AAR, does the basket push against the jet?

[Akula]

If I may, the hose and basket absolutely cause a drag effect on the aircraft being refueled. The extent to which this is felt and interpreted by the pilot flying the receiving aircraft isn't something I can accurately comment upon, but the effects are certainly there. For this explanation, my convention is: Force in the direction of the aircraft's travel = positive (e.g. thrust); force opposing the forward movement of the aircraft = negative (e.g. aerodynamic drag).

 

We've already established that the basket is connected to the aircraft. Any structure that is attached to an aircraft is going to create some amount of parasite drag, and the basket is no exception. The drag being produced is actually fairly significant, given that the basket is designed to produce drag in order to keep the hose taut and allow the receiving aircraft to hook up.

 

That being said, there is a spooling unit in the tanker that reels out or retracts the hose based on the forces being introduced to the hose system. However, this unit has necessarily high damping constants to make up for the positive feedback being produced by the hose, the receiver, and the environment. Notably, the hose is subject to rather complex catenary force, which is only approximated by the hose controller since catenary is notoriously difficult to calculate on the fly. This is in addition to the previously mentioned and ever-changing rigidity of the hose depending on fuel flow rate and any resistance introduced by movement of the receiving aircraft. Because these forces are only approximated, there is a dynamic push-pull happening between the tanker, hose, and receiver. The spooling unit does relieve some of the negative force being produced by the drag of the basket, but it is incredibly optimistic at best to pretend that retracting and extending the hose artificially would entirely negate the effects of the basket on the receiving aircraft.

 

There are also the "soft" effects of the basket, especially the interruption of smooth airflow over the receiving aircraft. This is one of the more negligable aerodynamic effects of refuelling, but it certainly contributes to the system.

 

I'd be curious to hear some real Hornet pilots weigh in, or really anyone who has flown on the receiving end of a drogue in real life.

 

My references are my own experience in avionics control systems and engineering flight test, as well as the papers:

"Modeling and Simulation for the Automation of Aerial Refueling of Military Transport Aircraft with the Probe-and-Drogue System" by Nicolas Fezans and Thomas Jann

and

"An Introduction to the Navy's Physics Based Model of the Hose and Drogue Refueling System - Design and Validation" by Kenneth E. Boothe, Robert Vess, Eric Koehler, Elizabeth Knoblauch, and Steve McLaughlin

 

Thanks for the clarification :thumbup:

[Svend_Dellepude]

There actually is a post from a real pilot in this thread. You just didn't notice.

[Akula]

There actually is a post from a real pilot in this thread. You just didn't notice.

 

Where is it?

[KidCharlemagne]

Thanks for letting us know! I did a quick search but didn't see the post. Could you point us in the right direction?

[Tenkom]

Thanks for letting us know! I did a quick search but didn't see the post. Could you point us in the right direction?

First post on second page.

WindyTX

[KidCharlemagne]

You're right, I had missed that post. Good to hear that it seems realistic!

[104th_Maverick]

but I'm sure pilots use this as a tiny tiny brace.

 

lol Keep telling yourself what you need too.

 

A crew member with 4000+ hours on a tanker and a real pilot have both told you you’re wrong in your uninformed assumptions but as long as your gamer logic tells you you’re sure then I guess you must be right.

[Akula]

;3795228']lol Keep telling yourself what you need too.

 

A crew member with 4000+ hours on a tanker and a real pilot have both told you you’re wrong in your uninformed assumptions but as long as your gamer logic tells you you’re sure then I guess you must be right.

 

Physics don’t lie pal. Anything with mass will resist an imposing force until that force overcomes it and even then, it is still imposing a force unless it’s in a weightless vacuum. As for Storm, lol 4000 hours and he still got it wrong.

Edited February 11, 2019 by Akula

[Deano87]

Physics don’t lie pal. Anything with mass will resist an imposing force until that force overcomes it and even then, it is still imposing a force unless it’s in a weightless vacuum. As for Storm, lol 4000 hours and he still got it wrong.

 

Except that analogy doesn't work here as the basket becomes part of the aircraft once its connected. so Its not imposing any magical force on the airframe from the tanker apart from the drag of drogue itself as discussed before... as such its no different from flying the aircraft with a bit of air brake out or an extra store. Its not going to fundamentally change how the aircraft reacts to application or reduction in thrust to stay in position.

