BOR-4 breakdown

ThunderStruck Spacecraft Development Begins

BOR-4 breakdownWinged Spacecraft Takes Form

Our Australian ThunderStruck team has commenced design of the ThunderStruck Spacecraft. This graphic (right), courtesy of Project Thunderstruck team member David Galea, is just a doodle to break down the benefits of the USSR BOR-4 design. Yes, we started with a 50 year old design and have worked our way forward as the basic air frame is a solid design that has a good flight track record. We then looked at Dream Chaser which looks surprisingly similar, but with a modern interior. We too will have a similar design to both of these but with some big differences. Our starting length will be 3m (10 feet); our unfueled mass is expected to be 400Kg and optimum payload return will be 50Kg. It will have hypergolic fuel for the space flight – main thrust and hypergolic thrusters. If our air-frame can’t support the mass, then we will increase the lift or size. The fuels under consideration are not like the very dangerous Hydrazine used extensively for most NASA missions, but much safer fuels that are pretty safe for humans. They often don’t pack the punch of Hydrazine, but safety is our biggest goal so long as the thrust is powerful enough to do the job.

This from Wikipedia: https://en.m.wikipedia.org/wiki/Hypergolic_propellant

A hypergolic propellant combination used in a rocket engine is one whose components spontaneously ignite when they come into contact with each other.

The two propellant components usually consist of a fuel and an oxidizer. Although commonly used hypergolic propellants are difficult to handle because of their extreme toxicity and/or corrosiveness, they can be stored as liquids at room temperature and hypergolic engines are easy to ignite reliably and repeatedly.

We are now go for liftoff in eerrhhhh …in 6 years… But we have started. We are choosing a suitable fuel at this time – one that is relatively safe for humans and still able to provide the thrust needed to de-orbit and maneuver. There are new fuels – not as powerfully as many of the well known thruster fuels, but sacrificing power for safety could be a really good thing if the numbers stack up.

Our Invasion of Space has Begun.

Let’s rewind a bit. ThunderStruck is a Spacecraft under development. This story is about our spacecraft that we are building for actual flight many years from now. We also have a transonic test vehicle that has yet to fly, but we hope early next year we will get permission to fly the craft in northern Queensland (QLD) – probably a little North East of Longreach, QLD. There may be more test vehicles and even the design of our spacecraft may end up radically different from our

At this time, the Thunderstruck transonic test vehicle has been on hold, but it too will benefit from the spacecraft design kicking off since they may share common components. The Spacecraft will be slow to design and build compared to the transonic testing flier, but we have to start this if we are to finish it in a timely fashion. So back to our spacecraft design.

It is expected that we will partner with a university that will assist with the build. At this time we are closest to Sydney University and we know that they have similar goals of working with a winged re-entry flier.

It is clear that we are not relying on using the Russian BOR-4 as a blueprint, but it is a starting point. It is also clear that the BOR-4 and the Sierra Nevada Corporation’s Dream Chaser share a lot of common air frame characteristics. So Dream Chaser was the next craft to go under the microscope.

Critical to the design and thus one of the first components to understand is the type of fuel that will be needed. This may determine that we need a bigger craft to carry the tanks or that the shape must be different to handle the large tanks.

Dream Chaser Graphic on top of a Rocket for LaunchDream Chaser (pictured right) is large and has a crew. Our craft does not have a crew and the ThunderStruck spacecraft is small in comparison.

Dream Chaser can launch on top of a rocket and we expect ThunderStruck to do the same. ThunderStruck is way smaller and potentially has folding wings and thus could sit inside a fairing making the ride more comfortable.

ThunderStruck will have a docking ring and the ability to swap old and new payload canisters. ie to provide a new empty canister to , say, an asteroid service craft and bring back a full set of samples.

ThunderStruck will evolve and its capabilities will change as we grow. Our aim is to make the smallest rocket launched spacecraft with wings for re-entry and an exchangeable payload.

 

Trimming ThunderStruck for Speed

X2 shadow Trimming ThunderStruck Needs Extreme Knowledge

by Robert Brand

This post is very technical. I will try and make it a little easier to understand. I will not go into very deep into the various aspects that slow the craft, nor will I get into every aspect, just the major aspects that will cause us issues.

Designing a supersonic aircraft needs knowledge of supersonic aspects of airflow and pressure/shock waves. In a previous post we looked at the basic limiting factors and those important to getting us past Mach 1. This post will look at other factors that will cause us to make small changes to ThunderStruck to ensure we reach the maximum speed possible and get as close to Mach 1.5 as possible. We previously discussed the following:

  • Varying gravity due to altitude
  • The angle of the nose cone
  • The width of the fuselage
  • Altitude
  • Vehicle mass
  • Wing and Vehicle Drag Coefficient
  • Reference Area of the object in the direction of motion

In this post we will now look at other aspects of the design that will slow the crafts acceleration during its flight:

  • Base Drag
  • Area Rule
  • Transonic Wave Drag
  • Supersonic Wave Drag
  • Friction Drag

These factors take into account compressible air flows and incompressible air flows. Look them up, but simply Transonic and supersonic flows are compressible, subsonic flows are incompressible.  They are reflected in the items above.

