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Author Topic: Landing Gear Question  (Read 423 times)

Offline Greg Rodney

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Landing Gear Question
« on: March 31, 2020, 01:32:40 PM »
Hey Folks, I've had quite a few requests to do a Wedell Williams Racer as a 54" profile kit. It would be based on Mike Garmon's plane. ( I think I got the right name!) Pix of it below.
His had an aluminum landing gear mounted on the fuselage...I want to go to a wing mount.
I pulled a few "3" view drawings off the net to work with. My question is, and I guess I'm polling for a general consensus on a wheel to wheel width.
If I scale from the real plane drawings it comes out to be about 11-1/2" I attached a screen shot from Fusion.
This seems to be a bit narrow to me. I'm kinda leaning toward 14" or more.
So I would appreciate some input.

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!


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Offline Tim Wescott

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Re: Landing Gear Question
« Reply #1 on: March 31, 2020, 02:51:50 PM »
Put the "semi" in semi-stunt scale and make the landing gear match current practice on full-up stunters (meaning -- wide).
AMA 64232

The problem with electric is that once you get the smoke generator and sound system installed, the plane is too heavy.

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #2 on: March 31, 2020, 09:38:59 PM »
This is what I got so far.
I'm actually thinking 16" wheel spacing.
Ya gotta have room for da pants!!!!
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #3 on: April 02, 2020, 04:21:29 PM »
After the brain dust settled, I wound up at 14-3/4" Looks about right...to me, anyways
Here's a couple more pix.
Tomorrow I'll "blow it apart" for the cut files, sharpen the axe, and start in on it. n~
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline MikeyPratt

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Re: Landing Gear Question
« Reply #4 on: April 05, 2020, 11:36:21 AM »
Hi Greg,
I'n my opinion part of the attraction to models like yours is the “How Close It Resembles the scale Aircraft and still provide a good airframe to perform for the required stunts.  Have you flown this model?  If so, are you happy with the CG location and it’s all around performance?  An old rule of thumb is the centerline of the wheel (where it contacts the surface) be located at 15 degrees ahead of the CG, if you fly entirely off grass, then move it forward slightly to 16 to 18 degrees.  I agree that making the stance wider helps in improving take-off and landings, but too many changes will detour from its scale appearance.  Of course you will have to make that choice as to how far off scale you want to go.  Good Luck and I hope to see your finished model on here.

Mike Pratt
Another of my opinions, I would have added a small amount of dihedral to the wing about 1/2” to 3/4” under each wing tip to get the leadout closer to the vertical CG.

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #5 on: April 05, 2020, 01:51:14 PM »
Mikey, I scaled this back (exactly) from Garmon's original, which was a 60". My goal is to get it to fly well with a healthy .40 or .46.
I haven't even cut this one out yet. The CG on the original was right on the center line of the bell crank, and all I can say is, in the air it looked smooth!!!
I attached a pic with some geometry. For right now I'm at about 25 degrees ahead of the CG. So I'm guessing I should be OK in that respect.
I'm going to leave the LG block length as they are. That will let me change out different widths of LG to see how it rolls in the grass.
I'm not good enough at this stuff to mess around with dieheidral yet!!!

I appreciate the input I've gotten so far on this project.
YES!  I will use a 4" bell crank
YES!  I will use carbon fiber push-rods
Also it will have a polyester reinforced, laminated fuselage.

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Online Trostle

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Re: Landing Gear Question
« Reply #6 on: April 05, 2020, 04:54:09 PM »

The CG on the original was right on the center line of the bell crank, and all I can say is, in the air it looked smooth!!!
I attached a pic with some geometry. For right now I'm at about 25 degrees ahead of the CG. So I'm guessing I should be OK in that respect.



I appreciate the input I've gotten so far on this project.
YES!  I will use a 4" bell crank
YES!  I will use carbon fiber push-rods
Also it will have a polyester reinforced, laminated fuselage.

Greg

From your drawing showing where the bellcrank is and you say the CG is at the center of the bellcrank, that means that your CG is 27% or 30% of the wing chord (depending whether you count the flaps as part of the wing chord).  Yet you said "in the air, it looked smooth".  Good luck with getting a good performing stunt ship from that CG location.

By the time you get a really honest CG location of somewhere between 20% to something probably less than 25%, the landing gear position you show where the wheels are now will start to approximate the 15o swept forward position from the CG as previously recommended in this thread (see Mike Pratt's recent post).

Keith

Offline Ted Fancher

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Re: Landing Gear Question
« Reply #7 on: April 05, 2020, 05:02:48 PM »
Greg,

Those pix/graphics are awesome!  You've got some skills and tools for sure.

