What engine is this???

Yes however the published number is just over 60,000, the target was for over 70.  In theory they believed they might get up to 90+ however the limitation of air and a prop driven plane of any kind proved to be the main issue.  General Atomics developed one similar with a single 2 stage turbo that proved very effective up to about 55,000.  The problems with these aircraft and the extreme wings they used is the decent actually.  On decent the only way to get down was to drop in steps, the engine had to maintain oil temperature (it was below -60 F at those altitudes) energy had to be maintained to stop the engine from literal freezing up.  

Here are the official specs on that project: (note the payload, very big compared to Perseus B) 

Altus II Specifications

• Wingspan: 55.3 feet
• Wing area: 131 square feet
• Wing aspect ratio: 24
• Length: 23.6 feet (7 ms)
• Maximum gross takeoff weight: 2,130 pounds
• Wing loading at gross weight: 16.3 pounds per square foot
• Payload: Up to 330 pounds in nose compartment
• Propulsion: Rear-mounted Rotax 912 four-cylinder piston engine rated at 100 hp, integrated with a two-stage Thermo-Mechanical Systems turbocharger. An 84-inch diameter two-blade pusher propeller was used for flights up to about 53,000 feet altitude; a larger 100-inch diameter lightweight carbon-fiber propeller was installed for flights above that altitude.
• Fuel capacity: 92 gallons
• Airspeed: 100 knots (115 mph) maximum; 70 knots (80 mph) cruise, varies with altitude
• Maximum altitude: Above 60,000 feet (19,500 m) with two-stage turbocharger; about 43,500 feet with single-stage turbocharger
• Endurance: Approximately 24 hours, depending on altitude
• Construction: Primarily composites
• Manufacturer: General Atomics Aeronautical Systems Inc., San Diego, California

Cheers

Hi RW

".............it also had a special ignition due to the fact that a normal one will not fire at those altitudes". 

Please explain😈

Howdy RW,

I didn't know that either. Interesting. I know engines were Mfg'd for other things, but I didn't recognize this one. I have a friend down by me that did tons of research for the military with the drones.

HI Sean

There are some very good papers on the subject of high altitude with piston engines, most are very difficult reads however.  The simple way to think about it is what we know from racing engines, particularly those with superchargers or turbochargers.  To get any performance we need to use one or the other.  

Think of the problem like this, the only way to get power is from the formula HP = T x RPM / 5252.  For KW, kilowatt power it is a little bit longer calculation.   

"To get the value in kilowatts, you multiply torque expressed in newton meters by the engine revolutions, and divides the obtained result by the constant value resulting from the change of units (formula  Kw = Nm × rpm/9549,3)."

So what happens when we want to get to high altitude?  To maintain any performance we need to "stuff" the cylinders and heads with very high pressure.  This compensates for the very low density of the air at these extreme levels.  in that way we'll have enough burnable oxygen for combustion.  The unfortunate part of this is the ignition at very high pressure can literally be "blown out" like a candle by the pressure.  The only thing we can do is run a higher spark voltage to jump the gap.  This is a common practice in race engines as they suffer from much the same problem with very high boost pressures.  Any check into race care or performance car parts will show you long lists of suppliers who make special ignition for high performance engines.  The basic Rotax ignition, especially the ones used in those old high altitude drones, was simply not good enough.  

Today we have a much more efficient ignition on the 915 and 916 engines.  Better coils and connections in those engines along with our turbochargers have allowed even out of the box performance well above our normal manned flight plans.  

Cheers

"The unfortunate part of this is the ignition at very high pressure can literally be "blown out" like a candle by the pressure."

This I did not know.

So it's not that the ignition itself is not working, it's the ability to sustain a spark due to high pressure.

Hmm!

I thought that the boost system (turbo/superchargers) job was to maintain sea level air pressure, as in turbo normalised or turbo enhanced.

In my (limited) understanding this should mean that at, say 80,000ft, the inlet manifold/combustion chamber pressures, should be around sea level pressures.

If this be the case the spark should "think" its at sea level😈