Blue on Top Posted September 29, 2020 Report Share Posted September 29, 2020 5 hours ago, ArtVandelay said: I wonder how much of the wing strength is necessary to support the landing gear and the shock loads from hard landings. I believe the plane is dropped from several feet for certification testing. @ArtVandelayLanding gear loads are typically not an issue for the wing (spar). The airplane is required to take between a 7 feet/second drop up to a 10 fps drop, depending on the aircraft wing loading. This works out to be ~2.7G ... and a carrier landing is 10 fps. So, a "C" will have a lot lower requirement than a new Acclaim. Regretfully, the Mooney rubber donuts don't dissipate much of that load. In airplanes with hydraulic struts, some use an orifice and metering pin to reduce the load going into the wing (if required). Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted September 29, 2020 Report Share Posted September 29, 2020 4 hours ago, RobertGary1 said: Isn't that test just for seat G forces? The gear can push up into the wing and dump fuel and still pass I thought. -Robert @RobertGary1 LOL on the gear being allowed to come up through the wing and leak fuel. Although leaking fuel would be a great indication that the spar caps are bent. A Citation V upper spar cap was bent during one of the landing tests that we got too aggressive on. Via sled testing, newer seats are tested to 26G. Many of the US manufacturers will do it here in town at NIAR (National Institute of Aviation Research on the campus of Wichita State University). It's not cheap ... $1M+. These tests are required to meet the HIC (Head Impact Criteria) ... it must be shown that large and small bodies don't hit any structure during a crash. Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted September 29, 2020 Report Share Posted September 29, 2020 Oops, missed Vno. Vno is defined by the FAA as the maximum structural cruising airspeed. Basically, it is the result of effects on the airplane due to vertical gusts. In other words, vertical gusts will increase (upward gust) and decrease (downward gust) the aircraft angle of attack. At airspeeds below Vno, the airplane will stall before structural damage. At airspeeds above Vno, the airplane can be structurally damaged before it stalls. Since the FAA made the current regulations for gust requirements, many airplane wings are designed for the gust factor which is higher than the maneuvering load factor (3.8G in normal category). On the new M10 the gust load factor was 4.2G, which defined the strength requirement for the wing design. 1 Quote Link to comment Share on other sites More sharing options...
flyer338 Posted October 1, 2020 Report Share Posted October 1, 2020 I have copy of Flying magazine from 1961. The magazine has a test of the Mooney B model, the first all metal Mooney. The president of Mooney is quoted as claiming the B model was dive tested to 300 mph. Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted November 7, 2020 Report Share Posted November 7, 2020 On 9/30/2020 at 8:02 PM, flyer338 said: I have copy of Flying magazine from 1961. The magazine has a test of the Mooney B model, the first all metal Mooney. The president of Mooney is quoted as claiming the B model was dive tested to 300 mph. @flyer338If you can make an electronic copy of that article, I would love to read it (solutions@blueontop.com). I am definitely NOT questioning you. Interestingly, the Chief Engineer would have been Ralph Harmon. At that time, it would have been common to exceed redline (Vne) by 25 mph for flight characteristics (Vfc) and by 50 mph (Vd or Vdd ... long story) for flutter characteristics. The airplane must be flutter free out to 1.2Vd. 1 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted November 7, 2020 Report Share Posted November 7, 2020 11 minutes ago, Blue on Top said: @flyer338If you can make an electronic copy of that article, I would love to read it (solutions@blueontop.com). I am definitely NOT questioning you. Interestingly, the Chief Engineer would have been Ralph Harmon. At that time, it would have been common to exceed redline (Vne) by 25 mph for flight characteristics (Vfc) and by 50 mph (Vd or Vdd ... long story) for flutter characteristics. The airplane must be flutter free out to 1.2Vd. My ex airplane partner was from Minot and knew the Pietsch’s He said the the senior Pietsch (I forget his name) did all those dive tests. He would dive them at full power and do whatever he could to make them go as fast as possible. 1 Quote Link to comment Share on other sites More sharing options...
Hank Posted November 7, 2020 Report Share Posted November 7, 2020 1 hour ago, N201MKTurbo said: My ex airplane partner was from Minot and knew the Pietsch’s He said the the senior Pietsch (I forget his name) did all those dive tests. He would dive them at full power and do whatever he could to make them go as fast as possible. Woo-hooooo!! Giddy-up!!! Quote Link to comment Share on other sites More sharing options...
