi.rr.com>
To: 'Larry Diamond' <ldiamond at diamondrc.com>; 'General pattern discussion' <nsrca-discussion at lists.nsrca.org> 
Sent: Wednesday, December 5, 2012 2:05 PM
Subject: Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED

Larry,
I think what must of us have done is to copy what was successful for someone else. There are lots of build articles on RC Universe in the pattern and electric pattern forums. Pick a plane, pick a motor, or some combination of the two and read. To my knowledge, there’s no single source point of information. Once you’ve narrowed down your choice, inquire right here and I’m sure you’ll get all the info you want or need.

Verne

From:nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Larry Diamond
Sent: Wednesday, December 05, 2012 2:30 PM
To: General pattern discussion
Subject: Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED

As somebody who is trying to get back into Pattern and those like me that have Zero experience with high power electric setups, is there an article or a something posted that we can reference?

Maybe something on the NSRCA Website that can be accessed by all under Tips an Set Up...Yada Yada Yada...

Larry Diamond

From:Verne Koester <verne at twmi.rr.com>
To: 'General pattern discussion' <nsrca-discussion at lists.nsrca.org> 
Sent: Wednesday, December 5, 2012 12:16 PM
Subject: Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED

I agree with Chris. I’ve personally had thousands of flights with nose mounted motors with rear supports and never had so much as a hint of failure. If you count all the flights I’ve seen Andrew fly with his nose mounted, rear supported motors as well as countless others at the practice field and on the contest trail, the number probably reaches into the tens of thousands. 

The only time I’ve ever witnessed a catastrophic motor induced fuselage failure was while I was judging an FAI pilot flying an Axi-equipped Smaragd a few years back. Following a turnaround, there was a short, deep, rumbling sound that sounded a little like flutter with heavy bass followed by the departure of the motor and a significant section of the nose of the fuse. The motor was nose mounted and had no rear support. 

My best guess, and it is just a guess,  was that the prop arc coupled with the forces of the looping turnaround, set up a harmonic, or flutter if you will, that the fuse couldn’t contain. The rumble was very brief before it came apart. 

I have no engineering data to report, just practical experience. A nose mounted motor without a rear support is a disaster about to happen. As Chris said, it’s just a matter of when.

Verne Koester

From:nsrca-discussion-bounces at lists.nsrca.org [mailto:nsrca-discussion-bounces at lists.nsrca.org] On Behalf Of Chris
Sent: Wednesday, December 05, 2012 12:50 PM
To: Bob Kane; General pattern discussion
Subject: Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED

Early in the electric transition, many of us found out the hard way that nose mounted outrunners without a rear support would lead to structural failures with nearly 100% certainty.  My nose mounted Genesis lasted 1 1/2 flights before failure.  Others had many more flights but even the best cases I know of had nose structure stresses and cracking due to the unsupported nose mounting.  Jerry Budd and I did a lot of testing and posting about this issue back in 2006 or 2007.  Newer designs have reinforced noses which help but bottom line, don't nose mount an electric motor without rear support. It "might" last 1 or 500 flights but 501 won't be as successful.