If you would like to look at the Maths for these issues, there is a great document from Sydney University that can be viewed on the link below:

http://web.aeromech.usyd.edu.au/AERO2705/Resources/Research/Drag_Coefficient_Prediction.pdf

Base Drag

My knowledge here comes from rockets – same as the document. A flat based rocket does not have Base drag when it is firing its engines as the air flow does not have a pressure problem when compared to having a flat rear end! Below is a snapshot of the pressure differentials at the rear of the craft. There are more and bigger pressures not shown here, but you can clearly see the problem. as a rocket flies horizontally with its engines ignited, there is no void. The moment the engine ceases ignition, these pressure waves appear – Base Drag.

X2 Base Drag Pressure snapshot

Looks like a tapered fuselage at the rear of the craft is super important to acceleration towards the ground and again as the craft decelerates due to the thickening air density. It will need to taper from half way along the main wing part to the rear and go from 300mm to 50mm– enough for a parachute to be deployed – about 50mm. Whether we add a tapered cap, taking the final taper to a point for even less drag is not important at this stage. It will look better without the cap in drawings.

This important diagram from the linked document. This shows the flight of a rocket accelerating to Mach 1.6 (Dashed blue line) and then decelerating to to low speed (the solid black line). All the various drag issues are in this typical diagram. Base drag however is the difference between the two. There is no base drag during the rocket burn and then there is base drag once the engine ceases ignition.Drag issues in Transonic and Supersonic Flight

By gently tapering the fuselage to a point, we avoid disruption the boundary layer and any turbulence. For the X2 ThunderStruck flight the fall and acceleration will also look like the deceleration. Base drag will almost be eliminated.

Area Rule

We have spoken about this in an earlier post. That is keeping the cross-sectional area of the craft constant – so thinner where there is space (area) allocated to the wings. Area ruling will be somewhat addressed by the taper to the rear as discussed above in Base Drag. It is a fairly small effect unless you were spending significant time near the speed of sound. The X-2 ThunderStruck craft will spend 15 seconds between Mach 0.9 and Mach 1.2. I believe that it will be small and this is where the area rule has the biggest effect – but still small. There will be no additional change for area rule.

Transonic and Supersonic Wave Drag

The taper of the rear of the craft will minimise Wave Drag – both Transonic and Supersonic. Some playing with Wing Design may change the Wave Drag, but we will ignore it at this stage. I am not looking to play with the design unless there is a strong case. In the diagram above the Transonic Wave Drag begins at about Mach 0.9 and Mach 1.2 and Supersonic Wave Drag continues upward from that point.

Friction Drag

Friction drag occurs at low speeds with laminar flow being disrupted and the airflow becomes turbulent. We will have stalled at that stage and thus this is of no interest since we have an aircraft. We should have landed! This is ignored.

Trimming the Design

We have determined that we need to do two things. Stop the leading part of the winglets from protruding in front of where it joins the wing and to taper the fuselage. We will provide a picture of the new design shortly. Here is a render of the current X2 design without the new modifications:

X2 - Clouds2

The X2 ThunderStruck craft will have minimal impact regarding its maximum speed. I will reveal the new graphs shortly showing the speed at any given altitude point. As the air is extremely thin at our launch altitude, the increase in drag above 35km from the items above will not likely to be affect our top speed much as previously calculated, but may increase the deceleration slightly. That is the max G force as we slow. I will publish the updated results soon.

Finally a scan of the pressure waves from front to back on the X2 craft before we trim the craft:

X2 Pressure_Cut_Raised

Renaming ThunderStruck’s Models

NASA X-15ThunderStruck’s Models Renamed to Avoid Confusion

It should have been clear from the start. We would have too many models of each craft to keep track of them. It is getting confusing for us and for you. So here is the deal, in honour of those that flew the early flights in NASA’s X flight series (image right), we will do the same. The ThunderStruck “X” series will be all test designs and test flights with experimental craft. Some will fly in space, where the X1 and X2 will be supersonic test design and test flight craft.

So the first bird in our list is:

ThunderStruck X1 – a Flightless Bird

Is was a flightless bird designed to give us a bench mark to start the design refinement process. It had a lot of what we wanted such as landing stability (wide wheel area); a large fuselage that would be more like a required in spacecraft with wings and symmetrical wings to keep it in a supersonic dive. Since we had models made and it appeared on TV, we have given it the name of the X1

Thunderstruck2

This is the model that was seen in Channel 7’s interview about ThunderStruck. In the end it was too fat and needed more wing area. Making the fuselage small effectively helped with the wing area! The X1 is a key design as aside from a few changes, it appears to be a capable design. What is not shown was that it was to have Pop-out canards for subsonic flight. The later craft should not need canards.

