A spar is made up of two components: the spar web and the spar caps. STC'D and PMA'D . Ailerons are used to provide roll control and do so by generating a large rolling moment through asymmetrical deflection. The lower spar caps, in tension, taper from 72 plies at the root to two plies at the tip. The spar caps/flanges and stiffeners only carry axial (bending) loads. The aspect ratio was introduced in the section above and is a measure of the shape of the wing. The finished spar extends from the wing tip to the wing root and into the spar end – in a 18 m wing about 9.30 m long. The ultimate load factor is therefore equal to 1.5 times the limit load specified in the FAR regulation. Ribs also form a convenient structure onto which to introduce concentrated loads. High-lift devices are a large topic on their own and are discussed in detail in Part 4 of this mini-series. A wing structure would be modeled using a Finite Element (FE) package and tested for many different load combinations before a prototype is built and tested to the point of destruction as a means to validate the paper calculations and computer analysis. The stiffeners are spaced laterally through the wing to support the wing skins against buckling. Additional ribs should be placed equidistant along the span of the wing such that the aspect ratio between the ribs and the skin remains close to one. Raytheon Aircraft Company considers this to be a mandatory inspection/modification and it must be accomplished as soon as possible after receipt of this Se rvice Bulletin, but no … This initial action is what requires the 12 hrs. Inspect the wing spar splice on strut-braced airplanes for cracks and corrosion. Spars are the main load carrying members in the wing running span wise direction. In the AD, the process calls for both visual and eddy-current inspections of the spar cap, corrective action, if needed, and the application of protective coating and corrosion inhibiting compound. By now, every Cherokee owner, from the earliest PA-28-180 to the most recent Arrow, has heard about the inflight wing separation that occurred April 4, 2018, to a Piper Arrow owned by Embry-Riddle Aeronautical University in Daytona Beach, Florida. , $$C_{D_{i}}:$$ Lift-induced Drag Coefficient Started: October 6, 2003. There are top and bottom spar caps riveted in a built-up I-beam fashion, with 1/8"-thick 2024 material stacked to thickness as required by stresses along the spar. A semi-monocoque structure is well suited to being built from aluminium as the material is both light and strong. The wing will fail when the stress in the stiffeners or spar caps reach their maximum crippling (failing) stress. If the pilot banks the aircraft at a 60 degree angle during a sharp turn, he needs to produce twice the lifting force to counteract the weight due to the angle of the lift vector relative to the weight (which always acts downward). Did you enjoy this post? If found cracked, repair cracking or replace the wing section. If you enjoyed this post or found it useful as a study aid, then please introduce your colleagues and friends to AeroToolbox.com and share this on your favorite social media platform. An investigation revealed that repeated high-load operating conditions accelerated the fatigue crack growth in the lower main wing spar cap. The wing area is defined as the planform surface area of the wing. Think of spars as the hub, or base, of the section in which they are located, even though they are not in the center. On a tapered wing it can be found using the formula: High aspect ratio wings are long and thin while low aspect ratio wings are short and stubby. WING SPAR CAP - Inspect the wing spar cap for corrosion as outlined fn Sectfon 4 of PEN 35-i900968 Shop Manual, Sectfon 3 of PEN 36-590001-38 Shop Manual or Chapter 57-00-00 of PEN 36-590001-9 (or subsequent) Mafntenance Manual. The spar web separates the upper and lower spar caps and carries the vertical shear load that the wing produces. If you have been following along from the start of this series then you’ll be familiar with sizing a wing with respect to plan area and aspect ratio, sweep and supersonic flight, and selecting a suitable airfoil profile in order to complete the planform design of the wing. that will give you 5400 to 6200 hours . A typical semi-monocoque wing structure is shown below with the various components labelled: These consist of the upper and lower flanges attached to the spar webs. C_{D_{i}} = \frac{C_{L}^{2}}{\pi AR e} The CAP 10 is a low-wing cantilever monoplane of wooden construction, with the CAP 10C having a carbon sandwich wing spar. “The wing is a very diverse part because of the complex loads to which it is subjected. Further to specifying the maximum maneuvering load factor, the aircraft must also be designed to withstand a gust loading during level flight. Note 2: FAA AD 2002-26-05 Amdt 39-12991 refers. 