Analysis of Aircrfat Engine Mount Loads

Hi,
I am looking for a text book or paper that can take me through the stress analysis of the loads a mult-engine turbo-prop and or radial engine will put
into the wing supporting structure. I am sure thirty or fourty years ago such references were commonly available, but they sure are hard to find now. Can anybody help me out?
Regards,
Steve __________________________________________________________________ Stephen Hall Celeris Aerospace Canada Inc. ICQ#: 9011995 Current ICQ status: ( Work Tel#: (613) 837-1161 7 Fax#: (613) 834-6420 + More ways to contact me i See more about me: __________________________________________________________________
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Stephen, Some of the "old" guys all used an old book written in the 50's but I cannot recall the title nor the author. However, I would advise to have a look at the FAA certification rules first which require that your structure must survive a, I think, 10G vertical load and a 3-4G longitudinal load. There were also angular velocity such as 1 rad/s too. I bet that these are the largest loads that the mounts will have to survive to. These are the modern requirements but I don't know the 50's or 60's requirements.
Hope this help.
Gilles Carrier
Stephen Hall wrote:

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Gilles,
If you could locate a reference to the book sometime it would be appreciated. My problem is not so much that of meeting the FAA requirements but rather that of assessing the reasonableness of the data I am obtaining from a strain gauge rosettete attached to the lower spar cap of an operational aircraft. In particular I am trying to estimate the sort of contributions I can expect from reacting the engine loads
Thanks for your help.
Regards,
Steve

put
now.
Stephen
Work
See
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They are evidently lower than you expected. I still recall a Rolls development engineer telling me that one of their (earlier) jet engines was hung on a single quarter inch bolt.
Brian W
wrote:

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That sounds a bit small on CSA but I believe that engines are weak mounted to break away in the case of a crash. The weak axis is probably in a longitudinal direction though rather than vertical.
John
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John Manders wrote:

The very first RR turbojet was, I think, the Welland, which produced 1700 lbf of thrust, and probably had a thrust to weight ratio of 1.3
If you want to hang that off a 1/4 inch bolt, fair enough. Strictly speaking you can hang any weight off a single bolt in shear, if you think about it.
As to the original question - if you know the max torque of the engine, and the reduction box ratio, then the overall torque exerted on the airframe can be worked out. If you know how far the mounting bolts are apart this will give you a good idea of the loads in the airframe.
Other loads will be the inertial loads due to maneuvers, and the higher frequency (crankshaft speed and above) vibrations due to the internals of the engine. I doubt you are interested in the latter, the former will be roughly engine mass* g rating of the aircraft.
Cheers
Greg Locock
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On Wed, 24 Dec 2003 23:55:27 +0000, Greg Locock

///
weight 1308 lb thrust 1700 lb
vectored: 1 ton
Load factor 4 (about right for commercial jet structure)
Stress from 4 tons on 1/4 in bolt: 82 tons.
So a 1/4 in bolt in 100 ton steel is slightly over specified. But that WAS Rolls-Royce!
:-)
Brian W
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Brian Whatcott wrote:

You didn't succumb to my trolling. Damn. Happy Christmas Brian.
Cheers
Greg Locock
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On Thu, 25 Dec 2003 08:33:57 +0000, Greg Locock

Ah yes: you too. This is a happy moment. No wars blowing up too badly. A chance at health care for the needy. A chance at a yacht for the not so needy. Merry Christmas - and may your equable nature be matched by your plush lined wallet next year.
Brian W
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Let's see where I went wrong, shall we?.....
On Thu, 25 Dec 2003 17:25:27 GMT, "Don Phillips"
///

[Don Phillips]

Hmmm... let's see where I went wrong, then.
you multiplied 82 tons by 2000 to preoduce a stress of 164,000 psi
Then you divided this stress by the area of the bolt to calculate the limit load: Area of 1/4 in diam bolt = 0.049 square inch Let's call it 1/20 sq in.
So you concluded that if one square inch of steel can handle 100 tons 1/20 square inch should be able to take a 1671 ton load.
I don't think so. Do you?
I'll leave you to work out this correction on your factor of safety calculations. (Remember that in those far off days, by the way, the British used a ton of 2200 pounds. Their hundredweight (cwt) was 112 pounds. Their quarter was 28 pounds their stone was 14 pounds)
Good riddance to Imperial units!