Roger WeissThe Roger Weiss

We are naming the X1 craft that started it all, the Roger Weiss. It is named after a very inspirational Facebook friend that is an inspiration and mentor to so many, my long time Facebook friend, Roger Weiss. Roger excites so many about the joys of space and he is prolific too. Roger lives the dream too. He lives in Houston Texas in the USA and has the job title of “International Space Station Program’s Research Integration Office, Technical Integration Lead, Barrios Technology at NASA Johnson Space Center. That is a mouth full. Hey Roger I will be in Houston in June 2016 and I will knock on your door!! Although this bird never got off the ground, like you Roger, inspiring others, it has been a truly key craft in getting us into space one day.

ThunderStruck X2

This bird is destined to fly fast. The fastest amateur craft in the sky. Set to break Mach 1 and expected to reach Mach 1.5, this bird will be the evolution of the X1. It is sleek and will break the sound barrier even if dropped from 40km. A good altitude for Plan B if things don’t go our way during the flight.

A bigger wing area and more wing forward compared to the X1. The rudders will be at the rear and tapered. there will be a tapered design for the fuselage.
X2 MainBody_Front_Perspective

Ann LornieThe Ann Lornie.

The craft that breaks the sound barrier officially will be called the Ann Lornie after a dear friend that was so encouraging when i first joined Facebook. She was inspiring and a lovely friend and I just discovered that she has cancer and about 3-6 months to live. This is named in honour of her and her friendship that underpins where I am today. She has not been well for many years, but this is new and I am devastated to hear this news. The Ann Lornie will go into the record books in October this year and I would love Ann to be still on this planet to witness this and her name going into our space flight history. Hang in there Ann, this one is for you! Ann Lives in Rusper, West Sussex, in the United Kingdom.

Since publishing this page, Ann passed on and the comments below reflect on that. She was very popular and very supportive of this project.

45km Free Fall Spreadsheet

ThunderStruck Phase 1 Version 2Fine Tuning ThunderStruck’s 45km Free Fall

By Robert Brand and Todd Hampson

This post will examine a drop from 45km. Todd has done an amazing job on this interactive Excel spreadsheet. We can change a few variable and see the change effects. It has done an amazing job in letting us see what changes produce the greatest “bang for the buck”.

The first thing was changing the diameter of the craft creates a great difference in drag. We have decided that we need to make the fuselage 300mm in diameter (down from 600) as it have a huge effect on when the craft stops accelerating. It adds Mach 0.3 to the top speed. from a 45km drop. We also noticed that if we get the craft the right dimensions  and mass, the need to get the balloon to 45km is reduced. We can still break the sound barrier with a release from 40km altitude. At 45km we get a top speed of Mach 1.54 and at 40km we get Mach 1.36. This is also with a mass of 15kg rather than 10kg as we previously had though would be sufficient. We do not want to release much lower as things change rapidly with the thicker air.

Thunderstruck Drop Test Simulator

Thunderstruck Drop Test Simulator

Above is the top part of Todd’s spreadsheet, the coloured cells to the left allow different inputs and the cells on the right are the snap summary. The model that we have made only just got us over Mach 1 with little to spare. Changing the diameter and elongating the nose (a smaller 1/2 vertex angle of the cone) made a huge difference and making the mass 15km means a huge leeway. As mentioned on TV recently, we are aiming for Mach 1.5 and now we have the maths to prove that we can reach that speed. One interesting aspect of the reaching Mach 1.5 is that the deceleration by the thickening atmosphere is about 1.3G. Barely more than standing on the ground. It is a really gentle load and it is mainly on the nose cone of the craft. The wing and tail assembly will keep the craft oriented in the denser air and we will rely on the ballast in the front of the craft to keep it nose down.  The ballast is likely to be antifreeze and we can shift it or eject it for a more stable and slower level flight.

We hope to have the fully interactive spreadsheet available on the site for those interested, but until then let’s have a snapshot of the curves that count. That is a free fall from 45km.
Thunderstruck Drop Test Simulator Max Speed

At sea level, mach 1 is about 340m/s. I say “about” because air pressure has little to do with the speed of sound. It is mainly air temperature. From the graph we should reach 530m/s and that is Mach 1.56.

Before we streamlined the craft to punch through the thickening atmosphere, the wider bodied version of ThunderStruck slowed down really fast and took some stronger G force on the nose (mainly). The version 2 craft slows almost at the same rate that it accelerates. This gives a very gentle change as can be seen below.

Thunderstruck Drop Test Simulator Deceleration

From the graph above it is clear that at 45km, as the speed increases, the air resistance has a greater effect. At that height air density is about 0.025 10-1 kg/m3 compared to air density at sea level which is about 12.25 10-1 kg/m3 (plus or minus about 5%).

This means that our air density at 45km as a percentage of air density at sea level is about 0.284% that of sea level and it increases as we go lower. The effects also increase with ThunderStruck’s speed as the drag has a greater effect with both speed and increasing density.

With the calculated drag of the craft, we find that all acceleration stops at 26 km and as we fall into denser atmosphere, we begin to slow. The graph above is calculated in metres per second per second (known as m/s/s or m/s2) and that can be directly converted in to G force. Since 1 g = 9.80665 m/s2 a simple rule of thumb conversion to remember is 10m/s/s = 1G.

