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Author Topic: Crosby CR-4 NoCal  (Read 1165 times)
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AAdamisin
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« Reply #25 on: April 05, 2020, 01:03:16 AM »

Here are my covered parts, right at 3.0 grams so far. Thanks for the skin files.

Don

Nice work!!

Archie Adamisin
Burlington, KY
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dslusarc
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« Reply #26 on: April 08, 2020, 09:29:47 PM »

Here it is less prop. Weight is 4.9 grams as seen in the photos. I went with a solid motor stick and tail boom. Stick made from some 5.5# 1/4" sheet I had and cut it by 3/8" wide then did some razor planning, shaping, and sanding until it ended up about 1.5 grams and the boom was around .15 grams.

Don
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Re: Crosby CR-4 NoCal
Re: Crosby CR-4 NoCal
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AAdamisin
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« Reply #27 on: April 09, 2020, 11:13:26 AM »

Here it is less prop. Weight is 4.9 grams as seen in the photos. I went with a solid motor stick and tail boom. Stick made from some 5.5# 1/4" sheet I had and cut it by 3/8" wide then did some razor planning, shaping, and sanding until it ended up about 1.5 grams and the boom was around .15 grams.

Don

Don,

You are a craftsman.  Your model looks great.  I can't wait to hear how it flies.

I like the motor stick idea.  I spoke with George B. and he does that same thing.  I don't have any 1/4" good enough for that weight.  I might use some thicker balsa for tubes.  I have really nice .040 I used for F5D molded wing skins. 

What prop are you planning on?

Thanks,

Archie Adamisin
Burlington, KY
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dslusarc
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« Reply #28 on: April 09, 2020, 05:27:44 PM »

Thanks! It came out nice and having good skins to print really helps. I went with a solid stick as there was enough weight left to do it. Plus on the 7" restricted prop, the motors are not so large. We would fly 12" diameter props on 6.2 gram models with .125" rubber so needed the rolled tubes on models to take the load. The smaller prop means rubber closer to .090 so the stick is fine. The wood I used  for the stick I harvested from a local hobby shop or craft store. I have been raiding the stores for years with my gram scale and pick through the wood one sheet at a time l so have found a lot of 4-6# wood over the years. I used 6# on the outlines and 5.5# on the ribs and 10# for the wing spars and the verticals at the leading and trailing edges. Prop will be next task.

By the way I went with a little more dihedral than you mentioned before, this is a low winger and you are allowed the greater of 1" per 12" span (1.33") or up to the bottom of the canopy on a low winger. So I am around 1.5". Now just need a place to fly! I did use a simplex airfoil, I am partial to a 5% on my nocals.

Don   
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OZPAF
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« Reply #29 on: April 09, 2020, 08:54:12 PM »

It looks great Don. it's interesting to see the effort made to keep the weight down and the reason for using a motor stick. You have done Archie's nice design proud. I guess fflight trimming will be a fair way off in the circumstances.

I'm curious to see how you get on with the strange behaviour that Archie mentioned on his.

John
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dslusarc
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« Reply #30 on: April 10, 2020, 08:37:32 AM »

John,

I am very curious if I can get it to fly correctly. The flight reports are the main reason I built this plane as I like a nocal challenge! I want to see if the recipe that my dad and I have come up with over the years for indoor nocals applies to this plane as well or is this another creature all together. So we shall see. I may just have to fly it in the back yard one evening for a lap or two if I get desperate.

Don
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« Reply #31 on: April 10, 2020, 02:45:20 PM »

Wonder if a flatter rib shape at the root would help reduce the pitch sensitivity?  0.5" thick on a 6.75" chord is >7%.  I usually use <5%, but I don't have any nocals with that sharp of a wing taper.  Do you think an arc shape would work better than a simplex?
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dslusarc
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« Reply #32 on: April 10, 2020, 03:05:55 PM »

My "5% Simplex" is actually thinner in reality, I take the 5% simplex template then go back about 1/2" from the leading edge then use the rest of the template to cut the ribs. This pushes the high point back and lowers the camber a little so probably like 4.5%. Never had a model with such high chord taper before so I am interested in seeing it fly!   
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Indoorflyer
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« Reply #33 on: April 10, 2020, 03:39:12 PM »

That's cool--trimming a bit off the front first, then using the remainder of the rib blank.  Hope you can do a smoke test sometime soon.  I vote for some "outdoor"/backyard guerilla flying time during calm conditions!  Good luck!
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OZPAF
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« Reply #34 on: April 10, 2020, 08:08:48 PM »

Don,I have been experimenting with laminated strips intended for my Mooney build without much luck. Your efforts on the Crosby fuselage as well as Archie's make it look simple although I am using 3 laminations of 1/16" which may be too much. They have been boiled in water and are still difficult to get around the necessary tight bend with out the outside lamination cracking - I am amazed at how much pressure is needed to form them around the curve . I know Archie used ammonia  but I would prefer not to do that. Am I missing something else?