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Don, you are embarrassing youself now.
Just sit back, relax, and realise that you are wrong, and I will explain again why you are wrong.
A load of 1 British ton is applied to a 1/4 inch diameter bolt by an early Rolls-Royce engine.
Suppose the bolt is made of a 100 ton steel - that is to say a steel with a yield strength of 100 British tons per square inch.
1/4 inch diameter is about 1/20 of one square inch in cross-section. So the maximum force allowable on that bolt is 1/20th of 100 tons.
1/20th of 100 tons is 5 tons.
But the load is one ton. And a relevant design factor is X4 or 4 tons.
So the factored load is four tons and the max allowable is 5 tons, so the bolt is overspecified by about 1/5th.
NOW do you get it?
Brian Whatcott Altus OK p.s. In case that doesn't get through, I annotated your calculations below.
On Sat, 27 Dec 2003 00:59:47 GMT, "Don Phillips"

Perhaps so: but its one ton on a 1/4 inch bolt!

Good! You understood that I meant the term "100 ton steel" to imply that number is specifying its maximal stress. And calling 100 tons/sq in = 200 kips is OK in an American context. So far, so good..

Although your units looked a little messy, you are saying the maximum allowable force on a quarter inch diameter bolt in this material is 10,000 pounds.
That *IS* what you wrote, isn't it?

Now this is where you go off the track. Remind yourself: the actual load is about 1 ton, and the allowable load is 10,000 pounds or 5 tons.
I'll write that again: the actual load on the bolt is about 1 ton, and the allowable load on that bolt is 10,000 pounds or 5 tons.

No,no,no,no!
allowable load 10000 lb actual load 2100 lb Factor of Safety about 5
An engineer cannot allow the actual stress to exceed the allowable stress Allowable stress 100 ton /sq in Actual stress is about 1 ton on 1/20 sq in or 20 ton/sq inch.

NO again! You worked out the actual load yourself, in an earlier post. You made it 2100 lbs. Remember?
Actual load X 4 = 8400 pounds.....

Wrong yet again.
Actual load = 2100 lb allowable stress (say ) 200,000 psi Required area is 2100/200000 = 0.01 sq inch

So you concluded after being told of an error, that the required number of bolts is now sixty-seven!
Good grief!
Alright, I am not going to be snide, or personal: but I should ask one question: what specialty of engineering did you pass the P.E in, and in which state?
Does it even make sense to you (or any engineer) that you would hold up a load of one ton with sixty seven quarter inch bolts?
Brian Whatcott Altus OK
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I hate to butt in to a good argument...
If Brian will agree that a load of 84 tonnes would need about 20 1/4 " bolts, and Don will agree that a 1 tonne load can be held by a single 1/4" bolt then all that remains is to specify the engine force.
At one point the stress from a 1 ton load was calculated to be 84 ton / in^2, but was noted as 84 tons.
I think Don took this to be the force of the engine...........
I still find it surprising that a ton load can be supported safely on a single 1/4 inch bolt, but then I mainly use stainless bolts, with a UST of 45 ton / in^2, and a yield of about 15.
Is a 100 ton bolt able to take this stress without yielding ?? -- Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
To reply remove AT
wrote:

produced
1.3
steel
typically
definition,
kips).
lbf
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Ah, the voice of reason appears....
On Sat, 27 Dec 2003 11:51:43 -0000, "Jonathan Barnes"

Yep, I can easily agree that 20 1/4 bolts of 100 ton steel can hold a load of 84 tons. Or you could use one bolt of just over 1 inch diameter: say 1 1/16 diam - for this unfactored load.
But I would expect a P.E to note that a one tonne load could be held by a 1/8th in diameter bolt (one eighth inch) in 100 ton material.

Actually, aircraft designers take a bare load, and multiply it by an expected g loading which varies for different classes of aircraft then apply a factor to reflect the uncertainties of production, installation and maintenance. So the actual stress on a 1/4 inch bolt from a 1 ton (say 2000 lb) load is really only about 20 X 2000 = 40,000 psi but it needs to be factored. I factored with X4 to put the upper working stress at about 160,000 psi. This is nicely contained by a 200,000 psi yield material

His working was frankly, too muddled for me to be sure.

