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Special: MW9 Plank

MW9 create by Mike Whittaker
I already have a page about two flying planks. Pelican is a sunday-flying machine, The Facet Opal is a record-breaking very speedy machine. This one, the MW9, is a bit like the Pelican.
Photo of the plank at the LAA Rally at Sywell 2018. Won the Tiger cup for best original design.
First hops of aircraft at Headon airfield on Friday the thirteenth July 2018. Pilot MW. I thought I should do the first flight before anyone else in case of mishaps. However, all went well. 6 hops. Thinking it may be like balancing on a knife edge, I was pleasantly surprised that the aircraft was extremely stable in pitch. See First flight NW9 on Youtube
Designer and builder: Mike Whittaker
Registration: G-CKAA
Location: UK
Goal of design: To produce a simple minimum microlight airplane that complies with the UK SSDR. Single seat deregulated rules.
English rules:
the full collection of rules, you can read here:
http://www.lightaircraftassociation.co.uk/engineering/TechnicalLeaflets/Operating%20An%20Aircraft/TL%202.17%20Operating%20Deregulated%20Microlights.pdf
The short edition says: the max all up weight is 300 Kg and the stall speed is not to exceed 35 Kts (= 65km/h or 40 mph)

How it all started

Let's start by saying that Mike says professionally he is an aircraft structures Engineer and only an amateur aerodynamicist.

He started by researching other similar Plank projects and gathering information. There is one item that helped him a lot in starting this project: the work of Al Backstrom, who designed and built a few flying planks. You can read about Al's projects at Backstrom EPB-1 Flying Plank - Wikipedia

Al Backstrom also wrote a few articles and it was that writing that helped Mike a lot. You can read one of those articles here.
The article shows most of the guidelines needed to design a successful Plank aircraft. Such as control surface sizing, thrust line etc.

Other publications found useful.
"Tailless aircraft in theory and practice" by Karl Nickel and Michael Wohlfahrt. AIAA.
"The wing and I" by Jim Marske. You can order this book from his web site.
Homebuiltairplanes forum: ANC 18 Wood aircraft structures.
Analysis and design of flight vehicle structures. Bruhn. Tri state offset company.
Formulas for stress and strain. Roark. McGRAW HILL.

 

Quotes from Homebuiltairplanes forum

It is generally said by people who have flown them, that planks with elevons are spin proof. Jim Marske mentions this in his writings. The reason is that in a pull up the up the elevons wash out the outer wing panels and move the loading inboard which prevents tip stalling . We hope to prove this when flight testing re commences. The outer washout also relieves the spar in bending. I found that the up gust case gave the greatest bending moment in the spar This also Suggests an inboard elevator would have the opposite effect. 
Under fins.
A friend built a 1/4 scale RC model of the MW9, to see if there were any nasty characteristics inherent in the design. This had fins extending above the wing and none below. Flight tests showed that at low speed with full up elevator the model developed Dutch roll, with an oscillation period of about a second. Dutch roll is normally associated with too much dihedral and not enough fin volume to damp it out. I increased the fin area and extended it aft also assuming the upper fin was having a dihedral effect as the wing had no dihedral, I extended the fin below the wing as much as I could. This cured the model instability and the full sized aircraft shows no sign of Dutch roll.

"MW10 Plank" on Youtube shows the model.
Like many of the previous posts I looked at the Opal when designing the MW9 while reading many of the posts on HBA. The many reports of people observing PIO's and from photographs, the aerofoil did not appear to have any reflex, although it was said the aerofoil was bi convex, like many others I came to the conclusion that the aircraft looked somewhat twitchy and that a severe PIO caused the wings to fail. This resulted in me going for a low AR wing with a large chord and selection an aerofoil with lots of reflex and high nose up Cm. So the chord was 5.5 Ft and the Fauvel 14 aerofoil was chosen.
The MW9 may have had a higher AR wing otherwise. However from the flight tests the pitch stability of the 9 appears to be good.
View of Mixer. The Hortons used the same system so did the Me 163.
First 3 view
In this proposal Mike used the tiny Cri-Cri as a inspiration for the fuselage and canopy.
New fuselage proposal
This canopy is formed from a single curvature wrap round sheet of clear polycarbonate with a fibreglass top moulding. Much easier to make.
Note by Mike: I was proposing to fit a Cri Cri canopy originally, but couldn’t locate one, so the next scheme shows the home-made canopy. Final configuration has a composite fuselage, built up from 25 mm urethane foam with fiberglass skins and wooden load points. The engine was a borrowed Konig SC430. Note the thrust line is angled to meet the criterion in Backstrom’s article. There is no noticeable pitch change with change of power.
Here you can see the shorter prop and the replacement of the tailskid by a tailwheel.

Construction

Because of the many many pictures, i placed a new page for the construction reports. You can find it here.

Test flight reports

Mike Whittaker wrote these in the Homebuiltairplanes.com forum. I collected them here for you.
Some airborne pictures.