Now for many the next part of this may be hard to grasp, but at free fall at 45km we have what is loosely termed 0G where, if we were in a craft also falling at the same rate, we would float inside the craft. Once we reach terminal velocity at 26km altitude ( I will ignore the lag in deceleration here), we have 1G acting on the craft. If we were inside that craft we could walk around the interior and feel the same as on the earth’s surface (again small variations in gravity, etc excluded). A skydiver that has reached terminal velocity has the air flow stabilising his speed and that air flow has a force of 1G on his body. G force real is only noticeable when there is change – ie a change in direction or acceleration or deceleration.

The “vomit comet” aircraft that simulates zero G does so by moving steadily in a straight line while accelerating towards the ground at 9.8m/s2.  If they just dipped the nose and began that arc, but stopped accelerating towards the ground we would all feel an initial 0Gs but then would be back on the floor when the rate of change returned to zero and we would be back at 1G. So, with ThunderStruck, it is the rate of change that determines G force and at 26km altitude, the G force is 1G on the overall craft, but since the greatest drag is caused by the nose, the 1G force is felt here. Other parts of the craft would be happy to continue accelerating! So at 26km, the structural form of the craft must allow the nose to hold the craft by the nose vertically – good to know, but it does not stop there.

The craft continues to slow and decelerate with the denser air and we have to slow way more. That now takes us into the realm of more than 1G. In fact at 17km we experience the greatest rate of deceleration or change and that is an additional 1.25G for a total of 2.25G on the nose of the vertical craft.  That is the base amount of structural integrity we will need in the nose assembly. If the craft weighs 15kg, then the nose assembly has to support 33.75 and then an amount that we required to ensure it is strong enough. My design had better look to supporting 50kg on the nose when the craft is stood vertically at least.

It seems that what you gain, you have to give back. The higher the speed and the longer the period in low Gs, then the the higher the Gs or the longer in negative Gs you need to complete the flight back to a complete vertical stop. I have not analyses the areas on either side of the 0m/s/s on the chart above, but I would not be surprised if they where equal. As we say here – swings and roundabouts. What you gain on the swings, you will lose on the roundabouts.

Mathematics is a wonderful tool for designers. From a few simple facts in a spreadsheet, we have calculated the speed at all points in the flight (vertical dive perspective) and also the internal forces on the craft at many points. ie the winglet tips will be a point of high drag so they will need to handle more than 1G vertically. The same with other leading edges and that also goes for surfaces affected by shock waves. All of which can be determined by design and software. You don’t have to be a maths genius, but you do need to know maths enough to ensure that you can use them in day to day work. Unless you visualise what is happening, you will have an unhealthy reliance on software for everything you do. That often denies the genius of innovation. It is also why a novice can invent something a seasoned engineer fails to see.

By manipulating the graph by fine tuning the inputs we found that our craft accelerated longer or you could say “the rate of deceleration was slower” by:

  • Making the nose cone pointier
  • Making the fuselage (and the nose cone) a a smaller diameter
  • Increasing the weight of the vehicle

In fact with the new design we have found that we can still break the sound barrier at a starting altitude of 40km. that is our plan B if the weather or winds in the atmosphere go against us. ie, we can launch early if the winds are taking our balloon out of range of our communications systems.

So what does our new design look like?

This is an early look as there are a few bits at the rear that still need adjusting.
ThunderStruck Phase 1 Version 2

We also took the opportunity to correct a few other aspects of the craft:

  • Bigger wing Area with a larger area ahead of the main wing
  • Longer spikes on the winglets (the winglets are not as high due to the smaller fuselage). This is to move the supersonic shock waves away from the control surfaces on the rear of the wing.
  • Twin rudders trailing the craft (there are some wing tabs in the drawing that need to be removed.
  • A tapered tail to stop high drag behind  the craft (we also need to remove some wing tags in the model above.
  • Tapered rudders on the bottom to stop it hitting the ground on landing (not shown)
  • Tapered rudders on the top for symmetry to ensure that it has little differential in forces on the craft to make it pull out of the dive.
Bruce Boler and Jason Brand with ThunderStruck Phase One 1/6 Model

Bruce Boler and Jason Brand with ThunderStruck Phase One 1/6 Model

So there you have the new design based on maths and simulations on a home computer. It seems that building a supersonic aircraft is child’s play as Jason (12) is jointly working on this design. This morning I asked him what G force is at work on a skydiver at terminal velocity and he confidently answered “1G”. Good one grasshopper. He then went on to clearly say that g force was related to change in acceleration (relating to a skydiver). I love it when he talks maths. He needs to know as he will be the remote control pilot for this Mach 1.5 aircraft.