I will ignore the implication that I would talk about unobtainium, and simply list some of the commonly obtainable 100 ton metals: Of those listed, 31 materials have tensile strength to yield of 250,000 psi or greater. These include "120 ton steels" and copper alloy(!), stainless alloy, beryllium nickel alloy (!), cobalt alloy, titanium alloy in appropriate heat treat conditions.
[ The results of a matweb search at <http://www.matweb.com ]
1 AISI Grade 18Ni (200) Maraging Steel, Aged, 16 mm round bar, tested in longitudinal direction [various other heat treats and sheet sizes excluded]
39 AISI Grade 18Ni (350) Maraging Steel, Aged, at RT, tested longitudinal, round bar 16 mm [various other heat treats and sizes excluded]
47 AISI 4140 Steel, oil quenched, 205C (400F) temper, 25 mm (1 in.) round [various tempers and variants excluded]
56 AISI 4340 Steel, oil quenched 845C, 650C (1200F) temper, tested at -195C (-320F) [various tempers and variants excluded]
74 Beryllium Copper, UNS C17200, TH04 Temper 75 Beryllium Copper, UNS C17300, TH04 Temper 76 Copper, UNS C71700 77 ASTM 897 Grade 5 (230-185-00), Austempered Ductile Iron 78 79Pt-15Rh-6Ru; Alloy 851 79 ASTM A228 80 AISI Type H11 Hot Work Tool Steel, air or oil quenched from 995-1025C 81 AISI Type H13 Hot Work Tool Steel, air or oil quenched from 995-1025C 82 AISI Type S1 Tool Steel, quenched 955C (1750F), tempered 150C (300F) 83 AISI Type S1 Tool Steel, quenched 955C (1750F), tempered 250C (500F) 84 AISI Type S2 Tool Steel, austenitized 845C (1550F), brine quenched to 55 HRC 85 AISI Type S5 Tool Steel, austenitized 855-870C (1575-1600F), oil quenched to 55 HRC 86 AISI Type W1 Tool Steel, water quenched at 775C (1425F), tempered 350C (660F) 87 AISI Type W2 Tool Steel, water quenched at 775C (1425F), and tempered 88 Titanium Beta C ST 815C, Aged 425C 89 Titanium Beta-CEZ ST 830C (1525F), Aged 550C 90 Titanium Beta-CEZ ST 860C (1580F), Aged 550C 91 Titanium Ti-6Al-2Sn-4Zr-6Mo STA-2 92 AISI A6, Type Tool Steel, austenitized 830-870C (1525-1600F) 93 AISI A9, Type Tool Steel, tempered at 500C 94 Vasco 4340 Specialty Steel, Heat Treatment: 899C (1650F) Q+T 95 Vasco D6AC Specialty Steel, Heat Treatment: 913C (1675F) Q+T 96 Vasco 9-4-30 Specialty Steel, Heat Treatment: 899C (1650F) + Age 97 VascoMax C-250 Specialty Steel, Heat Treatment: 927C (1700F) + Age 98 VascoMax C-300 Specialty Steel, Heat Treatment: 927C (1700F) + Age 99 VascoMax C-350 Specialty Steel, Heat Treatment: 927C (1700F) + Age 100 VascoMax T-250 Specialty Steel, Heat Treatment: 816C (1500F) + Age 101 Vasco 13-8Mo Precipitation Hardening Steel, Heat Treatment: 927C (1700F) + Age 102 Vasco 455 Specialty Steel, Heat Treatment: 829C (1525F) + Age 103 Vasco 440 C UNS S44004 Specialty Steel 104 Nickelvac 43-40 UNS G43400, UNS H43400 Specialty Steel 105 Nickelvac D6AC UNS K24728 Specialty Steel 106 VascoMax T-200 Specialty Steel 107 Brush Wellman Beryllium Nickel Strip - Alloy 360 1/2 Hard, 1.5 hr at 950F
113 Brush Wellman Beryllium Copper Alloy 25 Plate & Rolled Bar; HT (TH04) Temper; over 9.5 to 25 mm Thickness (UNS C17200)
115 Brush Wellman Beryllium Copper Alloy 25 Wire; 1/2HT (TH02) Temper; 1.3-12.7 mm Diameter (UNS C17200)
123 Carpenter Custom 455 Stainless Steel, Condition H900 (Age Hardened 482C)
125 Carpenter Custom 450 Stainless Steel, Condition H900 (Age Hardened 482C); Tensile/Impact Properties at -196C
129 Carpenter MP35N* Ni-Co-Cr-Mo Alloy, 55% Cold Reduction
141 Carpenter Custom 630 (17-Cr-4Ni) Precipitation Hardening Stainless Steel, Condition H 1100 (Heated 593C); Tensile Properties at -196C 142 Carpenter AerMet-for-Tooling Tool Steel, Double Aged 468C 144 Carpenter Extendo-Die Hot Work Die Steel, Tempered 560C
147 Carpenter Pyrotough 78 Hot Work Die Steel 148 Carpenter R.D.S. Alloy Tool Steel (Oil-Hard) (AISI L6) 149 Carpenter No. 484 Alloy Tool Steel (Carpenter Air-Hard) (AISI A2) 150 Carpenter Vega Alloy Tool Steel (Air-Tough) (AISI A6) 151 Carpenter No. 883 Hot Work Die Steel (Red-Tough) (AISI H13) 152 Carpenter S7 Alloy Tool Steel (AISI S7)
159 Elgiloy Co-Cr-Ni Alloy, Wire, 40% Cold Reduction, Heat Treated
167 Special Metals INCONEL 718SPF Nickel Superalloy, Annealed + Aged 168 Special Metals UDIMET Alloy 250 Maraging Steel 169 Allegheny Ludlum Stainless Steel Type 201, 60% Cold Work (UNS S20100)
173 Allegheny Ludlum Martensitic Stainless Steel Type 425 Mod, Hardened + 204C Temper
180 Alloy C-22, 60% Cold Worked
188 Alloy 718, 50% Cold Worked, Aged
191 AISI Type 308 Stainless steel, cold drawn wire, full hardened, 0.53-3.18 mm diameter
195 AISI Type 347 Stainless Steel, cold drawn wire, full hard, 0.53-3.18 mm diameter
197 AISI Type 348 Stainless Steel, cold drawn wire, 75% hard, 0.53-3.18 mm diameter 200 AISI Type 420 Stainless Steel, hardened and tempered bar
AISI Type 660 Stainless Steel (A286) room temperature, cold drawn wire diameter of 2.84 mm, aged at 480C (900F)
204 AISI Type S13800 Stainless Steel (PH 13-8 Mo) longitudinal properties, condition RH950
207 AISI Type S14800 Stainless Steel condition SRH950, tested at -73C (-100F) 208 AISI Type S14800 Stainless Steel condition SRH950, tested at 27C
220 AISI Type S15500 (15Cr-5Ni) Precipitation Hardening Stainless Steel tested at 425C (800F), condition H925
223 17-7 PH Stainless Steel, CH900, plate, sheet, and strip 224 AISI Type S20910 Stainless Steel, 6.4 mm diameter rod, annealed at 1120C, 60% cold reduction
226 AISI Type S21800 Stainless Steel tested at RT, 70% cold reduction 227 AISI Type S24100 Stainless Steel 6.4 mm diameter annealed rod, 50% cold reduction
229 AISI Type S45000 Stainless Steel, 25 mm diameter bar, tested at -195C (-320F), aged at 480C (900F) 230 AISI Type S45000 Stainless Steel, 25 mm diameter bar, tested at -195C (-320F), aged at 565C (1050F)
232 AISI Type S45500 Stainless Steel, hardened at 480C (900F) for 4 hours, air cooled, 25 mm (1 in.) round
242 AISI Type O1, Oil-hardening Tool Steel, oil quenched at 800C, tempered at 425C 243 AISI Type O2, Oil-hardening Tool Steel, oil quenched at 800C, tempered at 260C
[end]
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I emphasise that from my reading of both your calculations Don is working on an engine force of 84 tons.

