Author Topic: RW materials question for the Whiffverse:  (Read 16474 times)

Offline Daryl J.

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RW materials question for the Whiffverse:
« on: January 04, 2014, 08:18:51 AM »
The question: at what speed is it better to use titanium instead to aluminum in an airframe?  The follow-on question:  is it possible to have the high friction areas be titanium instead of aluminum on airframes, presuming an existing platform is being subjected to modifications?

Yes, this is a recce Phantom question. :)

Greg and I was chatting at the Spruce Goose Museum last year and he told of a certain high speed run that ruined some newly applied paint.   And there are rumors of some very high speed events with Syrian MiG-25s and Israeli Phantoms.   It kicked my OCD/AMS (aka imagination) in to gear.  :D.   And the Academy thin wing Phantom showed up today.  Mmmmm!  Thus the questions.

Thanks in advance,
Daryl j.
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Offline Cliffy B

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Re: RW materials question for the Whiffverse:
« Reply #1 on: January 04, 2014, 08:56:22 AM »
Keep in mind I'm not a metallurgist or aeronautical engineer but just considering the melting points of the two metals in question I'd go with titanium in the high heat areas and definitely not aluminum.  Aluminum will melt at around 1,200 degrees Fahrenheit and titanium at over 3,000.  If you can carry the extra weight, use the titanium.

Again, just the opinion of whiffer and Google  ;D
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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #2 on: January 04, 2014, 09:18:57 AM »
I'm thinking in terms of heat resistance, yes, but also things like coefficients of expansion, stiffness compatibilties, galvanic corrosion resistance, etc.   I'm utterly oblivious.   :-[

As little time as I have to model any more and given that I prefer a Near-RW Whifbuild, having something reasonably plausible it is the goal.   Ah, the things I choose to torment myself with!  ;D

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Offline Cliffy B

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Re: RW materials question for the Whiffverse:
« Reply #3 on: January 04, 2014, 09:19:59 AM »
Since it'll be high heat, it'll probably be unpainted right?  Just paint various natural metal shades and call it a special "alloy".  See, problem solved  ;D
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #4 on: January 04, 2014, 03:22:20 PM »
Biggest problem in substituting titanium for aluminum is that you suddenly have all sorts of galvanic corrosion potentials that you didn't have before and you may need special sealants and/or surface finishes.  That's something I deal with a fair bit, given that I'm currently working with structure around propulsion systems.

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #5 on: January 04, 2014, 04:49:12 PM »
Thought so.   Thanks.
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Re: RW materials question for the Whiffverse:
« Reply #6 on: January 04, 2014, 04:55:41 PM »
Interestingly though plastics reinforced with carbon fibers can induce galvanic corrosion in attached aluminum components.  This is one of the reasons why Titanium is finding greater application in platforms like the F-35 and 787.  Titanium does not suffer to the same extent.
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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #7 on: January 04, 2014, 05:07:40 PM »
Well how about that.   That was the next question.

Going back to all aluminum, are there ceramic coatings that adequately deflect/absorb heat that can be used on leading edges and other high heat areas?   
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Offline kitnut617

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Re: RW materials question for the Whiffverse:
« Reply #8 on: January 04, 2014, 11:28:39 PM »
Some time ago I was reading an article in a motorcycle magazine, it was about futuristic MotoGP engines that would rev to over 25,000 rpm (or even higher).  The plan was to use ceramic pistons, valves, heads and cylinder liners because of the heat generated while operating at these elevated rpms.  I don't know what ceramic was involved though --

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Re: RW materials question for the Whiffverse:
« Reply #9 on: January 05, 2014, 03:18:06 AM »
Another option (rather than simply change materials) is to introduce an active cooling system for the affected parts, probably using fuel as a coolant.
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Re: RW materials question for the Whiffverse:
« Reply #10 on: January 05, 2014, 03:22:00 AM »
It might depend upon the intended operational profile.  If only expecting to experience short term high temperatures, one might just as easily utilise an ablative coating to the affected areas - this could be replaced during BF/AF maintenance perhaps.  If however one wanted to deal with far longer term operations, one could consider some of the coatings utilised in gas turbine engines.
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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #11 on: January 05, 2014, 04:05:26 AM »
Useful info.    :)

Thanks!

