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Fat sparrow

#1
Hi guys, total newbie here I'm currently working on my 3rd build ever, after totalling my first 2 in a matter of moments (ripped the front end clean off of one of my simple scouts and totally bent the fuselage of the other)
Backstory: I decided to try building with 3mm coroplast / corflute since I have a never ending supply of free stuff from work, but turns out it's waaaaay heavier than FT foam board plus the only electronics I have so far is power pack B.

So I decided to have a go at the sparrow knowing full well that it wasnt going to end well but was curious how bad it would go. Well boy is she a heavy one. All things said and done 499grams! Like I said, running power pack b with a 3 cell 1300mah battery isn't helping at all. Plus still needing weights up front to balance her out! I haven't actually tried it out but I'm assuming it won't even get off the ground in its current state.

So I'm chasing thoughts, what can I do to get this thing flying. I've got a coupe ideas so far but honestly I don't know what I'm doing so any tips would be welcome.

I'm thinking:
- Increase length by 125-150% in the nose end
- Scale up the wings a bit
- Maybe move the motor up front to turn it into a tractor reducing need for added weights to balance
 

Merv

Well-known member
#2
All 3 are good ideas. I often need to make the nose longer to get FT planes to balance. I cut the nose off and splice in several inches, then glue the nose back on to the splice. I much prefer that to adding even more weight. Making the wings larger is an easy way to bring the wing loading down, something near 12oz/sqft will fly well. Making it into a tractor will help the balance problem but also makes the motor hit first in a crash.
 

quorneng

Well-known member
#3
I would certainly advise doing almost anything to remove having to add dead weight, you have enough of that already.
The other issue is that whilst the power pack B motor is powerful enough for the weight it will be turning a much bigger prop (10 x 4.5" against 6 x 4.5) to get the power. Such a big prop as a pusher could make hand launching dangerous as well as causing handling issues immediately after launch even with a bigger wing.
IMHO you would probably do better to select a design that was intended for a pack B motor.
 

The Hangar

Well-known member
#4
I say scale the sparrow plans up to 150% and then it will be the perfect size for your B pack. Also, like you mentioned above, lengthening the nose 3 or 4 inches would help with balancing it.
 
#5
IMHO you would probably do better to select a design that was intended for a pack B motor.
Yeah I totally get where you're coming from there, unfortunately I'm one of those people that always does things the hard way haha.

Definitely looking at swapping it to a tractor, that'll save me 80grams (I checked the amount of weight before leaving for work this morning) and bring my wing loading down to around 11.8oz/sqft.

When that still fails I'll try rebuilding from scratch and elongate the fuselage while also decreasing its depth and scale up the wing

Question though : when scaling the wing to I also increase the thickness of the spar by the same amount or just leave that thickness alone?
 
#8
The fat sparrow is ready to (maybe) fly, altered it to tractor configuration to fix the CG issues and dodgied up a little bit of motor protection (doubt it will do much in a cash but we shall see) reduced to 425g all up weight with a 3 cell 1300mah battery. (296g without battery)

Just need the wind to die off and a test will be in order.
 

Attachments

#9
Finally got a chance to test it.... Nope... Just nope. Pulled hard up and left on launch (could have been a trim issue) into a loop and pounded straight into the ground about 15 metres off to my 8 o'clock. Didn't hit that hard but almost every glue joint had failed in the fuselage including the firewall mount, one of the servos, esc and receiver. Turns out things don't like to stay stuck to corflute. Surprised the wings held up 100% well. Maybe the wing on top and held with rubber bands is good trainer tech?

Will re-evaluate and maybe just get to repairing foam scouts.... Maybe turn them into a biplane version since I have two busted up and just sitting there.