DMM Posted November 7, 2020 Report Share Posted November 7, 2020 I enjoy reading old Flying magazines on occasion. Is this the article? The author commented on the low VNE https://books.google.com/books?id=UVJTRxhEEo4C&pg=PA36&source=gbs_toc_r&cad=2#v=onepage&q&f=false August 1961 6 Quote Link to comment Share on other sites More sharing options...
carusoam Posted November 7, 2020 Report Share Posted November 7, 2020 Great find DMM... let’s send a notice to @Blue on Top Further into the magazine... is an article written by an author, Jules Bergman... Jules wrote a book in the late 60s(?) titled ‘Anyone Can Fly’... Some guy left that book lying around my house... he had two books... The other one must have been Anyone Can Sail.... I used the Jules Bergman book to learn about flying... Best regards, -a- 2 Quote Link to comment Share on other sites More sharing options...
N201MKTurbo Posted November 7, 2020 Report Share Posted November 7, 2020 9 hours ago, DMM said: I enjoy reading old Flying magazines on occasion. Is this the article? The author commented on the low VNE https://books.google.com/books?id=UVJTRxhEEo4C&pg=PA36&source=gbs_toc_r&cad=2#v=onepage&q&f=false August 1961 I loved the classifieds in the back, you can buy a T6 for $3400! Quote Link to comment Share on other sites More sharing options...
cliffy Posted November 7, 2020 Report Share Posted November 7, 2020 Engineers and/or materials sometimes don't meet first guesses Boeing made a calculation mistake in the 787 wing. When they went to ultimate failure test it broke (IIRC) at @98% of what was calculated. First time Boeing had a wing break below their calculations. First time also with a composite spar and not metal. The feds let them strengthen it by calculations and not do another wing break test. 1 Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted November 7, 2020 Report Share Posted November 7, 2020 Great article. Loved it! The mention of 230 HP and the twin didn't become production reality, but this was the beginning of Ralph Harmon's time as Chief Engineer (and his son, too). Btw, Al Mooney turned Hoffman down to metalize the airplane. I would guess the 330 mph is a typo ... and should be 230 mph. I don't know the early M20 Cd, but 330 is probably beyond terminal velocity (weight = thrust = drag ... straight down). The propeller would probably be creating drag at 330 mph. The other airspeed numbers seem reasonable. The climb rate going from 900 fpm to 200 fpm over 10 mph sounds excessive, but just a reminder to FLY THE PUBLISHED SPEEDS!!! (LOL, LOL, LOL) Six (6) G for the wing is not outstanding, either. It had to take 5.7 to certify. I LOVE this stuff! 2 Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted November 7, 2020 Report Share Posted November 7, 2020 3 minutes ago, cliffy said: The feds let them strengthen it by calculations and not do another wing break test. Almost a perfect wing! Anything over 100% is a weight penalty. Ummmmm ... like a Mooney. Ironically, a metal wing on the 787 would be lighter ... but it would have corrosion. On little airplanes, the 98% would be a weight penalty because the thickness of the failure parts would have to go up to the next standard material thickness ... adding weight. Oh, on the 787 wing a couple years of material were added ... to hundreds. Quote Link to comment Share on other sites More sharing options...
flyer338 Posted November 9, 2020 Report Share Posted November 9, 2020 On 11/6/2020 at 7:52 PM, DMM said: I enjoy reading old Flying magazines on occasion. Is this the article? The author commented on the low VNE https://books.google.com/books?id=UVJTRxhEEo4C&pg=PA36&source=gbs_toc_r&cad=2#v=onepage&q&f=false August 1961 I have been away, or I would have responded sooner. That is the article. I suspect @Blueontop is correct and the 330 mph claim was a typo. 1 Quote Link to comment Share on other sites More sharing options...
Rszent Posted August 8, 2021 Report Share Posted August 8, 2021 This is awful how did the wing fail?? The aircraft was on an IFR flight no abrupt attitude changes all within speed limitations. But as you can see a spar failure ??? Quote Link to comment Share on other sites More sharing options...
