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Author Topic: Scale beginner needs some geometry help  (Read 11014 times)

Offline Trostle

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Re: Scale beginner needs some geometry help
« Reply #50 on: January 05, 2016, 11:05:52 AM »
I agree with Bob Whitney on his comments about tip weight.  

I have no issue with Chuck Snyder's experience and comments about using no tip weight.  He has plenty of experience and is an accomplished builder/flyer.  However, some tip weight cannot hurt anything.  

If your model is coming in at around 6 pounds (96 oz!), a bit of tip weight would not make much difference.  So the question remains, how much?  Typically, a full size stunt ship (550 to 650 sq in and 50 to 60 oz) will have maybe around 3/4 oz of tip weight, more with equal span panels.  (Just a note about dihedral on stunt ships - dihedral does not affect performance on stunt ships.  But there is a problem in high wind on the up wind side of the circle but this is a whole other subject.)

On my small 1/2 A multi-engine scale ships, 36 to 42" span, 30 oz, I build in as much as 1/2 oz of weight.  On some larger scale models, 40 to 50 in span 40 oz, I will use as much as 1 oz.  My Martin Baker, .60 powered, 42" span, almost 5 pounds, I used something like 1.5 oz or more.  On your 6 pound model, I would recommend at least 1.5 oz.  It cannot hurt and will help keep that outboard tip down on the upwind side of the circle.  In my opinion, for a scale model one needs to compensate for more than just the weight of the leadouts and the amount of line weight that the inboard wing is supporting, particularly with a wing with any amount of dihedral.

Keith


Offline bob whitney

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Re: Scale beginner needs some geometry help
« Reply #51 on: January 05, 2016, 02:10:33 PM »

  and to add to Keith, when u slow down the lines add more drag to the inboard wing
rad racer

Offline Tim Wescott

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Re: Scale beginner needs some geometry help
« Reply #52 on: January 05, 2016, 02:16:00 PM »
Speaking only as a stunt guy, having too much tip weight (within reason) is mostly only a detriment when you're trying to do stunts more advanced than loops.

If you're not going to use any of the aerobatic options then some tip weight won't hurt at all.
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The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Danny Fenton

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Re: Scale beginner needs some geometry help
« Reply #53 on: January 05, 2016, 04:18:02 PM »
I appreciate your thoughts guys.
Bob I cannot quite see how the drag on the lines will increase when the model slows? Surely line drag increases dramatically with airspeed?

The PT-19 stunter I am doing my testing with definitely becomes much more stable by either slowing the model, or moving the c of g forwards. With the c of g rearwards the model is so much nicer to land and will float, I can place it where I like. With the c of g forwards it doesn't feel so balanced.

So my limited experience points to a nice flying model with the c of g more akin to an R/C model, when flown within the slower speed range of the model. However if you want to fly faster to allow for aeros etc then the more forward c of g makes for more stability and easier to maintain a constant height.
I have only flown in calm weather so I assume that a faster speed is required in higher winds, to maintain line tension upwind and therefore the c of g moved forwards?

It is all very confusing  HB~>

Offline Mike Lauerman

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Re: Scale beginner needs some geometry help
« Reply #54 on: February 06, 2016, 03:08:45 PM »
Just a funny note here on 'bellcrank unsightliness in cockpit'. A flying friend was impressed with my wife's flying, as there weren't many attractive women flying their own built planes in the '70s. Wife Joey was flying her immaculate Sterling S1 Ringer...
Ted insisted she fly his 'veteran' Sig Mustang, she was skeptical, as it was 54" W.S.? Thereabouts.
She flew it, couldn't get over its smoothness in flight...perfect 3 point landings...he made her a gift of it.

Joey liked the plane, but hated its 'finish'...She removed the canopy, engine, and all not to be detailed. Quick paint job, decals, and clean the canopy. But before replacing the canopy, she detailed the inside cockpit, finalizing it with a vacuformed pilot that she attached to the BELLCRANK, so when the control lines were active the pilot turned left and right slightly, it was a riot!
Looked real at a glance...

