4 engine V/STOL

I posted this on "guess the plane"

With huge flaps it was intended to be a true VTOL. It did not work but I thought it would make an interesting scale(ish) version even if it only managed STOL.
As I have neither built nor flown a 4 engine plane I decided I had better go in stages.
So first a simple plane with four props that cover the full span.
From an Ebay bargain I bought 4 brushed 28mm Mabuchi motors.

They weigh 1.8oz each and draw 2A driving a 8x4 on 10V giving 2.5oz thrust.
A sketch of the prototype. Built in Depron of course!

The motors are suspended on pylons beneath a simple braced 37" plank wing.
The deep motor pylons in the next version will also provide low pivot points for the big area increasing Fowler flaps.
The outer tip section is just an aileron but as it is still within the prop slipstream it should maintain roll control at slow speed.

As this is only intended to 'fly' rather than STOL its 80W total should be sufficient for an 18oz plane but with brushless motors, a counter rotating prop set and big flaps it might even get close to a VTOL performance.

By mostly using what I already have this 'prototype' will cost no more than £10 so it meets the "only risk what you can afford" criteria.

been watching this on the other site.

you build some interesting planes sir.

One advantage of being retired is you can afford the time to do this sort of thing - machine down the prop adapter to fit the prop.

The motor and 8x4 prop.

Just got to do the other three!

With such low power on each prop this is going to be seriously quiet even with all four running.

As I am building a sort of prototype for a scale Fairchild Fledgling I decided to do a bit of recycling.
My DuctFan has a 36" plank wing.

Which should be just big enough for the four 8" props.
With the tail booms retained and two motors installed.

I may initially fly it like this as any asymmetric thrust would be manageable.
With the outboard motors in place any thrust asymmetry would be much more serious.

Substantial twin fins and rudders will probably be required.

With the radio and ESC installed the first test of the inboard motors.

I had forgotten what a racket the brushed ESCs make but the low speed motor control is excellent, not that it is really required!

A little more progress.
The twin fin tail assembly.

The elevator servo buried in the left hand side of the tail plane.

The rudders will initially be locked for twin motor flying with no servo installed.
When the next 2 motors are added they will almost exactly counter balance the additional weight of the rudder servo mounted in the right hand fin.
The rudders will be connected by a simple tie rod.

The next problem will be the design of a light strong undercarriage with a long travel.

Fuselage under construction.

Should be enough room for the battery!

A bit further.

Not exactly pretty.
At 12.9oz I think it will just about fly but then it is only drawing 4A at full power.

When the 2 extra motors are added it should be a bit better.
As it was a recycled plane so far I have only had to buy 4 motors, props & adapters total £17 including postage!

Completed in its 2 motor 3ch form.

Provided I don't destroy it in test flying all the bits are ready and weighting for the 4 motor 4ch conversion.

I have even started to assemble the bits for the true V/STOL brushless flapped scale version but 4 motors and 4 ESCs significantly pushes up the cost!

Beautiful day for its maiden.
It flew, just, but not for long!
To my surprise the torque from even thos two feeble brushed motors was quite substantal. Lots of aileron just to keep the wings level and with the very modest power and the elevator trim too far back there was rather alot to do with the result I had very little control in the direction of iuts flight.
There is this rugby post........ and you guessed it.
Under repair.

You can see where it hit. I was actually trying to land so it was only a couple of feet off the ground but it was spun round and cartwheeled into the ground.
Badly crushed nose, dislodged RH motor, ripped out RH tail boom and a split tailplane.


Interesting.
Counter rotating props are a must!

Rather than mess about I fitted a pair of counter rotating props I had intended for the final version. Unfortunately they have a slightly coarser pitch (8x4.5) so tending to over load those feeble brushed motors even more than the previous 8x3.8s.

It now flies straight and true but boy! is it under powered. No matter how hard I tried it couldn't get it above 20'!
Damaged the U/C on the third flight (the ground/grass is frozen solid) so removed it all together to reduce weight and drag. A bit better but by this time both the motors and battery had lost just a touch of performance so I could still do no better than 30'!
It is however extraordinarily quiet.
I checked today and it takes 3.5A with the LiPo still reading a full 11V so 38.5W or 47W/lb.

With 4 motors it will weigh 17.5oz which will give a just about adequate 70W/lb.

I am not sure it has proved much yet, apart from the necessity of counter rotating props, but I think I will complete it with all 4 motors if only to have a 'quad' hanging on the wall!

The weather is a bit grim at the moment so here is a short video of a full power 4 engine run.

It now weighs 17.8oz and delivers a good 12oz thrust drawing 7A.
With counter rotating props the rudder servo has not been fitted so the battery has been moved to the rear of the fuselage to compensate for the extra motor weight ahead of the CofG.


It should now an adequate performance but heaven only knows what its glide angle will be with all that prop drag.
I expect all landings will need some power.

Why do things never quite work out like they should?
Despite the extra thrust it is just as underpowered as was with 2 motors!

I fear the increase in wing loading and possible prop interference (the tips run very close together) has just about negated the extra power.
So next back to two but brushless - I know it will have enough ooomph then!

Here we go again - a no motor version!

It will be rebuilt with a pair of Emax 2822, 'handed' 8x4.5s and a 1500mAh 3S.