ArtVandelay Posted August 8, 2021 Report Share Posted August 8, 2021 This is awful how did the wing fail?? The aircraft was on an IFR flight no abrupt attitude changes all within speed limitations. But as you can see a spar failure ???I think the right wing hit first, you can see the fuel spray, the shock destroyed the spar. The next frame shows only the tail, it literally pancakes, fuselage collapses, it must have been dropping extremely fast. There is a pole in the foreground, and wires, so I don’t know. Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted August 10, 2021 Report Share Posted August 10, 2021 On 9/28/2020 at 5:42 PM, ArtVandelay said: And our engines are held on by 4 such bolts. :-) Yes, but I believe the tail bolts are in shear and the engine mounting tension, shear loading is much, much stronger than tension. The Wings on a U-21 which is a Beech Queen Air are held on by three bolts, two for lifting up. and only one for neg G’s, they are in tension as well. Many helicopter rotor systems are held on by one nut. ‘Just silly observations. Unless I’m mistaken but Va has nothing to do when something will break, it’s simply when a full, rapid control movement will exceed Certified G limits. Even G limits really don’t necessarily have anything to do when something will break, Normal category aircraft are if memory serves are Certified to +3.8 and -1.52, doesn’t mean anything happens at those G numbers, just that the aircraft can handle Ultimate load, which again by memory is 1.5 times that amount without failing, it is allowed to bend or deform at ultimate, just not break, for three seconds anyway. ‘Some aircraft are much stronger than min required, some just barely meet the requirement, but ALL meet it. Most are I’d say well exceed it as it’s real hard to design to barely pass, it’s much easier to design to be much stronger so that if your off a little, you still pass, redesigning is expensive, costs weight though. What is not accounted for, at least I’m sure what isn’t accounted for in CAR3 aircraft is aging and fatigue,so it’s prudent for a manufacturer to well exceed min requirements for new parts so that when they accumulate thousands of fatigue cycles and decades of aging, that they are still strong enough. Want to bump Va to a higher number? It’s simple just turn control authority down to min required, Va will go up as control authority goes down. Of course you can’t do that will all types of aircraft, some require more maneuverability than others. 1 Quote Link to comment Share on other sites More sharing options...
PT20J Posted August 11, 2021 Report Share Posted August 11, 2021 On 8/10/2021 at 7:35 AM, A64Pilot said: Yes, but I believe the tail bolts are in shear and the engine mounting tension, shear loading is much, much stronger than tension. I think that's backwards. Most bolts are loaded in tension, and generally shear strength is not specified. But, according to The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8): “As an empirical guide, shear strengths of carbon steel fasteners may be assumed to be approximately 60 percent of their specified minimum tensile strengths. For example, an SAE grade 5 hex cap screw has a specified minimum tensile strength of 120,000 psi. Therefore, for design purposes, its shear strength could be reasonably assumed to be 70,000 psi.” 3 1 Quote Link to comment Share on other sites More sharing options...
Blue on Top Posted August 11, 2021 Report Share Posted August 11, 2021 All fasteners should be designed for shear and not tension. If possible, double shear is much better, too. Double shear, like wing attach bolts, are relatively small compared to what would be required in tension. In comparison, it would be MUCH easier to pop the head off (or strip the threads) of an AN-5 bolt than it would be to shear it in half in two places. Double shear means that there is supporting material on both sides (or the joint is symmetrical without a bending moment at the fastener). In addition, speaking of wing attach bolts, they don't need to be tight, tight, as there should be no load in the tension or compression directions. This is why when riveting 2 aluminum skins together, there is a minimum thickness to countersink the material. Below those values the skins will simply shear the rivet in half. Some thin skins are intentionally dimpled to gain surface area against the skin being able to shear the rivet. If the load was in tension, the skin would simply tear around the rivet head (or pop the head off). 1 1 Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted August 11, 2021 Report Share Posted August 11, 2021 (edited) 6 hours ago, PT20J said: I think that's backwards. Most bolts are loaded in tension, and generally shear strength is not specified. But, according to The Industrial Fastener Institute (Inch Fastener Standards, 7th ed. 2003. B-8): “As an empirical guide, shear strengths of carbon steel fasteners may be assumed to be approximately 60 percent of their specified minimum tensile strengths. For example, an SAE grade 5 hex cap screw has a specified minimum tensile strength of 120,000 psi. Therefore, for design purposes, its shear strength could be reasonably assumed to be 70,000 psi.” No, read the below post. ( on edit, actually the above post by Blue on Top) I first ran into this specifically on our old wing spice joint where the bolts were in tension, much easier for manufacturing, but the splice joint was weaker than the later wing that “pinned” on with a large pin in shear. Edited August 11, 2021 by A64Pilot Quote Link to comment Share on other sites More sharing options...
