Tuesday, April 7, 2015

The FireFlash report

The Gary Anderson's 'FireFlash' plausibility report (2015 edit).

The Gary Anderson's 'FireFlash' plausibility report 

What is the 'FireFlash'?
The Fireflash, a hypersonic airliner, appeared in the episodes "Trapped in the Sky", "Operation Crash-Dive", "The Impostors", "The Man From MI.5", "The Duchess Assignment" and "Security Hazard". (Thunderbirds TV series).

It has six atomic motors that enable it to stay in the air for a maximum of six months; however, their radiation shielding must be maintained frequently, or the passengers will only be able to spend a maximum of three hours in the aircraft before succumbing to radiation sickness.
Fireflash's maximum speed is Mach 6 (approximately 4,500 mph or 7,200 km/h), and can fly at heights above 250,000 feet (76 km). 

A novel feature is that the flight deck is built into the tail fin. Like the real-world Airbus A380 she has two decks, but also features luxury facilities such as a cocktail lounge housed within glazed sections of the wings leading edges. Fireflash was commissioned by Air Terranean (a.k.a.: Terranean Airways).

Basic design features:

Wings and fuselage:
The Fireflash is a fictional hyper sonic airliner. It's estimated size is about 1.2-1.6 of a Boeing 747. The FireFlash has a long and narrow fuselage. In the front nose section of the plane there are twin Cannard surfaces. Main wing is swept and located back in the aft section. Tail section is a "T-tail" configuration, just behind the main wing location.

Engines location and arrangement:
There are six engines located up on each wing tip of the "T-tail" horizontal stabilizer, in two nacelles (three engines in each nacelle). Two horizontal fins are connected to each nacelle at the outboard side of the nacelle.

Landing gears:
Main landing gears are located in aerodynamic pods, on each wing tip of the main wing. Nose gear is located behind to the nose section (like in the XB-70 or SR-71).

Cockpit location:
The cockpit of the Fireflash is located on the leading edge of the vertical fin at the tail section (!!).

Considering these basic structural features of the FireFlash, we can see some design problems which might not allow it to perform as planned, therefore not being a plausible aircraft.

Landing gears arrangement problems: 
Locating the main landing gears in the wingtips of a giant airliner can limit it's runway operations. Many airliners taxi on the runway, while their main landing gears travels on the middle 1/3 section of the runway width. This allows for example crosswind landings with the landing gears always in the middle 1/3 section of the runway, while the nose of the aircraft pointing sideways. Sometimes, while taxiing, airliner's wing tips gets out of the runway/taxiway area, as it's wheels most of the time travels on the middle section of the taxiway.

The landing gears arrangement feature of the FireFlash will limit it's taxiing operations on standard runways/taxiways. It will also narrow the possibility for directional correction in takeoffs, landings or any runway emergencies.  Until we change the design, runway operation is limited. (or it can be operated in a very wide taxiways and runways airports).

Engine location issues:
Locating the engines way back in the tail section, and way up on the T-tail horizontal stabilizer is basically wrong. This is the most severe design flaw which badly affects the FireFlash performance: Low speed, high speed and flight ceiling limitations.  

Low speed flying - a real trap in the sky:
When flying at low speeds, lift forces on the flying surfaces are maxed out and the aircraft is relatively close to it's stall speed. Flying slow (in a normal condition), while having six powerful engines which are located way aft and way up to the center of gravity, is not so smart; when engine thrust is needed while flying slow or close to the stall speed (for a 'go-around' procedure for example), the thrust of the engines will cause a nose-down moment (because of the moments it will produce, being way above and behind the center of gravity of the plane), therefore, In a low flying speed and a high engines thrust, the nose-down moment will be much higher than the lift forces on the flying surfaces, being close to the stall speed. This will cause major problems in controlling the aircraft in low flying speeds, when high engine thrust is needed. Adding power to the engines while flying slow will force the plane to nose down without having the needed lift from the flying surfaces to encounter this moment. Stalls at low altitude are not recoverable because of this reason. 

