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Author Topic: Any word on Div. C Wright Stuff planes for 2018-2019 season?  (Read 3737 times)
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leop
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« Reply #100 on: November 05, 2018, 07:48:17 PM »

In reply to the last two posts, this year's Wright Stuff event is made somewhat more challenging by the lack of restrictions on propeller specifications and maximum motor weight.  Further adding to the mix is that the stabs are free in design, only restricted by the need to be of lesser area than the wing.  This means that a team will need to do a great deal of work to optimize the plane design, construction, and setup to maximize the flight times.  There is more than aerodynamics involved in the optimization.  For example, a heavier motor may require structural changes to provide for the necessary air frame stiffness.  Also, the theoretical optimal motor weight is two times the air frame weight.  However, the relative gain from increasing the motor weight above about half than of the air frame weight is not large.  This, combined with the above mentioned structural considerations, will contribute to the challenges this year.  Lastly, flying well (winding, trim, and setup) will be a big factor in flight times.  A non-optimal plane flown well will nearly always have longer flight times than an optimal plane flown poorly.

By the way, the aerodynamic drag (the drag force) increases as the square of the speed.  But, the lift (thrust force for a prop) also increases as the square of the speed.  One advantage of a larger diameter prop is that the aspect ratio of the blade airfoil can be larger compared to prop with a lesser diameter when both have the same blade area.

LeoP
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bjt4888
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« Reply #101 on: November 05, 2018, 10:24:51 PM »

Leo,

Thanks very much for the analysis of this year’s design; much appreciated.

Brian
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calgoddard
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« Reply #102 on: November 06, 2018, 07:43:32 PM »

Crtomir -

Get the weight of your models down to 8 grams and you will see a significant improvement in your flight times. You must be using very heavy balsa wood as most 2019 WS models come in under-weight.  Certainly a balsa wood prop will solve your over-weight problem.  Indoor Ikara props are much heavier.  You may end up having to add ballast.

Actually indoor Ikara props are quite durable, probably more so than a lightweight balsa wood prop.  However the latter can survive many head-on encounters with obstructions without damage.  I must comment that the plastic film blades of the Ikara props have an annoying tendency to detach from their injection molded plastic spars.  I never had any luck re-pitching indoor Ikara props with heat or cold-forming.  I have cut off the blades at the base of the spars and then inserted the spars into a small segment of Aluminum tubing that serves as a hub.  You can then set the pitch and glue the spars in place in the hub.
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Crtomir
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« Reply #103 on: November 07, 2018, 05:01:24 PM »

calgoddard:

We will definitely try lighter wood to bring the model weight down.  The wood we used was a little heavy.  The wing and stab leading and trailing edges were 3/32" x 3/32" sticks stripped from 3/32" sheet that was about a 10-12# density.  The ribs of the wing and stab were 1/16" x 3/32" cut from 1/16" sheet that was about closer to 15# density.  The fins on the wing and stab were cut from 1/32" sheet that was very light, probably around 5-8#.  The motorstick was 3/16" x 1/2" x 10" long and was 5# density.  The tail boom was roughly 3/32" x 1/4" x 12" with a density of 10-12#.  The Ikara prop weighed about 2.25g.  The rear motor hook was too heavy for sure, although I don't remember what it was.  The music wire was thicker than we needed.  The plastic film covering for the wing and stab probably added up to 0.6-0.7g.  So there is definitely room for improvement. 

We also found that the Ikara prop blades tend to split away from the spars.  Definitely a drawback.  Can't wait to try some balsa props, but we need to build a prop block first to give the correct pitch to diameter ratio. 
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Olbill
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« Reply #104 on: November 07, 2018, 05:28:24 PM »

You can put some thin CA along the Ikara spars to make them stay attached. I've personally never had them come apart.
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calgoddard
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« Reply #105 on: November 07, 2018, 05:47:07 PM »

Crtomir -

Only use 1/16 x 1/16 balsa strips for the LEs and TEs.  3/32 x 3/32 strips are way too big and heavy for an indoor duration stick model like a 2019 WS airplane.

In general, don't use balsa wood any heavier than 6 - 8# density for constructing WS airplanes.  You probably can't find 3 - 5# balsa wood.  It is too light and not necessary for a WS airplane. It is also too weak for the durability needed in a model handled by students. Save your super light balsa wood for building serious LPP, F1L, F1D, A6, etc. models down the road.

Read up about using deflection tests for selecting the stiffest balsa wood strips from a pile of strips of similar weight.