Airflow_temperature

3D Files and ThunderStruck Phase One

Thunderstruck Half Scale3D Files, Printers, simulations and More

by Robert brand

In the past we used wind tunnels and that was fine for subsonic flights. ThunderStruck does have access to wind tunnels at a number of establishments, but it is unlikely that we will need them. In part because supersonic wind tunnels are rare and because subsonic tests do not translate to supersonic conditions. Why wont we need them? Simply because computer modelling allows us to test most things extremely accurately without  the need for wind tunnels. The first part of the equation is to “make” a 3D model of the airframe and from that the options are extraordinary. Simulations of wind tunnels are just one option. What else can you do with the computer files of your model? well, we are not doing everything possible, but here are a few things:

  • Produced images of the ThunderStruck craft in solid form (we use Solidworks)
  • Rendered the surface to appear metallic
  • Added the ThunderStruck Logo and artwork
  • Animated the control surfaces on the craft
  • Sent it to a TV animator who will use the flight profile to simulate the mission
  • Made 3D models of the craft with a 3D printer.
  • Made a scaled nose cone for the 1/6th size model for demonstrations. Nose cones are immensely hard to create, but so easy with a 3D printer
  • And finally (so far) carried out Mach 2 flight simulations
Thunderstruck Phase One plans and view

Thunderstruck Phase One plans and view 1/2 scale

These simulations show up any problems and thus they have already resulted in small changes to the Phase One craft design. The biggest change will be a longer and more slender nose. You will see why in a moment.

One the right are the original plans from three sides. The software automatically creates the view (top right of image). The 3D files are then produced and it is often that simple. Everything flows from the files. The extension for the files is STL. A printer may break the files up to print an object in two, three or more parts. It depends on the size of object a printer can handle.  we wanted a 22cm model of thunderstruck and that was printed in three parts as it was too wide and two high. The parts were simply joined with acetate. It melts the material slightly and the pieces are then welded together without glue.

The solid image looks like this with a little bit of shadow and a plain surface. A “light source” is placed where needed to create essential shadows for the right feel and look.
Thunderstruck1

The image above has been created to appear to sit on a grey surface. Remove that surface and add a metallic texture and a background image and you get this:

Thunderstruck Phase One Craft in Flight

Thunderstruck Phase One Craft in Flight. Credit Ben Hockley (ThunderStruck) and NASA (clouds and Moon)

The video below shows an animation for the control surfaces. Nothing much to see other than we are working on getting the smaller bits right for the big animations. You can also see our logo on the side so this is a two in one demonstration

Below is a rough picture of the printed 22cm model and the Nose Cone needed for our TV interview on Wednesday with Channel 7 (The Seven Network, Australia). It will be painted. If you look closely you will see the nose cone join and similarly you will see the join on the 3D model.

22cm ThunderStruck Phase One model and the nose cone on the right

22cm ThunderStruck Phase One model and the nose cone on the right

Below is the plan for the nosecone and it is simple to reproduce. Notice the curved area near the base of the nose cone. This is to ease the airflow over the surface and prevent the delamination of the airflow.

Phase One Thunderstruck 1.6 nosecone

Finally we can do simulations. I will explain what you are looking at below in the next post but wow this stuff is impressive. This si not the top end software, but just a basic system and it is more than adequate for our needs:

Airflow_temperature

Most of the work on this page has been provided by Team Member Ben Hockley of Brisbane. I am grateful that we have a person with his skills in the team.

 

Thunderstruck1

The ThunderStruck Evolution

ThunderStruck Phase 1

ThunderStruck Phase 1

ThunderStruck Evolution is Essential.

by Robert Brand

Over the couple of months since officially announcing Project ThunderStruck, I have received lots of comments about the craft and not having detailed drawing. I made it very clear that in the early days, my son Jason had to earn his keep and create the art work for the craft. He tried his best, but the only tools that he had were not CAD 3D tools, but he did have Kerbal Space Program (KSP)and he used that to crate the craft details that he was looking for. So let’s have a look at his first drawing.

Jason's CAD picture of ThunderStruck above the earth

Jason’s CAD picture of ThunderStruck above the earth

Well, everything is wrong about this craft, but he was stuck with fixed sizes and it got our website up and running. Fuselage too thin, wings are simply wrong and much more. We did add a supersonic spike, but that was actual dueling as a radio antenna and may end up on the final craft too.

We ended up agreeing that we needed wheels and that there was no way to fit them to this craft. This started the move to the current craft. Jason again resorted to using KSP. The results were closer to the current craft.

Now people really gave us a hard time over KSP and they did not really understand that we had given the responsibility for much of the work to Jason and he simply resorted to the tools at hand and KSP really did do more than I expected. It was a reasonable attempt at making a model close to the final product.

Below is the second evolution of the transonic ThunderStruck.

ThunderStruck mk2 closeup

ThunderStruck Design and 1-2 size measurementsSince then we brought in the big guns and I created the plans for the craft. Mind you the published file had an error. The length of the nosecone was 200mm too short!  That is now fixed in the later plans.

