Flite Test Spitfire

[Daren Cogdon]

So, what I initially thought was gonna be a bit of a dog to fly has actually turned out really, really good.

85%-sized FT Spitfire, but fitted with the full-sized Spit's power setup (1100Kv motor, 40A ESC, 2200 3S and a 9x5 prop). This one is made entirely from 3mm foam board from Amazon, instead of the more usual 5mm stuff from HobbyCraft. The wing spars are made from balsa instead of folded foam.

It's got a decent amount of speed compared to most of the others I've built.

I got some video of it but there's no sound, sadly, and most of the time the Spit is a bit of a dot in the sky!

 

 

 

[Daren Cogdon]

I love this thing....

 

 

[Daren Cogdon]

Little Spit's motor quit on me last week, right when I was in the middle of a half-Cuban.  Luckily I had plenty of height to fizzle back to base, but the motor had had it.  I've now swapped it out for a 1300kv that I had previously installed in one of the bigger Spits, and will give it a test flight soon.

 

I'm definitely going to build another 85% version, though, as this one has performed far and away better than any of the 100% examples I've built (even the legendary Pinky!).

[Daren Cogdon]

As I said before, I stuck a 1300Kv motor into Little Spit the other day, and finally had a chance to test her out last night.  Nothing else changed, other than the motor.  

 

Man, what a rocket ship she has turned into!  Just bags of power!  Loops from level flight, with more than enough energy for a roll straight after.  I can literally turn her on a sixpence at the end of the runway.  I had set my timer for 5m 30s as I didn't know how long I could fly for, but either the timer failed or I simply didn't hear it, as I overran by a good two minutes, and still had 54% left on the battery!  

 

The annoying thing is that the camera wasn't set at the right angle, so you only got to see the lower-down portions of the flight!  

[Daren Cogdon]

Now, this 100% version was flown again after the rather short flight the other day (in less than ideal conditions).  It previously had the 1300kv motor which is now powering Little Spit, but I swapped it for a heavier 1000kv motor to try and get a better CofG.  

 

The result is, it flies, but there's no great surplus of power.  I dared not do anything silly in case it went badly, but it does fly rather sedately.  

 

Flite Test specifies:

• Motor: 810kv minimum

So this should be OK, I would have thought.  The pink Spitfire, built in exactly the same fashion and with the same setup, flew fine on 1300kv.

[Lipo Man]

1 minute ago, Daren Cogdon said:

Now, this 100% version was flown again after the rather short flight the other day (in less than ideal conditions).  It previously had the 1300kv motor which is now powering Little Spit, but I swapped it for a heavier 1000kv motor to try and get a better CofG.  

 

The result is, it flies, but there's no great surplus of power.  I dared not do anything silly in case it went badly, but it does fly rather sedately.  

 

Flite Test specifies:

• Motor: 810kv minimum

So this should be OK, I would have thought.  The pink Spitfire, built in exactly the same fashion and with the same setup, flew fine on 1300kv.

Might be worth trying a higher pitch prop to get a bit more speed? As long as you're not at the limit of your ESC probably worth a try?  I've got a couple of planes that I fly with low Kv motors and higher pitch props and they seem to be very efficient.

[Daren Cogdon]

I can't recall off the top of my head what the prop is, but I *think* it's a 1050.  Would need to check for certain.  

[Daren Cogdon]

I was almost right - it's a 1060 prop.

[Lipo Man]

12 hours ago, Daren Cogdon said:

I was almost right - it's a 1060 prop.

It sounds like you don’t have enough pitch speed from your prop, so flat out throttle is barely over your stall speed. 
A drop from a 1300kv motor to 800kv has lowered the speed of the airflow from your prop by nearly 40% - because the prop is spinning so much slower. Increasing the pitch increases the speed of the airflow at any given rpm, getting some of the lost airflow speed back. The other thing you can do is increase battery voltage - say going from 3s to 4s. 
So - either trying a higher pitch prop (say a 9x8) or a 4s battery will help, but both would still be slower than your 1,300kv motor. On the upside, lower kv motors are more efficient so you may get a slightly longer flight time. 
 

[Daren Cogdon]

I have a few 9x5s already, and I think I did try this on the airframe when it still had the 1300kv motor.

 

The prop/motor/ESC combo on the 85% Spit gives it great performance - and it was good before!

Edited October 9 by Daren Cogdon

[Daren Cogdon]

OK, I've just quickly swapped out the 1000kv motor which I put in the bigger Spit originally, and put the 1300kv back in it, along with a 9x5 prop.  Just got to wait for a decent bit of weather for a test flight.

[Daren Cogdon]

While I'm waiting for a day where I can test fly two or three Spits (I'm beginning to feel like Jeffrey Quill!), I've been toying with making a larger version of the FT Spitfire.  I know that they did 200% scale plans, but I was thinking of 150% since it's about the biggest size I can fit in my car easily! (63ins)

 

Any ideas on what sort of motor/ESC/prop/battery might be required?  I'm guessing an AUW of about 2-2.5kgs, at most.