Where I hope to take this is a Photo Phantom variant with shorter high speed dashes available to it say, for instance, the higher Mach 2's. Alternative intakes, materials where appropriate,  recce setup, and nation of use.     Kit of choice is the Academy F-4B for the thin wing.   Eventually.
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Re: RW materials question for the Whiffverse:
« Reply #12 on: January 05, 2014, 04:24:04 AM »
I assume something in the '60s/'70s era?
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Re: RW materials question for the Whiffverse:
« Reply #13 on: January 05, 2014, 04:35:48 AM »
Speaking of ablative coatings on aircraft, the X-15 is probably the most extreme example - click on image for more details:

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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #14 on: January 05, 2014, 04:51:33 AM »
Quote
I assume something in the '60s/'70s era?

Correct.
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Re: RW materials question for the Whiffverse:
« Reply #15 on: January 05, 2014, 04:55:39 AM »
Then I would tend to simply go with some form of ablative coating that gets reapplied to key areas (e.g. nose, wing leading edges etc) before each flight envisioning high speed runs.  You might only need to do this if contemplating Mach3+ runs though).

BTW, another way to get the high speeds envisioned (and to have something visual on the model itself) would be to add in some sort of rocket booster - maybe as a belly attachment?
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #16 on: January 05, 2014, 11:22:20 AM »
Interestingly though plastics reinforced with carbon fibers can induce galvanic corrosion in attached aluminum components.  This is one of the reasons why Titanium is finding greater application in platforms like the F-35 and 787.  Titanium does not suffer to the same extent.
Oh, ghod, that's so true.  We have to take great care on finishes and sealants, of fasteners even, on the V-22.  When we release drawing/design packages, Materials and Processes is the first group to see them simply so that they can make sure we've got the finishes and sealants properly specified and applied.

Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #17 on: January 05, 2014, 11:50:10 AM »
BTW, another way to get the high speeds envisioned (and to have something visual on the model itself) would be to add in some sort of rocket booster - maybe as a belly attachment?
Perhaps in conformal units above the inlets?  That would take some careful alignment of the exhaust vectors, though, to keep things controllable.  An under fuselage pallet that would pick up the centerline hardpoints would work well, too, and the nozzle could nestle in-between the two J79 nozzles and look good there.

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #18 on: January 05, 2014, 12:07:50 PM »
Good ideas all but I want a Mcdonnell Model 98 that gives the educated Phantom fan a double take...the one where they wonder how/why they missed knowing about that version.      ;D


And I wish I'd never tossed my Aurora F4H kit away when leaving for Undergrad.   :icon_nif:   


That all being said, wouldn't a belly rocket booster leave an easily seen exhaust plume?   Even if operating at 60-65,000 feet?
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Re: RW materials question for the Whiffverse:
« Reply #19 on: January 05, 2014, 12:13:43 PM »
Not necessarily...it could be used in a boost-coast profile.
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #20 on: January 05, 2014, 12:17:25 PM »
Depends on what you're using for fuel and oxidizer in the rocket.  You really can't help but leave some kind of trail, be it rocket exhaust or just condensation into contrails (if you should happen to burn LH2 & LOX).  You need to remember that your thrust vector needs to go through the aircraft cg, or reasonably close, for controllability reasons (they found this out on one ZELL test using a F-100, the test was delayed and the fully-loaded test aircraft sat in the sun all day; when they did launch, differential thermal expansion had moved the cg and the pilot had quite a wild ride).

