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Aerospace & Aviation

¨  On a long flight, do you fly towards where your destination will be at the time you plan to arrive?
¨  I was wondering if you could tell me where to find propellent for model rockets.
¨  If I want to raise a family, should I forget about my dream to become a pilot?
¨  I dream about become a pilot someday but don't have the money to learn to fly.
¨  How does a flight simulator game compare in realism with piloting a real aircraft?
¨  How do I build a rocket which will carry an egg without breaking it?
¨  In what aspects in aerospace engineering do you need math?
¨  What is the next step after model rockets?
¨  Does saltpeter and sugar really work for homemade rocket fuel?
¨  What type of home-made fuel works best for model rockets?
¨  What are the main materials to make a rocket fly?
  What do rockets and airplanes have in common?

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If you are flying from north to south for a long flight - say 10 hours - do you fly towards where your destination will be in 10 hours because of the earth's rotation or do you just fly towards it?

ANSWER from Stephanie Wong on 4 August 2006:
No, one does not because the plane is moving along with the Earth.  A person standing upon the ground does not feel that they are in motion, turning about the Earth's axis.  An airplane does not feel this motion because it is already moving with the spin of the Earth.  It's relative motion.  Because the Earth, atmosphere and everything on it is moving with this relative velocity, one can't "sense" the movement.

On the other hand, when a spacecraft travels to another planet, then you have to think about where it's going to be months or years down the road.  That's because the starting planet and the destination planet are not moving at the same velocity with repsect to the the sun.  So, in that case, a spacecraft needs to aim to get to where the destination planet will be in the future!

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Where can I find a cheap and easy propellent for model rockets?

ANSWER from Imagiverse on 24 July 2006:
Get your propellent from a hobby store.  Only use propellent specifically designe for your type of model rocket.  Be sure to use safety precautions and work with an adult supervisor.  Safety is extremely important as this hobby can be as dangerous as it is educational and fun!

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I am a female high school student and not very clear about my future professional career.  I have always dreamed of becoming a pilot, however, I fear that you spend your whole life flying and don't have any time for family.  If I want to raise a family, should I forget about my dream to become a pilot?  How would taking time off for maternity leave or to raise children impact my career?  Would I have enough time to spend with my children when they are growing up?  I have also considered studying engineering or economics and I love ballet.  Would it be possible to study these things while pursuing a career in aviation?

ANSWER from Bob Raab on 19 July 2006:
Dear Future Pilot,

Being a family oriented professional pilot is definitely something that you can do.  There are a number of occupations for professional pilots.  One is the military, however, I don’t believe Costa Rica has an Air Force.  Which is probably just as well, since that would be the least family friendly flying job I can think of.

When one says professional pilot, the majority of people think airline pilot, specifically the major airlines.  I spent seven years flying for the military, where I learned to fly, followed by twenty-eight with a major airline.  You could also fly for a charter service, a corporation, or as a flying instructor.  Of the four civilian options I have listed, there may be others I am not aware of, the airlines are the most lucrative while being the most family friendly.

Being a flight instructor is a "day job".  You would probably work five days a week and be home every night.  However, if you are the sole provider for your family, I doubt that you could make an income sufficient to support your family.  As an instructor, unless there is a large number of students, there is a lot of idle time for which you do not get paid.  You receive pay only for the time you fly.

Corporate flying, or business flying, can pay well, but it's harder work than airline flying.  You often have to load baggage, supervise the fueling of the aircraft, and always do your own flight planning.  Depending on the company you worked for, you could be on call 24 hours a day and be away for days at a time.  However, you would be aware of the job requirements before you were hired and could make the decision to take the job or not.

A charter service is like a small, unscheduled airline.  The charter service owns the airplane and clients pay the service to fly them to wherever they want to go.  Charter pilots probably work harder than corporate and for less pay.  Sufficient pay can be a real issue here.

With the airlines, at least in the U.S., maternity leave is your right.  The amount of time you get to spend at home will depend on your seniority.  The more years you work for the airline, the more control you have of your work schedule.  The airline I worked for has many women pilots who also have families.  There are also those who decide to devote that lives to their career and are happy being married but without children, or remaining single.

With a charter service or with a corporation, maternity leave would depend on the employer's policy.  In the U.S., labor laws would require that you receive maternity leave.  The amount of time off to spend with your family would vary widely from company to company.

