My failed attempt at making a supersonic prop aircraft

[GoodHunter14]

Since I saw videos on YouTube of how many people made propeller based aircrafts in the last month, I wanted to try my luck and make a stock supersonic propeller plane. Obviously I failed, and since I've failed and given up on propeller aircrafts, I wanted to share with you my design. It's my most stable prop engine I've ever built. My highest level top speed I achieved was 170 m/s  . I don't understand how I didn't achieved more... but I'll explain to you why I don't understand. Here are the 3 models for my aircraft:

Aircraft V1.1

Top speed: 110 m/s

Torque: 7 Medium SAS modules per engine => Total of 14

This is the most stable prop based aircraft I ever made. It's a joy to fly.

Aircraft V2 

Top speed: 150 m/s

Torque: 13 Medium SAS modules per engine => Total of 26

I'm dissapointed that I didn't get an at least 70% improvement of speed over the first version. I have almost double the torque and the stability of the aircraft is almost the same! I don't understand why I couldn't get to at least 190 m/s. This was a total let down for me.

Aircraft V3

Top speed 170 m/s at 7000 m altitude

Torque: 19 Medium SAS modules per engine => Total of 38

This is where I stopped. Obviously I had no chance of increasing the speed anymore. Stability was an issue here, but I managed to make it fairly stable with that many modules per engine. The engines won't woble to death so that's good enough for me.

 

Now why is that with so much torque I get little speed increase? This is what I don't understand. I have tried numerous ways to improve the speed but I've failed. I tried different elevons but that didn't improve the speed. But anyways, you can download the craft files and maybe make a miracle and achieve Mach 1 if you find the solution. If not then at least you have now one of the most stable prop engine designs at your disposal. I can't wait and see what you guys will make out of this engine design and what aircrafts you'll design.

P.S. I used Advanced Tweakables to make those engines as they are now. No cheats involved. If the engines won't spin when you decouple just Re-edit the fairings and it should solve the problem. Hold shift if you want to offset something on the aircraft. If you can't offset to infinity go to settings.cfg and do this: VAB_FINE_OFFSET_THRESHOLD = 20 . 

EDIT: 

I've finally made an almost supersonic aicraft. It has the same engines as the V3 but this plane is faster. Here it is:

The aircraft

 

 

 

 

Edited June 14, 2017 by GoodHunter14

[Bubbadevlin]

Cool plane, but if i had to guess your problem was drag. All of those solar panels in the open like that are very draggy, plus if i am not mistaken all those breaks in your fuselage are treated as blunt ends to the wind 

[klond]

4 hours ago, GoodHunter14 said:

I wanted to share with you my design

 I've set goals and had several failures on here too.  Alot of times I'll go through 20 different versions of the same craft before stuff starts to work.  There's alot of weirdness and quirks that can be hard to diagnose.

 If you have VOID addon installed you can see your radians on the spinning craft.  Since torque is fixed, power will increase with radians per second.  Stay as close to 49 rads/s as you can by tweaking the angle of the propellers in mid-flight (watch the line with F12).

 Oh, here's a weird one.  If ANY part of the spinning craft has Rigid Attachment (and/or autostrut I think) turned on, your power and RPMs will be severely limited.

 I hope it's one of those two things.  Take a break, make something else, sleep on it, then try again.  170m/s ain't bad.  Faster than anything I've made.

Edited June 13, 2017 by klond

[selfish_meme]

I didn't touch your bearings at all, I covered the whole thing in a fairing, and moved the elevons a bit further apart, ditched a lot of the wings (and made the controls work properly) 260ms, which is .74 Mach on my meter, I think if you move the propellers further out again you will be able to achieve Mach 1 at least, good job, some more reaction wheels and you might be pushing the record

Oh I also rocket boosted it to launch it

Craft File

https://drive.google.com/open?id=0B8-nkDP75eETUjM1VDFPc2s5ZDQ

Edited June 14, 2017 by selfish_meme

[GoodHunter14]

1 hour ago, selfish_meme said:

I didn't touch your bearings at all, I covered the whole thing in a fairing, and moved the elevons a bit further apart, ditched a lot of the wings (and made the controls work properly) 260ms, which is .74 Mach on my meter, I think if you move the propellers further out again you will be able to achieve Mach 1 at least, good job, some more reaction wheels and you might be pushing the record

Thank you for the kind words. You motivated me to continue with my engine design. Dumb me wasn't thinking that the problem was drag (facepalm). I'll try to reach at least 300 m/s with the V3 aircraft and then update the thread with the improved version of it soon. So keep on eye on this thread!

Edited June 14, 2017 by GoodHunter14

[selfish_meme]

On 6/14/2017 at 4:32 AM, GoodHunter14 said:

P.S. I used Advanced Tweakables to make those engines as they are now. No cheats involved. If the engines won't spin when you decouple just Re-edit the fairings and it should solve the problem. Hold shift if you want to offset something on the aircraft. If you can't offset to infinity go to settings.cfg and do this: VAB_FINE_OFFSET_THRESHOLD = 20 . 

 

 

 

1

Get a mod called Editor Extensions Redux, it will help you greatly with the placement of parts.

