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Old Sep 13, 2007, 03:44 PM
Registered HotGlue Addict
chaosMurphy's Avatar
Joined Dec 2006
1,455 Posts
My BB-33 build log 13 Sep 07
Bottle[1] to throttle in less than 6 hours[2].
She came in at 5.75 oz … profile / no BATT

Flew right out of the box, only adjustment needed was less throttle.

Reason for build…
I’ve seen several newbe posts/questions of late plus
Grandkids looking for something new :>)

[1] ink ‘bottle’ that is, printer was dry this morning
[2-1] not my first foamy build
[2-2] all hot glue
[2-3] brown truck arrived just in time to save stripping a hanger queen :>)

Tony, Thanks for sharing…

Gramps
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Old Sep 13, 2007, 03:56 PM
AKA Don
bz1mcr's Avatar
United States, MI, Houghton Lake
Joined Dec 2002
7,542 Posts
I agree the instability looks like it is associated with wing flex. I looks like when the dihedral increases the wing also twists increasing lift more. It does make for an impressive climb out.
Don
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Old Sep 13, 2007, 07:13 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by Truglodite
argh, i should've read your whole post first. i think your priority should be wing bracing. if you're getting that much flex, you need struts. the other adjustments are kind of pointless if the wing is going to be all over the place. got bamboo skewers?
Quote:
Originally Posted by bz1mcr
I agree the instability looks like it is associated with wing flex. I looks like when the dihedral increases the wing also twists increasing lift more. It does make for an impressive climb out.
I was afraid of that. Now I need to figure out how to brace a wing that big without adding too much weight. The goal is still to carry as many mAh's as physically possible. Double struts underneath? Something across the top? How far out on the wing?

I could always cut the wing back and make it a regular 60" BBAP1, but really want to make this work.
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Old Sep 13, 2007, 09:10 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Gramps, congrats on your maiden flight. You'll have fun with it and when you're ready, you can spiff it up with the full fuse build!

Kendall, I agree with the other comments you are getting. Wing flex. And not just up and down. When the wings are flexing like that they tend to twist, to go up at the TE even more than the LE. Kinda like SUPER washout! This of course changes the angle of attack across the wing and makes it all but impossible to trim it right. A change in the angle of attack obviously makes a change in pitch trim so that certainly could account for the pitch problems.

The other issue you will face is when you load the plane. If you think the wing flexes badly now add eight ounces of payload. You'll be able to stretch a string across the tips and shoot arrows...until it breaks. Oh, and don't dive or you will discover the wonderful world of flutter. You won't like it.

I faced this with the original 60" UC wing I had on the 52" BBAP1. It was moderately OK unloaded (flexed some) but when I put a payload into it the flex, pitch changes and flutter were downright scary.

The cure: I did two things to cure it. I put on four wing struts attached at the 70% span mark and at the 25% and 75% chord marks. As well, take some filament tape, you know, the 3/4" wide stuff with the fiberglass strands, and make a series of X's across the bottom surface of the wing. This will greatly strengthen the bird and drastically reduce the torsional and longitudinal flexing. Make sure when you size the struts you get the rigging angles right. Better yet, leave one end of the strut adjustable so you can correct any minor rigging issues. The struts are a pain but they are strong, light and they work.

I apologize for not thinking of this before. When I built the KFm2 wing for the BBAP2 I deliberately went with the two step wing because of the torsional rigidity

Try these fixes. I think they will help.

Tony
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Old Sep 13, 2007, 09:17 PM
Mike
USA, OH, Westerville
Joined Aug 2007
285 Posts
Well I tried to maiden my 52" BB with a kfm tonight. Plenty of power, plenty of lift. She took flight, but the wire I used for pushrods is way to weak so it could only pull, not push on the elevator and rudder. What do people use for pushrods on these big boys?

Also, my motor came with the mount in this pic (http://unitedhobbies.com/UNITEDHOBBI...idProduct=4708) and I wasn't sure how to attach it, so I just loaded it up with hot glue. It was fine for the flight, but popped off when checking if everything was working after my "landing". How should I go about securely mounting this motor?

Thanks,
Mike
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Old Sep 13, 2007, 10:25 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by muidaq
Well I tried to maiden my 52" BB with a kfm tonight. Plenty of power, plenty of lift. She took flight, but the wire I used for pushrods is way to weak so it could only pull, not push on the elevator and rudder. What do people use for pushrods on these big boys?

Also, my motor came with the mount in this pic (http://unitedhobbies.com/UNITEDHOBBI...idProduct=4708) and I wasn't sure how to attach it, so I just loaded it up with hot glue. It was fine for the flight, but popped off when checking if everything was working after my "landing". How should I go about securely mounting this motor?

Thanks,
Mike
Congrats on your maiden Mike. To answer your questions: A) Use bigger wire (I bet you were waiting for that). B) Your motor attaches to the mount with the machine screws provided and the mount attaches to the aircraft with a 10mm square stick. If you drill into the monobloc with a 10mm (or slightly larger) drill you can put the stick in the hole lightly covered with Gorilla glue. The glue will expand to fill the hole and give you a nice tight fit

Like Kendall, you may have to put struts on that wing. Careful of the wing flex.