While I think most of Mikey's suggestions are right on I'm not so sure I'd mess with dihedral on it.  Comparing the various pics it doesn't look to me like the power train will be (on center) much higher than the wing centerline and the landing gear and wheels will be opposing any roll moment that it would produce.  Given the nature of profiles attraction (and this one is damned attractive) to less experienced builders the additional complexity involved in getting it all put together right might put some of those builders a little behind the eight ball.  For the roll moment liable to result from what I can see I wouldn't worry about it.

The design/ship looks awesome as well.    Can't wait to see what the final package looks like.

Ted Fancher

p.s.  What the heck is the aspect ratio of that wing????  It looks looooong!

Ooops. Added p.s.  I meant to ask if the pictures reflect the construction of the finished product.  I'm a little concerned about the wing mounted gear in a wing without sheeting/cap strips and especially no ply doublers on the gear mount ribs.  Are those lack simply due to the drawings being preliminary??  Some flying fields play havoc with landing gears and the structures to which they're attached.  Please don't ask my how I know such things!!!

Offline Motorman

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Re: Landing Gear Question
« Reply #8 on: April 05, 2020, 06:08:50 PM »
I would have added a small amount of dihedral to the wing about 1/2” to 3/4” under each wing tip to get the leadout closer to the vertical CG.

I like this idea because the lead outs always seem to snag on the grass on a low wing model.


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Offline Greg Rodney

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Re: Landing Gear Question
« Reply #9 on: April 05, 2020, 08:21:10 PM »
Ted,
FUSION 360 says the area is 484.94 sq in, span is 54", so if my arithmatrick is correct...

54 x 54 = 2916... 2916 /484.94= 6.01:1 ???
Did I do that right?
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #10 on: April 05, 2020, 08:37:01 PM »
Keith, Your point about the CG...you ARE correct. When I had FUSION calculate the "Center of Mass", I forgot to add the mass of the motor and empty tank when I did it.
I'll have to finish up my Brodak .40 solid model to do that.

That's why I'm in here, looking for guidance and fresh eyes on the project!

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Howard Rush

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Re: Landing Gear Question
« Reply #11 on: April 06, 2020, 02:03:35 PM »
Looking at your pictures, I see that your structure is made out of oak.  That could result in a CG that's too far aft.

Hope this helps.
The Jive Combat Team
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Offline Greg Rodney

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Re: Landing Gear Question
« Reply #12 on: April 06, 2020, 05:42:38 PM »
Howard ya needs ta git yer specticles checked!!! That's not oak!!! It's Teak!!! LL~
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Ted Fancher

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Re: Landing Gear Question
« Reply #13 on: April 07, 2020, 03:50:10 PM »
Ted,
FUSION 360 says the area is 484.94 sq in, span is 54", so if my arithmatrick is correct...

54 x 54 = 2916... 2916 /484.94= 6.01:1 ???
Did I do that right?

that's the same number I get, Greg!  Ain't mathematics wunnerful. 

How about that structure matter I mentioned.  Will the wing be as shown or leading/trailing edge sheeted and ribs cap stripped?  Again, my concern is the structure to support the landing gear on "unimproved" runways!!

Ted

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #14 on: April 07, 2020, 07:34:30 PM »
Ted,
Ya, I still have a bit more detail to get into the design.
The ribs at each end of the landing gear blocks are going to be .115 lite-ply.
The spars are going to be bass wood.
And I'm planning on using 1/16 plywood to vertically sheet the rear side of the spars, rib to rib in that area.
I know it's going to add a few ounces, but you have to understand when I go out to the center of the circle, earthworms put on their hard hats LL~

I'll post some more screen shots after I get that stuff added.

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline John Miller

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Re: Landing Gear Question
« Reply #15 on: April 07, 2020, 08:40:41 PM »
Greg, I've typed and lost two long answers, that would have made Ted blush. I even used "Quotation marks".

You've done good work with Fusion 360. You made me download it to see if I could update my 2D skills.

The problem as I see it, is that you may have misread Mickey's directions for setting up your gear.

You measure from the CG to the point where the tire touches the ground, not through the axle as you have done.

The proper angle varies from 14% through 19% depending on your use.

Team Racers, who come in and land at high speeds use an angle of 14%. Our slower planes, sport, and stunters, do well using 14%~19% depending on the surface you are landing on. !9% is a good compromise for times when you may need to fly off, and onto short grass. If you fly exclusively off of normal grass, consider 20~24% or even more,  but  be  careful. Too far forward and you may start bouncing your landings.

Best wishes, John Miller

ps: Ask Ted how to locate the MAC on any wing, and then how to use the "Rule of Thumb" to estimate the CG based on the stab and elevator's percentage of the wing-flap area.