I encourage you to pursue your dream.  The best career advice I received as a young man was, "think of something you would do for free and then find someone who will pay you to do that."  As you build your flight time you will become aware of the professional opportunities that are available.  While you are working to complete you training, put as much time as possible into researching those opportunities.  Flying has to be one of the more enjoyable professions.  Many times when you are flying at 35,000 feet and you’re looking at a sunset, a mountain range, a coastline, a big city at night, or a string of small towns along a highway stretching into the distance, you will think to yourself, "I can't believe that someone is paying me to do this."

I wish you the very best for your future.
Bob Raab

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I dream about becoming a pilot someday but don't have the money to learn to fly.  Do you have any advice?

ANSWER from Bob Raab on 10 April 2006:
First I must state that I have been out of aviation for 11 years.  However, some things never change.  For teens, the best place to learn to fly is the local airport.  That is done by trading work, washing airplanes, keeping the parking area clean, cleaning the maintenance area, for flight time.  Apply just as you would for any job, stressing how much you want to learn to fly eventually making it your career.  Since flying is more expensive that it used to be due to fuel costs, it may be difficult to find a flight school that will offer such an arrangement.

I have known many pilots who came from a low income background.  My hand is up.  I worked my way through college making only minimum wage, which at the time was fifty cents an hour.  It's like anything else in life, if you want it bad enough you can achieve it.  The Marine Corps and the Navy have air cadet programs.  Maybe the Air Force also.  You must have completed two years of college to apply.  To get up to date information on those programs go to a military recruitment office for each service.  I am partial to the Marine Corps and Navy.  The flying is much more interesting.  An Air Force pilot never gets to land on an Aircraft Carrier.  If you go to a recruitment office, and you are old enough, do not, I repeat do not, let them talk you into signing up now.  Stress that you are interested only in a flight program after you have the required college.  A military recruiter will give you the highest pressure sales pitch you will ever experience.  Make your mind up before you walk in that you are not joining anything until you have at least two years of college, and that you are definitely not signing anything before that.  I hope that is very clear.

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How does a flight simulator game compare in realism with piloting a real aircraft?  How about flight simulators used by airlines?

ANSWER from Bob Raab on 7 April 2006:
You can learn a lot fror simulator games, but the flying is not even close.  The simulators used by the airlines and the military are so advanced that they are identical in performance to a real aircraft.

ANSWER from Steve Alessi on 1 April 2006:
The [professional] simulators today are very realistic.  They can simulate every aspect of flying a plane (even the tar lines in the pavement).  Pilots can conduct their entire training in the sim.  They can even take the flight test and get their license in the sim.  The ability to practice emergencies in the safety of the sims can not be duplicated in the aircraft.  The airlines today do all their training in simulators.  The first time a pilot touches the actual aircraft is with passengers onboard.

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I am in Calculus II and I need to build a rocket which will carry an egg without breaking it.  Where do I start?  Any suggestions on books, etc.?

ANSWER from Michael Bastoni on 30 March 2006:
Here is a time saving tip... Mark Sullivan posts a great rocket altitude predictor that deals with thrust, accelerations, altitudes, flight times and BEST of ALL... launch angles less than 45 degrees!

Look here:

Finally... a tool that lets you play rocket golf!

Estes is a good source of cheap engines and the Altmark altitude predictor has the thrust curves for nearly any engine!

Here are my recommendations:
Do your time thrust (Impulse), launch angle, F=ma, etc. integration and use the Altmark online tool to check you answers...  Then fly and compare!

You will also need to do some rocket building research.  Estes used to publish great materials.  I have really old stuff I still use since... well the numbers have not changed and the (Newtonian) natural world has remained constant throughout my lifetime... thank goodness.

One thing you will absolutely be responsible for... and that is STABLE FLIGHT.  This refers to the relationship between center of mass and the center of pressure.  Look it up 'cause it's vital knowledge.

Rule of thumb.  Keep the center of mass above the center of pressure.  Again...look it up.


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In what aspects in aerospace engineering do you need math?

ANSWER from Jenny Alvarez on 5 February 2006:
As an aerospace engineer you will use math on a daily basis.  Engineering is a profession deeply dependent on mathematics.  Physics is also heavily used in engineering.  Mathematics is used to decipher things like the proper vectors necessary to build structures that will sustain various weight and environmental stressors.

