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Author Topic: Scale Nats question #3  (Read 351 times)

Offline Hemi Steve

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Scale Nats question #3
« on: October 03, 2019, 06:00:20 AM »
I'm beginning to do a scale profile design for my winter build. In the scale rules, the discussion of the maximum width of a profile fuselage is confusing me. The paragraph says the max width is 1.00 inches.  Then it goes on to describe the allowable width  for a variety of motor mounting situations.  The article is silent about  the fuselage width allowance for electric motor mounting.  An example electric motor mount dimension is attached. 

1. The rule allows a vertically mounted engine to have a fuselage width of the width of the engine mounting lugs plus 1/2".  So does that apply to the "x" shaped mounting plate as shown?  If so, could I use the maximum (70mm) and add 1/2" to establish the maximum fuselage width?

2. Can a spinner diameter exceed the  width of the fuselage?

Thanks

Steve

Offline T.J. Vieira

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Re: Scale Nats question #3
« Reply #1 on: October 03, 2019, 06:05:11 AM »
yes to both.

however, don't try to take advantage of the rule by trying to taper it back to the allowable dimension so that just the tail is correct  n1 hahahahaha

Offline Hemi Steve

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Re: Scale Nats question #3
« Reply #2 on: October 03, 2019, 06:51:38 AM »
Thanks T.J.

I'm not sure I understand the "However..." line. 

Lets say my maximum width is 82mm (70mm + 1/2").  How far back can that dimension carry?  The rule also talks about additional reinforcement that can go to the 25% chord point. Is the increased width to clear the engine mounting ( the 82mm dimension in this example) considered the "reinforcement"? That portion of the rule is confusing as well.

For reference, The airplane I'm considering is a Dornier Do 335 which of course has an engine in the tail and would also need added width for the motor mount.

Steve

Offline T.J. Vieira

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Re: Scale Nats question #3
« Reply #3 on: October 03, 2019, 10:18:29 AM »
you are correct.  it's to also allow for ply doublers, apple cheek cowls, etc.  however, from that point back, you are constrained by the definitions of a profile model.

Offline T.J. Vieira

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Re: Scale Nats question #3
« Reply #4 on: October 03, 2019, 10:19:25 AM »
however, for a pusher motor, i don't think you could get away with a ply doubler going all the way from the back to, essentially, the front of the plane...

Offline Bob Heywood

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Re: Scale Nats question #3
« Reply #5 on: October 03, 2019, 02:55:16 PM »
This is Fred Cronenwett's Profile B-29. You can see the pad for the motor mount. Use the simple solution.
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Offline Bob Heywood

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Re: Scale Nats question #3
« Reply #6 on: October 03, 2019, 03:29:51 PM »
"Clockwise Forever..."

Offline Hemi Steve

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Re: Scale Nats question #3
« Reply #7 on: October 03, 2019, 04:48:49 PM »
Ok, I think I understand now.  What I think I'm seeing is that the fuselage can be made wider in a VERY localized area. essentially just enough to create an adequate mount for the motor. Am I understanding that you can add reinforcement to the 1" fuselage width like most profile ukies where there is a plywood doubler extending to a point a bit beyond the wing leading edge.  The scale rule doesn't describe a limit on the thickness of such a doubler reinforcement as I read it.  Have I read this correctly??

Steve

Offline Bob Heywood

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Re: Scale Nats question #3
« Reply #8 on: October 03, 2019, 07:32:37 PM »
Ok, I think I understand now.  What I think I'm seeing is that the fuselage can be made wider in a VERY localized area. essentially just enough to create an adequate mount for the motor. Am I understanding that you can add reinforcement to the 1" fuselage width like most profile ukies where there is a plywood doubler extending to a point a bit beyond the wing leading edge.  The scale rule doesn't describe a limit on the thickness of such a doubler reinforcement as I read it.  Have I read this correctly??

Steve

Not exactly.

According to the chart the fuselage for Scale may not exceed 1" thickness, period. There is  no allowance for doublers, etc. However you decide to construct the fuselage the end result may only be 1" wide at its widest point.

The electric motor mount sticks out from the sides of the fuselage simply because of the motor dimensions. There is no way around it. As you can see the motors on the B-29 are centered in the nacelle width. It looks like the motor is outboard of center on the La-5 so all of the hardware is on one side, leaving the other side clean.

If you want to be really clever, rig the plane so the motor and all of the other stuff is on the inboard side of the fuselage, leaving the out board side clean. This will present the full fuselage to the judges and spectators instead of a flying hardware store.
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Offline Trostle

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Re: Scale Nats question #3
« Reply #9 on: October 04, 2019, 01:12:44 PM »
Not exactly.

