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My Take on the 100 MPH for <$100 Challenge

Graeme

Junior Member
#1
Hello,

This is my first post on this forum, and I'd like to share a project I just began last night. I am relatively new to electric models, so take everything below with a grain of salt!

I was inspired by the Flight Test video "100 MPH for under $100.00", and the concept of a cheap speed machine. Unfortunately, I did not have any bespoke high performance components laying around, so I tweaked the concept a bit. I decided to determine how fast my low end components are capable of going, and aiming for that speed. This way, the challenge changes from a set speed, and instead focuses on airframe efficiency. This to me is an interesting idea as it means that any components can be used in any airframe, and the challenge is just as relevant with a 50 dollar aircraft vs a 2000 dollar aircraft. Naturally, more efficient electrical components will also help, too!

My setup consisted of a generic 1300 kV bell-style outrunner, an 18 amp ESC, 10C 3s 1300 mAh LiPoly, and a Tornado nylon 7-4 prop.

Doing the math, this should equate to [(11.1 V X 1300 kV) X 4 inch pitch] / 1056 (to bring it back to miles per hour) = 55 mph.

That's not very fast. Of course, though, that makes it a bit easier, as drag increases exponentially at higher speeds. This means that it should be easier to achieve my goal, and any inefficiencies will be less pronounced.

If there are any incorrect assumptions or inconsistancies with anything above, I'd be happy to hear about them.

Now onto the airframe!
 

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Graeme

Junior Member
#2
Okay, so here's a bit more work on the fuselage.

I used Elmers wood glue to laminate three sheets of pink foam, and then sanded it to shape. The middle sheet was cutout for the ESC, receiver and elevator servo, as well as a slot in the top for the battery. I then used generic Hobbyking covering over the fuselage. The eppenage / tail surfaces are balsa sheet, covered in the same material, and utilising the film as the hinge.
 

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Foam Addict

Squirrel member
#3
Welcome!

That's some very nice craftsmanship.
I'm assuming you were a balsa builder then?

I use the 2000KV version of that motor on a 5x5 prop, and I can get some speed on 36" flying wings. I also have tested your motor on a four cell battery spinning a 4.75x5.5 prop. That is speed!
Good luck, I will enjoy seeing the outcome.
EDIT: you will need a higher C rate battery, 10c x1300mah=13 amps max
 
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pgerts

Old age member
Mentor
#4
Hello,
I was inspired.. ..
a generic 1300 kV bell-style outrunner, an 18 amp ESC, 10C 3s 1300 mAh LiPoly, and a Tornado nylon 7-4 prop.
..as drag increases exponentially at higher speeds.
There are some comments:
As told by FA - look at the battery. If you need speed - get a smaller high C battery.
Cooling - dont hide the esc and battery to tight. Try to use the cooling surface of the esc as an outher surface of the plane.
I love the Tornado props (and Top Flite) - but not for small electric ;-) The 1300 kV motor will probably need a much higher pitch like 8 or 10 on a 7" prop.
I assume that you will make a slim wing and you will probably need some carbon fiber internally and 25 g/m2 glass instead of the plastic for cover. To save weight you will only need one small aileron.
100720-08.JPG
 
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Graeme

Junior Member
#5
Hey everyone- thanks for the feedback!

Foam Addict - yep, I'm a part time balsa-cruncher! My battery is pretty low end as of right now, but I like to think of this model of a test bed, and will no doubt be upgrading it soon.

Pgerts - great suggestions; I've since finished the build, but am going to be modifying the fuselage so that the ESC is exposed to the relative airflow. I'm also going to be using a higher pitch prop to get some more speed out of her. Granted, I'm going to take it slow for the first few flights; I don't have much experience with sub 30'' wingspan models, and certainly not ones built to go fast.
I thought about using one aileron, but decided against it only because if the model turns out to be...lethargic, I could re-purpose her as a sport aerobatic model.

Thanks again for the advice, and I hope to have a finished model here shortly.

Graeme
 

Graeme

Junior Member
#7
I thought I should throw in a few pics of my ship in its current state:

I figure it looks a bit like a small Club 20, so I'm calling it the "Club .02" !

photo (6).JPG
 

Graeme

Junior Member
#8
Well it flies!
Of course, I didn't bring a camera, but I gave it a go yesterday with the two cell pack. Not to abuse the metaphor, but she flew off the board. The C of G seemed spot on, and trim was fine. The only complaint was that the tiny amount of elevator throw seemed to be too much, and anything above 3/4 max deflection would cause a rapid snap left. Of course, with only 7.4 volts, I figured it would be impossibly slow, but it was the biggest impression of "speed" that I've had with a model, probably because of the model's diminutive size. Flight time was only about two minutes because the wind was picking up, but I'm suitably encouraged for the next outing, this time with the three cell.

Happy Flying!
Graeme