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I'm watching footage from Red Bull Air Race 2017 in Kazan (one example is

) and clearly at least some of the airplanes used have non-retractable landing gear.

I was under impression that non-retractable landing gear increases drag and also makes the airplane larger which is hardly good for application where maneuverability and speed are important.

Why are planes with non-retractable landing gear used in such competitions?

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    $\begingroup$ anyway the video is accelerated, just to seem more impressive. $\endgroup$ – Gianni Alessandro Jul 25 '17 at 12:09
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    $\begingroup$ Weight, plus 6+ G's on the gear may cause them to extend. $\endgroup$ – Ron Beyer Jul 25 '17 at 12:18
  • $\begingroup$ Related: Why do most aerobatic aircraft have conventional landing gear? $\endgroup$ – fooot Jul 25 '17 at 21:45
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    $\begingroup$ Your title says aerobatics but the question references a race series. They are not the same thing. Many of the considerations in the answers apply to both, but it is not obvious that the same answer is right in both cases. $\endgroup$ – Ross Millikan Jul 26 '17 at 4:58
  • $\begingroup$ I think the course design in the Red Bull Air Race makes turns (i.e. acceleration) more of a limit than outright speed. Compare with the Reno Air Race. $\endgroup$ – Nick T Jul 26 '17 at 19:16
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As you mentioned, drag is one of the reasons why retractable landing gears are used in the first place. But in order to use it, there are way more considerations than just drag.

  1. Scale: Size of the aircraft plays a big role here. Big aircraft have more room to keep the retracted landing gear. This is an issue as planes get smaller.
  2. Weight: Retractable landing gears not only require more space, but they impose more weight
  3. Cost: They add extra costs in installation and maintenance.
  4. Application: High speed applications justify a retractable landing gear for a more aerodynamic shape. Does the present situation really need the application of a retractable landing gear?

These are some considerations that go into it, but not all of it. In the case of a high performance sports plane (like in the video above):

  1. Scale: the planes are small. The retractable landing gear systems (system) need a lot of space. This is not what we want in a sports plane
  2. Weight: A high percentage of the overall weight is taken by the system. This in turn increases the inertial forces* and decreases the overall maneuverability.
  3. Cost: It is expensive to install. And it may cost even more due to the low volume requirements.
  4. Application: More than high speed, high maneuverability is needed.

* Inertia is the tendency of a body to stay in the existing state of rest or motion. So inertial force is the force that keeps the body in its existing state of rest or motion.

[EDIT] Based on a very good response below (from @Devil07), I am adding this important point here (just for a better overview of all important aspects):

  1. Complexity: Retractable landing gears are complex piston mechanisms. Eventually it adds to the cost of installation and maintenance of the system.
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    $\begingroup$ Also short flights mean the fuel savings from retracting the gear would be minimal, especially combined with low speeds. $\endgroup$ – Chris H Jul 25 '17 at 15:00
  • $\begingroup$ Excellent answer and comments. Just a note though, Bob Hoover in his Shrike Aero Commander would do almost his entire routine with the gear retracted. $\endgroup$ – 757toga Jul 25 '17 at 15:35
  • $\begingroup$ @MichaelKjörling. I will keep your suggestion in mind for the next time. Thanks for your input. $\endgroup$ – tegginamaniss Jul 25 '17 at 23:55
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    $\begingroup$ I'd argue that installation and low-volume manufacturing costs would be pretty low on the list for the top performers. Zlin Z-50 (about 80 were built between 1975 and 1994) uses fixed single-piece titanium spring, which was veery expensive to manufacture. $\endgroup$ – Pavel Jul 26 '17 at 7:35
  • $\begingroup$ To add to point 5, complexity would also add a point of failure to emergency landings. At low altitudes the time to deploy landing gear may be to great. $\endgroup$ – Jammin4CO Jul 26 '17 at 16:42
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Strictly speaking, a 'pure' aerobatic aircraft doesn't need a retractable landing gear. For such an aircraft maneuverability is much more important than speed. In fact, the aircraft can't fly too fast or the spectators are going to miss the show.

In case of air races, the weight penalty of having a retractable landing gear is huge- in addition to the problems associated with complexity. For example, all the aircraft used in the Red Bull air races are lightweight with carbon fiber wings. As Popular Science notes,

Extreme weight reduction techniques are employed to give pilots even a minor advantage, such as discarding plastic tie wraps in favor of lightweight string, or drilling holes in heavy brackets

Trying to fit a retractable landing gear inside would incur a weight penalty too large to negate the drag reduced especially since the propulsion system (engine + propeller) is fixed. In this case, the drag is reduced by putting the landing gear inside aerodynamic covers. Not to mention, larger wings reduce maneuverability.

Note: In case of Red Bull air races, it appears that the fixed landing gears are mandatory:

The following key rules and regulations were taken from the Red Bull Air Race World Championship Regulations 2010 Edition ... Regulation 6.4 states that each aircraft must have fixed landing gear on board.

