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:
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.


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

Lets end the wrong idea about bad pitching stability

It happens a lot that i read in forums that people talk bad about flying planks and pitch stability. I heard that same bad news about the SWIFT hangglider. Flying wings are pitch instable. But ... i flew the SWIFT and i never had that feeling of pitch instability. So i contacted Mike to ask his opinion about the pitch stability of his flying plank.
Me: "Hello Mike, people ask me how bad the pitch stability is on flying planks. Short arm of moment of the controlsurfaces and so are the reasons they give me. Reasons i all know, but ... i am wondering ... how does it feel for real? How does the plank react to turbulences? Does it make it worse or does it autocorrect?"
Mike: "When I started my Plank project, like most people due to the narrow chord straight wing I assumed at the worst it would be like balancing on a tightrope in pitch. Also people on HBA also reported having witnessed the Opel exhibit PIO's on occasions, which led me to suspect that this caused the breakup in flight. All this influenced my design. So I went for a broad chord 5.5 Ft and the Fauvel 14 aerofoil which has a large reflex. Later Jim Marske sent me a copy of a letter from the co designer explaining the rear skid had weakened the spar and caused the wing failure. Had I known this earlier my plank might have been a bit different.

When I did the initial hops I was pleasantly surprised to find the aircraft was extremely stable in pitch. This is backed up by test pilot Eddie Clapham who remarked that, "You will be surprised how normal the aircraft feels" in his second test report which you have.

We are hoping to commence test flying in August, The first thing is to sort out a pitch trimmer so that the aircraft will fly hands off in pitch. To counteract the back pull on the stick due to the reflex on the control surface, I have fitted half round strips under the elevon TE, this will be reduced in size until balance occurs and a screw/bungee fine trimmer fitted.

If I was ten years younger I would build another plank with a higher AR wing and one of Jim Marske's later aerofoils. Jim states the Cl max for the Fauvel 14 to be 0.78 whereas the value for his later sections is around 1.2.

So in conclusion a plank aircraft built and balanced properly. (See Al Backstroms article) can fly as good as conventional aircraft, with the added good points listed below. Cg range to be investigated.

1. No tail and rear fuselage to build. Simpler, lighter, cheaper.
2. Nicer to fly in rough conditions, due to weather cocking into the gusts. ( From other pilots reports}
3. Up elevon washes out the wing towards the tip, reducing the risk of tip stalling and spin.
4. Up elevon when pulling max g reduces the lift at the outer section reducing the wing BM resulting in less wing weight.
5. I found the gust case to give the greatest wing loading. 3.6g.
6. Must be the simplest light aircraft to construct, transport and store. "

Test flight reports

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