Lancaster 74 Inches

[GuyOReilly]

Project is in early stages of planning.
It will start ice the Minimoa is completed.

[GuyOReilly]

Previous information regarding motors and prop, etc.

My opinion on how to power a draggy 6 pound four engine airplane.

Let's do the math.  (proof I listened to Piker's power math classes over the years)

Objective: approx 100 watts per pound for a 6 pound airplane should be 600 watts for 4 motors.  Each motor should deliver 150 watts.

Reasons i) "always overpower an airplane.  You can always throttle back..... if you have to".
             ii) there is nothing more difficult than flying a marginally powered airplane.  Guess when the first time is when you realize you have this problem.
             iii) multiple engines have much more pulling power than a single engine of the same total wattage.  Look at Michael's Albatross.  You probably only need 80% of the power equation.  Mathematically each engine probably delivers 185 watts.  That's a safety margin.

The best value motor to develop 150 watts is a bell motor like the ones in the photo.  There are some 4 motor combos offered for quads that include motor and ESC but make sure they are lower kv for larger props.  The KV range will probably be 1000-1500 for 9" props.  These motors safely produce 150 watts on 3 cells and draw about 15 amps max.  A 20 amp ESC would fit perfectly.

Here are photos of two of the motors that would fit the bill.  The red motor is the smaller length one (2805*) but its taller brother (2822) is perfect.  The red EMAX 2822 is the one I have powering my 52" span Stinson Voyager... single motor.  Death by 100 sticks post http://temac.ca/smf/index.php/topic,7329.0.html   The second photo (29) shows the nose cone of the Stinson with that motor inside.

Props:
- If you like the look of a 3 bladed prop, the equation is that you can reduce the diameter 2".  A 10x5 two bladed prop and a 3 blade 8x5 have roughly the same output.
- Opt for a lower pitch prop for a draggy airplane like a Lancaster.  I would not go higher that a 5" or 6" pitch.

FWIIW

Frank

* when you see these numbers, the first one is the diameter in mm (28mm) and the second (05mm) is the length of the rotor.

[GuyOReilly]

Another random thought on powering 4 engined plane from @Frank v B .

A second option is to have two sizes of motors.  More powerful ones inboard and smaller motors capable of swinging the same size props as the inboard ones.
The advantage is that when accelerating, the power is concentrated inboard.  It is much safer.

I have used two options on previous planes:
- a GWS C-130- I used two bell motors inboard and freewheeling props on the outboard nacelles.
- my own design 62" span with 4 IC engines.  The inboards were 15's, the outboards were .10's.  It flew like a trainer.

Frank

[Frank v B]

The photos of the motors for my first post on this topic.

Frank

[GuyOReilly]

Thank you for re-posting the pictures.
Guy

[sihinch]

Just my gut, but a 72" four engined aircraft may weigh more than 6lbs.....did you get the 6lbs from somewhere, Guy?

[GuyOReilly]

@sihinch , the weight is just a guesstimate based on years of being incorrect and vaguely unaware of anything to do with engineering...  Just a building goal I had in mind.  Also, the construction techniques outlined on the plan will not be followed 100% as some increase weight, for example fully sheeted sides and bottom.  I plan on using sticks whenever possible, but keep the outline.

[sihinch]

Personally, I would plan for an 8lb aeroplane and get a prop/motor combo capable of delivering 150-200 watts per motor.  Just my 2c, and I've never flown a 72" balsa 4 engined model!

[piker]

This is awesome!  With you and Michael doing similar projects it'll be so nice to see them coming along together.

I just have a couple of thoughts.  First, Frank suggests reducing the prop diameter by 2" when going to 3 blade.  My understanding is it's appropriate to just reduce by 1", but I haven't really studied the scenario.

I agree with Simon and I would leave just a little extra room for error when choosing the power system.  However, I powered my Sandringham with 4 motors running on 3 cells each and drawing about 35amp (about 420A/motor).  On that 96", 16 lb plane there was tons of power.

I really encourage your goal to try to keep the plane a light as possible.  Your enemy will be a high wing loading.  You want a plane like this to float along at a scalish speed, not race around like a pattern ship.

[GuyOReilly]

@piker , you are correct.  light is key. The build will start once my Minimoa is completed...   Not enough room in the basement for 2 large models under construction at the same time.   

[GuyOReilly]

Site to calculate power/batteries, motors, etc.
https://www.ecalc.ch/motorcalc.php

[GuyOReilly]

Look at what the postman delivered today! 
Construction will start soon, I hope.

[GuyOReilly]

Whilst waiting paint to dry on the Minimoa, I made some progress with the power plants to be used in the Lancaster.
This is the test bed.
A bit more soldering and should be able to fire these babies up.
Should counterrotating be on the left side or the right side?   

[Michael]

My experience is that the top of the props turn towards the fuselage.

It looks like you have them set up correctly.

[GuyOReilly]

A test bed for the motor installation. 
I ran out of solder to make additional connections and a "Y" connector   
@Michael what size of wires should be used?  I am thinking 14Gauge as appropriate.

I am thinking about eliminating the landing gear to reduce weight and simplify build. 
Hand launch and belly landing. - Doable or not advisable?   

NOTE: @Andy Hoffer and @Frank v B and @Michael before you ask, the 2X4 will not be installed as a wing spar.