C-17 Globemaster III

[Trebor]

ohhh, I see. hehe I misunderstood ^^'

 

[Burmese Bandit]

I know that the C-130 has sucessfully been tested for a carrier landing and takeoff. Could a C-17, perhaps at light weights, do the same? Is it totally impossible, 'possible but the pilot had better write his will first' or just possible?

 

[Matt308]

I don't think the carrier deck is rated for such weights. And the island would get in the way of the 170ft+ wingspan.

I would say possible. Once.

 

[Burmese Bandit]

So clip the wings! Or build bigger carriers...

 

[Trebor]

I don't think the carrier deck is rated for such weights. And the island would get in the way of the 170ft+ wingspan.

I would say possible. Once.

heh, yea. and that once would bee a 99.9% chance made of fail. XD besides, I don't think that even with the carrier being full into the wind, and the plane hooked up to the catapult, that sucker could get airborne

 

[HoHun]

Hi Matt,

>I don't think the carrier deck is rated for such weights. And the island would get in the way of the 170ft+ wingspan.

Here is a screenshot from my favourite simulator, X-Plane ...

The C-17 is not parked there, it's in the middle of a bolter.

Without arresting gear, it won't stop even at minimum weight. Retro-fitted with arresting gear, it is tricky to find the correct angle-of-incidence for a trap. I'd have to retro-fit an AoA indexer, but this still would leave the question of the correct AoA. I've managed a couple of bolters so far - and a couple of ramp strikes, I'm afraid. Somehow, the cockpit has to overfly the #4 wire at considerable height to place the main wheels safely on the deck ... takes some getting used to!

Regards,

Henning (HoHun)

 

[Matt308]

HoHun, your pic doesn't leave much margin for error.

Even with an angled deck, you are only talking about 25ft on either side to the edge of the deck. Add in some other objects, like the island, equipment, and aircraft. Not sure if it's gonna be possible.

And just because you are accomplishing touch and goes on a simulator, I still say the deck won't hold up. But fun information nonetheless.

 

[FLYBOYJ]

Also consider that if a C-17 was fitted with a hook, upon landing it would have to throttle up - SOP on carrier landings. If you find a practical cable to make this work, I doubt it would contain the aircraft after landing.

Either way I think the aircraft would wind up 2 decks lower when it came to a stop!

 

[SoD Stitch]

So clip the wings! Or build bigger carriers...

You might be able to launch a C-17 from the newest Nimitz-class carrier, the Gerald R. Ford (which actually hasn't even been laid down yet), as the island is much further back than on the standard Nimitz-class carriers.

 

[HoHun]

Hi Matt,

>Even with an angled deck, you are only talking about 25ft on either side to the edge of the deck. Add in some other objects, like the island, equipment, and aircraft. Not sure if it's gonna be possible.

In the picture above, the wing tip would have struck the two E-2C aircraft parked there - fortunately, they're not "hard" objects in the simulator. (They can't be re-spotted in the sim.)

>And just because you are accomplishing touch and goes on a simulator, I still say the deck won't hold up.

Absolutely correct There is a simulator that does take material strengths into account too, but I haven't tried that one yet. Tends to use a lot of computing power, and my 6-year-old box just doesn't have it.

Rigs of Rods

Still worth a look for all lovers of fine machinery

Regards,

Henning (HoHun)

 

[HoHun]

Hi Flyboyj,

>Also consider that if a C-17 was fitted with a hook, upon landing it would have to throttle up - SOP on carrier landings. If you find a practical cable to make this work, I doubt it would contain the aircraft after landing.

Hm, I think a cable that wouldn't break upon arresting 275000 lbs would probably hold an aircraft with "just" 160000 lbs of thrust easily.

You're right with regard to the standard procedure ... but on the other hand the C-17 at minimum weight will fly at a surprisingly low speeds, so you can still throttle up if there is no deceleration.

I think it might even be possible to fly off the carrier deck without catapulting the C-17, but the simulator insists on putting the plane on the catapult if I select a carrier start. I'd have to land first, then taxi into a position aft of the catapult to try an unassisted start. (Which reminds me ... does the C-17 do JATO?

>Either way I think the aircraft would wind up 2 decks lower when it came to a stop!

Quite likely!

Regards,

Henning (HoHun)

 

[FLYBOYJ]

I think a cable that wouldn't break upon arresting 275000 lbs would probably hold an aircraft with "just" 160000 lbs of thrust easily.

Actually the normal tinsel strength is 215,000 lbs. You'd have to consider the 160,000 pounds of thrust plus the kinetic energy of the aircraft as it lands and catches the cable. My guess you're going to see over 215K on the cable.

 

[beaupower32]

The thrust reverser system on this airplane is garbage. We have done so many T/R Rigs, changing actuators, prox sensor adjustments, and blocker door rod changes. They should get rid of the core reverser and make it like a normal civilian with just the fan. But no. Air Force had to be different. Anyways, hate to ramble. Im a C-17 Jet Engine Mechanic stationed at Charleston AFB, South Carolina. Been here 2 years and cant wait to leave.

