V-2 with wings rebuild 2021

Think I'd be tempted to move the motor forward and drive the fan via a carbon shaft, itll need carefull alignment and possibly a support bearing.

Forgot to add to aid cooling I would add a couple of "Naca ducts", there very low drag and ideal for printing!

I did wonder about moving the motor forward and using an extension shaft but two things rather put me off.
1. It is pulling about 30,000 rpm at full chat (80% of 2300kV at 16 V). There is a danger that at those RPM an extension shaft would create more problems than it solved.
2. It would be necessary to open up quite a bit of the airframe to mount the motor fully inside the airframe.

So I chose a partial solution.
Turn the motor round and use the prop as a pusher.
Where the fuselage 'necks down' to create the inlets gives a natural strong point to mount the motor.

It moves the motor forward by nearly 2" (50 mm). Not that much but every little helps.
A further benefit is the prop duct is no longer carrying the motor so it can be just a Depron 'tube' supported by the fins. The full printed duct weighed 24 g. I would expect a Depron tube to be less than half that and any weight saved is from right at the back.

Still toying with what to do with the servos. 4 together represent a total of about 20g that in theory can be placed as far forward as the battery.

I know moving the motor forward would have been a pain but personally I think the prop.at the back spoils the look, I do think the shaft idea is sound.
Been thinking about things and I'm confused (easily done!) Earlier you said a true ducted fan drew more current than your ducted prop set up.. in that case why when glow motor driven "jets" where popular did they use a multi bladed fan when you've found out a ducted prop needs less power?
Just a bit of information but modern F1 engines use a turbo with the exhaust driven impeller at the rear of the engine and the compressor at the front driven by a shaft and they spin at well over 100'000 rpm....food for thought and all interesting stuff.

Paul
That pusher prop will be hidden inside a cowling just as it was before.

For props and fans there is a big difference between efficiency and power.
A 12 bladed EDF fan can turn a lot of power into thrust but its efficiency (g thrust/W) in doing so is poor. A prop, particularly a 2 blade, is more than twice as efficient in converting Watts into thrust but for the same diameter can only handle a limited amount of power.
So for a prop to produce a particular thrust it needs to be a bigger diameter than a multiblade fan but it will need less power to do it.
Most jets are limited in the diameter of the fan they can use so power hungry multiblade fans have to be used hence the limited flight times.
Unless of course you cheat a bit and use a super light weight airframe so a small diameter internal 2 blade prop can be used.

In its original form my V-2 used an 8 blade 70 mm fan but needed close to 600 W to achieve a VTO.
By going up to a 102 mm diameter 4 blade prop it looks like I can get something like 80% of the thrust but it only needs 250 W. The reduced power requirement will allow a smaller lighter battery and electrics so 'making up' for the 20% reduced thrust.

Well that's the theory however at the moment the lighter weight of the electrics has upset the position of the CofG. The reduced thrust rather limits the options of what can be done about it.

ps I don't have the same budget as F1 for long high speed shafts.
I note an F1 piston (and there is remarkably little of it) can cost £50.000 each.

Thanks for clearing that up Simon, as I said before it's all interesting stuff, I do enjoy your projects, always thought provoking!
Klippy, yes it was Mercedes that came up with the concept, it took a couple of years and a lot of guys with long lenses before the others twigged.

There is nothing wrong with the balance of a 60 degree V6 just so as long as you put 2 end to end on a common crankshaft. Then the balance is brilliant

The Depron duct on the 102 mm pusher prop.



I still have a CofG problem but it is not quite as severe as it was. The motor, the pusher mount and the Depron duct weigh 40g whereas the motor and the full printed duct weighed 58 g. Not a huge saving but its centre of mass is nearly 2" (50 mm) further forward.
The 4 servos are the next installation that should result in the CofG moving forward quite a bit.

put me out of my misery....where "should" the cg be?

X marks the spot!

I never took a picture of it actually 'balancing' but I did record the CofG at 42% root chord on the small scale Depron chuck glider.

Experience tells me to always move a powered model CofG a bit further forward.
I also have a picture of the 'finger holds' I used for the hand launch on its maiden flight.

The remains of the index finger 'hole' are till visible on the skin.
The actual CofG would have been sufficiently ahead of the index finger hole so it could be balanced between thumb, index and 2nd fingers. On my hand that would put it about 35 mm ahead of the index finger hole which where I have marked it. It is at 36% of the root chord.
It does seem a long way forward but there is considerable fuselage lift to contend with as well.

Talk about a convoluted way of guessing a dimension!

Well seeing as Paul was the only one to take a stab at it. Congratulations, You have won an Admiral pro 2200 4s 45c Lipo, almost new !
All you have to do to claim your prize is take a dip in the lake & find it ! Oh & get a short flight, plus a train. I will pick you up from the station though.