High Altitude

Supersonic UAVMMAE 452 Propulsion Project

-Kevin Boldt

-Alex Landis

-Connor McGuire

-Jacob Fogarty

-Grayson Watson

-Kraig Van Wieringen

-Mike Dobben

-Leana Osmer

Group Members

Mission Goals

Create an innovative and efficient UAV

that is capable of high speed supersonic

flight by using an advanced hybrid

engine.

▪ For low altitude flight (under 13km)

the goal is to operate using only a

low bypass turbofan engine

▪ For high altitude cruise (24km) the

the goal is to use an onboard oxygen

supply to supplement the missing

oxygen that is not available at

higher altitudes.

▪ To minimize takeoff and climbing

weight we will utilize an

experimental system that compresses

the incoming air into liquid oxygen

(LOX) at low altitudes and stores it

to be used in high altitude flight.

Why is this mission plan effective?

Benefits

▪ Higher altitudes have

lower ram drags

▪ On board oxygen allows

comparable thrust at

these altitudes

▪ Net thrust is greater

overall

▪ Overcomes a classic

problem of traditional

airbreathing engine’s

being unable to operate

at extreme altitudes.

Disadvantages

▪ Liquid oxygen is heavy

and can drastically add

weight to the aircraft.

▪ Difficult to compress

and store in liquid form

while in flight

1Low Altitude Flight

Conditions

For takeoff and climbing

at altitudes below 13km

(40,000 ft)

Flight Conditions

▪ Climbing Conditions (Turbofan):

-Transition Altitude = 13 km (40,000 ft)

-Transition Temp = -57 C = 217 K

-Air Density = 0.27 kg/m^3

-Absolute Pressure = 170 kPa

-Transition Mach Number = 1.5

-Mass Flow rate m0 = 100 kg/s

▪ Operates as a low bypass turbofan at altitudes below 13km, but instead

of the fan stream providing thrust it runs through our LACE system

(discussed later) and is stored as LOX.

▪ The engine obtains all of its thrust from the core stream

▪ The ram drag is still affected by the fan stream, so the loss of thrust

and increase in drag is noticeable.

http://www.aircraftenginedesign.com/pictures/gp7000_cutaway_high.jpg

Turbofan Specs (some values based off Pratt & Whitney F100)

○ Pressure Ratios

■ Πd = 0.995

■ Πf = 1.6

■ Πfn = 0.98

■ Πn = 0.98

○ Temperature Considerations

■ Τλ = 8

■ Q (jet fuel) = 42,800 KJ/kg

○ Efficiencies

■ ec = 0.9

■ ef = 0.9

■ et=0.85

■ ηb = 0.922

■ ηm = 0.995

▪ To reduce the scope of this project we fixed all of these variables and

focused only on changing the bypass ratio as it would have the greatest

effect on the engine performance.

Engine Values

Net Thrust for different Bypass ratios

To find the ideal thrust to

bypass ratio we plotted the net

thrust for varying low bypass

ratios (0.3-0.5). We found that

a median bypass of 0.42 would

provide the necessary amount of

thrust while using the minimum

amount of ram drag. This is

important because we are trying

to minimize the amount of drag

we have to overcome when the

plane is flying at a cruise

altitude of 24km.

2High Altitude Flight

Conditions

For cruising

at an altitude of

24km (80,000 ft)

Cruise Conditions

-Cruise Altitude = 24 km (80,000 ft)

-Cruise Temp = -60 C = 220K

-Air density = 0.04008 kg/m^3

-Absolute Pressure = 29 kPa

-Cruise Mach Number = 4.5

▪ It is clear that the density of

air significantly decreases as

the altitude increases.

▪ There is a linear relationship

between air density and drag.

Because of this the ram drag at

24km is 6.75 times less than at

13km.

http://www.electronics-cooling.com/1998/09/cooling-electronics-at-high-altitudes-made-easy/

LACE (Liquid Air Cycle Engine)

The idea for our engine originated from Reaction

Engines Limited’s design of the SABRE rocket engine.

How it works...

▪ At an oxygen rich altitude (< 13km) the engine bypass

collects air which is immediately fed into the Helium

heat exchanger

▪ In this heat exchanger the gaseous air is cooled to

below 90K and compressed where it becomes liquid air,

after this point the oxygen and nitrogen are separated

from each other.

