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Pumpkin drop event

Supersonic prop

#1
Build a FT type of plane around the notion of a prop that spins fast enough that part of the prop goes supersonic. I know a supersonic prop loses efficiency, but that isn't the point. The point is to build an electric airplane that flies and is really noisy because the prop is supersonic. I have seen and heard full scale planes with supersonic props and I can assure you that it is almost unbelievable.
It will take a high kv motor driving a fairly low pitch prop, of course, but it will also probably take using more cells than a motor is really designed to use. The prop will have to be on the small size so the motor isn't overloaded.
I'm thinking an F-22 type plane with mid-ship motor to maximize the noise. A bigger plane would be noisier too. And, yes, it has to be electric so we know all the noise comes from the prop.
 

buzzbomb

I know nothing!
#2
Build a FT type of plane around the notion of a prop that spins fast enough that part of the prop goes supersonic. I know a supersonic prop loses efficiency, but that isn't the point. The point is to build an electric airplane that flies and is really noisy because the prop is supersonic. I have seen and heard full scale planes with supersonic props and I can assure you that it is almost unbelievable.
It will take a high kv motor driving a fairly low pitch prop, of course, but it will also probably take using more cells than a motor is really designed to use. The prop will have to be on the small size so the motor isn't overloaded.
I'm thinking an F-22 type plane with mid-ship motor to maximize the noise. A bigger plane would be noisier too. And, yes, it has to be electric so we know all the noise comes from the prop.
Nice! Not the just idea, but where FT could take it! That's wonderful!
 

Hai-Lee

Old and Bold RC PILOT
#3
Actually I do not think it is wonderful but rather an extremely dangerous venture.
The one thing not considered in the OPs post is the structural integrity of the propellers we use. I have exploded Props at high speed and watched the front of the plane almost instantly disintegrate due to the severe imbalance and this was with new props!. The prop tips were WAY sub-sonic! What forces would be unleashed it the prop tips actually managed to break the sound barrier?

Just a note of caution on experiments with high speed rotating objects!

Have fun!
 

Vimana89

Well-known member
#4
Sounds dangerous and impractical, if it could even work at all. What could possibly be done along your line of thinking that would work, is to come up with a system that looks and behaves a lot like a turboprop, but scaled down to be practical for RC. Everything is scale in RC, sizes, miles per hour, and whatnot. I'm sure a setup could be made with a small diameter prop with many blades and the right high KV motor, that would perform well and be very noisy. Just don't expect it to break the sound barrier. This is something I'd really like to see myself.
 

buzzbomb

I know nothing!
#5
LOL, ya'll. The OP is not saying he's going to try it. It's a show suggestion for the FT team. Personally, I hope they take it on. They've the know-how and experience. Me personally? Hard pass. That's a Big 'Ol, Heck No! Still doesn't mean I wouldn't like to see someone else do it! :geek::eek::D
 

tamuct01

Active member
#6
Just for grins, I did the calculations. At sea level, the speed of sound is 767 mph (give or take due to temperature, etc.). This is 809,952 in/min once you change the units. The circumference of a prop is its diameter * pi (2 * pi * r if you remember geometry). So a 5" prop has a circumference of 15.708" and a 10" has 31.416". Divide the speed of sound in inches per min by the circumference to get the revs/min of the prop. For a 5" it's 51,563 rpm and a 10" is 25,781 rpm.

Probably doable with some motor/ESC combinations, but the stresses will likely destroy the prop.
 

Vimana89

Well-known member
#7
Just for grins, I did the calculations. At sea level, the speed of sound is 767 mph (give or take due to temperature, etc.). This is 809,952 in/min once you change the units. The circumference of a prop is its diameter * pi (2 * pi * r if you remember geometry). So a 5" prop has a circumference of 15.708" and a 10" has 31.416". Divide the speed of sound in inches per min by the circumference to get the revs/min of the prop. For a 5" it's 51,563 rpm and a 10" is 25,781 rpm.