According to the chart the fuselage for Scale may not exceed 1" thickness, period. There is  no allowance for doublers, etc. However you decide to construct the fuselage the end result may only be 1" wide at its widest point.

(Clip)


What "chart" for Scale are you looking at?  There is no "chart" that defines any fuselage widths in the Control Line Scale rule book.  In the Control Line General rule book, there is a chart that defines "Profile Fuselage Width" for the various profile control line events.  For Scale, that chart shows the "Maximum Fuselage Width" to be "1 inch" and the "Max Width of Additional Reinforcements" for "Engine Mount Vertical" to be "Mounting Lugs Plus 1/2 Inch" and for "Horizontal" to be "1/2 inch"

So, there is an "allowance for doublers, etc" and there are portions of the fuselage and/or nacelles that can exceed 1" wide.

If we are going to go by the CL Scale rules for Profile Fuselages, we need to look at Paragraph 5.2 of the scale rules which does not conflict with the Control Line General rules for profile fuselages use in Control Line Scale.

"The maximum width for profile fuselages and nacelles will be on (1.0) inches.  For upright and inverted engine(s) the maximum reinforced fuselage and/or nacelle width may be one half (1/2) inch wider than the engine mounting lugs.  The maximum width of the reinforced fuselage and/or nacelle of horizontally mounted engine(s) will be one and one half (1.50) inches.  Additional reinforcement [may] be made in the engine/motor area of the fuselage extending from the front of the fuselage to a point twenty five percent (25%) of the maximum wing chord aft of the leading edge of the wing.  For engine(s)/motor(s) mounted in nacelle(s) the maximum reinforcement length will be from the front of the nacelle to a point twenty five percent (25%) of the maximum wing chord length aft of the wing leading edge at the nacelle location.  For multiengine models the width of nose section of the fuselage may be increased to one and on half (1.5) inches extending from the front of the fuselage to a point twenty five percent (25%) of the maximum wing [chord] aft of the leading edge of the wing."

Note:  The brackets - [ ] - shown above are to correct typographical errors in the rule book.  [may] is shown to replace the incorrect word "many".  [chord] is shown to replace the incorrect word "cord".

A profile scale model of the Do 335 presents interesting design challenges.  First, a decision needs to be made if the aft engine will be mounted in the scale position which is just behind the wing trailing edge with the requisite long shaft to the rear propeller or if the aft engine will be located at the very rear of the fuselage somehow, somewhere between the horizontal tail sections.  If the engines/motors are not larger than 0.20 cu in or even 0.25 cu in (or the battery powered equivalents), then the 1" maximum width to mount these power plants would seem to be enough  to provide enough structure for these power plants.  If larger power plants are planned, then some additional doublers/reinforcement might be used around the area of the motor mounts but would probably not be necessary unless rather large engines are used like 0.45 cu in or larger.  (Then you are probably going to have a HUGE Do 335.)  That would create a rather unsightly "bulge" on the fuselage for the mid-engine approach and would complicate how to mount the engine if it is mounted in the tail section between the horizontal tail sections.

Keith 


Offline Hemi Steve

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Re: Scale Nats question #3
« Reply #10 on: October 04, 2019, 04:56:18 PM »
Keith
The two models (B-29 and La5) take completely different approaches to dealing with the width question and neither, as I look at them, clarify the application of the rule.  The Do 335 that I'm contemplating does indeed create a rule interpretation problem if there is a second motor which is why I'm asking the question here.  I'm looking at an electric model.  A couple of years ago I built an r/c semi scale version for a local competition. Instead of using 2 motors I designed it to have a free wheeling rear prop that was driven by the prop wash of the front motor.  There's some information on the design of the prop to minimize the drag of the free wheeling prop.  It worked great and made a very unique sound in the air.  Anyway the width rule is still confusing to me. The model really flew nice.  Even if I take the same approach for the rear prop, the width question remains for the front.

The La5 inside surface to outside surface asymmetry is obvious in the pictures but the why do it that way is not obvious.  It looks to me that the fuselage is more than 1.0" wide and it also looks to me that the "reinforcement" goes beyond the 25% point. 

It looks to me that the B-29 approach takes an approach that is the least challenging to the rule.