A64Pilot Posted August 11, 2021 Report Share Posted August 11, 2021 (edited) Things get counterintuitive, The lower spar cap on a 500 Gl newer Thrush is massive, it’s a 3 inch by 3 inch solid 4340 steel section, has to be for a 10,500 lb aircraft to be continually maneuvering at the G level crop dusters do, for a life limit with scatter factors of 60,000 hours. However those massive spar caps and of course the whole spar is attached to the fuselage by two 1/8” x 3” aluminum angles with four .25” bolts in shear, these were mis drilled so I had the paint shop paint them for me to use as chocks. If you saw that massive spar cap, it’s so massive as the older smaller one broke several times of course killing the pilots and ended up with AD’s and a 5400 life limit, it’s just not logical that they are attached to the aircraft with aluminum angles and four .25” bolts, but that’s why I’m a test pilot and not an Engineer The attach angles didn’t change with the stronger wing. Edited August 11, 2021 by A64Pilot Quote Link to comment Share on other sites More sharing options...
PT20J Posted August 12, 2021 Report Share Posted August 12, 2021 3 hours ago, A64Pilot said: No, read the below post. ( on edit, actually the above post by Blue on Top) I first ran into this specifically on our old wing spice joint where the bolts were in tension, much easier for manufacturing, but the splice joint was weaker than the later wing that “pinned” on with a large pin in shear. Sorry for any confusion. I was responding to your comment that a bolt in shear is much, much stronger than a bolt in tension. Steel has greater tensile strength than shear strength. I learned that in my first year undergraduate strength of materials course. (Why can I remember stuff like this from 50 years ago, and I can't remember where I left my car keys last night?) However, as @Blue on Top noted, a joint designed for shear loads can be strengthened by designing it for double shear which requires three layers of material appropriate loaded such that there are two shear planes. I don't know for certain, but I do not believe that the tail cone attachments are designed this way. Here's a document that does a much better job of explaining all this than I can. Skip Article - Bolted Joint Design.pdf Article - Bolted Joint Design.pdf 1 1 Quote Link to comment Share on other sites More sharing options...
Guest Posted August 12, 2021 Report Share Posted August 12, 2021 The tail section is held on with two double shear fittings. Clarence Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 12, 2021 Report Share Posted August 12, 2021 In the machine world… which may be different than the aviation world… Some bolts are designed for use in tension, vs. others to be used for shear… The bolts holding my M20C’s engine to the fire wall were tiny with a very fine thread… They seem to be doing both…. Supporting the weight against gravity… and the thrusts against drag… One thing for sure… use the exact bolt that was intended to be used in that location… No matter how hard it is to get a replacement… Fastener guesses have caused a few engine failures…. Around here… Like the guess that thought re-use of star washers was a good idea… (dollar category) Or the re-use vband clamps on turbo exhaust systems… (AMU category) One drops the magneto off of the engine… the other allows exhaust gasses to escape under high temp and pressure… blow torch style… +1 on knowing your hardware… accept no substitutes… When it comes to dimensions… Standard hardware also has a range in diameters… Speaking of wing bolts…. Yooper Tom’s turbine plane had a squeaky wing bolt… upon investigation… he found the diameter of the bolt was on the low side of the range… he replaced the bolts… hand selecting their diameters…. Go MS! Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
carusoam Posted August 12, 2021 Report Share Posted August 12, 2021 As far as why we can remember some details clearly… But can’t remember what we had for lunch… or where Skip’s car keys are… The location for some memories is different than others…. Every day memories are in an area that isn’t well fed by the blood stream… Important memories are closer to the fresh O2 stream… The older you get, more of those not well fed memories are dying from starvation… So… get up, walk about, get that heart rate going… preserve those memories! PP thoughts only… not a brain doctor… Best regards, -a- 1 Quote Link to comment Share on other sites More sharing options...
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