SR71 BUILD - The Blackbird.

Inlet larger than the fan - tube and outlet no smaller, or you lose thrust. Too small an inlet will strangle the fan, and a smaller exit will choke it.

I generally agree with Eric's comment. I use Frank Fanelli's book - RC Ducted Fans - as my bible, it's admittedly a few years old and refers exclusively to nitro power but the principles are the same. The Author recommends inlets at least as large as the fan shroud and outlet tubes no smaller than 90% of the fan swept area but preferably 100%.

How much will it weigh BB?

I have a fan at 127mm and the outlet is 100mm
The weight is still unknown but im looking to get a minimum of 10kg hopefuly up to 14kg from the fans on 12s each, the fans according to people that have got them give 7kg each, and i have fitted Scorpion motors .
I hope it comes in at around 15-17lbs
Then again i have never built anything like this before, im new to the leccy stuff and have been away from model aircraft for the best part of my life.
am on a learning curve, a very steep one, lol

My understanding is that the inside of the ducts should be glossy smooth, especially the outlet duct.

Done some more sheeting and planking to the underside today,










And sheeted one of the engine spikes

Finished planking the top, now its sanding down and filling then sanding and filling ect. ect .ect
Boring, boring.

12 o-clock today got fed up with sanding so i started this.








134" LANCASTER

The Blackbird
Cracking build but will not the engine 'spikes' seriously reduce the inlet area or are they removable?

The principle I have used is to leave the air leaving the fan strictly alone.
A lot of energy has been used to speed it up and almost anything tends to slow it down.

The inlet the air stream has a fairly constant velocity across the width of the duct but aft of the fan it is not, being fastest from the tip region of the fan and slowest from the root. Hence the benefit of really smooth outlet ducting with little or no change in direction.

Is that 12S LiPo - 44.4V?

On the 12" to the foot model, the cones are to keep the intake air subsonic, although the aircraft is travelling supersonic. Quite how they work, I never figured out, unless it is something to do with reducing the ram-air inlet area, thus causing a reduction of pressure, and therefore speed, in the expansion chamber behind the cone.

Hi Beard
thats the bloody esc's i have, they came from giant cod, and today giant cod tell me they are no good for the motors im useing, i also programed them in.

Yes thats true an as Timbo has said its just a matter of elimination.He thinks you should try the other motor BB your in a difficult situation having taken on a compicated set up,as was previously suggested,maybe start with 1 6s Battery and work from there.Fortunately Ive never had a problem with electrics and its only when problems arrive you learn from them.Also check the motor you did run up for any possible damage before you run it up again,good luck BB and have the fire extinguisher handy.

Giant cod said the Black Mantise 120amp HV OPTO ESC would do the job with the Scorpion motors
@£84 each
I want to get it right this time opinions please
Tried to donwload the artical and put on here, but my computer skills are wanting

this one?


Black Mantis 120amp OPTO esc Speed Controller High Voltage Specifications:
120amp OPTO Speed Controller
Nixx: 18-38NC
Lipo: 6-12
Weight: 149g
Bec Output: No
Dimension (W*L*H) : 34*52*20mm
Programmable: YES

Features:

Extremely low internal resistance
Super smooth and accurate throttle linearity for better flying experience
Saftey thermal over-load protection to save problems occurring
Auto throttle shut down in signal loss situation
Supports high RPM motors
New Advanced programming software


note MAX battery is 12 cell lipo.

Probably good idea to get a programme card also that should help.But also safe to test in stages from 6s up to make sure everything is working ok before trying it out with the national grid of 12s.