Probably doable with some motor/ESC combinations, but the stresses will likely destroy the prop.
Sound like you would need a very sturdy prop. It sounds like if this were doable, you want alloy props and a fiberglass airframe or something along those lines.
 

quorneng

Well-known member
#8
Not quite sure why the OP wants to create a super sonic prop.
It will indeed be very noisy and pretty inefficient and even worse if anything more than just the extreme blade tips go supersonic. This is all well understood and historically proven.
Difficult to see how such an experiment advances anything much and as Hai-Llee points out it has significant dangers associated with it.
 

Vimana89

Well-known member
#10
This all sounds much more like a suggestion for a Mythbusters espisode than FT. I can see this being tried in some room or enclosure with plexiglass windows and a camera running. I can't see anyone wanting to be near that motor when it starts up, and I can't see it ever powering a plane made of any type of foam.
 
#11
I'm thinking a carbon fiber prop and a lot of common sense could make this doable in a large area like the new FT facility. Worst case scenario is the plane blows up when the prop fails. That would be good video. Best case scenario is it doesn't blow up, but just makes a huge amount of noise. That would be good video too. Certainly you wouldn't want to be standing too close, but something light, made of carbon fiber, and shaped like a propeller blade will lose most of its kinetic energy pretty quickly. This would be good TV in any case. The science value for their STEM program would be an additional reason to try it. There would be the usual "don't try this at home" message, of course.
 

Hai-Lee

Old and Bold RC PILOT
#12
I'm thinking a carbon fiber prop and a lot of common sense could make this doable in a large area like the new FT facility. Worst case scenario is the plane blows up when the prop fails. That would be good video. Best case scenario is it doesn't blow up, but just makes a huge amount of noise. That would be good video too. Certainly you wouldn't want to be standing too close, but something light, made of carbon fiber, and shaped like a propeller blade will lose most of its kinetic energy pretty quickly. This would be good TV in any case. The science value for their STEM program would be an additional reason to try it. There would be the usual "don't try this at home" message, of course.
At a time when the legislative powers are trying to find reasons to legislate the "Drone" community out of existence such a video posted on-line would just be further proof of the dangers that RC Drones present to the general public as well as a somewhat dangerous and radical element in the RC community in general.:rolleyes:

The use of CF would give a high strength prop but one the disintegrates into razor sharp shards on failure. If the prop is to propel an aircraft then the pitch would not be zero and the serious forces would be generated trying to rip the blades forward as well as the cyclic oscillation or movement of each blade as it rotates, (high pressure part of the disc to low pressure part of the rotational disk). When you add to the blade flexing, (fore and aft), under load you then must add the extreme change in blade drag at the tips as the prop tip reaches the sound barrier.:unsure:

Assuming that you could manage to design and manufacture a prop that would survive the vibratory effects upon the motor/gearbox/mount/fuselage would be very high to extreme. Whilst the vision of a prop disintegrating might be appealing to some and possibly even seem harmless:eek:, the extremely probable result would be the motor separating from the mount or the fuselage exploding allowing the motor and or gearbox to be propelled from the craft at a speed where its mass would make it a lethal projectile!

If you wish to do it yourself do so but no video please! If not send the idea to Mythbusters where it belongs!

I love flying RC and promote its safety and campaign to expand and keep the hobby legal for all responsible users. Please remember the hobby is under threat globally!

Have fun! (safely)!
 