Chris
On 12/5/2012 12:38 PM, Bob Kane wrote:
Great observations.  I am curious about the numbers myself, maybe in my spare time (ha!) I'll pull out my old physics books and crunch some numbers. 
> 
>Bob Kane
>getterflash at yahoo.com
>From:ehaury mailto:ejhaury at comcast.net
>To: mike mueller mailto:mikemueller at f3aunlimited.com; General pattern discussion mailto:nsrca-discussion at lists.nsrca.org 
>Sent: Wednesday, December 5, 2012 11:02 AM
>Subject: Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED
> 
>I don't know what caused Charlie's failure, we've discussed possibilities - obviously forces occurred that were beyond what the structure could handle.
> 
>Torque & precession have been with us since we stuck engines & props on the front of airplanes. They really haven't changed much with the advent of E power - actually went down with the use of lighter props.
> 
>I'd just like to offer that the Hacker Q80 design doesn't change much. The rotating outer member (Q80-14) weighs about 100g and rotates up to 7K rpm with an 1 1/2" radius. The rotor in a C50 also weighs around 100g, but it rotates up to 40K rpm on a 3/8" radius. The latter, with the gearbox, can probably apply torque quicker than the outie. Most other popular outrunners fall somewhere between these. (Be neat if someone actually made the calcs.)
> 
>I've lots of flights with the Q80-11 without issue (the Q80-14 is less powerful). It is firmly front mounted with also a solid rear mount. I think we all know the importance of a nose ring on a YS and there's been no success running inrunners without a rear support. While some have had success running the Q without a rear support (bet the prop was light), these things really need a more sturdy rear support (or very stout front mnt / fuse nose) than may be obvious.
> 
>Essentially something slightly different that adds to the learning curve, hopefully Charlie's experience and these discussions will prevent further occurrences.
> 
>Earl
>----- Original Message ----- 
>>From:mike mueller 
>>To:Bob Kane ; General pattern discussion 
>>Sent:Wednesday, December 05, 2012 8:26 AM
>>Subject:Re: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model- RESUBMITTED
>> 
>>Very cool video. I've learned a lot of neat things watching Youtube video's. Thanks Bob
>> 
>>From:Bob Kane <getterflash at yahoo.com>
>>To: Generalpatterndiscussion <nsrca-discussion at lists.nsrca.org> 
>>Sent: Wednesday, December 5, 2012 7:07 AM
>>Subject: [NSRCA-discussion] Fw: Serious Torque on the Nose of the Model - RESUBMITTED
>> 
>>Charlie was spot on with his comment on torque, but there are two torque vectors at work, the first is the obvious force required to turn the prop and the "equal but opposite" torque the motor transmits to it's mount. If that was all we had to worry about, the single mount would probably be fine. But there is the other torque (gyroscopic precession)  resulting from attempting to move a rotating mass in the pitch or yaw axis.  Here is a good youtube video demonstrating the effect . .. .  
>> 
>>http://www.youtube.com/watch?v=ty9QSiVC2g0
>> 
>> 
>>Bob Kane
>>getterflash at yahoo.com
>>From:mike mueller mailto:mikemueller at f3aunlimited.com
>>To: Bob Kane mailto:getterflash at yahoo.com 
>>Sent: Tuesday, December 4, 2012 4:34 PM
>>Subject: Re: [NSRCA-discussion] Serious Torque on the Nose of the Model - RESUBMITTED
>> 
>>Say what?
>>"a large reactionary force called gyroscopic precession"
>> I feel infinitlty smarter
>> Is it violent warble?
>> What prop were you running????
>> Mike
>> 
>>From:Bob Kane mailto:getterflash at yahoo.com
>>To: mailto:vicenterc at comcast.net mailto:vicenterc at comcast.net; General pattern discussion mailto:nsrca-discussion at lists.nsrca.org 
>>Sent: Tuesday, December 4, 2012 7:54 AM
>>Subject: Re: [NSRCA-discussion] Serious Torque on the Nose of the Model - RESUBMITTED
>> 
>>The Q80 has a large diameter rotating mass, and it brings with it a large reactionary force called gyroscopic precession when it is spinning.  In laymen terms it will strongly resist changing direction in yaw or pitch.  A rear brace would help keep this force in check. 
>> 
>>
>> 
>>Bob Kane
>>getterflash at yahoo.com
>>From:mailto:vicenterc at comcast.net mailto:vicenterc at comcast.net
>>To: General pattern discussion mailto:nsrca-discussion at lists.nsrca.org 
>>Sent: Tuesday, December 4, 2012 8:27 AM
>>Subject: Re: [NSRCA-discussion] Serious Torque on the Nose of the Model - RESUBMITTED
>>
>>I understand that a rear brace is a must for this motor.  
>>
>>Vicente "Vince" Bortone
>>Sent via BlackBerry by AT&T
>>
>>-----Original Message-----
>>From: "Charlie Barrera" <charliebarrera at consolidated.net>
>>Sender: nsrca-discussion-bounces at lists.nsrca.org
>>Date: Tue, 4 Dec 2012 07:02:47 
>>To: <nsrca-discussion at lists.nsrca.org>
>>Reply-To: General pattern discussion <nsrca-discussion at lists.nsrca.org>
>>Subject: [NSRCA-discussion] Serious Torque on the Nose of the Model -
>>    RESUBMITTED
>>
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