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The Wright Flyer II could reach about 20 mph of airspeed on the track alone. The aircraft needed an airspeed of about 30 mph to make a proper takeoff (without hanging in ground effect). Before the catapult was developed, the Wrights needed at least a 10 mph heawind in order to reach the proper airspeed.

My question is: suppose the airplane reached 20 mph after 250 feet (76 meters) of track, which was the longest track length they ever had. No wind is present. Now suppose the track is not 250, but 500 feet (150 meters) in length. Would doubling the track distance allow the airplane to compensate for the lack of the 10 mph wind it normally needed?

I know that aerodynamically speaking for an airplane performing a takeoff, if you have 30 mph of airspeed, it doesn't matter if this airspeed was obtained by partially using a headwind or not. Airspeed is the only thing an aircraft "feels" for takeoff purposes. What I'm really in doubt for my hypotetical scenario is about the acceleration. Since the acceleration is non-linear for an airplane taking off, I'm not sure if by doubling the length of the takeoff distance the aircraft would be able to compensante for the 10 mph headwind it normally relied at the start of the takeoff.

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  • $\begingroup$ You are asking a theoretical question which no one can really answer because the Wright brothers never built a longer launching catapult. You are also assuming that longer means faster. That might not be true. $\endgroup$ Apr 11 at 12:46
  • $\begingroup$ Lauching rail, actually. The catapult and the track were different systems. But yes, I think longer may not mean faster. $\endgroup$
    – user63046
    Apr 11 at 13:10
  • $\begingroup$ You'd have to calculate the maximum speed the Flyer could achieve on the track with the available thrust in still air, and for that you'd have to know the increase in rolling friction of their track system to be able to calculate if the thrust could overcome that friction plus air drag and how far it would take. They built their catapult system with the weight tower to overcome just that problem when demo-ing the Flyer inland. $\endgroup$
    – John K
    Apr 11 at 13:23
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    $\begingroup$ The Wright monument is on a large dune next to the site of the first flight. When "why did they not put the rail on the hill?" was asked, the answer was they needed flight from flat ground to be "official". (but headwinds apparently were allowed) $\endgroup$ Apr 13 at 1:00
  • $\begingroup$ I think the low angle of attack and therefore low induced drag during takeoff roll easily compensates friction, yet I cannot prove it. $\endgroup$
    – qq jkztd
    Apr 14 at 13:40

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The Wright Flyer II, at 15 hp, was underpowered, but still able to fly a full circle by the end of the 1904 season, in spite of several crashes$^2$.

Lengthening the rail (with a lot of grease) may have helped, but the Wrights realized running down a longer rail really wasn't their issue, having enough thrust to stay airborne at the very bottom of their drag curve was.

Approximation$^1$ of Velocity given rail length and acceleration:
Wright Flyer II glide ratio 8 : 1
Weight around 420 kg
Prop thrust: around 55 kg
Rail length: 76 m


Acceleration = Newtons/Mass = 55 kg × 10 m/s$^2$/420 kg
= 1.31 m/s$^2$

V$^2$ = 2 × acceleration × distance
= 2 × 1.31 m/s$^2$ x 76 m
= 199 m$^2$/s$^2$

V = 14.1 m/s = 31.7 mph !

A little push from the wing walkers would have helped, and aerodynamic drag and rail friction would increase as airspeed increased, but rail length beyond a few meters more really would not get it to a higher speed once airborne under any circumstances.

This is why they developed the catapult. If they were lucky, they could get up and trimmed just right for lowest drag, hoping their early internal combustion engine would run well. The Flyer II also had issues with excessive pitch throws, adding to the adventure.

Their early flight logs noted that, somehow, it flew at around 30 mph, but lost airspeed and crashed if slightly slower. Top speed was 35 mph. Later models had more horsepower.

$^1$ updated thrust and Flyer II weight information
$^2$ Huffman prarie field, near Wright-Patterson AFB, has an elevation of 800 feet, but was probably a bit lower humidity than Kitty Hawk.

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    $\begingroup$ They do demo runs of an exact replica of the Flyer engine at Oshkosh, complete with crankshaft blank cut out of a slab of steel using a drill press like the original. The intake valves were suck-ins, with the cam only working the exhaust valves. It sounded like a typical farm tractor motor. $\endgroup$
    – John K
    Apr 11 at 20:48
  • $\begingroup$ Robert, thanks for the comment. But regarding why they developed the catapult, several sources mention how impractical it already was was for them to use a track of 75 meters. They always wanted to takeoff with a headwind, so when the wind changed direction (and that happened a lot in Huffman Prairie), they had to change the whole track with it. This was a very laborious process. $\endgroup$
    – user63046
    Apr 12 at 1:36
  • $\begingroup$ Thanks, Robert. Let me ask you something: in the case of the 1903 Flyer, the plane took off against a wind averaging 20 mph. It is correct to assume that if the aircraft had thrust to advance against a 20 mph headwind, it would also have thrust to reach 20 mph without wind? (Assuming a longer track, of course). $\endgroup$
    – user63046
    Apr 12 at 15:46
  • $\begingroup$ @MarceloJenisch reaching a higher groundspeed on the track would have meant slightly higher friction forces from the track with no wind (if windspeed is adequate, they need no track at all, i.e. kites). With a bit of grease or oil, maybe. $\endgroup$ Apr 12 at 16:11
  • $\begingroup$ I'm not sure if I understand you correctly. If there's no wind, the ground speed is the same as the true airspeed. I guess you mean that without wind the friction would be larger at the start of the takeoff relative to a takeoff with wind. In that case, yes. But friction also decreases with increased airspeed. So, without wind, after reaching 20 mph the friction would be the same as if the airplane was starting a takeoff with a 20 mph wind. The question for me is if the plane would still have acceleration capacity to go from 20 to 30 mph, as it reached 20 mph without any help from the wind. $\endgroup$
    – user63046
    Apr 12 at 22:03

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