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Old 01-10-2021, 04:26 PM   #1
Dutkoski
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Airframe Weight Comparison


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Last night I got the bug to design and build a small delta wing pusher prop foam board aircraft. I used 1.5 sheets of dollar store foam board. The wingspan is 28Ē and overall length is 30Ē. So itís small enough to just chuck it into the car and go have some fun. However, after constructing it, although not a brick, it did seem heavier than I would have liked, so took out the scales and it was 7.25 oz..

I weighed the equipment and battery which brought everything up to 13.8 oz. so Iím still under my 16 oz target goal. I forgot to weigh the 25 amp ESC, so that will need to be included, but they are very light.

This afternoon, I duplicated constructing a second airframe, but this time, I peeled off the white paper covering. The airframe was constructed in the identical method using the same hot glue. When finished, it was noticeably lighter. On the scale it went, total weight is 4.4 oz.

This is a 2.85 oz weight saving on a small model.

Also, both wings were built using a double layer of foam, so an airfoil could be used. Long wedge shaped foam spars were inserted to produce the desired airfoil shape. I figured this was faster than cutting a groove and laminating a carbon fibre rod. The wing is very rigid and light.

Iíll fashion a small nose cone tonight so itíll look pointy.

There are no plans or anything intended for this post, this is just information. Have a great day guys, keep building
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Old 01-10-2021, 09:44 PM   #2
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Re: Airframe Weight Comparison

hi John,

Yeah, it's amazing how much the thin cardboard sheeting weighs.

I had thought that you usually remove the cardboard sheeting from the "dollar store" foam sheets.

Nice design.... the wedge shaped foam spar between the foam sheets; where was is placed: 1/3 back from leading edge at the fuselage to the wing tip?
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Old 01-11-2021, 11:53 AM   #3
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Re: Airframe Weight Comparison

Yes, appox 1/3rd back from the leading edge and a secondary one at the 2/3rd location. The secondary one is mainly to provide some support to keep the wing airfoil shape.

I tested the setup with a 2 cell and a 3 cell battery. The model has a little better than a 1:1 thrust ratio on a two cell battery, pretty docile too, 7Ē x 5Ē prop. When I hooked up a 3 cell, the amount of thrust is well over 2:1 ratio, itís more than needed. Iíll probably reduce the prop to a 6Ē to reduce the toque though and also reduce the amp draw.

Just waiting for Amazon to deliver the 1500 mah 3 cell battery and then Iíll do the CG calculation, basically, chuck it and adjust the battery location until it glides nicely
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Old 01-11-2021, 12:27 PM   #4
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Re: Airframe Weight Comparison

John, thanks for the information and good luck on the first flights.
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Old 01-14-2021, 07:05 PM   #5
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Re: Airframe Weight Comparison

Cool.
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Old 01-24-2021, 11:22 AM   #6
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Re: Airframe Weight Comparison

I used the heavier paper covered airframe as a chuck glider, to determine the location of the CG. I then completed the bare foam airframe, installing the electronics. At first I used a 7x4 prop, which the motor was happy with, lots of power, but the toque roll was unacceptable. So I attached a 6x5 prop, not as much thrust but it almost eliminated the torque issue, still, the thrust to weight ratio was better than 1:1

So, motor is a Mega Acn 16/15/6, APC 6x5 prop, Turnigy 25 amp Plush ESC, Spektrum 4 channel reciever, an HRB 1300 mah 3 cell battery, two 9 gram cheapie servos ...... and some velcro.

Ready to fly weight is a staggering 7.95 oz

The delay in finishing was caused by the battery, the one I ordered from Amazon turned out to have been used and defective. I contacted Amazon support service and spoke to a real person, amazing, huh. I explained everything to her regarding the condition of this battery and that mailing it back could be dangerous and I think, unlawful. She was quite concerned that the company had actually mailed the battery in the first place and that she would see to it that they would investigate it further. She then confirmed that I will receive a full refund, which I did. The battery was a Goldbat brand and someone had removed the stock XT60 connector and poorly attached a Deans connector. Plus, one cell was discharged well below minimum and the battery charger would not recharge the pack. I did reattach a XT60 connector properly so I could try and charge it. The Deals connector is to the right, the person used ordinary electrical tape, just one strip, first wrapped around the positive wire, then wrapped the negative wire against the positive wire.

The upside though, Amazon told me to keep the defective battery, so, I’ll strip it, remove the defective cell and I’ll have a 1500 mah two cell, for free
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Last edited by Dutkoski; 01-24-2021 at 11:40 AM.
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Old 01-26-2021, 12:13 PM   #7
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Re: Airframe Weight Comparison

Dressed the little plane up with some spare decals I had made for the Arrow kits and others. Makes it come alive I think. Total flying weight, 13.25 ozís

Of course, today ...... a blizzard is taking place ...... maybe later this week Iíll give it a go.
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Old 01-26-2021, 01:40 PM   #8
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Re: Airframe Weight Comparison

Quote:
Originally Posted by Dutkoski View Post
Dressed the little plane up with some spare decals I had made for the Arrow kits and others. Makes it come alive I think. Total flying weight, 13.25 ozís

Of course, today ...... a blizzard is taking place ...... maybe later this week Iíll give it a go.
Hey John. All you are missing is the classic figure "4" on the wing.....
( I always thought it was red..was it black??)
C'mon.. you know you gotta do it!!
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Old 01-26-2021, 03:19 PM   #9
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Re: Airframe Weight Comparison

😂😂👍

Ok, ok Max, after I finish up finish sanding a big grey delta wing today. Iíll seeif I have some black pin striping tape.
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Old 01-26-2021, 08:17 PM   #10
Dutkoski
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Re: Airframe Weight Comparison

There ya go Max, just for you 😋👍
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