300+ aircraft were built, and in 2007 the CAP 10C is still in production as the CAP 10C NG. Lift is an aerodynamic force which is produced as a consequence of the curvature of the wing and the angle of attack of the relative velocity flowing over the surface. When the wing is subjected to a positive load factor it will tend to deflect upward and load the upper spar caps and skin in compression, and the lower structure in tension. Think of spars as the hub, or base, of the section in which they are located, even though they are not in the center. A better gauge of the relative size of the wing is the wing loading which is calculated by dividing the aircraft mass by the wing area. The foam traps moisture against the lower surface of the carry-thru spar cap, which can increase the development of corrosion,” according to the AD. Both control surfaces work by modifying the local camber and lift distribution over the area in which they operate. A typical wing internal structural layout is shown in the image below: A wing is comprised of four principle structural components that work together to support and distribute the aerodynamic forces produced during flight. 997, dated May 14, 1987. It is good design practise to locate the main spar near the aerodynamic centre. Conditions at wing root: wing span : b = 78 in wing load : F = 160 lb (winch line force) spar height : h = 0.9 in (9% airfoil with 10 in chord) The moment at which the structure will collapse is determined once the crippling stress (critical stress in spar cap) and the moment of inertia (function of extent to which skins have buckled) is known. Lower wing spar cap. The Main Spar is basically a "C" channel of .032 2024-T3 aluminum with 2024-T4 bar stock built up in varying lengths and stacked in varying thicknesses, then riveted top and bottom on the web part of the "C" channel. Limit loads are therefore multiplied by a factor of safety to arrive at a set of Ultimate Loads which provide for a safety margin in the design and manufacturing of the aircraft. Wing ribs are spaced along the span of the wing and give the wing its aerodynamic shape. We Sell and Install the Above SPAR CAPS!!!! The spar is the main supporting member of the wing. Spar caps are generally continuous from root to tip, so messing one up during construction can mean expensive shipping for the long replacement. So an aircraft that weighs 12 000 lbs and is designed to an ultimate load factor of 4.5 must thus be able to produce 54 000 lbs of lift up to a speed governed by the FAR regulations (dive speed). The 150 has very few access panels under the wing so inspection of the entire spar requires an intentional desire to see it. CAUTION: WHEN CUTTING SKIN ACCESS OPENING IT IS OF UTMOST IMPORTANCE TO NOT CUT OR NICK THE UNDERLYING STUB WING SPAR CAP. It can be differentiated into two types: â€¢ Right and left wing are joined together and later attached at … The span of the aircraft carries flight loads and the weight of the wings while on the ground. Many light aircraft make use of a strut which reduces the bending moment at the wing root, allowing a smaller (lighter) wing-to-fuselage attachment. This allows the spar caps to act in pure tension and compression (bending) during flight. Wing spar is usually in Fixed wing aircraft. Since the bending moment is a maximum at the root of the wing, the spar caps will need to be large enough (sufficient area) so as not to fail in bending. These make up the longitudinal components of the structure. The primary objective of the wing’s internal structure is to withstand the shear and bending moments acting on the wing at the Ultimate load factor. issued A.D. We have Answers for it, and our Answers … A panel section of the wing can therefore be modelled as a set of skins where thickness is a variable, and once the shear flows acting on each of the skins are known, the thickness of the skins can be varied until the shear stress in each skin is below the material allowable shear stress. Ultimate loads can result in plastic deformation of the structure but must be held for three seconds without failure. Buckling of the skin does not necessarily result in failure of the whole wing structure as the buckled skin will transfer load into the spar caps and stiffeners that border the skin. JOHNSTON AIRCRAFT SERVICE, INC. WHERE WE DO EVERYTHING