Flight Testing the e-Go

e-Go aeroplanes

RAeS 17 February 2015

Keith Dennison Chief Test Pilot

e-Go aeroplanes

The Background

• Our CAA’s ground-breaking decision on de-regulation

e-Go aeroplanes

UK CAA de-regulation

Then (2007)

• Single Seat

• Max 115kg basic empty weight

• <10kg/m2 wing loading @BEW

• <35 knots stall speed

Now (2015)

• Single Seat

• Max 300kg MAUW

• Or 315kg with BRS

• <35 knots stall speed

Then NO airworthiness regulation…!

e-Go aeroplanes

The Background

• Our CAA’s ground-breaking decision on de-regulation

• Winning the PFA’s SSDR competition in October 2007

e-Go aeroplanes

Concept

• Desire to make a

‘nice’, fun

aeroplane

• Design-driven

• Specific interest in

canards

• Cherry-pick

technologies

• Blank drawing

sheet – free to

iterate

e-Go aeroplanes

• Pilot first: exceptional view

ideal position

• Efficient: aerodynamics

structure

• Safe: very difficult to stall

protected pilot

Why a Canard?

e-Go aeroplanes

The Background

• Our CAA’s ground-breaking decision on de-regulation

• Winning the PFA’s SSDR competition in October 2007

• Significant interest in the concept

• Development of aircraft and commercial proposition

• Launch of Ltd company and fund raising - Sep 2011

e-Go aeroplanes

Development: simulation and tests

• Working with Cranfield and Cambridge

Universities

• Wind tunnel & CFD

e-Go aeroplanes

Development: structure and tests

• Manufacturing technique trials

• Load tests

• Times and costs

e-Go aeroplanes

The Background

• Our CAA’s ground-breaking decision on de-regulation

• Winning the PFA’s SSDR competition in October 2007

• Significant interest in the concept

• Development of aircraft and commercial proposition

• Launch of Ltd company and fund raising - Sep 2011

• First flight in October 2013

24 October 2013

e-Go aeroplanes

Flight Testing the e-Go

• Flight test approach

• Immediate issues: Braking, steering, canopy misting and engine cooling

• Air data calibration

• Propeller selection

• Rotation characteristics

• Engine characteristics and failures

• Directional stability and control… and stalling

• Adverse aileron yaw

• Longitudinal stability and control… and stalling

• Flightpath control on the approach

e-Go aeroplanes

Flight Testing the e-Go

• Lessons learned

• What next?

• Questions…

e-Go aeroplanes

Flight Test Approach

• 1/3-scale model

• Tibenham – large, hard, quiet, 3-runway airfield

• Taxi – braking steering and ground stability in wind/crosswind

• Hops – three-axis stability & control

• High hops for performance check

• First flight

• Progressive envelope expansion

• Development

• Grass airfields

• Transits, displays and demonstrations

e-Go aeroplanes

Brakes

• Mountain bike brakes

• Finger-actuated

• Problems: binding or

ineffective, hard to use

• Re-engineered mechanism

• Change in regulations

allowed adoption of foot-

actuation

• Very effective

• Mown grass accumulation

e-Go aeroplanes

Steering

• Fixation on brakes!

• Realisation that the braking was

OK

• Lightweight nylon bearing was

wearing and binding

• Redesign to incorporate ‘proper’

bearings

• Now very agile and precise on

the ground

• Shimmy

e-Go aeroplanes

Canopy misting

e-Go aeroplanes

Engine cooling

• Limited time on ground

and taxi distance

• High coolant

temperatures in the climb

in summer

• Modified top surface

louvres

• CFD on cooling ducts

• Duct splitters

• Good cooling

performance

• Ideas for the future…

e-Go aeroplanes

Air data calibration

• No air data boom for first

flight

• Need to calibrate pitot-

static system

• GPS triangle method

• Need to gather credible

angle of attack and

sideslip data

• Air data boom

• Comprehensive data and

video gathering and

collation

e-Go aeroplanes

Propeller selection

• Range of propellers flown

• Thanks to Helix!

• Maybe we could have applied

more science…

• Chosen propeller is achieving

~85% propeller efficiency

e-Go aeroplanes

Rotation characteristics

• Key driver in selection of a

slotted, ‘Fowler’ elevator

• Rotation is delayed

• Impact on take-off distance

• Nose-down moments from CG

and thrust-line exceed canard’s

ability to provide lift at low AOA

• Nose-leg lengthening

• Thrust-line

• Exploding nosewheel leg!