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  • $\begingroup$ May be worth noting the weight wouldn't increase by the weight of the landing gear alone. Increasing the weight of the landing gear system would mean the entire airframe would be under a heavier load in every manoeuvre (f=ma), and, assuming they are built to the limit of performance, every load bearing part of the aircraft would need to be strengthened, increasing the total weight further. (and increasing the total weight means you need stronger, heavier landing gear to withstand the landing forces!) $\endgroup$ – JeffUK Jul 27 '17 at 7:45
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In the case of the Red Bull Air Race, the engine and propeller are specified by the race officials, and must remain unmodified, so the airframes are designed to get the most out of that combination. The (relatively) tight layout of the course benefits a highly aerobatic aircraft of the Extra 300 style. Fixed gear is also required.

As a result of those requirements, the cost of both purchasing and maintaining the competition aircraft in the Red Bull series is relatively low, meaning more competitors and more races.

While the Red Bull series (which I really enjoy) holds numerous races in multiple locations each year, the faster and infinitely more expensive aircraft in the Unlimited Warbird Racing Class race once a year at Reno, NV.

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Less weight: (as others have stated)

Less complexity: which translates to higher reliability

Robustness: retractible landing gear on small aircraft tends to be a bit flimsy (and if it isn't flimsy then it adds to the weight penalty), imagine pushing and pulling on all those moving parts with 6gs of force back and forth and back and forth. Fixed landing gear is less likely to fail, especially under those repetitive forces on all the moving parts.

And finally, as mentioned, most aerobatics are done as slower speeds where the penalty of fixed landing gear is not much of an issue. Slower speeds = tighter turns and maneuvers.

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  • $\begingroup$ Retractible landing gear on small aircraft is flimsy, have you got a source for that? If most items are mentioned before, what does thiss answer add? $\endgroup$ – Koyovis Jul 25 '17 at 22:30
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    $\begingroup$ Personal experience. It adds brevity/conciseness. Feel free to vote it down if you disagree. I appreciate lots of answers when I ask questions, so I'm just contributing the best I can. $\endgroup$ – Devil07 Jul 26 '17 at 1:22
  • $\begingroup$ @Koyovis if a small aircraft is not designed and certified to be aerobatic, there is no point designing landing gear (ether fixed or retractable) which will handle high G loads, flying inverted (including the effect on hydraulic systems, not just the moving mechanical parts), etc. For aerobatics, you have to consider all of those options - plus either designing the gear so it can be extended/retracted while flying inverted, or in the middle of a +6G or -6G turn (because some aerobatic pilot is going to want try that just because it looks "kool"!), or adding some interlocks to prevent it! $\endgroup$ – alephzero Jul 26 '17 at 3:05
  • $\begingroup$ @alephzero Yes a retractable landing gear on an aerobatics machine must be designed for 6g and therefore becomes not flimsy, but robust and heavy. Weight, as others have stated. This answer adds nothing to aeroalias' answer. $\endgroup$ – Koyovis Jul 26 '17 at 3:37
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    $\begingroup$ Also, slower aircraft means more time over the crowds at air shows. Not much point in aerobatics at 300+KIAS, they'll be out of sight of the crowd that pays for the event very quickly. $\endgroup$ – tj1000 Jul 26 '17 at 14:41
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Well, drag slows the speed down which is good for a spectator sport. It also gives the plane visual legs which give turns and spirals optical anchor: this makes them look more like acrobatics than swimming. If you use sleek jet planes for aerobatics, stuff becomes quite faster and more dangerous (both to pilots and spectators) with much larger turns while looking actually more bland.

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Safety

Engine Failure @ Low Altitude Followed by Gear Malfunction

Aerobatics and racing are performed at low altitudes. If you lose the engine at 500 ft AGL, and the gear are stuck (due to your aerobatic maneuvers) or you have an electrical or hydraulic issue, what are you going to do? Hand crank the gear down in an plane with really high wing-loading (meaning higher rate of descent at best glide)? You won't have time and you'll be belly-landing.

Engine Failure @ Low Altitude above VLE/VLO

Additionally, lets suppose you are racing at low altitude, and going fast because that's the point of racing... you lose the engine, which will slow you down, but not necessarily enough to get below VLE/VLO. What do you do? Pull some crazy maneuver at low altitude to bleed airspeed? Wait it out and hope you slow down enough and still have enough time to drop the gear? Drop them anyways and risk damaging the gear, or worse, the air frame, all while getting buffeted like crazy due to the huge and sudden drag and while trying to perform an emergency landing? No thanks. Fixed gear pls.

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  • $\begingroup$ This looks like the most practical answer however it's rather hard to read it because it's formatted as a single large block. Could you please split it with newlines? $\endgroup$ – sharptooth Jul 27 '17 at 14:17
  • $\begingroup$ If you lose an engine at low altitude and high speed, why not pull up and convert that speed to altitude? $\endgroup$ – Sean Dec 10 '18 at 3:57

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