Monthly Archives: July 2015

G-Force

This post is pretty technical – all about physics and stuff, but hopefully we’ve explained things in a way everyone can understand. Remember if you have any technical questions, or don’t understand anything, you can tweet us @thewhiffletree1 using the hashtag #whiffletreetechquestion and we’ll get back to you.

shutterstock_86879950So here goes……

We’re testing the aerobatic aircraft to +/-10g……. but what does that mean?

Well, let us try and explain……

We’ve all heard of apples falling on Issac Newton’s head and his subsequent questioning which lead to the development of the laws of gravity – he didn’t discover gravity, it’s always been there, he just explained what was going on with this weakest of physical forces.

When an apple falls from a tree, gravity accelerates it downwards at 9.81m/s. We call this 1g as it’s what we have grown up with and are used to. g on the moon is 1.62 meters per second or roughly 1/6th of g on the earth.

Generally on the surface of the earth the amount of matter (mass) is the same as weight. For example, say an object has a mass of 10kg on earth and we multiply the mass by the gravitational attraction of 1g we have a weight (which is a force) of 10kg on earth.

If we measure the weight of a 10kg mass on the moon it would be 10kg x 0.165 (1/6th) = 1.65kg. So on the moon our Show Boss (Phil) would only weigh 13kg, or just over 2 stone, meaning that he could easily eat a few more slices of lemon drizzle cake!

So how does all this relate to us testing this aircraft? Well since weight is a force dependant on the acceleration acting on an object, g is often talked about in the aerospace world.

When in orbit we talk of weightlessness or zero g, but g can also go the other way, for example, if we accelerate at 20m/s we will experience 2g for the whole period that we’re accelerating. This means Phil would suddenly weigh twice as much as he did on the moon! Instead of weighing 13kg, he’d now weigh close to 160kg – definitely time for him to lay off the cake! If he was accelerating at 10g he would weigh over a tonne and a half and a small slice of cake would effectively weigh 2kg!!!

So, back to our plane – if we need to test our plane to +/- 10g how is that force generated and what does it mean?

Well let’s think of the hammer thrower in an athletic stadium, the athlete spins around holding the handle of the hammer, whilst the ball part of the hammer is constantly changing direction as the force in the wire pulls it around in a circle. When the hammer thrower lets go, the hammer flies off at a tangent to the circle.

In the same way, when you are doing a loop in a plane, the force that moves it in a circle is generated by the wings on the air – the tighter and faster the loop is flown the higher the force generated. The reason we get positive and negative forces is because both outside and inside loops can be flown – where the pilot is either on the outside or to the inside of the loop.

Not only does the g force increase the loading on the plane, it has some profound effects on the human body. In a traditional loop with the pilot to the inside of the circle it has the effect of forcing the blood in the body to the outside of the circle i.e. the pilot’s feet. This causes a lack of blood to the pilot’s brain. In an inverted loop (pilot on the outside of the circle) the blood would be forced to the head.

A lack of blood to the brain can very quickly cause a blackout so manoeuvres such as loops are generally short in aerobatic aircrafts. In military aircrafts, pilots wear a ‘g-suit’, which squeezes the midriff in high g manoeuvres to restrict blood flowing away from the head.

+/- 10g generates the largest loads on our little plane so we will be applying loads that are 10 times the mass of the fully fuelled aircraft (with pilot), both upwards and downwards.

Alone we can do so little; together we can do so much

IMG_1179We’re moving on nicely with the whiffletree build. Hopefully we’ll be getting the plane this week so it’s all hands on deck.

We’ve been building the load application frame. It’s all tacked up ready for the plane arriving – once we’ve mounted the plane onto it to ensure it fits we’ll then get it fully welded together. The load application frame doesn’t move (or so we hope!), it’s where the load is put onto the plane to move it.

All the bearings have also been delivered – the bearings will support everything and allow us to get the plane into the exact position we want.

IMG_1126Steve P has also been securing the interface plates to the strong floor. We’re using interface plates because; although our strong floor has specific coordinate holes pre-drilled; the rigs’ mounts don’t necessarily match where the holes on our strong floor are pre-drilled. Therefore we’ve had the interface plates made – we’ll attach these to the strong floor and then attach the rig to these. Basically it’s an adaption technique that prevents us having to drill further holes in the strong floor which could potentially weaken and damage the floor.

It really is a team effort to get everything ready but we’re soldiering on and keeping spirits high with lots of cake (what else?!).

Image Captions

Top right: The load application frame.

Bottom right: The interface plates.

Keeping it in the family

IMG_4633The plane has now been on its first test flight and we should be taking delivery of the main structure early next week! We’ve been working hard to ensure the test rig (the whiffletree) will be ready for its arrival.