Edited June 15, 2017 by selfish_meme

[selfish_meme]

5 minutes ago, GoodHunter14 said:

Thank you for the kind words. You motivated me to continue with my engine design. Dumb me wasn't thinking that the problem was drag (facepalm). I'll try to reach at least 300 m/s with the V3 aircraft and then update the thread with the improved version of it soon. So keep on eye on this thread!

I only made 30ms on the aerodynamics alone, the most speed came from increasing the elevon/propeller distance,

and you can probably do with even less wings, wings=drag, once it's up to speed you should hardly need any

Edited June 14, 2017 by selfish_meme

[GoodHunter14]

54 minutes ago, selfish_meme said:

Get a mod called Editor Extensions Redux, it will help you greatly with the placement of parts.

Alright then, will do.

[GoodHunter14]

Finally! I achieved 300 m/s with the same engines! Here is the proof:

The aircraft

EDIT:

I've done the same thing for the V2 aircraft. The future of this design doesn't look good. Being able to reach 300 m/s with 38 SAS units compared to 250 m/s and 26 SAS units is bad. I have no idea how to push more than 300.

Edited June 14, 2017 by GoodHunter14

[GoodHunter14]

Made the V4 for this aircraft. Here:

The aircraft

I've hit a brick wall. I can't get over 310 m/s with 25 SAS modules per engine... I've got nothing left to improve other than stability to perfection but there's no point... Drag is minimum tried the aircraft even without the wings, still the same speed... I guess this is it, 310 m/s. I could try different elevons and see if I get better results but I've spent too much time on this thing. Maybe someone else will be interested to continue this aircraft and maybe improve it's speed somehow.

Edited June 14, 2017 by GoodHunter14

[selfish_meme]

If you install the VOID mod you can see how many rads per second you are getting, then loosen the bearing until you are hitting like 49 rads per second. So your top speed will be determined by how close you can reach that rotation speed and how much thrust the elevons generate. The more thrust the elevons generate the more torque you need to keep the rads up. The elevons move faster the further away from the craft they are, have you hit the limit there? Have you tried fewer or more elevons? The angle of the elevon is also very important, if you adjust the angle in flight can you achieve higher speeds?

[qzgy]

Also, what about moving the elevons even further away? Also reducing the pitch to reduce drag.

I aslo have to agree with @selfish_meme here. VOID is a very useful mod for this, along with editor extensions.

[GoodHunter14]

11 hours ago, selfish_meme said:

If you install the VOID mod you can see how many rads per second you are getting, then loosen the bearing until you are hitting like 49 rads per second. So your top speed will be determined by how close you can reach that rotation speed and how much thrust the elevons generate. The more thrust the elevons generate the more torque you need to keep the rads up. The elevons move faster the further away from the craft they are, have you hit the limit there? Have you tried fewer or more elevons? The angle of the elevon is also very important, if you adjust the angle in flight can you achieve higher speeds?

I've hit 310 with angling elevons mid flight for optimal performance. Tried different configurations as for how far the elevons are from the aircraft. If I try to move them further than they are now the top speed decreases to 300. Isn't VOID outdated?

Edit: Never mind I've found the updated version.

Edited June 15, 2017 by GoodHunter14

[GoodHunter14]

47 rads with adjusted elevons gives me the top speed (in this picture the craft was still accelerating but slowly) having the elevons at -66 Authority limiter (The V3 craft had it at -45, increasing it more only slowed it down so I kept it at -45 for V3)

Default elevons (absolutely no adjustments) top speed 230 m/s at 49 rads

See now? I can't find anything else to improve here (increasing the distance of elevons further away from the craft will slow it down, I've hit the limit/sweet spot). Maybe I could try reducing the number of elevons for reduced drag? Therefore increasing top speed in exchange of acceleration?

 

Edited June 15, 2017 by GoodHunter14

[selfish_meme]

56 minutes ago, GoodHunter14 said:

47 rads with adjusted elevons gives me the top speed (in this picture the craft was still accelerating but slowly) having the elevons at -66 Authority limiter (The V3 craft had it at -45, increasing it more only slowed it down so I kept it at -45 for V3)

 

Default elevons (absolutely no adjustments) top speed 230 m/s at 49 rads

 

See now? I can't find anything else to improve here (increasing the distance of elevons further away from the craft will slow it down, I've hit the limit/sweet spot). Maybe I could try reducing the number of elevons for reduced drag? Therefore increasing top speed in exchange of acceleration?

 

 

It's all about tinkering, how about weight? I know some of the record breakers only flew for a few minutes and ran out of charge

[GoodHunter14]

1 minute ago, selfish_meme said:

It's all about tinkering, how about weight? I know some of the record breakers only flew for a few minutes and ran out of charge

Same with my craft, only a few minutes to fly with it. I tried to reduce the weight as much as I could with the fairings (that's why you see those rings at the SAS units). I tried to find a balance between drag and weight with the fairings. Also, the Power to Weight ratio of those Medium SAS units is the best in comparation with those smaller ones that have more weight but less power. I don't have any other ideas of how to improve this design. Maybe I'll come up with a better one in the future.