John
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dslusarc
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« Reply #35 on: April 10, 2020, 09:32:18 PM »

I always use tap water but also don't use heavier than 6 lb density wood. I do pull some tension when forming around the form.  Maybe the glue is starting to grip and the breaking is due to the strips not sliding relative to each other when bending.  Maybe try two then add a third layer?
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DHnut
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« Reply #36 on: April 11, 2020, 01:29:50 AM »

John I am puzzled as when I do the laminated sheet that is stripped for ribs I do not always soak the 1/32" sheet before clamping them between the former blocks. Usually in the vice before going up to bed and leaving it overnight or longer before releasing the block. I normally use aliphatic. I understand that ammonia does not have any effect on balsa because there is not sufficient lignum to soften and that water is just as effective.
Ricky
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billdennis747
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« Reply #37 on: April 11, 2020, 02:15:01 AM »

Don,I have been experimenting with laminated strips intended for my Mooney build without much luck. Your efforts on the Crosby fuselage as well as Archie's make it look simple although I am using 3 laminations of 1/16" which may be too much. They have been boiled in water and are still difficult to get around the necessary tight bend with out the outside lamination cracking - I am amazed at how much pressure is needed to form them around the curve . I know Archie used ammonia  but I would prefer not to do that. Am I missing something else?
John, 1/16" is for bigger models with big radii. Try 'thin' 1/32. No need to boil, and ammonia doesn't work with balsa - basswood yes,  Start at the 'peak' of the curve and then work it back to each end; don't start and on end and try to pull it round
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OZPAF
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« Reply #38 on: April 11, 2020, 09:41:22 AM »

Thanks Don, Ricky and Bill. Yes I was coming to the same conclusion Bill. It shouldn't take that much force to pull the strips around the form. Your idea of starting at the peak is interesting as well. The rest of the curve is mild - it's just the tip that is a pain. I'll try your method.

Don  - definitely my balsa is heavier than 6# so that doesn't help.

Ricky - I have had no trouble forming sheets for ribs using just a male form but I do it in 2 steps. Wet form first and then use heat to polymerise the dry PVA glue while the 0.8 sheets are bound to the form.

Take care all.

John.



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tross
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« Reply #39 on: April 11, 2020, 11:54:43 AM »

You can roll them dry John. Just glue 3 or 4 together.
This is .075" 7.5 # b grain.
Tony
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Re: Crosby CR-4 NoCal
Re: Crosby CR-4 NoCal
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Instructions: Step One...Assemble the pile of sticks shown in pic "A" to look like the model airplane shown in pic "B"........
dslusarc
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« Reply #40 on: April 11, 2020, 05:12:10 PM »

Prop blades are in the oven. Using two lams of 1/32" 6# wood for each blade. Laminated as it hold the twist better after baking and you need some thickness on a 6.2 gram prop blade as they can hit hard on the prop when hitting the girders. Once dry then I will sand an airfoil into them. Formed on 4" diameter can at 22 degrees. Shooting for around 11" pitch.
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OZPAF
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« Reply #41 on: April 12, 2020, 05:08:57 AM »

Thanks Tony - I'll give that a go as well, but at the moment my trial form has 3x 1/32 on it gluing, with another 3 to go.

John
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dslusarc
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« Reply #42 on: April 14, 2020, 08:31:07 PM »

Prop done and painted. AUW is around 5.7 grams so needs 0.5 grams ballast.
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AAdamisin
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« Reply #43 on: April 16, 2020, 05:51:04 PM »

Prop done and painted. AUW is around 5.7 grams so needs 0.5 grams ballast.

Looks great.  Amazing how small a 7in prop looks on that airplane.   

Can't wait to hear how it flies. 

Archie
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