Samantha Biddlestone, assistant welding technician at Nuclear AMRC, has been working alongside us in the structural testing workshop to weld together various components which make up the whiffletree structure.

Samantha was a former apprentice at Nuclear AMRC and is also the step-daughter of our Mission Controller, Shane Smith.  Shane was keen to get Samantha involved with the project when he discovered parts of the whiffletree would need to be welded together.

IMG_4659When asked why he enlisted Samantha’s assistance Shane said “I’ve worked in the university since I was 21 and in civil engineering most of the test rigs are welded together. I actually did most of the welding on the majority of the big test rigs in the civil engineering laboratories but if I did the welding on the whiffletree parts it would be nowhere near the standard that Samantha can do. She’s good – really good, and I’m not just saying that because she’s related! We needed someone like her to make sure the whiffletree looks the part but also works as we need it to.”

Samantha is thrilled to be part of the project. Not only does it allow her to develop her skills and work collaboratively with other AMRC groups, it also gives her the opportunity to be involved with an exciting project that’s new to the AMRC.

Image Captions

Top right: Samantha Biddlestone welding parts of the whiffletree

Bottom right: Samantha looking a bit grubby after a welding session.

ASTC’s interesting fact of the week.

This week we have three!

  1. On the 20th July it was 46 years since man first landed on the moon.
  2. The accuracy that was required when scientists guided the probe, that successfully captured images of Pluto’s surface, last week, is equivalent to throwing a grape from New York and it landing in someone’s mouth at AMRC in Sheffield.
  3. It has been 20 years since Robbie Williams announced he was leaving Take That and left millions of teenage fans heartbroken!

The best preparation for good work tomorrow is to do good work today

We’ve now received the drawings for the plane’s test rig (the whiffletree!) and are gathering the materials we need and making parts for the rig.

A clevis - designed and machine at the AMRC All parts will be made at the AMRC and some have been designed in-house too. The clevis; which fastens the plane to the strong floor (a large robust floor used in structural testing); has been designed in-house by Steve Partoon – our project set designer. The part has also been machined in-house by AMRC apprentices.

The clevis will form part of the whiffletree – a commonly used testing mechanism. See our first blog post to learn more about whiffletrees. In this instance we will use several whiffletrees  in series to distribute the force further.

The rig (the whiffletree) moves with the plane to  replicate how it will behave in the air – the wing tips will deflect more whilst the part of the wing closest to the fuselage will be more rigid, despite the load being distributed evenly across the whole length of the wing. Tests of this nature need to be performed a number of times to replicate how the plane will be loaded when doing loop-the-loops, inverted barrel rolls and the like in flight.

By testing in this way we’ll be allowing the aircraft to respond in the way it wants to – pretty important as aerobatic planes carry huge loads and need to be able to resist too much bending!

Parts of the whiffletree - laser cut by the DPGOther parts that make up the whiffletree are currently being laser cut out of flat sheet by the AMRC Design and Prototyping Group (DPG). These have also been designed by Steve P. Once all the parts are cut they’ll be assembled and welded together by Samantha a former  Nuclear AMRC apprentice.

Come on plane – we’re almost ready for you!!!

Image Captions

Top right: A clevis – designed and made at the AMRC

Bottom right: Other parts that make up the whiffletree, also made in-house at the AMRC

We’re getting a plane!

The Advanced Structural Testing Centre, at the University of Sheffield AMRC with Boeing, is awaiting the imminent arrival of a small aerobatic aircraft.

We’ll put the plane – which has been designed, and built in the UK – under rigorous structural tests to prove that it’s okay to fly and enable it to go into manufacture in the UK.

It’ll be the first plane that has been tested for full certification in the UK for 30 years! It’s normal that planes are tested overseas, with the nearest facility being in the Czech Republic.

We’re here to prove that the AMRC with Boeing (and the UK) has the capabilities to do this sort of work and are really excited about the project so will be blogging every step of our journey – the ups, the downs and even the loop-the-loops.

We hope you’ll share our excitement in the project and keep up-to-date with our progress. We’re trying to make this blog for everyone so it’ll not be too technical however we are more than happy to answer any technical questions you have – tweet us @thewhiffletree1 using the hashtag #whiffletreetechquestion and we’ll get back to you.

Definition: Whiffletree 

A whiffletree (also known as a whippletree) is a mechanism to distribute force evenly through linkages. The mechanism may also be referred to as an equalizer, leader bar or double tree. It consists of a bar pivoted at or near the centre, with force applied from one direction to the pivot, and from the other direction to the tips. Several whiffletrees may be used in series to distribute the force further, such as to simulate pressure over an area as when applying loading to test plane wings. Whiffletrees may be used either in compression or tension.