Offline Cliffy B

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Re: RW materials question for the Whiffverse:
« Reply #21 on: January 05, 2014, 12:26:11 PM »
How about using the rocket booster to get up to speed only and not maintain the speed?  Top speed duration would be lower but you could pickle the booster before entering the photo run.  Although dropping anything from that speed might do more harm than good.  Any merit to the idea?
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Re: RW materials question for the Whiffverse:
« Reply #22 on: January 05, 2014, 12:29:05 PM »
Of course any discussion of high speed recon phantoms cannot go long without mention of the RF-4X:



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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #23 on: January 05, 2014, 12:48:38 PM »
Looking at that picture, I'm thinking that the rocket booster should be part of a conformal pallet that attaches to the fuselage underside with the nozzle between the existing J79 nozzles.  You need to position the exhaust nozzle such that the expansion cone of the exhaust does not impinge on the tail structure.

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #24 on: January 05, 2014, 01:27:48 PM »
What I have in mind is a pre RF-4x.
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Offline tankmodeler

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Re: RW materials question for the Whiffverse:
« Reply #25 on: January 05, 2014, 01:29:39 PM »
Going back to all aluminum, are there ceramic coatings that adequately deflect/absorb heat that can be used on leading edges and other high heat areas?
No, n ot really. Ceramics are too brittle and don't bond well enough in thin coatings to stay with the structure as the aluminum flexes. You're better off with titanium.

The problem with titaniun is not corrosion or CTE (although that one can be a problem), it is cost, density and, worst of all, formability.

Aluminum forms easily and then can be heat treated to get the strength you need. Titanium is too springy to form worth a d@mn. To get it to smoothly curved shapes requires either machining it from billet (= $$$$$$) or superplastic forming (= $$$$$). While it is stronger, for most aircraft structure, it is stiffness that counts, so you really can't reduce the thickness of the material to counteract the increased density, thus whatever you replace with Titanium instantly becomes 60% heavier, which is a bad problem for an aircraft that is supposed to go fast.

In thinking about a super fast Phantom, your real problem is that the aerodynamics really aren't there to go a whole lost faster than the Mach 2 that the design is rated for. The Phantom really is as aerodynamic as a brick and would need a huge aerodynamic clean up and reshaping to hit much faster than about Mach 2.7 even with higher thrust and lighter engines.

Paul

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #26 on: January 05, 2014, 01:38:42 PM »
I randomly chose 10-15% slower than the RF-4x.   Why?  Why not!  ;D :D :D
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Re: RW materials question for the Whiffverse:
« Reply #27 on: January 05, 2014, 01:56:24 PM »
What I have in mind is a pre RF-4x.

In that case I would probably go with the brute force/simple solution..i.e. standard RF-4 + rocket booster ( possibly two - mounted in aft Sparrow points) + some ablative coating applied to wing and empennage leading edges, front canopy and nose.  The bright white (or scorched, depending upon at what stage you show your model) coatings plus the rockets would certainly constitute enough of a difference so as to be able to achieve your goal of giving "the educated Phantom fan a double take".  Maybe also give it an appropriate code name and say it was planned for China overflights or similar?
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #28 on: January 05, 2014, 02:19:35 PM »
One little problem there, Greg, the US RF-4's had all their Sparrow wells closed and faired over.  Still, I could see a twin-booster installation using that structure that remains internally or just a single centerline-mounted booster with the fuel in a conformal underside pallet.

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Re: RW materials question for the Whiffverse:
« Reply #29 on: January 05, 2014, 02:36:33 PM »
Maybe convert a centreline fuel tank to have a rocket in the rear end then.  This would allow the rocket system and its fuel to be kept separate from the rest of the airframe...and also be jettisonable if need be.

To be honest, I actually prefer a single rocket solution since that has less risk.
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #30 on: January 05, 2014, 02:40:33 PM »
The conformal pallet could pick up the pylon attach points and be just as jettisonable.  I'd rather go with a conformal pallet to keep the interference drag down.  Too, the pallet allows you to better spread out and arrange all the components and tankage.