Offline Danny Fenton

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Re: Scale beginner needs some geometry help
« Reply #55 on: August 28, 2017, 05:08:28 AM »
I know it has been a while since I have posted but due to problems that I wont go into i was not able to compete at the british Nationals until this year. I didn't get a chance to maiden the model in its C/L format until the first round. I managed second in static, and after three flights was getting a good feel for the model and the manouvres, and how to fly them. What the rule book says and what the judges wanted however weren't quite in allignment. I will do better next year.
But I am really pleased to say I managed a second place in F4B :)


Offline Paul Smith

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Re: Scale beginner needs some geometry help
« Reply #56 on: August 28, 2017, 08:21:45 AM »
Thanks John, yes I am doing something similar. That's a very tidy unit you have there :)
Thanks Chuck, good advice on the bellcrank. I have not been able to do that as the fuselage has a fairly visible cockpit :( This is what I have done, shout if you think it may not be strong enough. I hope to get the model down to around 5lbs max, it is 1/6th scale and 68" span.
Cheers
Danny

You can beef up the bellcrank mount by using a longer bolt and making a plywood brace to the top of the bolt, thus creating a DOUBLE SHEAR mounting.
Paul Smith

Offline bob whitney

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Re: Scale beginner needs some geometry help
« Reply #57 on: August 28, 2017, 12:57:58 PM »
Sorry ,I haven't been keeping up with this p0sting.  the faster u go ,the more the plane pulls to the outside keeping the lines tight /when it slows down it looses that pull and lets the lines  drop,which tends to make the plane swing inward
rad racer

Offline Danny Fenton

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Re: Scale beginner needs some geometry help
« Reply #58 on: August 28, 2017, 05:07:33 PM »
My first round and maiden flight. I kept catching the throttle stick when feeling for the flap switch. I increased the throttle stick tension for subsequent flights and it was much better.



Cheers
Danny

Offline john e. holliday

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Re: Scale beginner needs some geometry help
« Reply #59 on: August 28, 2017, 09:02:38 PM »
I like it.   H^^
I was always taught to respect my elders, but it keeps getting harder to find one.
Today I broke my personal record for most consecutive days lived.
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Offline Paul Smith

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Re: Scale beginner needs some geometry help
« Reply #60 on: August 29, 2017, 08:30:22 AM »
How much tip weight?  There's no clear answer to that because nobody knows how the plane balances before the tip weight is added.  Maybe your leadouts and leadout guide weigh 1, 2, or 3 ounces.

I say this:

Test balance the model from the crankshaft and tail.
Add enough tip weight to make it balance.
Then add an ounce more.

This will give you an ounce of TRUE tip weight.
Paul Smith

Offline Danny Fenton

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Re: Scale beginner needs some geometry help
« Reply #61 on: August 29, 2017, 10:17:28 AM »
I am not sure what you are saying? from the video I have posted, do you think the tip weight is insufficient? The lines do not bow hardly at all even when I fly slow. The prop is CCW so the torque of the motor is helping keep the lines tight.



Cheers
Danny

Offline Paul Smith

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Re: Scale beginner needs some geometry help
« Reply #62 on: August 29, 2017, 10:57:08 AM »
One way to find out is to fly the model and see it it crashes.  Since it didn't crash, you did OK.

My suggested procedure for determining the tip weight before flying.
Paul Smith

Offline john e. holliday

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Re: Scale beginner needs some geometry help
« Reply #63 on: August 29, 2017, 01:05:50 PM »
I am not sure what you are saying? from the video I have posted, do you think the tip weight is insufficient? The lines do not bow hardly at all even when I fly slow. The prop is CCW so the torque of the motor is helping keep the lines tight.



Cheers
Danny

Watching the video it looks like it was staying tight on the lines and the wings seemed level to me.  You are flying it in scale competition not aerobatics so as long as it stays on end of lines you must have enough tip weight.   You just need to get more experience flying it. H^^
I was always taught to respect my elders, but it keeps getting harder to find one.
Today I broke my personal record for most consecutive days lived.
John E. "DOC" Holliday
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AMA 23530

Offline Fred Cronenwett

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Re: Scale beginner needs some geometry help
« Reply #64 on: August 30, 2017, 07:46:18 PM »
Looking at the video the model looks like it's flying fine, maybe move the CG forward to see if it's not so responsive to the elevator. The key will be to get some practice flights in and get the line guide, CG and other items trimmed out. Consider using a handle with a tighter line spacing to reduce the control throw.  You want know what options you are going to use and have the model trimmed out before attending a contest. If you have good line tension during taxi, take off run and flight then you are in good shape.

The AMA requires that pilots have already flown the model before flying it in competition.

Fred
Fred Cronenwett
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Model Aviation CL Scale columnist


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