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Author Topic: 220mph Proximity  (Read 15799 times)

ched

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Re: 220mph Proximity
« Reply #105 on: November 21, 2020, 04:26:06 PM »

I think it was to do with speed that they wanted out of the heli or maybe it was lift. One thing to note is that commercial aircrafts have to comply with noise regs. Military aircrafts don't :-) So it could be that the tips help speed or lift but create lots of noise. Again civilian aircrafts have fuel consumption specs that they must adhere to, military aren't very bothered. Can't remember much, had a few chats over a coffee with a few of the blokes that used to work on testing the blades. Quite often when testing stuff you were never told why the tests were being carried out as that might bias the results. Some of them also worked on the Concorde engine and intake development and testing way back. Used to be some interesting conversations. There was a Red Dwarf episode where part was filmed in the test cell where Concorde intake ducts were developed!!!
 
I remember doing flight certification test for RR Trent 500  (civilian) and they were trying to get me to 'tweak' the thermodynamic calcs. I thought it was a bit iffy so had a chat to our mathematician to confirm that the 'tweaks' would alter things in their favour!!!! I was in charge of the data and calcs that would be submitted to CAA to gain the engine flight certification. Unfortunately we never did the chicken ingestion tests :-) Lots of water and ice but no chickens.

As for your props, way above me mate. Thermodynamics I had a reasonable understanding of, well calcs anyway not theory.
Always interesting to hear about the lengths you go to to build your crafts.

omegooliebird

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Re: 220mph Proximity
« Reply #106 on: November 22, 2020, 06:56:32 PM »

Another quick test today to see amps at full throttle on 14s.. peaking around 180a.. guessing 50v under load....so, 9kw... that's 12 horsepower according to Google..through a 7 inch off-the-shelf prop!! It is so insane I can't quite make sense of it.. Some losses along the way, but that prop hub is still probably seeing 7 or 8 kw .. it's just incredible.

« Last Edit: November 23, 2020, 02:29:01 PM by omegooliebird »
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Coyote

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Re: 220mph Proximity
« Reply #107 on: November 23, 2020, 06:03:27 PM »

That sounds vicious :) :)
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omegooliebird

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Re: 220mph Proximity
« Reply #108 on: November 27, 2020, 09:20:09 PM »

Another speed project for LOS @ 500kmh. Roughly the same power as the FPV plane, so it will be interesting to compare the speeds.







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ched

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Re: 220mph Proximity
« Reply #109 on: November 27, 2020, 09:37:05 PM »

That looks built for speed. Looks great, beautiful finish you have achieved. Can't wait to see vid.

FPVSteve

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Re: 220mph Proximity
« Reply #110 on: November 27, 2020, 11:39:34 PM »

Looks awesome, love the paintwork.

.... I assume the vertical stabiliser is coming?
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omegooliebird

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Re: 220mph Proximity
« Reply #111 on: November 28, 2020, 12:43:17 AM »

I didn't build the airframe, this was purchased from HJK Speedwings in Germany. I bought the motor second hand from Germany also. The finish is actually the carbon with a tinted laquer, it is spread-tow carbon fabric that is used in the outer layer of the layup. The quality of the work is incredible. A work of art.
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omegooliebird

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Re: 220mph Proximity
« Reply #112 on: November 29, 2020, 12:16:26 AM »

Also got this off the wall and went through it, put a different motor in (Leopard 3674 v2 1900kv) and will be using it as a prop test mule for the 14s Fusion. It's previous best was 412kmh, but think it is capable of much more with these new carbon oversquare props at lower rpm. Glassed wings and vac moulded carbon rear end to take the bigger motor. It is a heavy old beast though for what it is! So much speed addiction going on at the moment!








« Last Edit: November 29, 2020, 11:26:32 AM by omegooliebird »
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omegooliebird

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Re: 220mph Proximity
« Reply #113 on: November 29, 2020, 05:16:57 PM »

Did another motor test today, with the German folding prop (7x14) on the 14s system. It stayed together which was pleasing, it really loaded the motor, showed a peak of just over 9kw. But more battery sag, so hopefully it will unload a bit in the air. But it works and the efflux speed has got to be 400mph+, so it should push that Fusion past 300mph if the thrust volume is enough, this high revving motor wont take 3 blades, so would need lower KV to use more blades.. The noise though is on another level, it is absolutely deafening in the garden, the echo's when it stops are pretty mad. Neighbours on the other hand..
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omegooliebird

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Re: 220mph Proximity
« Reply #114 on: December 08, 2020, 01:45:21 PM »

Quick catch up..