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #31 on: January 05, 2014, 04:42:24 PM »
Would said pallet allow for the doors in the Phantom's aft belly?
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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #32 on: January 05, 2014, 04:46:08 PM »
Secondarily, what would be a maximum velocity for the factory stock alloys?   Mach 2.4-.5?
« Last Edit: January 05, 2014, 04:51:40 PM by Daryl J. »
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Offline PR19_Kit

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Re: RW materials question for the Whiffverse:
« Reply #33 on: January 05, 2014, 10:06:54 PM »
The three IDF F-4E(S)s, which grew out of the F-4X project, retained their Sparrow bays as they were build from F-4E airframes IIRC.
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Re: RW materials question for the Whiffverse:
« Reply #34 on: January 06, 2014, 02:06:16 AM »
Secondarily, what would be a maximum velocity for the factory stock alloys?   Mach 2.4-.5?

Apart from some key areas such as radome, windscreen, engine faces,,,and paint ;), I think you will find that most of the materials would last until at least 2.7/2.8 unless of course you were doing extended runs at high speed and thus temperature.  That is without the suggested ablative coatings though since adding these would alleviate the problem regardless of the materials below.
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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #35 on: January 06, 2014, 08:16:08 AM »
Would said pallet allow for the doors in the Phantom's aft belly?
It would probably need to be designed around them for routine servicing but major maintenance would likely require removing the pallet.

Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #36 on: January 06, 2014, 08:19:50 AM »
Secondarily, what would be a maximum velocity for the factory stock alloys?   Mach 2.4-.5?
ISTR that the Phantom had a max. limit of Mach 2.8, though that generally required component replacement afterwards.  For your purposes, I could see the use of ablative material and possibly a special engine build allowing this somewhat more regularly.

Offline tankmodeler

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Re: RW materials question for the Whiffverse:
« Reply #37 on: January 06, 2014, 10:53:22 AM »
I could see the use of ablative material and possibly a special engine build allowing this somewhat more regularly.
Ablatives have the disadvantage that as they ablate they create a rough surface, increasing drag.

Mach 2.7 in a Phantom might be the "do not exceed" speed, but it's not somethiing that could be maintained for more than a second or two, much less minutes. And probably not obtained in level flight. You probably needed to be in a serious dive, with a tailwind, to get near it.  :)

Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #38 on: January 06, 2014, 12:24:08 PM »
I'll have to ask Bill, my co-Dr. at work how fast they got their F-4J to.   High altitude, shallow dive, full AB.  1750 is what comes to mind but will ask again.   
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Offline Daryl J.

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Re: RW materials question for the Whiffverse:
« Reply #39 on: January 06, 2014, 12:31:23 PM »
Same questions apply to the Starfighter.   And presumably the same answers. 

I just prefer the Phantom.  ;D
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Re: RW materials question for the Whiffverse:
« Reply #40 on: January 06, 2014, 02:38:46 PM »
Mach 2.7 in a Phantom might be the "do not exceed" speed, but it's not somethiing that could be maintained for more than a second or two, much less minutes. And probably not obtained in level flight. You probably needed to be in a serious dive, with a tailwind, to get near it.  :)

That's where the suggested rocket helps...
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Offline tankmodeler

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Re: RW materials question for the Whiffverse:
« Reply #41 on: January 07, 2014, 12:08:25 PM »
That's where the suggested rocket helps...
Generally, when you exceed the "do not exceed" speed, the wings fall off immediately, they don't take the time to melt. :)  DNE speeds are almost always structural limits.

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Offline elmayerle

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Re: RW materials question for the Whiffverse:
« Reply #42 on: January 07, 2014, 09:28:03 PM »
Not necessarily wings, the DNE speed for the XF8U-3 was, so I've read, set by where the canopy started melting.  So DNE values are set by reality, the Mach .82 DNE for the Learjet is set by where the wing is almost at a Mach tuck condition where the flow over the wing goes supersonic and generates a severe nose-down pitching moment.  There were some cases in the early 1980's where Learjets made big smoking holes from 45,000 ft. and it was found that the pilots had prevailed on the maintainers to put in an over-ride on the Mach limit function on the autopilot to allow them to go faster; unfortunately, this got them into this range.