• Move mainwheels forward

e-Go aeroplanes

Engine characteristics

• Generally robust and reliable

• Light and simple design

• Long service intervals

• Thanks to Rotron

• First manned application of the

engine

• ECU set-up a challenge

• Failures:

• Earthing strap

• Catastrophic voltage drop

e-Go aeroplanes

Directional stability and control

• Initial characteristics were poor

• Low yaw stability

• Very low at stall speed

• Low yaw control power

• Fin stall in sideslip

• Rudder induced sideslip

• Rapid rolling – adverse aileron yaw

e-Go aeroplanes

Directional stability and control

e-Go aeroplanes

Directional stability and control

e-Go aeroplanes

Directional stability and control

• Initial characteristics were poor

• Low yaw stability

• Very low at stall speed

• Low yaw control power

• Fin stall in sideslip

• Rudder induced sideslip

• Rapid rolling – adverse aileron yaw

• Minimal air-brake effect

e-Go aeroplanes

Directional stability and control - Solutions

• Increased vertical tail

volume

• Fins, rudders and ventral

fin

• Increased rudder area

• Flettner strips

• Stall strips

e-Go aeroplanes

Directional stability and control - Final design

• Larger fin and rudder areas

• Rudder extended below the wing

• Greater fin sweep

• Moment arm

• Stall resistance

• Good stability and control at all points of the flight envelope

• Possible to balance all manoeuvres

• Airbrake effect still poor

• Ventral fin?

e-Go aeroplanes

Directional stability and control - Final design

e-Go aeroplanes

Adverse aileron yaw

• Differential, Frise ailerons

• Roll control is excellent

• Adverse aileron yaw was large

with the original fins and rudders

• Yaw control power inadequate to

offset adverse aileron yaw

• But… was it bad ailerons or

poor directional stability and

control?

e-Go aeroplanes

Adverse aileron yaw

e-Go aeroplanes

Adverse aileron yaw

• Differential, Frise ailerons

• Roll control is excellent

• Adverse aileron yaw was large

with the original fins and rudders

• Yaw control power inadequate to

offset adverse aileron yaw

• But… was it bad ailerons or

poor directional stability and

control?

• Sharpened leading edge

experiment

• Improved differential for

production

e-Go aeroplanes

Longitudinal stability and control

• Stability was OK

• Pitch control was poor

with extremely light

stick forces

• ounces/g @ 85KCAS!

• Poor feel around trim

• Poor trimming accuracy

• Very poor response to

gusts through ‘manikin’

effect

• Pitch PIO on first ever

hop lift-off

• A very light touch was

required!

e-Go aeroplanes

Longitudinal stability and control

• Root cause was the

elevator design

• Low hinge moments

• Deep hinge offset

• Light stick forces

• Slotted flap elevator

• High CL for rotation and

minimum airspeed control

• Experiment with sealed

slot

• Good control

• 3lbs/g @ 85KCAS

• Good feel and trimming

• Improved gust response

NORMAL G (g)

1

2

3

4

5

Stick Force(lbf) CANARD & ELEVATOR v1 – SLOT SEALED

MANOEUVRE STABILITY – MID CG

1½ 2

6

45 KCAS

65KCAS

85KCAS

e-Go aeroplanes

Longitudinal stability and control

• Redesign

• Very similar handling to

the ‘sealed slot’

experiment

• Good control

• 4½lbs/g @ 85KCAS

• Good feel and trimming

• Good gust response

• BUT…

NORMAL G (g)

1

2

3

4

5

Stick Force(lbf) CANARD & ELEVATOR v2

MANOEUVRE STABILITY – MID CG

1½ 2

6

45 KCAS

65KCAS

85KCAS

e-Go aeroplanes

Stalling

• Behaviour with original canard

and elevator and Mk2 fins and

rudders was good

• Pitch nod at <35KCAS

• No mainplane stall

• Ability to climb in the stall

• New canard and elevator gave

far larger CL than expected

• Very slow airspeeds achievable

• Directional stability eroded

• Mainplane stall achievable

• Experiment with progressive slot

sealing…

e-Go aeroplanes

Flightpath control on the approach

• Glide performance is very good

• Very flat approaches

• Contrary to PPL teaching

• Drive to improve the airbrakes

e-Go aeroplanes

What next?

• Aggravated stalling

• Proving spin resistance

• Airbrake testing

• Envelope expansion to VD and G

limits (+4 and -2g)

• ‘Certification’ testing

e-Go aeroplanes

Lessons Learned

• Get the basics right

• Get some time in

• Shake it about a bit

• Use domain experts where

appropriate

• Beware the tyranny of weight-saving!

• First applications of critical

components – eg engine – can

absorb time and effort

• Everything takes longer than you

expect

e-Go aeroplanes

The e-Go

e-Go aeroplanes

With support from:

Plus many, many individual volunteers…

e-Go aeroplanes

QUESTIONS?

e-Go aeroplanes

Questions…

Keith Dennison

Chief Test Pilot

e-Go Centre Main Hall Farm, Conington Cambridge CB23 4LR www.e-Go.me