J-15 carrier fighter thread

[thunderchief]

Well I dispute your calculations with the stats above

I hope you understand which one I trust more. Your calculations, or stats from a book specifically written from an acclaimed Russian aviation historian.

Well , I don't thrust anyone and would like to see some proofs . Pictures of J-15/Su-33 taking off with full combat load would be just fine

The modernized Mig-29K uses newer RD-33 variants.
A modernized Su-33 would use newer Al-31 variants as well.

I doubt that . But J-15 would certainly get better engines in the future . When that happens I would recalculate possible combat load .

 

[Blitzo]

i have zero desire to argue here, but my position on fomin's info is "we dont know know for sure but if i had to pick, id pick those values as operational ones, meaning always at least a little headwind".

No special reason for that, it just sounds right and sounds sane and practical. Plus he talks about various loadouts for first launch positions, 26 to 28 tons, which again sounds like he's stating exact operational choices, not some theoretical limits. taking off with no headwind would constitute a theoretical take off in my book, i don't think that's ever operationally done. and even if it has to be done, in a situation where sea is calm, no wind, and ship's propulsion has broken down, the safety margins i talked about earlier may still allow for a take off, as there's no additional ship pitch or sudden wind gusts to be concerned about.

All that being said, a 20 kt headwind sounds about right as a safe, prudent operational condition. but as we know, if one adds a bit of real wind to it, it can go twice that. so theoretical loads of su33 may easely be a few tons more.

Fair enough.

also, calculations that don't take into account whole part of the "virtual air-strip" after the ramp, that don't take into account drag (Even if it is a small part of it all) and don't take into account difference between installed and uninstalled thrust are meaningless.

Agreed.

 

[thunderchief]

These calculations are entirely arbitary. How can we say say that a ski jump angle of 20 degrees can be equated to an extra one hundred meters on take off??

Sin(angle) * exit_speed / (9.81m/s*s) * cos(angle)* exit_speed . With exit speed of 200km/h (calculated above for 33000 kg ) you get around 100 m . Although I don/t know exact angle of ski jump , I assumed it is 20 degrees .

 

[Engineer]

The conclusion drawn from that calculation is flawed. Any increase in upward velocity is taken from forward velocity, which is not a performance gain. You need to look at this in terms of kinetic energy, rather than simple trigonometry.

 

[bd popeye]

Popeye's opinion on the launch ablity of the J-15.

No way no how can an airplane that large take off from a CV fully loaded and fully mission capable without the aid of a catapult.

Just my opinion. I could be wrong. But........

I will not argue with anyone.

 

[SteelBird]

Sin(angle) * exit_speed / (9.81m/s*s) * cos(angle)* exit_speed . With exit speed of 200km/h (calculated above for 33000 kg ) you get around 100 m . Although I don/t know exact angle of ski jump , I assumed it is 20 degrees .

I could be wrong but I remember I saw it somewhere that the ski jump's angle is 14 degree.

 

[snake65]

I could be wrong but I remember I saw it somewhere that the ski jump's angle is 14 degree.

Exactly 14.3 degrees.

 

[delft]

Two things are lacking in the current discussion. First the length of Adm K was determined by the needs of the aircraft chosen to fly from her. Second if a two engine aircraft would be lost if the critical engine fails at the critical time it is prudent to go to a single engine aircraft. This was known at the start of the project. Before the first steel was cut for the ship simulations must have been run with the aircraft and engine characteristics determined as well as possible to determine the optimal ski ramp profile and the places of the starting positions for the aircraft considered at the store and fuel loads considered at relevant winds over deck without and with engine failure. After an engine failure at the moment the ship retracts the wheel blocks the aircraft accelerates at a reduced rate to achieve about two third of the speed it would have without engine failure, it will drop its external stores immediately after leaving the ski ramp and flies at a reduced angle of attack, that is in a curved flight in order to continue accelerating, flying a profile that will not end in the water.

It would be decidedly odd if the aircraft chosen would only be able to take off with a very reduced weight. This should already be enough to decide that the numbers given by Fomin are at least reasonable.

 

[thunderchief]

The conclusion drawn from that calculation is flawed. Any increase in upward velocity is taken from forward velocity, which is not a performance gain. You need to look at this in terms of kinetic energy, rather than simple trigonometry.

That is why you have cos(angle) part . Basically , we are calculating distance plane would go before it starts descending . Best results are for 45 degrees , but this is a very rough first order calculation . For a better results you would need integral calculus , incorporating increase of speed . And then you would need to incorporate all forces acting on the plane , height of the ramp etc ...

I could be wrong but I remember I saw it somewhere that the ski jump's angle is 14 degree.

For a 14 degrees you would get 73.9m "deck extension" and 232.5 km/h speed

 

[Intrepid]

If an aircraft can take off without assistance, it can even better* take off using assistance

*better:
shorter distance and/or
more payload and/or
safer speed and/or
guided path in low visibility and/or
less stress to undercarriage due to a plain path

Any assistance is a plus in energy for the short moment of high acceleration. For a patrol aircraft an assisted take off means lighter engines and more range.