For more information look at http://www.aero.org/

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I have been launching rockets for some time now but I have been becoming bored of the simplicity of model rockets.  I would like some info on how to make my own rocket engines.  I am planning on becoming an aerospace engineer so I would like the extra challenge.

ANSWER from Roger Herzler on 30 January 2006:
Have you looked into high-powered rocketry?  It's definitely the "next step" up from model rockets like Estes.  They do some nearly professional work and altitudes.  It is defintely where you can take rocketry to the "next level".  Here are some resource links for you to research it further:

Relevant Google search

Resource listing

Tripoli Rocketry Association
NOTE: This link is a biggie in this hobby.

High Power Rocketry

National Association of Rocketry
NOTE: Another great organization

These clubs do high-power solid AND liquid propellants and can custom make their own engines.  DISCLAIMER: You should ONLY attempt to get into these hobbies with proper supervision and knowledge.  They are high-risk due to the materials involved.

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OK, if you wont tell me a good homemade fuel just tell me if saltpeter and sugar really works like Homer Hickam used.

ANSWER from Michelle Mock on 11 November 2005:
I am truly sorry, but at Imagiverse, we can not give you a direct answer to your question.  Homer Hickam also makes this a rule at his own site.  He will not answer any questions about how to build rockets.  He is also quite busy doing research for the novels he is working on (he's a writer NOT a rocket scientist)and not able to give you a personal answer.  He did direct me to a story he has posted at his site.  I think this will tell you everything you ever wanted to know about making homemade rocket fuel:


If you need more information about rocket fuel, maybe you can ask a chemistry teacher at your school for information.  We hope that you take the advice of our experts and not try to experiment with your own homemade fuel.  Work with experienced teachers and advisors when you are experimenting with rockets.  While it is pretty funny to read in Rocket Boys how Homer blew up his mother's fence, he's very lucky he didn't blow himself up or kill one of his friends in the process.  He learned a lot through his experimenting but he also took huge risks.  Did you read the part in the book where Homer wrote: "I prayed it wouldn't blow up in my face"?  There is a lot you can learn about rocketry without getting yourself killed.

You can read more about rockets in our Q&A Archives.  Also we have two "rocket scientists" interviewed at Imagiverse: Dean Davis and Paul Woodmansee.  Read their interviews (and Homer's) and if you have more questions for them, please write again.

Thank you for writing and thank you for the follow up question.

Michelle Mock
Imagiverse Educational Consortium

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What type of home-made fuel works best for model rockets?

ANSWER from Michael Bastoni on 4 Nobember 2005:
Let me please begin with the best advice I can possibly offer with regards to making home made rocket fuel....DON'T MAKE IT.

What distinguishes rocket fuel is its characteristically high, in fact, astronomically high, energy density :).  Energy density refers to the amount of available energy (joules, kilojoules or even gigajoules) in a given mass of a substance.  Substances that have high energy concentrations are inherently dangerous.

It gets even more dangerous when those substances are specifically designed to release their energy very quickly.  Fast release of energy is often (but not always) associated with proportionately high temperatures.  High temperatures often yield high pressures that are extremely difficult and dangerous to control and contain safely.

So...stay away from making your own rocket fuels...there are some very smart people who I know, that have done some very dumb things, and one of those dumb things is playing with high energy density substances at home.  For more on rocket fuel visit this website.

I’ve taken the liberty to research the energy densities of various fuels.  I thought you might appreciate this:

Hydrogen 122,000,000
Natural gas 55,000,000
Heating oil 42,000,000 (gasoline the same)
Coal 30,000,000 (lots of ashes)
Wood, air dried 17,000,000
Gunpowder 3,000,000 (contains own oxidant)
Notice that hydrogen leads the list...although there are problems with putting lots of kilograms of hydrogen in a small space like a fuel tank...but it’s clear why hydrogen is used to power the space shuttle, and nearly every other heavy payload rocket in the world.

Although gunpowder yields a (lower) energy density than other high energy substances, it is important to note that gunpowder contains its own oxidant and therefore can release energy extremely quickly and within a highly confined space...thus the elements for danger exist: High temperatures and high pressures...  Not to mention that most of this stuff is highly toxic.