I just can't get into typing that all in a third time.......
« Last Edit: April 07, 2020, 08:58:11 PM by John Miller »
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Offline Greg Rodney

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Re: Landing Gear Question
« Reply #16 on: April 08, 2020, 02:49:53 PM »
Ted,
Here are a few more screen shots.(top sheeting removed for clarity) The ribs that are gray will be .115 lite-ply. The spar to spar bracing will be 1/16 ply.
Your thoughts!

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Ted Fancher

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Re: Landing Gear Question
« Reply #17 on: April 08, 2020, 03:44:47 PM »
Ted,
Here are a few more screen shots.(top sheeting removed for clarity) The ribs that are gray will be .115 lite-ply. The spar to spar bracing will be 1/16 ply.
Your thoughts!

Greg

Awesome, Greg.  I expected as much but wanted to check.  Gotta say again, I love whatever program that is you used for the drawings.  Do you program it with specs of all the components so it can accommodate pictures from biased angles accurately?

Couple of other questions: 1. Will the plans show the trailing edge sheeting square "butt-joined" on center-line as depicted or angled in opposing directions top and bottom?  2. In that image showing the control system the flaps appear to be very narrow in chord...maybe less than an inch.  Is this accurate or only that way for ease of quick drawing?

Ted

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #18 on: April 08, 2020, 04:14:25 PM »
Ted,
The software is called FUSION 360. Believe it or not IT IS FREE to home hobbiests! There is a hell of a learning curve...but worth the time to learn it!
Yes all components are specd... right down to the 5-40 NyLock nuts from McMaster CArr Pic below.
Those flaps are THAT narrow in cord. They were only an 1-3/8" on Mike Garmon's original 60 incher. Pic below.
Ya, I see that butt joint in the trailing edges. I still have a ton of details to tweak yet!

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Greg Rodney

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Re: Landing Gear Question
« Reply #19 on: April 09, 2020, 10:55:40 AM »
John,
WOW! Quotations and all!!!??? HEHE
It's happened to me quite a few times, and I think the issue is with the timer setting when you log in. If it's set at 60 min, let's say your frequenting your favorite threads for 45 min, now you take 20 min to write a lengthy post... when you hit the "POST" button, you were logged out 5 min ago, and all your typing gets dumped. I got into the habit of highlighting my post, and hit "control C" before I hit the "POST" button. Saved my hiney a few times!

About FUSION 360, it seemed really hard at first. What I can tell you is watch all of Lars Christiansen's videos. He is a great teacher. Think of everything we look at all day long, it has height, width, and DEPTH! Once you start thinking that way in FUSION, it all clicks, and it becomes second nature. I'm not THAT good at it but if you have any questions I MIGHT be able to help you out ...wait until you see my PT-19 Ringmaster! All done in FUSION. Another thing that is a great function in FUSION is you can create a Library of "parts" bell cranks, control horns, DuBro hinges, push rod ends, wheels, tanks, even motors, and just import the parts into you NEW design, you don't have to re-invent the wheel every time (cox production motor attached)

Had to read your last post a few times before it soaked into the gray matter! I see that I'm going to have to get my tail wheel in place, a ground plane set, and my prop put in before I can establish my landing length and angle.

Awhile back, I had downloaded "Guru Ted's" article on stunt design. Still trying to absorb it all.

Greg
Never grow up!
If you grow up, you grow old.
If you grow old, you grow slow
If you grow slow, they catch you. When they catch you, they stick you in the ground! ...let's go play with airplanes!!!!

Offline Howard Rush

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Re: Landing Gear Question
« Reply #20 on: April 09, 2020, 03:58:52 PM »
https://stunthanger.com/smf/stunt-design/landing-gear-question-56129/?action=dlattach;attach=310196

Excellent craftsmanship.  The parts fit is splendid, and that's hard to do with such hard wood.
The Jive Combat Team
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Offline John Miller

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Re: Landing Gear Question
« Reply #21 on: April 09, 2020, 06:37:31 PM »
Greg, you don't need to wait to set up your landing gear. It appears that you have the fuelage set up with the thrust line at 0-0, as if the plane is in level flight.

That's the most useful starting point. 

Since your wing is straight, the chord can be measured at the root, or most anywhere along the wing. The 18% number is normally good for this type of un-flapped wing to use.

You already have a line representing the ground surface. You just need to run your angle line from the CG to the point where the ground line contacts the tire.

It's a good idea to give yourself enough prop clearance , and that of course will determine how long your gear will have to be.

As soon as I finish a few projects, I plan on doing some serious study on Fusion. thanks for the suggestions.

John
Getting a line on life. AMA 1601


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