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I was just looking at some documents and several of them have said under 4 seconds from IDLE to initial A/B light on the F404. I know A/B light time is random as engine has to go through the process etc. I have tried to time it in the sim and even if only count time after I push throttle full forward its 5.5-6.5 seconds from idle to 100% I wonder if this is why some feel the drag is to high or very easy to get behind the power curve. This is measuring it after I already pushed throttles up so thats letting engines get up about 75% before I even hit timer lol. If I time from when I start moving throttle it takes about 6.5 or little over like theres a bit of lag for the command to hit FADEC or we. I am only timing to 100% on display not A/B light etc.

 

Is the throttle response to slow? I know the turbines spool from Low RPM slower then High RPM but even on the Wiki it says the F404 was known to respond fast for carrier ops. Says around 4 seconds for idle to lighting A/B. This is what several documents show online aswell.

 

In the GE document it says on average 3.25 seconds from idle to full thrust.

 

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Several Official Sources.

http://www.dtic.mil/dtic/tr/fulltext/u2/a164562.pdf

https://www.icas.org/ICAS_ARCHIVE/ICAS1984/ICAS-84-5.4.2.pdf


Edited by HawkDCS
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I wonder if this is why some feel the drag is to high or very easy to get behind the power curve.

 

Not looked right into spool times. I would bet tho that ED would have some good detailed real world "Not Wiki" reports on engine tests from Boeing.

 

I think it could be a little bit of FM drag that needs tweaking perhaps and user throttle technique. If your not flying a good controlled pattern you will have troubles coming right off the throttle to much. She is a lot better when you keep the throttle between 60% and 90%. It's like keeping a turbo engine spooled up.

 

I have changed my technique a little after watching Lex and how he injects a little power into to aircraft first when level before you lose lift when going into a turn. You then only have to catch the aircraft on the descent rate your after.

 

It's still all WIP, so it could be many little things that need tweaking here and there until it all comes together and everyone's happy.;) OK that's a little silly and I'm joking, that's never going to happen LOL.:D

 

.


Edited by David OC

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  • 1 year later...

Since we're just about to get the new SC module, is it possible to have this being looked at finally? The 404s in our Hornet take somewhere around 7-8ish seconds to spool from idle to MIL where as the Tomcat's 110s take ~6s to do that - given the fact that the Hornet's being known for cranking up quicker than the 'cat which was advertised as an advantage even IIRC since it makes life easier in the groove as well as in formations due to quicker reaction. At the moment (well, for 2 years now) it almost feels as if I was sitting in a 262 however where you'd have to carefully watch not to turn your engines into a burning mess by throttling up too quickly.

dcsdashie-hb-ed.jpg

 

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There are two diagrams there. One "from idle" and the other "from mil". Both indicate how long it takes to light-off the afterburner at given speed/alt. To get the spool-up time from idle to mil you'd basically substract the time given in the "from mil" from the time given in the "from idle" chart. Which, at 0/0, is 3 seconds, being almost bang on to the 3.25 seconds given by the GE specs, most probably taken from an engine mounted in a test chamer - which rougly is 0/0. The same applies to altitudes up to 10kft and speeds up to M 0.4 though, which includes all the pattern work around the boat or a base ashore. But if you're gonna hit a tanker at 20kft, the spool time is increased to 6s already, and at 30k you might even end up with a spool time of 9 seconds. So basically (which is actually new to me as I take some time to understand those charts), it heavily depends on speed and altitude and my guess is that ED doesn't incorporate that and just went for some value in the middle that suits most flight regimes as good as possible without modelling the alt/spd diffs and that's the 6s we have for most of it.

 

So basically the question changes to "are we getting the spool-up time differences taking speed and altitude into account?", still with the aim to make the thing more realistic icon_exclaim.gif

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  • 2 weeks later...

+1!

 

 

I think the reason why the Hornet is subjectively (that is: for me) much harder to plant on the boat than the Cat is the combination of long engine spool-times and a high drag configuration when flaps set to FULL.

 

 

Correcting the spool-value to actual low speed/ altitude spool-time values should tremendously help bringing the Bug aboard ship.

 

 

I think it's one of the most pressing FM-issues left.

