Okay wingnuts and rotorheads, considering a shipboard situation, how much of an ramp angle can you realistically tow an aircraft up or down? (I suspect that the down part would be most concerning) Is 6 feet over 75 feet (8% slope) too much? How about 4 or 6% ?
I realize that some aircraft do not have a lot of ground clearance to start with, so I know that is a factor.
Interesting question.
The FAA mandates maximum grade changes for areas like airport runways and aprons at +/- 2%…but that’s likely a ‘safest’ number, considering commercial conditions. Plus, it strikes me that a carrier underway could easily surpass that simply due to prevailing sea conditions.
Not much help, I’ll admit…but I’m curious to see what more informed replies develop.
One is naturally curious to ask…is there a ‘project’ of some sort, behind your qustion?
With aircraft having an average empty weight of 35,000 lbs(estimated), anything over 3-4% would be problematic in my opinion.
As a truck driver, a 6% slope is considered potentially dangerous especially the longer it goes. 8% + is “Awww, hell no!” territory if loaded.
Aboard a ship this may not be an issue since the distances would be much shorter but momentum has its own ideas.
Bottom line, I can’t see using ramps for moving aircraft aboard any ship just due to the weight causing safety issues.
GregBale & Straycat1911, Thank you. That was exactly the kind of information I was hoping for.
As for the shipboard environment, both of your inputs apply completely.
The question was concerning the possibility of having a ramp from a flight deck down to the hanger spaces that will sit forward of the flight deck. I was feeling doubtful as to whether or not it would work but wanted some outside opinions.
I know here are slight ramps from the flight deck / landing spot to the main deck on the Iowa class ships, but I don’t know the angle.
I will be reassessing the build plan.
Again, Thank You.
I know the Harrier is not as heavy as some carrier aircraft and i don’t know the angle of the ski jump on RN carriers, but this Harrier was clearly towed onto the ramp.
Bish, As that was at the International Fleet Week event, and in port, I suspect it was done strictly for display purposes, not operational.
But Thank you none-the-less.
I didn’t make it to the stern of Missouri the one time I visited her but I suspect those ramps you’re referring to are for movement of personnel (mobile or ambulatory) rather than any aircraft.
Not exactly the same thing, but Section 508 of FAA AC150/5300-13A lays it out for airport design. Maximum allowable grade is 2% and depends on aircraft category.
https://www.faa.gov/documentLibrary/media/Advisory_Circular/draft_150_5300_13a.pdf
We have two ramps that are at the maximum of 2%, and they both have a nice, big, red and white sign to tell you that they are 2% grade.
i Imagine the transition is a big issue.
FWIW, I seem to recall having read or heard somewhere that the original ‘transit ramp’ areas on the first (WW1-era) iteration of HMS Furious were a 6% grade…and reportedly proved troublesome, even given the much lighter aircraft of that day.
Granted, that may have been due as much to a cobbled design and primitive equipment, as to the ramps themselves.
Straycat1911,
I did find this picture, so I know it’s possible. And I would assume (not a good word) that for operational purposes the flight deck may need to be cleared in an emergency, so it makes sense. And if you look close, you can see that there is a ramp, but it is pretty slight.
That ramp is about the same length as the helo, an SH-2 Seasprite, which is 52 feet long, and the ramp height looks to be about a foot or so. That would be close to a 2% grade, which fits the requirements per se.
Mr Hoo-Yah,
I’m not sure what kind of ship you had your sea duty on… Maybe this helps or maybe not. One of my ships was a CV, where I stood watch as Engineering Officer of the Watch, and we had to be very sensitive to the amout of ship’s list at any given moment. Contributing factors included our even use of tanks for water, fuel oil and JP-5, as well as the airdales’ management of aircraft on the deck(s).
The nighttime respots were the worst. A movement of a 17 ton F-14 from the stbd side to the port side made a net change of 34 tons. Two or three of those made a one degree change in the list. If we weren’t notified in advance so we could manipulate water in the list control system, then we would be getting calls from Pri-Fly about how hard it was for them to move planes uphill. We had a camera with a view of the flight deck and sometimes we could tell when a respot was in progress even before they told us. From Main Control we had no way to tell if birds were being moved in the hangar bays, but since it was narrower than the flight deck, the movement arm was not nearly enough to worry about.
We were one of the last CVs to have a manual list control system, so that a person would have to go and line up valves to flood a tank or to pump one dry. The fun part was that we only had X number of voids on each side. They took about 5 minutes to fill and 30-45 mins to pump out, so once they had all been filled, there was no instantaneous list correction available.
So my bottom line for your question was that our Air Dept was very unhappy when they needed to move a bird up a two-to-three degree hill atwartships, and I’d imagine a ramp fore-and-aft would be just as difficult.
Rick Heinbaugh
The rise isn’t your issue, the run is.
8% is 1/12.5 so a 10 foot rise will take a 125 foot run, plus an aircraft sized flat spot at each end. IMO an elevator is the only solution.
Bill
I thank everyone for their respective comments and I’ll say that you have adequately convinced me. With this build (as I’ve said, as if it were a real ship) I will need access beneath the flight deck for regular ship’s functions, so I can’t lower it much. Therefore I will probably have to raise the hangars to the same level. The hangar structures aren’t that heavy (primarily aluminum) so I don’t think that stability will be affected that greatly. So, again, Thanks for the input, It makes a difference, and the varied backgrounds all seem to say the same thing; so it must be correct.
Bill, I was considering a deck edge elevator for a time, but I’m not sure I want to go there as I was only looking at moving the aircraft one deck level. It’s still an option.
Oh, and Surface Line, Sir, I’ve served in a CV, an LSD, and LKA, two tenders, and a salvage ship. I was a hole snipe, a fresh air snipe, and a Diver; and the diver part means I was also a Boatswain’s Mate, an Electrician, a Engineman, and several other ratings as needed.
Thanks everybody.
Yeah, I was a snipe too, but as the Main Engines officer, I got to receive the personal calls from Pri-Fly about the $^)*# list and get it fixed NOW! And Independence was old enough that we didn’t have some of the cool automated systems that the newer CVs had.
It meant that if we weren’t staying busy keeping steam and wind over the deck sufficient for flight ops that we needed to focus on the *&%$ list, that we’d be nagging the List Control guy with all our free time.
So if you were both a hole snipe and a fresh air snipe, I’m taking it that you were an MM? They’ve been consolidating rates so much in the past few years that I’ve completely lost track of what rates are in use nowadays.
Which CV did you serve on?
Rick