Well from the plans, Ben Hockley created a view using SolidWorks software. From the plan came a rendered image that been added to a cloud image as seen at the top of page.  Here are Ben’s plans and view:

Thunderstruck plans

Thunderstruck plans

Below the composite image showing the craft in the transition from the dive to horizontal flight:

Thunderstruck Phase One Craft in Flight

Thunderstruck Phase One Craft in Flight. Credit Ben Hockley (ThunderStruck) and NASA (clouds and Moon)

I know that this is a long time coming, but if we hit you with too much to soon, you would probably think we were cheating. We may change the odd thing or two before the flight, but this is essentially the craft that will go into the record books.

CAD composite ThunderStruck Images

Thunderstruck Phase One Craft in Flight

Thunderstruck Phase One Craft in Flight. Credit Ben Hockley (ThunderStruck) and NASA (clouds and Moon)

ThunderStruck Images and Animation.

It has been a long time coming as there are only so many hours in the day. The images and our ability to do 3D renditions and even 3D printing is courtesy of Ben Hockley from Brisbane, Australia.

Ben has created this fantastic image of the Phase one Thunderstruck craft. It is pictured just after going subsonic and making the transition to horizontal flight. At this point it will be slowing to about 500kph and is about to slowly deploy the canards. These are little wings at the front of the craft. Unlike the wings, the canards will have lift and will be set to work with a nose down angle of about 10 degrees. Tests will determine whether we will need to change the angle for landing or whether the canards will remain in line with the fuselage at all times during the flight. I suspect the later will be the correct arrangement and much easier to build, but testing is always required.

Thunderstruck1Why not a slender body? Simply we will achieve supersonic speeds due to lack of air. Well very “thin” air. A tiny fraction of 1% at sea level. Drag is not the issue here until we are in level subsonic flight. There we will be taking a step glide path anyway as there is no lift in the wings. I will be happy with a 10 to 1 glide slope. We lose a metre for every 10m flown. The drag on the body will not be the greatest issue and I would like the body big enough to add the Patch antennas. They stick on the outside of the craft and I will want that to be on top of the body and under the body so that there is signal no mater what the orientation of the craft. The added benefit is that we have plenty of room to work on the electronics, servos and other gadgets that need to move within the body of the craft. The diameter of the craft at full scale will be about 600mm in diameter. This may change with flight testing, but we are now in the final stages of the paper design and the engineering of the mechanical components will all fit comfortably in this size craft.

Thunderstruck_drawing

The drawings were done with Solidworks and you can, if you are a student, pick up a copy for US$150 and since this is Jason’s project and he is a year 8 student, he qualifies. The images at right are the craft’s plans and the top right shows a view of the craft, including the lines differentiating the sections used to create the fuselage. ie the nose cone joins the first half of the fuselage. These lines are removed for rendering a coloured and textured model as seen in the top image.

Although we do not yet have animation of the flight, it can now be produced with the 3D files that come from the rendering process. These are STL files and moving the background and the view of the craft (angle of attack), vibration, etc, can give the required feel of flight. The files will be sent to an animator to see if this can easily be achieved. If yes, we hope to have the animation ready to show you and also use it in the ever so essential crowd funding video. The three images above are shown below. All are courtesy of Ben Hockley and the picture with clouds in the background is courtesy of NASA and taken from the International Space Station (ISS). Ben thanks again for these fantastic ThunderStruck images.

Thunderstruck Phase One Craft in Flight

Thunderstruck Phase One Craft in Flight. Credit Ben Hockley (ThunderStruck) and NASA ISS (clouds and Moon)

A plain rendered view of ThunderStruck Phase One with shadow

A plain rendered view of ThunderStruck Phase One with shadow. Credit Ben Hockley

Thunderstruck plans

Thunderstruck plans. Credit Ben Hockley

Aerodynamics of Supersonic Craft

Supersonic Glider-spacecraftSupersonic Shock Waves

by Robert Brand

Phase 1 Test Craft

As you all know by now, Jason, my 12 year old son, will attempt to break the sound barrier mid year – he will be 13 by then. This is the first test of a high drag system that should limit our airspeed at supersonic speeds. It is the Phase 1 testing that we talk about in our documents. We need to go fast for this experiment, but returning from space we need to slow down. Our transonic tests will be with a very different looking craft than our future spacecraft.

To the right, you will see where Jason’s design started. As you may have noticed, the ThunderStruck’s current design looks nothing like the image to the right. At each stage he has had to modify the craft to achieve the goals of going supersonic and get up to around 2,000kph ThunderStruck Design and 1-2 size measurementswith full stability. Only then will we deploy the experiment and hopefully slow the craft dramatically. As you are aware, it now looks more like the craft to the left. These are massive differences and we will explore the choices he made in another post. Right now we are looking at how we get rid of the major shock waves and also how our Phase 2 test aircraft may look. The main differences in the 2 craft are:

  • No supersonic Spike
  • No central tail
  • Winglets above and below with a ganged rudder
  • Delta wings that have two angles of protrusion from the fuselage
  • Elevators and ailerons are at the rear of the wing
  • The wing extends to the rear of the craft

Phase 2 Test Craft

In Phase 2 the craft that we design will need to travel straight up into space on a sounding rocket. We will separate from the rocket and continue our climb (momentum) to apogee (top of the flight) and then fall back to earth. Apogee may be as high as 200km. The air is so thin that we can conduct what we call weightlessness experiments for several minutes. Once the air starts to create drag, the experiments will end as the craft will slow. At this time we do not want the craft to accelerate further, but it will. Unless we feather the wings(like Virgin Galactic’s Spaceship 2) or create massive drag in some other way (our Phase 1 experiment) we will go too fast for our craft’s well-being. We need to go slow as possible. We do not want to have to slow with unusual braking as this may de-stabilise the small craft.