I wanted to use the Goblin as a prop test mule, and also try lower kv on it, but ran into problems... more drag than I was expecting, the Goblin was 50kmh slower that the Fusion with the same setup.. so it will be no good as a test mule. But it raised enough questions to do a couple of tests with other props, which I have just done this morning:

I tested Goblin motor against Funjet/Fusion motor to see why the Goblin was so much slower... The RPM are the same, amps the same. So it is a drag thing. I am shocked it has so much more drag than a Funjet, and I'm still not convinced, having seen similar speeds with the higher KV motor. I just don't understand. But it would also make sense as to why other people aren't well past 200mph with it already. It is very slippery for sure, but maybe I am used to how much more slippery composite planes are. Also, maybe the Goblin performs much better with a dive (was foggy so couldn't) because of energy retention or something? i don't know, but it isn't much use as a test mule with so much lower speed than the airframe I'm testing for. Goblin will probably go back on the wall for the rest of it's life now which is sad for it!

But something was apparent, and that is how astonishingly more powerful the 14s system is, it is twice the wattage and twice the noise! Going back to running up 6s setups again was like going back to the early 3s days lol!! It just feels weak and pathetic hahah. So I will give up with mule testing and just go for it with the Fusion airframe. I am still waiting on firmware from APD so that I can get RPM/amp data out via telemetry output to an osd, whilst using a pwm input for throttle..it is currently only possible if driving the ESC with a DSHOT throttle input... they said before Christmas.. but that probably means February or something.. Other than that, I'm ready to go for the 500kmh electric. Could just run it without data, but would really love to know RPM and amps in flight.

Something else I would like to understand, is the effect of kv on torque.. Having run 2650kv at 300a, my plan was to run lower 1900 kv with a bigger prop at 300a so it was putting the effort into torque more than silly RPM, but it seems like the lower kv simply hasn't got any more torque to drive the bigger prop.. I suspect that a given motor size will produce a given amount of torque no matter the KV. It seems like the motor size has an ideal torque/rpm, and you use KV to set voltage you wish to use to obtain that rpm/torque.. So with the 1900kv, for it to run in the sweet spot, it should be on maybe 8s and producing the same rpm as the 2650kv to obtain it's full power output in watts. I loaded the 1900kv up with the 7x14 on 6s and it had no rpm at all, simply couldn't pull it, but was only showing 230amps.. Now if that was the 2650kv, it would have been showing over 300a before it was saturated and couldn't pull any more... does this make sense, it is hard to put into words!!
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ched

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Re: 220mph Proximity
« Reply #115 on: December 08, 2020, 02:42:14 PM »

Interesting stuff. I would guess that the torque is within a relatively small band for a given motor size irrespective of kv but I have nothing to base that on. My motor theory college days are near 30 years old now :-) I seem to remember that greater efficiency was achieved by using thinner copper windings as there was then less air gap between windings but that of course limits current. I think increasing number of turns reduced rpm and increases torque but no idea how you find that out, I suppose resistance.
All interesting stuff, cheers for posting.

FPVSteve

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Re: 220mph Proximity
« Reply #116 on: December 08, 2020, 05:10:58 PM »

Are the propellers the same pitch? Increasing pitch will surely require more torque to maintain a specific RPM at given voltage thus more power consumed?
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omegooliebird

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Re: 220mph Proximity
« Reply #117 on: December 08, 2020, 06:03:12 PM »

Yes, increasing pitch does require more torque, but lowering the kv does not increase the torque the motor can produce is my finding. It may be different at lower power levels, but I am working at the point when the motor is becoming over saturated. The lower kv motor became saturated at less amps, so the overall wattage was less.
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omegooliebird

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Re: 220mph Proximity
« Reply #118 on: December 28, 2020, 03:46:27 PM »

14S maiden was going to be today. Got everything charged, prepped and ready, (including our baby), got to the field and it was so muddy the van got stuck in the gateway, it was too windy for the launch drone, and too foggy to fly a speed-plane. F**k English winters, they are good for nothing! And F**k 2020. I'm going to do this next year.
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Coyote

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Re: 220mph Proximity
« Reply #119 on: December 28, 2020, 03:55:59 PM »

Lol I would think that's a brilliant idea given this year so far :)
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