Results

I've finally done my homework (half a year too late) and judged the Mach challenge. There were many great entries and I have now test flown and compared all of them.

The results were the following:
1. lowobservable 2116 mph
2. ETheGodly 1614 mph
3. Stingray 1584 mph

Everyone of you will receive your prizes accordingly.

Alternate Winner

But there was actually an entry that would reach speeds above 7000 mph. Puredeath did an astonishing job, but the reason it wasn't featured in the top 3 was that it was just so unusable and didn't fulfil (at least not easily) the requirement to be able to land. But, because he reached such high speeds with stock engines he will receive the special alternate first prize. This is the same as the actual first prize, so good job!

Judging Notes

Here are the complete notes from the judging with links to every entry:

@adam99 | 1450 mph @30,000 ft
+ fast
- take off
- unstable
- not much fuel
- landing
- high stall speed
Looks: 4/10

@Delphinus | 1246 mph @30,000 ft
+ take off
+ stable
+ low stall speed
+ landing
Looks: 5/10

@Dominik | 1337 mph @30,000 ft
+ leet
- unstable
Looks: 3/10

@Dullwolf | 1044 mph @30,000 ft
- unstable
- slow
Looks: 8/10

@ETheGodly | 1614 mph @30,000 ft
+ stable
+ fast
- not agile
- landing
- long braking distance
Looks: 7/10

@Exumer | 1407 mph @30,000 ft
+ lots of fuel
+ fast
Looks: 6/10

@Jettison | 1367 mph @30,000 ft
+ stable
+ short landing
- not agile
- narrow landing gear
Looks: 4/10

@lowobservable | 2116 mph @40,000 ft
+ take off
+ landing
+ air brakes
+ super fast
- unstable
- not much fuel
Looks: 4/10

@Lucky13 | 1003 mph @30,000 ft
+ take off
+ stable
+ landing
- floppy wings
- slow
Looks: 7/10

@Nickasaurus | 1000 mph @30,000 ft
+ take off
+ stable
+ lots of fuel
+ awesome pitch
+ landing
+ low stall speed
- slow
- sluggish roll
Looks: 2/10

@NovaTopaz | 1330 mph @30,000 ft
+ stable
Looks: 4/10

@Onenail | 1486 mph @30,000 ft
+ fast
- rolls to the left
Looks: 4/10

@Puredeath | >7000 mph <10,000 ft
+ incredible fast
+ air brakes
- laggy
- flies very sluggishly
- stall speed
- take off
- landing
- landing!
- LANDING!!!
Looks: terrible (-999/10)

@Reaper9 | 1555 mph @30,000 ft
+ stable
+ fast
Looks: 3/10

@Stingray | 1584 mph @30,000 ft
+ stable
+ fast
Looks: 6/10

@Ta1ton | 1303 mph @20,000 ft
+ take off
+ stable
+ roll
+ landing
Looks: 8/10

@TopSecret2 | 1200 mph @17,000 ft
+ stable
- take off
- sluggish pitch
Looks: 7/10