THRUSH!! The total lift force is increased in proportion with the wing area. and the estimated location of the tail. In a semi-monocoque structure both the outer skin and the internal substructure are load bearing, and both contribute to the overall stiffness of the structure. Designing the planform or shape of a wing is a complicated process undertaken to optimize the aircraft for a particular mission. The two primary contributors to the total stress are the vertical lift force and the resulting bending moment. In both cases it is clear that the location of the highest shear and bending is the wing root. Learn more. Shipping one across the country is not cheap, since it needs to be packaged well to prevent it from being bent. The left aileron deflects upward which modifies the flow field, generating a downforce at the left wingtip. Return the upper spar cap angle to its position in the wing. The extract shown above pertains to an aircraft that is to be FAR Part 23 certified which is the airworthiness standard for Normal, Utility, Acrobatic, and Commuter type aircraft. The spar is the main supporting member of the wing. $$e:$$ Oswald Efficiency Factor. It follows that larger wings of a greater planform area are able to produce more lift; this is easily shown mathematically from the lift formula: $$L:$$ Total Lift Force Wing shapes are, of course different with early PA28 having Hershey bar wing while later one have outboard portions of the wings tapered. There is no need to make the wing any stronger than it needs to be, and any excess strength (wing weight due to extra material) will reduce the payload capacity of the aircraft making it uncompetitive or uneconomic to operate. Thicker skins are advantageous as these are less likely to buckle under load. The secondary objective is to make the wing as light as possible without compromising the structural integrity of the design as described above. The spar caps are designed to the carry axial loads (tension and compression) that arise from the bending moment produced by the wing under load. Of course the Legacy has a much larger engine which allows it to reach a far higher cruise speed (drag is proportional to V^2), but the point still stands that an aircraft that is designed to cruise at higher speeds will do so most efficiently with a higher wing loading. The lift produced by the wing results in a large bending moment at the wing root that must be transferred to the wingbox (the structure that connects the wing to the fuselage). An example of the distributed lift load and resulting shear and bending moment diagrams arising from this loading is shown below. Today, I mocked up the right wing main spar cap strips and drilled cleco holes at the wing root and center splice locations to hold everything together. The spar caps are responsible for transferring the bending moment generated by the wing into the surrounding structure. Once the planform is frozen, a preliminary structural layout should be drawn up using the following rules of thumb: A layout for a simple rectangular wing is shown below taking into account the rules of thumb described above. Likely, most people involved in General Aviation are aware that the airworthiness directive is birthed by the harrowing crash of a Piper Arrow at a flight school in Daytona Beach, Florida. Usually our skins are thinner and softer than the spar caps, and they buckle first. Unless previous installed during compliance with SID57-10-10 or SID57-10-14 an approximately 7”x4” or 7”x8” (dependent on model) access panel must be cut in the lower skin to see the actual stub wing spar under it. The density of an aluminium alloy is approximately one-third that of steel which allows for thicker structural sections to be built from aluminium than would be possible with a steel structure of equivalent mass. There will be a minimum speed below which the wing is incapable of producing the full 54 000 lbs of lift and this is governed by the maximum lift coefficient of the wing and resulting stall speed. The foam traps moisture against the lower surface of the carry-thru spar cap, which can increase the development of corrosion. The FAA issued the AD, which affects model 401, 401A, 401B, 402, 402A, 402B, 402C, 411, 411A, 414, 414A, 421, 421A, 421B, 421C, and 425 airplanes, following a report of a fully cracked lower forward carry-through spar cap on a Textron Aviation 402C airplane (formerly a Cessna Aircraft Co. type certificate) caused by metal fatigue. 300+ aircraft were built, and in 2007 the CAP 10C is still in production as the CAP 10C NG. 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