If you want to fly rockets, then by all means do so...but purchase your engines from reliable manufacturers...and there are many.  Apogee and Estes are good companies that make time tested and proven products.  These companies also provide mountains of very good educational resources.

I offer an engineering instructional unit called Rocket-Golf.  We launch rockets using accurate altitude and azimuth values.  We also utilize long hand math and computer simulations that both account for the total impulse and (changing) mass of the rocket.  In addition we determine the displacement of the rocket while it is powered as well as its displacement after burnout.  We determine acceleration, velocities and positions of the rocket throughout its flight...but most important...and of course most fun is that we predict where the rocket will land.  We do cool things like make 100 yard field goals and try to land in hula hoops across the football field.  Admittedly we don’t often hit the hula hoops but we often score a field goal, while landing just 25 ft beyond the goal post as predicted!  We can maintain 10-15% accuracy most of the time...but over 300 feet this means we can miss by as much as 45 feet and still be 85% accurate!

We make our own rockets...but we DO NOT make our own rocket engines or fuel!

So good luck...  Playing with rockets is a way cool way to get smarter faster.

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What are the main materials used to make a rocket fly and how do you relate the materials to physical science?  How do you think physical science deals with rocket scientists?

ANSWER from Dean Davis on 27 September 2005:
Rocket skins and structural frames need to be made out of extemely strong and lightweight materials to offset the high g-force acceleration, thus, they are made of aluminum or graphite composite materials which have these properties.  The rocket engines, themselves, require heat-resistance to the extemely-high temperatures generated from rocket exhaust, so steel, titanium and carbon-graphite materials are chosen for this area of the rocket.  Aluminum materials are chosen for tanks for cryogenic (super-cold) fuels such as liquid hydrogen (LH2) and oxidizers such as liquid oxygen (LOX), since they are resistant to extreme-cold tempteraures.  Due its corrosion-resistance, aluminum is also the material of choice for hypergolic (fuels that ignite upon contact with each other) corrosive fuels, such as dimethyl tetroxide and monomethyl hydrazine.  Because of its corrosion and thermal resistance, aluminum is also the material of choice for liquid-fueled rocket plumbing lines.  Strong, lightweight, filament-wound, composite fuel tanks, as well as aluminum, are used for solid-propellent fuel-oxidizer combinations.

Thus, the physical science forces of high-speed, high-acceleration, and extreme temperatures, combined with the need for strength and light-weight drive rocket material secection.

Physical science dictates the operational environmental conditions under which rockets are designed.

Dean Davis
Boeing Integrated Defense Systems

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What do rockets and airplanes have in common and how does it deal with physical science?

ANSWER from Homer Hickam on 23 September 2005:
I think it's first necessary to narrow our terms.  Rockets can be anything from small fireworks to the Space Shuttle.  The same with aircraft which can be tiny models propelled by rubber bands all the way to giant passenger/cargo aircraft.  So let's forget about all the smaller, simpler rockets and airplanes and compare a big rocket spacecraft that carries humans into space with a standard passenger aircraft such as most airlines fly.

What are the similarities between the two?  Well, both carry people and both have pressurized cabins so that the people inside are comfortable and have plenty of oxygen to breathe.  They also have very similar airframes which means the way the cabin is built.  But there the similarities mostly end.  Rockets (spacecraft) are propelled by the reaction of a fuel and an oxidizer carried on board.  This reaction we see in the form of flames and smoke spurting through the tail of the rocket through a nozzle.  The action that results causes the rocket to move forward.  This is according to Newton's Third Law of Motion, that for every action, there is an equal and opposite reaction.  So the energy of the burning propellant is translated into thrust.  Rockets can fly in space because they carry their own oxidizers aboard.  This is different from airplanes which operate within our atmosphere.  They carry only fuel which utilizes the oxygen in the atmosphere to create the energy to turn a propeller or produce the thrust of a jet engine.  Airplanes also use wings to produce lift within the atmosphere.  Rockets don't need wings.  The Space Shuttle has them so that it can glide like an airplane when it comes back into the atmosphere.  All of its rockets are out of propellant when it has to act like an airplane.  Still, it is a bit of a combination of both.

As to the physical sciences, of course both rockets and aircraft operate according to the laws of physics, specificially Newton's laws of motion.

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15 August 2006

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