Hyabusa reentry sequencWe could use a capsule, an ablative heat shield and a parachute like JAXA’s Hyabusa, but we are creating a winged vehicle, although the capsule will always be another option. I guess the cat’s is out of the bag. We will have a couple of configurations possible with capsule or winged reentry as an option. The ThundrStruck craft will be a modular design in the style and electronics. The picture to the right is the landing sequence for JAXA’s Hyabusa that landed in the centre of Australia. It is not complicated, but you do have to know what you are doing and the downside is that it lands where ever the winds take the parachute.

I want to fix that problem for those customers that need a precision landing or effectively or a smooth landing. I would love to be able to direct the returning spacecraft to a point on the map that allows us to land it without having to recover it from an unknown place in the desert.

Supersonic Aircraft SpikeThe picture at the top of page is where we started. I expect that the spike will not be on the spacecraft and it is also now unlikely to be on the transonic test vehicle, but it is important to understand why we see them on supersonic craft. Sometimes a very long sharp nose can also produce the desired effect.

The picture at right is a NASA test vehicle with a spike. There are many supersonic aircraft that either have a spike of a very sharp nose well ahead of the wings. Why? We discuss this after the following paragraph.

Returning from space the spike would be a liability in the heat of reentry. It will also not be an asset in slowing down a craft. We only need to have the spike as an option to help lower the Resistance to breaking the sound barrier for our tests. At the time of posting, Jason has gotten rid of the spike and opted for wings tucked back behind the shock wave.

In our tests we will use gravity to accelerate the test craft to way past the speed of sound, but shock waves (pressure waves) would slow us down and limit our top speed. We would probably still break the sound barrier dropping the craft from around 40km altitude, but the quicker we transit the sound barrier the higher our top speed and the better the results from our experiment.

So What Does the Spike Do?

supersonic shockwaves in a windtunnelAs I said a sharp nose is the same as a spike and the image to the left shows the effect of the nose/spike as it moves the shock wave to a point well ahead of the main body of the craft and away from the wings. A sharp point is a very low area of shock and in the image you can see the shock waves from the wings as very low level compared to the shock from the tiny front of the aircraft. So long as the wings are tucked in behind the initial shock wave than the drag is lowered considerably. The reason that it was so hard to break the sound barrier was simple. The craft used had their wings in the high drag area caused by shock waves.

Now I may have been a bit simplistic here, but none the less, the spike is important to supersonic flight. Since we are wanting to slow down in Phase 2 tests returning from space via a sounding rocket, we can actually round the nose of the returning spacecraft and still get the supersonic shock to clear the wings

So Why Didn’t the Shuttle Need a Spike?

WPointy nose and shockwaves at mach 6.ell it did need to slow down and so you might think that a blunt nose is a good thing to create drag, but that is not the reason. Wouldn’t a sharp nose be good for takeoff, spike or no spike? Well, in some ways, yes, but the shuttle had wings that were very wide and a spike could not be placed that far forward. The resulting shock waves on takeoff and especially re-entry would be a bit problem as they would hit the wings.

Re-entry would be the biggest problem. The shock wave from a sharp nose would hit the wings and further heat the air. You would be adding thousands of degrees to the heat that it is already being generated on the leading edge of the wing – not a good idea! See the image above right. This would be a poor design for such a craft. The image shows a pointy nose model in a mach 6 airstream. You can see the shock waves hitting the wings midway along their leading edge.

So What Happens with a Blunt Nose?

The image to the right says it all. The blunt nose acts as a ram and pushes the shock wave way to the sides. This misses the wings by a long way – and the tail of course. The blunt nose does add to drag so that is another benefit to slowing down, but a minor one. It is the additional heat caused by the shock wave over the wings during re-entry  that had to be eliminated

What Else Protected the Shuttle from Shock?

Ever consider the orange main fuel tank? Where was the shuttle positioned relative to its nose. It had a point, but was really broad.

What effect did that have during launch at high speeds. The shock wave that resulted missed the shuttle entirely. It is important that the top of this tank was far enough forward to protect the shuttle. The whole design and shape of the combined modules on the launch vehicle was super critical and not just a random bunch of sizes. Minimizing shock waves means being able to both protect the vehicle and increase the payload as you have less drag.

In other words, if the main tank had needed less fuel and had been smaller, then it would still have needed to be as high to push the shock waves aside.

Each and every part of an aircraft that changes its size or sticks out causes shock. You must account for it or suffer the consequences.

The image at right clearly shows the shock wave of the jet disturbing the water. You do not have to be traveling at supersonic speeds to produce shock waves, but the faster you go, the more power is lost and the stronger the shock wave.