 

[HoHun]

Hi Flyboyj,

>Actually the normal tinsel strength is 215,000 lbs. You'd have to consider the 160,000 pounds of thrust plus the kinetic energy of the aircraft as it lands and catches the cable. My guess you're going to see over 215K on the cable.

The good news is, I just managed to accomplish a trap with C-17

The bad news is, I didn't think of checking the G factor of the deceleration - which would have been easy as the simulator has a pretty comprehensive "telemetry" function. I will have to give it another go tomorrow.

Anyway, here a screenshot of the trap. I added an AoA indexer and set desired AoA to 15 degrees, using 32 degrees of flaps to achieve the correct (as it turned out) touch-down angle. Unfortunately, the actual functional hook geometry is invisible in X-Plane, requiring some guesswork with a plane of the size of the C-17.

(Increasing the horizontal viewing angle from 50 degree to 80 degree proved the key to avoiding ramp strikes ... it's all about the sight picture, I guess. No peripheral vision, no depth perception in the simulator.)

Regards,

Henning (HoHun)

 

[Matt308]

HoHun, you are not serious in your analysis are you. You/re just yanking our chains right. You surely are not basing a position on a PC game simulator. Please tell me so.

 

[HoHun]

Hi Matt,

>HoHun, you are not serious in your analysis are you. You/re just yanking our chains right. You surely are not basing a position on a PC game simulator. Please tell me so.

Hm, which position? The question whether the arrestor wire would be overstressed? I'm pretty sure X-Plane will show a realistic deceleration, but I'm just as sure that this will only yield the "best case" tensile stress on the cable - in real life, the cable will be stressed quite a bit more in off-centre landings, and I don't expect the simulator to take this into account.

I could also calculate the "best case" deceleration on the back of an envelope, but it's more fun to fly a trap in the simulator and look at the data readout afterwards. You can actually check the time history to find out what kind of deceleration characteristic the simulator is using.

(Don't underestimate X-Plane though - it has been used by, and praised by, quite a few aircraft designers. The key is that to learn something from a simulator, you have to be aware of its limitations.)

Regards,

Henning (HoHun)

 

[Matt308]

HoHun, I was hoping you would take the subtle out. Have you ever taken an engineering strength of materials class? Assuming not, I am a bit incredulous that you would base a technical position on a game. I have better confidence in you than that, buddy.

I remember my professor actually teaching us about the catapult launch forces. For those who do not know, the airplane is attached to the shuttle with a known tensile strength length of stock metal. At the end of the shuttles run, the airplane momentum carries it past the shuttle c0ck. With a huge "bang", the metal connection is actually broken, or snapped in half. I know. I actually examined one as part of my engineering curriculum.

The weight of the airplane actually determines the diameter of the shuttle connection. The knowledge of the connection metalurgy and its diameter determines the absolute strength of the material.

I don't recall the problems that we worked in the mid 80's, but I want to say that the absolute tensile strenght to launch an aircraft in the A-6/F-14 range was already in the 200,000+ lbs/sqin range.

Now compound that with an aircraft that is MGW of close to 600,000lbs and you are talking a completely different animal. Launch is impossible. And even landing with hydraulic compensation to minimize wire tensile stress (even with minimal cargo) is going to result in stresses that cannot be supported by the arrestor gear.

And this is not even contemplating the deck forces. In all likelihood, a C-17 landing on a carrier would not only destroy the arrestor gear, but also damage the decking to the point of being catastrophic due to both massive tensile an compressive forces.

 

[beaupower32]

HoHun, I was hoping you would take the subtle out. Have you ever taken an engineering strength of materials class? Assuming not, I am a bit incredulous that you would base a technical position on a game. I have better confidence in you than that, buddy.

I remember my professor actually teaching us about the catapult launch forces. For those who do not know, the airplane is attached to the shuttle with a known tensile strength length of stock metal. At the end of the shuttles run, the airplane momentum carries it past the shuttle c0ck. With a huge "bang", the metal connection is actually broken, or snapped in half. I know. I actually examined one as part of my engineering curriculum.

The weight of the airplane actually determines the diameter of the shuttle connection. The knowledge of the connection metalurgy and its diameter determines the absolute strength of the material.

I don't recall the problems that we worked in the mid 80's, but I want to say that the absolute tensile strenght to launch an aircraft in the A-6/F-14 range was already in the 200,000+ lbs/sqin range.

Now compound that with an aircraft that is MGW of close to 600,000lbs and you are talking a completely different animal. Launch is impossible. And even landing with hydraulic compensation to minimize wire tensile stress (even with minimal cargo) is going to result in stresses that cannot be supported by the arrestor gear.

And this is not even contemplating the deck forces. In all likelihood, a C-17 landing on a carrier would not only destroy the arrestor gear, but also damage the decking to the point of being catastrophic due to both massive tensile an compressive forces.

 

[Burmese Bandit]

Looks like I started quite a discussion there guys!

 

[HoHun]

Hi Matt,

>Assuming not, I am a bit incredulous that you would base a technical position on a game. I have better confidence in you than that, buddy.

How about you try and sum up my "technical position" so that I can tell you that you got me completely wrong in order to restore your confidence?

I won't even comment on the rest of your post because I see no connection to anything I wrote here.

Regards,

Henning (HoHun)