[Akula]

Except that analogy doesn't work here as the basket becomes part of the aircraft once its connected. so Its not imposing any magical force on the airframe from the tanker apart from the drag of drogue itself as discussed before... as such its no different from flying the aircraft with a bit of air brake out or an extra store. Its not going to fundamentally change how the aircraft reacts to application or reduction in thrust to stay in position.

 

It doesn’t matter. the basket and hose all have mass and will resist any imposing force like say, a jet and I’ll bet that once that jet is hooked up it is pretty stable as a result of this resistance.

[KidCharlemagne]

Except that analogy doesn't work here as the basket becomes part of the aircraft once its connected. so Its not imposing any magical force on the airframe from the tanker apart from the drag of drogue itself as discussed before... as such its no different from flying the aircraft with a bit of air brake out or an extra store. Its not going to fundamentally change how the aircraft reacts to application or reduction in thrust to stay in position.

I think you're right, any new mass or drag imposed on the aircraft from a free-body perspective will just result in needing a little more thrust to balance the new negative forces in order to return to equilibrium.

 

It doesn’t matter. the basket and hose all have mass and will resist any imposing force like say, a jet and I’ll bet that once that jet is hooked up it is pretty stable as a result of this resistance.

That's true, but only from an inertial standpoint. The mass will resist any new force while it's in the transient state. Once any initial oscillations have been damped out, the aircraft reaches a steady state from a mass/inertia perspective. At that point, oscillations or resistance are most likely aerodynamically caused and probably aren't due to mass.

 

;3795228']

A crew member with 4000+ hours on a tanker and a real pilot have both told you you’re wrong in your uninformed assumptions but as long as your gamer logic tells you you’re sure then I guess you must be right.

What part of the original assumptions are you objecting to?

[Repth]

What part of the original assumptions are you objecting to?

 

These two specifically:

 

the jet hooks up and the basket acts as a brake once connected

 

 

Is there at least *some* resistance to slow the jet down once it connects

 

We can argue physics all day long, but the simple fact is a half ton hose is not going to impart enough resistance to stop a 16-20 ton aircraft. It may provide enough aerodynamic force to seat the drogue to the probe and create a seal but it won't act as a brake or brace keeping the aircraft stable by resting against it. The system would simply retract the hose if too much pressure is applied.

 

Too much lateral or vertical force and the drogue is designed to shear off preventing damage to both aircraft.

 

the "braking action" that Akula is noticing is most likely the pilot reducing throttle after connecting to the basket and settling into formation with tanker.

Edited February 11, 2019 by Repth

[KidCharlemagne]

We can argue physics all day long,

I'd love to!

 

but the simple fact is a half ton hose is not going to impart enough resistance to stop a 16-20 ton aircraft.

 

I definitely agree there! From a purely mass-related standpoint, the initial collision with the hose is not much of an issue. From my post #36: "At that point, oscillations or resistance are most likely aerodynamically caused and probably aren't due to mass."

 

It may provide enough aerodynamic force to seat the drogue to the probe and create a seal but it won't act as a brake or brace keeping the aircraft stable by resting against it. The system would simply retract the hose if too much pressure is applied.

 

the "braking action" that Akula is noticing is most likely the pilot reducing throttle after connecting to the basket and settling into formation with tanker.

 

Here's where I disagree. The aerodynamic force that seats the drogue to the probe is the same force that imparts a braking action. It's true that the control system responsible for extending/retracting the hose will begin to retract the hose if too much pressure is applied, but that doesn't completely alleviate the resistance on the receiving aircraft (see my passage in post #25 for an explanation of why this is). At its most basic, the connection of the basket to the receiving aircraft is increasing the aircraft's coefficient of drag and is probably roughly equivalent to extending the airbrake slightly. This is exactly as Deano said above. So the "braking action" is due to the pilot reducing throttle, but also due to the aerodynamic drag.

 

I agree that this doesn't create a seal, nor does it need to, as that is already accomplished by the equipment inside the drogue.

[Akula]

Who said anything about a basket or hose stopping a jet?

