After some rendering and changing in pitch to get that curve perfect, its no doubt at all, depending on how i click on the first line its anything between 227 and 232 MPH doppler speed, as the guy filming was a bit away from the plane, the real speed should be maybee 1-2mph more.

So 229 to 234mph is the speed when the plane passes.. ,, and this if the temp was 25 degress celcius, its higher if the temp was warmer?


REALLY good, this makes the talk about supersonic speeds and very inneficient props no good... to me 130 amps on 5s on a regular apc square prop to reach +230mph is to say at least OK

Very good... and as you can see in the video, there is no tailwind at all, maybee a slight headwind if any..

This makes me want to go back to my old thinking of putting my mega direcdrive with small prop in my Viper, hmmmm

Sebbe

The temps must have been over 100F, then the speed of sound will be high anough.

Greetz Rene

Originally Posted by sebbe

REALLY good, this makes the talk about supersonic speeds and very inneficient props no good... to me 130 amps on 5s on a regular apc square prop to reach +230mph is to say at least OK
Sebbe

If the definition of supersonic is when the tips move faster then 340m/s you are still subsonic. 315m/s @ 50000rpm and 4.75" diameter.

Hallo,
As most of you seem to be focused at these mph numbers of one pass, no matter if it is dopplered or radared i would like to add some of my thoughts.

Most of these Jolt, Swist, Viper or whatelse "build" threads turn sooner or later into comparison who pulls the highes amps,takes the biggest battery, and scores the highest rpm and mph.
F5d legal power seem to be already a chickendrive,some are talking about 2,5 Kw and more than 230mph!!

This is really impressing but let me do a small calculation:

The fastests guys in F5d competition ( not me)are able to score lower than 52 sec for 10 laps at the FAI pylon course,which is in theory 4 km, but as nobody (even the best) might be able to get 10 perfect laps and even the best plane can only perfom curves not corners, i assume 4500 m would be a perfect run.
No discussion about accuracy, as your favorite is calculating speed by distance and time (doppler and radar usually is not even a second!) and the longer the distance and time the more accurate it gets!

So the average speed of the 52 sek run is about 200mph,and this average includes the start from almost 0 mph,and 10 times 40g turns and 10 times maybe 25g turns and defintely no dive!!
Average power is less than 1200 watts and this also includes the average voltage , its not just a mesurement at the first pass with almost full accus!!

Dont you think its worth to think about improvement options beyond just adding batterys and amps?

Dont take me wrong , just want you to open your mind a little!!

Yello

Thanks for taking a look at the numbers.

It's really hard to tell but I'm thinking the camera guy is somewhere around 50' off the line of the plane. Below is a map to the field. I was about mid runway when the plane passed me and it come in to just over the south edge at the end of the runway. The fence was about 25 feet from the runway.

http://www.smmac.com/MAP.html

Temp were low 80s.

Guys,

Why not try designing around some setups with a little larger than 4.75X4.75 props?

4.75X4.75 at 46K , ...even 50K is fractional power of what these longer 28mm motors are capable of.

Consider trying something with little more diameter and more pitch.

5.25 X 6.25 APC E should draw about 3KW at over 41K (on ground)
lower prop tip speeds, more pitch speed, and larger diameter for more thrust.
Pitch speed: RPM X Pitch / 1056 = MPH
Tip speed: RPM X Diameter / 336 = MPH (static, will be little higher in flight)
[Pitch and diameter in Inches]

If the motor that you have can not do it, then find a prop inbetween those two sizes.


Guys running land speed records do not try to make it a 24 hour event.


Find a prop that works for you and someone will make it stronger than APC.


Different people have different goals and no one setup is perfect for everyone.


Lets see which setup goes the fastest.


Without inflight data it is hard to compare…..death dives do not help compare setups either.



Gryphon

Gryphon,
Looks like you did not understand my post, maybe its still a language issue.
replace an 4,7x4,7 to a 5,25x6,25 means adding 50 % current on a already massive overloaded drive!!!

Yes, this for me really seem to be open minded!!

Yello

guys, the thing I was refering to was the discussion some while ago, where some said: no way a square prop could go this fast, I guess not,, and I dont think this is the limit either.. same discussion also when F5D planes would explode over 230mph, hehe, well I guess not..

Dive or not, one thing is true, this pass was a true 235mph run, as the temp was a bit higher then I used in doppler readings.. One thing is sure, there was no headwind, and also an regular plastic apc 4.75x4.75 was used...

Even with a dive before, Im impressed of the speed achieved with the setup used and the wattage used.. as this setup probably would be "inefficient" by many.... well 2.3kw is not that much, so something must be OK with that setup, else either those speeds would not been achieved or mor power would have been needed..

so why is this particular video so special, at least to me, well first it is a setup with a high kv and square prop, second, the doppler are same as radar, which confirms speed is true. other videos often show high radar speeds, an slower doppler....

to me this shows a square prop can be really fast with not so high wattage, this is good..

the more exciting part now is, what would a 4.5x5.5 prop do in that plane and same setup ?

Originally Posted by sebbe

the more exciting part now is, what would a 4.5x5.5 prop do in that plane and same setup ?

Dind, ding, ding! What I was thinking too.

Originally Posted by henke

If the definition of supersonic is when the tips move faster then 340m/s you are still subsonic. 315m/s @ 50000rpm and 4.75" diameter.

Henke, I think its not that easy to calculate, Jacko did explain ot a while ago, dont remember, but I think a 4.75" prop @ 50K is supersonic...

but this really dont matter, the speeds we are seeing shows that square props indeed are fast, faster then some think could be..

Remember that that was in a dive sebbe, what that other thread was talking with square props about was flat and level.

You cant break the laws of physics, just bend em a lil bit

Still a damn fast plane!

Tip speed isnt just rotational, ie RPM, the tips are moving forwards with the plane too, so you end up with a helical tip speed.


Ampfest in NZ is this weekend coming btw, will get some real world speed trap numbers off the HJK1.1 with teh 4.5x5.5 @50k rpm

what does dive or not has to do with tipspeed?

I am saying to reach a bit over 235mph pitchspeed with a squareprop, you have to push it beyond what is "efficient" , but to me even with a dive 235mph flattened out at 2.3kw is damn good.. now think further, what will happened with oversqaure props ?

ok, put it this way, how fast is the tipspeed of that prop, when the plane is going 235mph ?

and what rpm/pitchspeed is needed to get to 235mph ?

Originally Posted by Mreyello

Gryphon,
Looks like you did not understand my post, maybe its still a language issue.
replace an 4,7x4,7 to a 5,25x6,25 means adding 50 % current on a already massive overloaded drive!!!

Yes, this for me really seem to be open minded!!

Yello

Hi there Yello,

I heard you clearly the first time.

You might have missed this part of my post:
"Different people have different goals and no one setup is perfect for everyone."

As far as being over loaded drive; My 4+KW 28mm testing is over loaded....not the weaker 3KW setup I mentioned.
If prop size is large and direct drive on any fixed motor then fewer cells can be used and over loading will happen at fewer Watts (same high AMPs). But we are talking little props. They don’t overload the drive so easy. Again, I’m talking about making top speed runs, not general sport flying.


Edit/Note: I did not say that which setup should swap prop from 4.75X4.75 to 5.25X6.25 .
People can design around a setup with intension of running larger prop...with matching KV and cell count.

Gryphon