▪ The LOX is then stored in a cooled tank, this will be

used later in our cruise flight at 24km utilizing a

splash plate injector.

▪ The liquid Nitrogen is then pumped and used to cool the

burner and turbine.

▪ After being heated, the gaseous Nitrogen is used to turn

the turbine that drives the liquid air compressor.

▪ The Nitrogen is then expelled through a bypass system in

the engines.

Pros and Cons of the LACE system

Pros

▪ Onboard system converts

gaseous oxygen from the

bypass stream into LOX

▪ Onboard liquid helium

coolant allows for

efficient cooling of the

LOX in flight

▪ Nitrogen and other non-

oxygen air components

are used to power the

compressor and turbine

of the LACE system.

Cons

▪ Extra weight from system

components (compressor,

heat exchanger, etc.)

▪ Loss of thrust from the

bypass stream

▪ Extremely difficult to

keep helium cold enough

to allow system to

function (Helium needs

to be below T= 4K to be

liquid)

Comparison of thrust at 13km to 24km

At 13km…

▪ Total Gross Thrust

▫ 230 kN

▪ Total Ram Drag

▫ 125 kN

▪ Net Thrust

▫ 104 kN

At 24km…

▪ Total Gross Thrust

▫ 230 kN

▪ Total Ram Drag

▫ 18 kN

▪ Net Thrust

▫ 211 kN

As you can see, net thrust is doubled using this system.

*Turbofan calculations were done using an excel spreadsheet provided by Dr.Raman

Calculation for fuel and oxygen

Using an assumed mass flow

rate of 100 kg/s we

calculated the constant AV

term in the continuity

equation. From there the

mass flow rate of the core

stream was determined using

bypass ratio. The fuel rate

and percent oxygen by mass

were then determined at

13km. These calculations

were then done at 24km to

find out how much oxygen

needed to be provided to

maintain the same operating

conditions as at 13km.

Sample Mission Plan

In a typical mission this

plane would act as a normal

surveillance UAV. In a

dangerous/combat situation

the plane then has the

capability to ascend and

outrun any threat without

using extra fuel. This

engine is designed to

essentially act as an

afterburner using altitude

instead of extra fuel.

▪ To hold 6 hours worth of

total fuel onboard the

plane will require

approximately 27,000kg

of jet fuel.

▪ We found that it takes

roughly twice as long at

13km to gather the

oxygen needed to operate

at 24km

▪ 1 hour of flight at 13km

provides 21,000kg of

oxygen, this allows for

30 min of high altitude

flight.

Project Conclusions

▪ We get higher thrust

despite using no extra

fuel.

▪ We can function at

higher altitudes than a

conventional turbofan

engine.

▪ Offers protection from

combat situations for

surveillance drones.

▪ Utilizes a LACE system

so oxygen does not need

to be carried at takeoff

and can be refilled in

flight. This allows low

takeoff weight and

multiple high altitude

trips.

▪ Storing and obtaining

liquid helium and oxygen is

extremely difficult to do

while in flight due to

weight, pressure, and

temperature considerations.

▪ The aircraft needs to spend

twice the amount of time at

low altitude as high

altitude

▪ Due to weight issues the

aircraft can only carry

about 30 minutes worth of

oxygen at a time.

Benefits Disadvantages

Thoughts

-Assuming Liquid helium carried onboard can cool oxygen to the point we can liquify it.-Oxygen needs to be below 90K to liquify-@24km we are injecting oxygen directly into chamber assuming it is perfectly efficient (not the case)-Found Area using mass flow rate calculations at 13km-LInear proportional A to V @24km-i.e only density is changing when out mass flowrate changes from one altitude to the next-Can’t use rocket fuel since combustion temperature is too high-heat transfer coefficient assumed high enough to cool oxygen with low amount of helium utilizing only an onboard compressor-There is a service ceiling where pressure gradient is too great to allow for oxygen combustion-Only getting thrust from about 80% of the bypass stream (nitrogen portion).- Fuel per hour 4588.7 kg- twice the flight time at 13km to fill up o2 tanks for enough to fly at 24km-Almost twice the net thrust at 24km cruise-Alex will add in all equatioins as pictures later today (fuel and oxygen)-problem is that liquid oxygen is heavier than the jet fuel and the engine requires 10 times the amount of it for operation-