DamoRC

Well-known member
Mentor
#14
At a time when the legislative powers are trying to find reasons to legislate the "Drone" community out of existence such a video posted on-line would just be further proof of the dangers that RC Drones present to the general public as well as a somewhat dangerous and radical element in the RC community in general.:rolleyes:

The use of CF would give a high strength prop but one the disintegrates into razor sharp shards on failure. If the prop is to propel an aircraft then the pitch would not be zero and the serious forces would be generated trying to rip the blades forward as well as the cyclic oscillation or movement of each blade as it rotates, (high pressure part of the disc to low pressure part of the rotational disk). When you add to the blade flexing, (fore and aft), under load you then must add the extreme change in blade drag at the tips as the prop tip reaches the sound barrier.:unsure:

Assuming that you could manage to design and manufacture a prop that would survive the vibratory effects upon the motor/gearbox/mount/fuselage would be very high to extreme. Whilst the vision of a prop disintegrating might be appealing to some and possibly even seem harmless:eek:, the extremely probable result would be the motor separating from the mount or the fuselage exploding allowing the motor and or gearbox to be propelled from the craft at a speed where its mass would make it a lethal projectile!

If you wish to do it yourself do so but no video please! If not send the idea to Mythbusters where it belongs!

I love flying RC and promote its safety and campaign to expand and keep the hobby legal for all responsible users. Please remember the hobby is under threat globally!

Have fun! (safely)!
I agree with the sentiments here but I think @Larry Laitner is not contemplating this himself, rather he is proposing it as a suggestion for the FT crew (thus the posting in the "Show Suggestions" sub-forum).

Hard to imagine that, if FT took on this challenge, they would not take the appropriate precautions both for their own safety and for the reputation of the hobby.
 

Hai-Lee

Old and Bold RC PILOT
#15
I agree with the sentiments here but I think @Larry Laitner is not contemplating this himself, rather he is proposing it as a suggestion for the FT crew (thus the posting in the "Show Suggestions" sub-forum).

Hard to imagine that, if FT took on this challenge, they would not take the appropriate precautions both for their own safety and for the reputation of the hobby.
I do not doubt the safety measures that the FT crew would implement if they ever undertook such a challenge BUT it is not the abilities of the FT crew but rather the somewhat ill-informed and fear-filled masses, that would see such a build/experiment and the forces it unleashes as an indication of what EVERY RC model builder does and the power they could wield, is what I am concerned about!

Just as the 3D printed pistol, and the Quad copter that it was attached to, were shown around the world as news of what drones can do! (The inference is/was that all drone pilots are capable of undertaking such a build with the obviously evil intent! The recent item of the airport in the UK being shutdown because of a drone, (still not proven), has caused Drone regulations world-wide to be the subject of review and even further legislative restrictions. These 2 items have caused plenty of hurt to the RC model aircraft scene so I question the value of doing and publishing experiments that can show how a drone can be made more dangerous and apply extra reasons for their being outlawed all together!

Just an old blokes thoughts!

Have fun!
 
#16
Holy crap. This discussion really went sideways. I have seen this happen on RC forums, but I somehow thought a Flite Test forum would have a sense of curiosity and a bit of playfulness. I hereby retract my suggestion. Maybe Peter Sripol will be interested. Y'all stay safe and righteous, if that suits you, but I like life with fun, whimsy, and maybe a bit of danger.
 

buzzbomb

I know nothing!
#17
Holy crap. This discussion really went sideways. I have seen this happen on RC forums, but I somehow thought a Flite Test forum would have a sense of curiosity and a bit of playfulness. I hereby retract my suggestion. Maybe Peter Sripol will be interested. Y'all stay safe and righteous, if that suits you, but I like life with fun, whimsy, and maybe a bit of danger.
No need to retract. Let it stand. Remember we are a forum family here, and yes we argue like family. For the most part we keep it light, but sometimes we push a button. Hai-Lee trains children to fly RC. Safety is absolute priority in his book, regardless of circumstance. I'm new to the whole RC flight thing, so everything sounds cools to me. Plus you've got every opinion in between.

Also, if there is any chance it'd be cool but stupid? You are right. Peter Stripol is your guy! I love his channel.
 
#18
Maybe he should start his own thread about 3D printed guns, drones as weapons, and the ignorant masses and leave Flite Test alone for the curious folks who love thinking about innocent stuff.