ThunderStruck Design and 1-2 size measurements

Unveiling Phase 1 ThunderStruck Design

ThunderStruck Design and 1-2 size measurementsTransonic Test Design

In the first phase testing of our ThunderStruck spacecraft, we want to go fast so that we can test some “drag” experiments. As such, the airframe proposed looks nothing like what our spacecraft design will probably resemble. After all we wish to slow down returning from space, not speed up.

Below are the design shapes and dimensions for a 1/2 size model of our flight aircraft. Why 1/2 scale? Simply, a full scale mockup would be too big to fit into my car!

After looking at the figures our modeller has recommended that we actually use a 1/3 size model as the 1/2 scale model is too big to fit his lathe! We will talk about the design in another post. I just wanted interested people to have a look at the craft ASAP.

The final craft may have a supersonic spike that will double as a VHF antenna, but it will not need a spike. The wheels will have brakes to stop them spinning during flight. There is a lot to do yet, but we are enjoying the challenges. Note that we may tweak the design further plus I have not included the canards for subsonic flight. They will deploy slowly as we slow the craft. They will not deploy until the craft is subsonic.

ThunderStruck Design and 1-2 size measurements

Above are the dimensions for a 1/2 size ThunderStruck airframe.

 

Aircraft Design Changes

ThunderStruck mk2ThunderStruck Design on the “Fly”

We now have 2 major changes to the ThunderStruck aircraft. The first is shown in the image to the right. Winglets. The second is a square-ish cross-section to the fuselage rather than a round fuselage – this is under consideration to aid in landing the craft.

The image to the right still shows the aircraft with a round fuselage, but it is obvious that we will miss out on some lifting ability from the body at landing by making the fuselage round. A flat surface on the underside if the craft will provide more lift at the right angle of attack.

winglet_effect_Winglets

The image right is from Wikipedia:

Line drawing of wingtip vortices behind a conventional wingtip (on the left) and a blended winglet (on the right).

This is important as it reduced the vortices behind aircraft that cause so many dangerous incidents at airports when aircraft get too close to each other. It also reduced drag and thus efficiency in aircraft.

The ThunderStruck craft will certainly use the winglets to reduce drag by reducing vorticies, but this will have no impact at supersonic speeds because we will be using symmetrical wing. Normal wings have a flat bottom and a rising leading edge and a trailing edge on the top surface.  This makes the air flow faster over the top compared to the steady flow over the bottom. This reduces the pressure on the top pushing the wings up. This would be nice for the cruising stage after the dive, but bad for holding the craft in a supersonic dive. Any air flow over any asymmetrical surfaces may produce drag or lift that could pull the craft out of a supersonic dive early. The effects could be catastrophic.

Many high altitude model aircraft dropped from high altitude balloons (usually illegally) follow a roller coaster ride due to the thin air and lift in the wings. We don’t want that so the wings will be symmetrical – no lift. We do not need them for the supersonic dive. What we also need is symmetry in the aircraft at any cross-section, vertical or horizontal. The closer to total symmetry, the more likely that ThunderStruck will reach speeds of near 2,000kph. So if we have winglets, they need to extend top and bottom.

So Why the Winglets?

Simply we need wheels. The winglets hide the wheels and any need to lower wheels for landing. We may use a retractable wheel for the front, but not the rear wheels.

The Winglets will also house twin rudders, making a dedicated rear stabiliser (top and bottom) unnecessary. The rear cross-section looks like the picture below:

ThunderStruck Cross-section

Lifting Body (at Landing).

In the cross-section above the flat surface of the lifting body is obvious. This will only be important when landing as the craft assumes a significant nose down attitude during the gliding phase. Since we have no lift from the wings, the craft needs strong elevators to redirect the airflow at the rear of the aircraft to keep control. We will stay aloft by having speed due to a high angle of attack (nose down). Large elevators will keep the aircraft flying at this high angle of attack. It will be a poor glider – but so was the space shuttle – for different reasons – more to do with the delta wing configuration. A round fuselage cross-section would not aid the lift of the craft at landing. A square fuselage will increase the drag as the surface area is greater, but it will help fly the craft at lower speed when landing. It will have little effect during the glide phase. We may add canards to the front of the craft to increase the lift at the front during low speed flight, but they will pop out after we go subsonic. Delta wing craft work well at supersonic speeds, but are poor performers at low speeds. In the picture at the top of screen, the craft does not have a supersonic spike. We will need this for the Transonic tests, but not for return from a sounding rocket or re-entry from orbit.

Below is a closer look at the Winglets. We have yet to show the square cross-section in an image, since this is still under test. It is felt that the flat surface will help drive a higher pressure under the craft (between the ground and the craft) allowing it to land at a slower speed. This is a form of “ground effect” making the need for a long runway important to drop off speed until the effect lessens and the aircraft eases to the runway. Tests may find little difference in the landing speed and thus we may revert to a cylindrical fuselage. Time for some wind tunnel testing.

ThunderStruck mk2 closeup