I'm sorry to have given the impression that I thought 100 ton steel was not obtainable.
My work is in the area of bottling equipment, in the drinks industry. weight is never important, but the machinery is maintained by gorillas equipped with worn adjustable spanners.... It's not unusual for me to use 2 x M6 ( approx. 1/4" ) stainless grade A2 bolts simply to hold a limit switch bracket in position.
I am constantly amazed by what can be done with materials.
Most people will not believe a perfectly ordinary piece of paper rolled to give a long cylinder, held with a couple of elastic bands will support a full 2 l drinks bottle.
I digress... :-)
To return to my original question, is the 100 tons a yield, UTS, or working load ?
Jonathan
Barnes's theorem; for every foolproof device there is a fool greater than the proof.
To reply remove AT
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On Sat, 27 Dec 2003 18:24:59 -0000, "Jonathan Barnes"

The hundred thirty plus materials I excerpted in a post earlier today were selected for tensile strength at yield point of at least 200,000 psi. I mentioned that more than 30 of these, would not yield until stressed to 250,000 psi or more.
I urge you to register with the material properties site I mentioned earlier - it is a useful resource. You have no need to take my word for such things as yield strengths.....
It is typical of high performance materials in this class that the yield point is not far below the ultimate, however.
It is also true that aluminum alloys in aerospace service often do not have a well defined knee at yield. For these, it is customary to specify the 0.1% yield stress.
Ultimate Tensile Strengths of engineering materials are all but unused in aerospace applications. Yield point is never intentionally exceeded. (This contrasts with some other structural design fields where the ductile nature of lower performance steels allows some load sharing in less than perfectly built structures as bolts etc. stretch)
Did this response answer your question understandably?
Brian Whatcott
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mounted
Fuse pins react a shear load which in a crash would tend to be upwards and rearwards. On Boeing commercial widebody airplanes, the engine struts are held on by four fuse pins. One in the front spar pitch load fitting, two in the midspar fittings on the lower wing and one in the aft drag brace fitting also on the lower wing. There is another fitting on the lower front spar/wing surface that reacts side load and prevents fitting flange bending loads on the other fittings as well as acting as a fail-safe for failure of one of the fuse pins. Development of loads is achieved by consideration of engine weight and thrust and inertia loads from operation of the aircraft and is not any easy thing. Fatigue spectrum loads being one consideration and protection of the wing structure under ultimate conditions (fuse load) being the other.
Phil Holman
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