Low speed/high power pitch input and trim limitations:
Pitch input change or trim will be needed each time power settings is changed. This equation is somewhat manageable while managing power or flight level during a cruise. But when continues changes of power setting are needed, for example: flying manually on final, each power setting change will cause a need for a pitch input correction and a pitch trim. Beside adding to pilot's workload In a low speed flight condition (takeoff/landing), a new low speed limit will occur, (which is not the 'aircraft's stall' but higher than the stall limit); It's the maximum possible pitch input in a given airspeed and angle of attack, on a given maximum engine thrust. Below this speed limit, a pitch input or trim will get to it's maximum, while the angle off attack of the aircraft (and it's attitude) remains relatively low (because the high power setting of the engines produces a nose-down moment). Control surfaces stall may occur in this situation, making the aircraft uncontrollable in the pitch axis. A 'go around' procedure in the FireFlash, is a classic example for dealing with this limit.

High altitude flying - not possible?
High altitude flying problems or the FireFlash, in general principle, are similar to it's low speed problems. high engine thrust is required to obtain high altitude sustained flight (simply, this is because of the thin atmosphere). Lift forces are reduced as the flying surfaces not generating enough lift to counter the needed engine thrust moment (because of it's location far behind and higher than the center of gravity of the aircraft). Adding thrust to accelerate/maintain a high airspeed and high altitude will cause the FireFlash to have a high pitch-down moment, and, a low-speed limitation which under it, flying surfaces will stall or reach maximum pitch input while trying to eliminate the pitch-down moment.

Hyper Sonic flight - not possible?
The FireFlash designed to be a Hyper sonic airplane. Maximum thrust is needed to reach Hyper sonic speeds, while high drag values are rising. To reach speed of mach 7, with it's given weight and size, the thrust must be so powerful, reaching a new high-speed limit, which above it, leveled flight will not be possible, because the flying surfaces will not be able to encounter the thrust and maintain the airplane leveled. So, practically, reaching Hyper sonic speeds with the FireFlash is not possible. 

Cockpit location issues:
Locating the cockpit inside the leading edge of the vertical fin, way back in a very long tail section will cause severe limitations in the pilot's field of view, especially when landing and taking off (taxiing is also a challenge). The needled fuselage and the Cannard surfaces will hide the runway.Think about the Concorde, reducing it's nose when landing in order to allow the pilots to see the runway. In the FireFlash, there are couple hundreds of feet of fuselage and nose ahead of the cockpit. We have to design the FireFlash to generate it's lift in relatively low angles of attack, and land at relatively high speeds. We can use cockpit camera (like in the XF-103).

Now, when we theoretically understand the basic design features and it's effect on flight, here are some practical flying tips for the FireFlash:
(The 'FireFlash' will be available soon for free download here, so you could practice your flying skills, flying it in X-Plane).

Lift-off speed is about 200kts (this number is reflecting the equation off all of the FireFlash features, mass and configuration, in X-Plane advanced flight simulation). Do not use 100% power. It will "GLUE" the nose gear to the runway and you might not take off on the given runway. Use flaps (1 notch). If you have good hands - at about 190kts, reduce power to 50%. It will allow the canards to counter engine thrust force, but, you will have to manage power and stay away from the low-speed-limit that will cause the engine thrust "take over" the forces equation over the flying surfaces lift forces, and pitch you down. As you are airborne, retract flaps, trim and add power gradually until there is enough airspeed to fly safely.

Slow down and extract the flaps. Final speed at 250kts. You can fly the final slower, but it depends on your trim skills, and the low-speed limitation. Take into consideration your wing-tips landing gears location, and the cockpit location. When flying at 250kts, with flaps down, you can use the HUD and place the velocity vector on the touchdown zone. It is surprising, but it can be done, even when looking forward from the vertical fin's cockpit.

The rest of the flying-phases are very educational and fun. Once you up in the air, you are on your own!

The FireFlash in some action:
(This is X-Plane v9.70 video. X-Plane v10 version will be ready soon)


  1. Cool project! Would you be able to send me a download link so I can have a go? [email protected] Many thanks!

    1. Hi!
      This is a rather old add-on...but I will make it available soon, and will send you the link.
      Thanks again :)



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