Ribs cut from 1/16 sheet balsa are fine for a WS airplane.  It is better to laminate two 1/32 sheets on a curved form, and slice the ribs from the cured laminated product with a balsa stripper. Ribs cut from a 1/16 sheet can break along the grain.

There is one exception regarding the density of the wood that you use to build a WS airplane.  Use the heaviest balsa wood you can locate for the wing posts. They should be 1/16 x 1/16.
 
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Olbill
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« Reply #106 on: November 17, 2018, 01:27:45 PM »

I did a few prop tests today. The 12" LPP prop didn't work very well. The models didn't want to turn and looked really shaky in the air. I think a 12"prop might be too much for the small wing area.

Prop #1 is a thinned Ikara SO prop with area behind the spar removed. This prop looked about the same in the air as the #3 prop. There were lots of hits on the walls above the 22'-11" ceiling. A bad hit when it was almost out of power lost about 10' of altitude. It still did 2:48.

Thhe #3 prop with tha carbon rod hub climbed a lot more than the last time I flew it. There were numerous wall hits above the low ceiling. Time was 3:15.

All flights were on the same 5/16 TSS motor I used last time - 20" of 1/8" wound to 1720 turns with 100 turns backed off.

I think this will end my testing of this model. I got a late start today and have a few more models to fly in not very much time.
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Re: Any word on Div. C Wright Stuff planes for 2018-2019 season?
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Crtomir
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« Reply #107 on: November 18, 2018, 04:59:50 PM »

As a follow-up to my posts over a week ago, here is a link to a video I took of one of our flights last Sunday night (11 NOV 2018): https://www.youtube.com/watch?v=CcyknLi6Ovk  The plane weighed about 9.2g and used an unmodified Ikara symmetric 24cm prop with an 18in loop of 1/8in rubber.  The plane reached a maximum height of about 18ft and hit a basketball goal on the descent with about 8-9ft left to go for an abbreviated 1:24 min flight time.  I suspect it could have been about a 1:40 min flight if it had not hit the basketball goal.  Also, to add to suspense, it landed mere inches away from being stepped on by one of the younger students.

I mentioned before, but the design of the plane was based off of Joshua Finn's "Senior Flyer".  We had ordered the kit, but were impatient, so we his build instruction videos and tried to guess what the dimensions and densities were.  I think we were pretty close on the dimensions, but off on the densities of some key components.  Also, the Ikara prop is heavy and we used too thick of music wire for the rear motor hook which added more unnecessary weight. 

Now, we have received Joshua Finn's kit, so we will try building that.  It will be interesting to see how well it does.  I am very optimistic about it.
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Olbill
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« Reply #108 on: November 18, 2018, 05:10:17 PM »

Nice flight!

I christening Josh's design as the Finn-Finny.
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Crtomir
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« Reply #109 on: November 18, 2018, 05:17:52 PM »

I was skeptical about the short motorstick.  We had always been using motorsticks closer to 40-42cm, but the "Finn-Finny" is a fine design that flies with finesse.

Hoping to take some more videos at tonight's practice. 
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Maxout
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« Reply #110 on: November 19, 2018, 11:01:39 AM »

Nice flight!

I christening Josh's design as the Finn-Finny.

LOL. I love it.

Crtomir, that flight really did look excellent. Looked like you could go a little higher too. Depending on turns remaining, I think you might get over 2 minutes in there with that setup.

-Josh
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Olbill
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« Reply #111 on: November 19, 2018, 11:22:15 AM »

If the hot setup for these models continues to be 1/8" rubber then the shorter motorstick has a big advantage in stiffness. Having a longer motorstick means the stick's resistance to bending will be lower and also there will be much more tension from a fully wound motor.

If you must use a long MS then bracing is a good idea. Just add a post an inch or so high at the midpoint of the motor space and run a piece of kevlar thread (6# test fishing line is good) from the front of the stick to the rear hook.
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Olbill
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« Reply #112 on: November 19, 2018, 11:22:18 PM »

Correction on Finny 19 prop pitch - I've been saying the prop was set to 11" pitch. Tonight I saw in my notes that it was actually 15".
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ZoranD
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« Reply #113 on: December 03, 2018, 05:48:48 PM »

For Bill, what is the pitch you have the Finny prop at (how would you find the degree of a 15" pitch)?
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Olbill
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« Reply #114 on: December 03, 2018, 07:21:07 PM »

45 degrees at radius of 2 1/2".
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