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I don't understand. Has someone done a test to show that this is incorrect? OP said 6.5 seconds which is inline with the RL docs.

 

Take care not to blame pilot error on a simulation error.

 

 

 

 

Not at pattern speeds and altitudes - should be closer to 3 seconds there (flight idle to MRT). And that's right out of the NATOPS.

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Sure! There is a diagram on Page I-2-2

 

 

It shows afterburner light-off times from Flt Idle to Afterburner and from Mil to Afterburner at different portions of the steady-state flight-envelope.

For an estimate of the Flt Idle to Mil-time, subtract each other.

 

 

That gives you 3s up to 10000ft and Mach 0.4

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Sure! There is a diagram on Page I-2-2

 

 

It shows afterburner light-off times from Flt Idle to Afterburner and from Mil to Afterburner at different portions of the steady-state flight-envelope.

For an estimate of the Flt Idle to Mil-time, subtract each other.

 

 

That gives you 3s up to 10000ft and Mach 0.4

 

I see thanks, I guess its now up to OP to provide the test conditions. So we can compare accurately.

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I concur there's an issue with the spool time. It's a little longer than it should be (6-7 sec, when it should be 3-5 sec), and this is according to Hornet pilots, NATOPS, and real life videos. No wonder it's so hard to trap on the boat.

 

Here's an interesting video.

Engine test, and then the pilot brings both throttles back to idle, and then immediately full burner. Takes 3.58 seconds for the right engine to get to full AB, probably because it was still spooled up from the test. And 5.54 for the left engine, which was truly at idle.
Edited by mtpiperpilot
corrected time mistake
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  • 4 weeks later...
  • 7 months later...

adding to this: i literally just hung up the phone from a lengthy conversation with a colleague from work, who happened to fly the A-model hornet -like for real 😁. he concurs that engine response was "almost instant". he also spoke of "walking the throttles" during approach rather than making large power changes.

 

in my opinion the evidence given in this thread sounds very convincing: there is data from an official flight manual and a video clip showing that spool up times are significantly shorter than what we currently have. and these are backed by statements from SME's.

i really wish ED could have another look at that topic 👍

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There was a show on Discovery called Jet Stream about Canadian Air Force training on the hornet, and they too spoke of "walking the throttle" on approach, as a movement would be too much. My throttle movement required on approach is quite large, walking wouldn't do enough.

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exactly! in my opinion, the reason why such large power changes are required in our hornet lies in the latency (spool time). at the time the power changes become effective, the aircraft has already deviated that much from flight path that an even greater power correction is required. this quickly escalates to a point, where you constantly have to make large corrections.

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I agree with this thread. That’s probably why when putting in full flaps on the downwind there is a considerable sink. To recover, you have to add more thrust because you’re already behind the power curve. Thus, the whole throttle dance begins.


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I have a **very** strong suspect that ED misread the chart at page I-2-2 of the NATOPS and forgot to subtract FLT-IDLE and MIL to obtain the result. 

 

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I fly an airplane with high-bipass ratio turbo fan engines.

 

The certification requirement for civil aviation from flight idle to take-off power is 5 seconds. Often they perform better ~4 seconds and change. I've tested the hornet and its ~6 seconds to MIL from flight idle. Way too slow.

 

Even 5 seconds is a long time, try counting it and imagine the ground is coming up fast. If you're coming off turbo-props you notice the power doesnt respond as quickly resulting in popping overhead bins and a bruised ego on your first landing attempt after getting the type rating. 

 

One of the advantages of low bipass ratio engines is they spool faster at the cost of increased noise. 

 

Ground idle to Go Around thrust with the CFM56 can take 12 seconds as it tries to protect the engines. One of the reasons we allow to engines to spool a bit on the ground before applying takeoff power, and why it takes a few seconds for the engines to go to ground idle with WOW. If youve ever done touch n goes in an airliner you eat up a lot of runway before you see any power if it goes into ground idle.

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I sure hope ED takes a look at this. I found both AAR and trapping more difficult in the Hornet than in the Tomcat thanks to the latter's near-instant throttle response. The Hornet always felt sluggish on approach, I thought it was correct behavior (based on some F-16 guys saying it reacted slower than the Viper), but if it's not, it really should be fixed.

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