Steve

Offline Trostle

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Re: Scale Nats question #3
« Reply #11 on: October 04, 2019, 05:53:47 PM »
Keith
The two models (B-29 and La5) take completely different approaches to dealing with the width question and neither, as I look at them, clarify the application of the rule.  The Do 335 that I'm contemplating does indeed create a rule interpretation problem if there is a second motor which is why I'm asking the question here.  I'm looking at an electric model.  A couple of years ago I built an r/c semi scale version for a local competition. Instead of using 2 motors I designed it to have a free wheeling rear prop that was driven by the prop wash of the front motor.  There's some information on the design of the prop to minimize the drag of the free wheeling prop.  It worked great and made a very unique sound in the air.  Anyway the width rule is still confusing to me. The model really flew nice.  Even if I take the same approach for the rear prop, the width question remains for the front.

The La5 inside surface to outside surface asymmetry is obvious in the pictures but the why do it that way is not obvious.  It looks to me that the fuselage is more than 1.0" wide and it also looks to me that the "reinforcement" goes beyond the 25% point. 

It looks to me that the B-29 approach takes an approach that is the least challenging to the rule.

Steve

I do not know what clarification to the profile scale rules are needed.  The fuselage and nacelles cannot be more than 1" wide.  Any additional material around the engine cannot be more than 1 1/2" wide.  The wider width cannot go past 25% of the wing chord.  What is the problem you see with these requirements/limitations?

What is it that you see that makes that La-5 appear more than 1" wide and that extra width goes beyond the 25% position of the wing?  I have an idea the whole front end of that LA-5 is not more than 1" except for all of the machinery that is mounted on or in the nose.  What is it that you see that you do not understand why "it was done that way".  You are getting into the vagaries of CL Profile Scale.  You should realize that just the event name - "Profile Scale" is a dichotomy and some people believe it to be an admonition.  Nevertheless, it is a popular event, serves to help get people into the scale events and some really good CL scale builders/flyers/competitors do compete in it.

Keith

Yes, the Do 335 presents a problem in execution but it is not the way the rules are written.  You probably could add additional material around the engine, but for your electric, what Fred did with his B-29 would certainly be a practical approach and it does not "challenge" the rule as you just suggested.  If you see that is is challenging the rule, please explain.

Offline Bob Heywood

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Re: Scale Nats question #3
« Reply #12 on: October 04, 2019, 09:30:28 PM »
Keith
The two models (B-29 and La5) take completely different approaches to dealing with the width question and neither, as I look at them, clarify the application of the rule.  The Do 335 that I'm contemplating does indeed create a rule interpretation problem if there is a second motor which is why I'm asking the question here.  I'm looking at an electric model.  A couple of years ago I built an r/c semi scale version for a local competition. Instead of using 2 motors I designed it to have a free wheeling rear prop that was driven by the prop wash of the front motor.  There's some information on the design of the prop to minimize the drag of the free wheeling prop.  It worked great and made a very unique sound in the air.  Anyway the width rule is still confusing to me. The model really flew nice.  Even if I take the same approach for the rear prop, the width question remains for the front.

The La5 inside surface to outside surface asymmetry is obvious in the pictures but the why do it that way is not obvious.  It looks to me that the fuselage is more than 1.0" wide and it also looks to me that the "reinforcement" goes beyond the 25% point. 

It looks to me that the B-29 approach takes an approach that is the least challenging to the rule.

Steve

the chart I refer to is in the C/L General Rule on pg 10. There is nothing written in the Scale box under Max Width of Additional Reinforcements so I interpreted that to mean that nothing else was permitted. I do stand corrected in that I did not dig through the Scale rules to see what was said about Profile. I would say, however, that everything written is directed to I/C power installations. Electric has different requirements. My view is that the fuselage and motor mount (s) are two separate and distinct elements. The motor mount is not part of the fuselage, it is attached to the fuselage just as in a full scale aircraft. Ultimately, you have to be able to mount the motor (s).

As for why John Rist mounted the motor on the La-5 the way he did, I refer you to Reply #10 on PG 1 of the referenced thread. There are two excellent photos of the model under construction and a brief explanation of why it was done that way. As I said previously, I would hang all of the hardware on the inboard side of the model so the outboard side looks like a Do 335.

I was Chief Judge for C/L Scale at the 2016 NASA Scale Classic and had the opportunity to judge Joe Eiben's Profile Hustler. It is electric powered. Joe built the model with retracts and had to come up with a novel way to mount the electric motor and have room for the nose gear to retract. The result was a semi mid-mounted motor with shafting to the nose and prop driver. He nicely faired in the motor mount. The fuselage met the 1" requirement from nose to tail. You could easily solve the Do 335 install in a similar manner.

Good luck!
« Last Edit: October 04, 2019, 09:47:38 PM by Bob Heywood »
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