Ton
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Old Sep 13, 2007, 11:30 PM
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Truglodite's Avatar
Carmichael, CA
Joined Feb 2007
3,511 Posts
kendall, i agree with tony's recommendation to use a 4 point strut arrangement, as long as the material is strong enough. thicker skewers may work with 4-point, thinner ones will need an 8-point config.

for example: i tried 4 point 0.08" cf struts, and the cf was so thin they buckled under light compressive loads. you can test buckling by cutting a stut to approximate length & pushing the ends together. the longer & thinner the strut, the more likely it is to buckle. if it bows easily without much pressure, you need 8-points.

i placed my 8-points at 1/3 & 2/3 span (measured from the fuse sides), and 25% & 75% chord (including flaperons). i then positioned the 4 shorter struts so they are perpendicular to the 4 main struts. then i added a brace between each of the main struts where they short ones attach. unfortunately at those wingspans kendall, your struts will be so long that 8-points are probably going to be necessary.

like tony mentioned, getting the rigging so the wings are straight can be a pain, and adjustable joints help. as long as you ensure your wings are flat & have no twist induced by the struts, you'll be fine.

beyond the struts, i added only a 1" strip of filament tape chordwise between each pair of strut attachment points along the wing to secure the airfoil shape against deformation caused by pressure from the struts. i thought about making an "x" connecting the 4 strut points on each wing half, as this would greatly improve torsional stiffness. however i haven't found more reinforcement necessary yet.

there are other ways to add torsional stiffness to a wing, like gluing cf strips to the LE & TE, but the "benefits per ounce" are not as great as good old fashioned struts.

kev
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Old Sep 14, 2007, 07:48 AM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
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But 70% span is over 33" down each wing! That kind of length is going to need a fairly stout strut to keep from buckling. I have some 36"x1/4" bamboo skewers that should be just long enough to be the hypotenuse of that triangle.
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Old Sep 14, 2007, 08:56 AM
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230@10's Avatar
Jacksonville FL
Joined Dec 2006
33 Posts
motor mount

Also, my motor came with the mount in this pic (http://unitedhobbies.com/UNITEDHOBBI...idProduct=4708) and I wasn't sure how to attach it, so I just loaded it up with hot glue. It was fine for the flight, but popped off when checking if everything was working after my "landing". How should I go about securely mounting this motor?

Thanks,
Mike[/QUOTE]

Mike,

I use the same setup. Don't use the stick mount. Get a piece of lite plywood from your LHS or use a stripped PC board or anything hard and flat. Install the alum. mount to whichever you choose with blind nuts, and then 5 min. epoxy to the fire wall. You now have a removable motor mount. It works great.

Mark
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Old Sep 14, 2007, 03:37 PM
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warhead_71's Avatar
Chicago, IL
Joined Dec 2006
5,112 Posts
Quote:
Originally Posted by tuppertn
I was afraid of that. Now I need to figure out how to brace a wing that big without adding too much weight. The goal is still to carry as many mAh's as physically possible. Double struts underneath? Something across the top? How far out on the wing?

I could always cut the wing back and make it a regular 60" BBAP1, but really want to make this work.
If you don't intend to fly inverted, then you can simply use fishing line or dental floss to add flying wires to hold the wings in place. At 1/3 and 2/3 span of each wing, at both the LE and TE of the chord, add some sort of hard-points so you can run the string from the hard-point to the belly of your fuse.
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Old Sep 14, 2007, 03:52 PM
Always Ready!
warhead_71's Avatar
Chicago, IL
Joined Dec 2006
5,112 Posts
Quote:
Originally Posted by muidaq
Well I tried to maiden my 52" BB with a kfm tonight. Plenty of power, plenty of lift. She took flight, but the wire I used for pushrods is way to weak so it could only pull, not push on the elevator and rudder. What do people use for pushrods on these big boys?
Use bamboo skewers for the middle of the pushrod and lash/glue wire ends to it. Bamboo is strong and light. You can also use heatshrink tubing to hold the wire to the bamboo - and use a tiny bit of PU glue so it won't slip.
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Old Sep 14, 2007, 04:19 PM
I'm not flying backwards!
Tony65x55's Avatar
Oshawa, Canada
Joined Sep 2004
3,753 Posts
Quote:
Originally Posted by warhead_71
If you don't intend to fly inverted, then you can simply use fishing line or dental floss to add flying wires to hold the wings in place. At 1/3 and 2/3 span of each wing, at both the LE and TE of the chord, add some sort of hard-points so you can run the string from the hard-point to the belly of your fuse.
Took the words outta my mouth, well, outta my keyboard anyhow.

Tony
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Old Sep 14, 2007, 09:40 PM
Mike
USA, OH, Westerville
Joined Aug 2007
285 Posts
Thanks for the info guys. I got some music wire from the mom and pop hardware store for the pushrods. Seems much better. Found some 3/8 inch square basswood to mount the motor and it seems rock solid with PU glue.

Can't wait for the re-maiden tomorrow. Hopefully I have a camerawoman.

Mike
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Old Sep 14, 2007, 09:49 PM
Postcards From The Purple Edge
tuppertn's Avatar
United States, OK, Sand Springs
Joined May 2007
3,919 Posts
Quote:
Originally Posted by warhead_71
If you don't intend to fly inverted, then you can simply use fishing line or dental floss to add flying wires to hold the wings in place. At 1/3 and 2/3 span of each wing, at both the LE and TE of the chord, add some sort of hard-points so you can run the string from the hard-point to the belly of your fuse.
No up-side-down silliness for my BBAP. Her purpose is endurance flight. Will having the wires at both TE and LE fix the twisting issue as well? That would be much easier to do than struts, though it still seems that it could be difficult to adjust properly.
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Old Sep 14, 2007, 10:36 PM
AKA Don
bz1mcr's Avatar
United States, MI, Houghton Lake
Joined Dec 2002
7,542 Posts
I do not think adding stiffness (wire or CF) to the leading or trailing edges will increase torsional (resistance to twisting) stiffness much. To increase torsional stiffnes you need to add strength to the "skins" top and bottom. Closing in the bottom of the airfoil would help a lot, but add some weight and reduce lift. Someone suggested Fiber reinforced tape in an X pattern (several X's) on the top and bottom. That would be my next suggestion, but I don't have high hopes that will do the job.
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