[KidCharlemagne]

Who said anything about a basket or hose stopping a jet?

 

I just treated that as a hyperbolic way of saying "slow down a jet". We all know it won't actually stop it.

[XtraChrisP]

KC-130 Specific; can't speak for any other platforms:

 

Engagement force is 140 lbs. Hydraulics in the pod respond to a change in dynamic pressure and reel in or out the hose in order to prevent drooping which leads to sin wave formation which leads to more parts or less parts. Disengagement force is 420 lbs. Your hose response (force the jet exerts on the hose/force the drogue exerts on the jet) is somewhere in that range.

 

What's 140-420 lbs of force compared to the aero drag on the jet at refueling speeds (220-250 KIAS)? Probably pretty negligible but also not zero.

[Akula]

KC-130 Specific; can't speak for any other platforms:

 

Engagement force is 140 lbs. Hydraulics in the pod respond to a change in dynamic pressure and reel in or out the hose in order to prevent drooping which leads to sin wave formation which leads to more parts or less parts. Disengagement force is 420 lbs. Your hose response (force the jet exerts on the hose/force the drogue exerts on the jet) is somewhere in that range.

 

What's 140-420 lbs of force compared to the aero drag on the jet at refueling speeds (220-250 KIAS)? Probably pretty negligible but also not zero.

 

Chris,

 

By “engagement force”, do you mean it takes 140lbs of pressure to seat the probe in the basket?

[XtraChrisP]

When the tanker does its hose checks, it sets a reference pressure against which the hose is responsed. 140 lbs is the engagement force to seat the probe. The reel won't response until the dynamic pressure on the drogue has decreased by at least this much, otherwise it would start responsing spontaneously without a receiver in the drogue.

 

So I'm going out on a small limb here by claiming that the 140 lbs represents the lower limit of force applied from the drogue to the receiver. Anything more than 420 lbs and you disconnect. That's how I'm applying those mechanical connect/disconnect limits to the forces experienced by the receiver.

[Akula]

Gotcha! Thanks :thumbup:

[KidCharlemagne]

That makes sense. Thanks!

[pete_auau]

Interesting because what I see in videos is the pilot mating with the basket and then using the drag of the basket to brace the jet and help the pilot hold it in position while he refuels. This makes more sense given the fact that at 200-300 knots the bow wave most likely won’t extend past the engines (KC-135). Obviously this is a guess but based on what I’ve seen in wind tunnels during Mach 1 speed tests, the bow wave will extend pretty far out so I’m guessing at much lower speeds it is relatively smaller. Also there are a lot of factors influencing the drag the basket creates. Bow wave, Wing vortices, low and high pressures exerted on or around the drogue as a result of jet wash.

 

One thing is certain though. The way it’s modeled in DCS is nowhere near as accurate enough. It would be nice to make contact and then feel a slight push back to simulate the drag on the basket.

what you see in videos is completely different in real life operations

[Akula]

what you see in videos is completely different in real life operations

 

 

Just like the way you re-fuel in a game is completely different in real life ops.

[WindyTX]

Just like the way you re-fuel in a game is completely different in real life ops.

Only talking about probe and drogue but I don't see it as that different.

 

The hoses should be trailed so you can go to the pre contact position.

 

The hose should have markings on it so you know how far to push the hose in when in contact.

 

The bow wave from the jet should affect the basket as previously mentioned but depending on the basket it's not that much maybe 6-8 inches.

 

The basket should hit the jet if you mess up not pass through it.

 

I would love silent procedures to be implemented so I don't have to use the radio but that might be asking too much.

On Ops we always ran silent procedures.

 

However these are all relatively minor things if you can AAR in game now you will still be able to if it's realistic. You may scratch the canopy if you joust too much or break the probe off or spokes the basket but you will still get in most of the time.

 

 

Sent from my ONEPLUS A6013 using Tapatalk

[Rennes]

I would love silent procedures to be implemented so I don't have to use the radio but that might be asking too much.

 

Out of curiosity, how did that work? Was it hand signals, lights, just timing?

[Akula]

Out of curiosity, how did that work? Was it hand signals, lights, just timing?

 

 

Shadow puppets :megalol: