insight into low drag problem of Jeff?

[Tiger-II]

Bell curves being what they are, max/min are at the edges.

 

How did he get 2200 NM?! Did he actually achieve this in the sim? EDIT: References state 2200 KILOMETERS. This makes more sense!

 

@MagicD: I'm sorry if I was a bit defensive. Lots of people are OMG 17 OP NERF NERF NERF as if this is a sci-fi game with balance issues and they want ALL TEH POWA.

 

Not sure what you mean about low speed alpha. Looks right to me.

 

For sanity checks I've been comparing to the F-16 in BMS, and I'm not seeing anything that deviates outrageously.

 

I maxed the -16 in BMS, unable to get to max gross, with the heaviest munitions and tanks I could fit, and she's an absolute basket case of performance. i.e. there isn't any.

 

Given the similar wing on the JF-17, and maxed out (weight or drag) I'm seeing similarly reduced performance, which is to be expected.

 

JF-17 benefits from higher TwR vs. F-16 so unsurprisingly she can take a bit more before showing signs of performance loss.

 

Again, quick calc shows JF-17 TwR range: 1.32-0.70 vs. F-16 Blk 50. of 1.26-0.60.

 

To answer an earlier question about top speed: it's not an absolute. You can fly many aircraft faster than their stated limits, but you'll either start ripping parts off the airframe, overheating some leading sections, or destroy the engine.

 

My guess with the Jeff is it is an engine limitation (intake design).

Edited January 27, 2020 by Tiger-II

[shaHeen-1]

Hmm this depends on config.

 

Boresight is "along the longitudinal axis". The FPV shows the current flight path, and depending on the angle of incidence and lift, it's possible for it to be higher.

 

I guess so. Maybe it's because this plane is so unstable. Engine can be pushing slightly down while plane is going slightly up XD

[Tiger-II]

If I'm not mistaken, even the same thing can happen in the F-16 under certain conditions.

 

It requires a light aircraft and relatively high speed.

 

It's purely to do with lift vs. flight path. AFAIK there is no offset thrust in the JF-17. If anything it would be canted upwards very slightly (F-104 is a particularly noticeable example).

 

The reason is as it is behind the CoG the result would be a very slight pitch-up with power. Looking at it though, the JF-17 thrust line appears to be straight down the longitudinal axis.

[MagicD]

if you lower speed of the plane the wings create less lift. to compensate this you have to fly with more alpha..more alpha create more drag. more drag must compensate with more thrust. more thrust needs more fuel...absoluty basics of areodynamics. in Video posted at #1 .. JF17 show here an anomaliy...that looks to me like the programmed pyhsik model only use the parasite drag. if that true ...its for me hard to believe that everything is correct simulate in the jf17 projekt.

[AeriaGloria]

If you flew it you would notice the lift induced drag. I don’t know what you mean by more power is needed the slower you are but there is lots of extra drag at high alpha that you need power to get through while turning or during an aggressive liftoff. If there was no lift induced drag you would be seeing very ridiculous results. It has lower wing loading then the Viper, it does not need to pull as much alpha for the same speed if all other things were equal

 

EDIT: Rewatched the end of the video to see this low alpha thing you are referencing. When Cap “called BS” on its low alpha at 200knots it looked like he was pointing at the fuel burn graph? I didn’t see AOA numbers anywhere?

Edited January 27, 2020 by AeriaGloria

[shaHeen-1]

Anyone else struggling to land? It doesn't slow down easily with idle and airbrakes. Only throwing the nose around gets it to slow down. Problem is I don't know whether "problem" is with Jeff or with other jets I've tried like mirage and hornet. Hornet is a bit greasy for me too but manageable. I can control the E bracket and the fpm. Jeff not so much. Mainly because I can't get it to decelerate.

[Tiger-II]

200 kts in a clean jet and he says the AoA is too low?!

 

The guy in the video has no idea what he's talking about.

 

IIRC the Jeff is around +4 degrees AoA at that speed.

 

I guess he has no idea the AoA limit is +27 degrees - a whole 2 degrees or 8% higher than the F-16.

 

You can happily fly the Jeff at the limiter at around 86 kts, but you'll damn near need afterburner to do so. That is a mile away from maintaining 200 kts which requires around 78% N1 with a clean jet.

 

"No AoA drag" - mate, get a clue! :megalol:

 

From all the testing I've done, Jeff is higher performance than the F-16.

 

The only limit I found that is significant is max g - I get limited to +8 g. Any way to override this?

 

I'd like to see these YouTubers fly the JF-17 against the F-16. The F-16 may be WIP but the basic flight model should be comparable in finish, so would be a far fairer test of the -17 to go up against a more equal rival.

 

There is only one reason none of them have done so...

Edited January 27, 2020 by Tiger-II

[AeriaGloria]

I think what Cap was trying to say that in his opinion it should struggle more at that speed with a higher fuel burn in comparison to F-16. He was “calling BS” based off his tests where fuel burn didn’t increase at slow speed the way it does in F-16(you can see the Lbs/Hr graph on the right at the end of the video). Otherwise I don’t think he would’ve made the alpha comment(rewatched and caught him also suspecting the alpha is too low during takeoff)? I guess he is saying in his opinion he thinks it doesn’t pull enough AOA at 200knots to have its fuel burn increase from optimum cruise the way the Viper fuel burn curve is

Edited January 27, 2020 by AeriaGloria

[Tiger-II]

I guess he isn't considering several things:

 

1) IT ISN'T THE SAME ENGINE

2) Jeff is a lighter aircraft

 

There are lots of reasons why it could very likely burn less fuel.

 

Here are a few:

 

1) Jeff has higher TwR meaning less power required for a given condition

2) The engine is more efficient generally

3) The engine is more efficient in that part of the flight envelope

4) More advanced engine resulting in greater fuel economy

5) Viper engine is a gas-guzzler compared to everything else

 

Why the hell does he remotely think the JF-17 should be burning more fuel?!

 

All things being equal, JEFF IS LIGHTER! It requires less thrust ANYWAY. There is your instant fuel saving.

 

If he wants to do a fairer comparison, load both aircraft up to the SAME TWR and drag. Now compare stats.

 

The only other fair comparison would be similar load-outs and see which is more efficient in a given role (e.g. two sidewinders, two SD-10/AIM-120, 2 wing tanks and a centerline jammer). At least this would be a "comparable role".

 

Jeff would still win I think because it is still the lighter aircraft.

Edited January 27, 2020 by Tiger-II

[AeriaGloria]

I think the engine might actually fall behind F404(using it for comparison instead of F110 since F404 is in same size/thrust class as RD-33/93) in efficiency, because currently used RD-93 still doesn’t completely combust all of its fuel causing the smoke in military power.

 

It’s also important to note it’s Super Hornet sized LERXes creating stronger vortices then Viper while also increasing its instability. The original FM video series Deka did noted it becomes more unstable(and thus potentially less downforce needed) the slower it gets.

 

I would calculate wing loading to see how that compares but first I need to look up what parameters are usually used to measure it in regards to internal fuel/armament. It’s wing area is 24.4m squared if anyone wants to check it.

Edited January 27, 2020 by AeriaGloria

[MagicD]

pls look at "The power required curve" diagramm http://www.pilotfriend.com/training/flight_training/aero/man_force.htm hope you can understand me what i mean with fuel consumtion at low speed and alpha

[MagicD]

lower and higher of the minium power/drag airspeed ... you have to use more power and have more fuel consumtion

[MagicD]

pls look at the model of mig 29 in the video from post #1 ..it shows a true power curve diagramm like all other planes in DCS

[AeriaGloria]

Yes different planes can have different curves. I don’t think it’s completely implausible that the cruise curve is a larger shallower curve that is hard to notice on the slower end. If you account for testing/rounding errors and that the FM is supposed to be accurate to 3%, I don’t see how a shallow cruise curve as tested by Cap shows there is something wrong with the flight model

 

Looking at the fuel burn graph it looks like the data starts at 383 MPH GS for JF-17 and Viper. That’s pretty fast, why judge it’s AOA as too much at 200 knots with that metric? I wonder what it would show if tested and graphed as low speed as the F-14 or Mirage. On the left it looks like JF-17 was tested slower but I don’t see the data on the graph? Look at the A-10 curve and how flat it is, is that flight model also wrong, or could it possibly just show that the A-10 is optimized for efficiency across a wide range of speeds?

 

Keep in mind a pound is a higher percent of weight to the JF-17 then F-16, like a smaller car it makes sense to be below the F-16 curve when measured in Lbs/hour. The other dark blue line is F-15 right?

Edited January 27, 2020 by AeriaGloria

[MagicD]

but the jf17 dont not have a curve. it is linear

[MagicD]

yeah the blue one is from f15

[MagicD]

but the Diagramm shows that the mig29 is really effencent it has two engines and is more effencent as f18 or F15

 

 

i see from the data (video post #1) that it is is possible, if just one russian Klimov RD-93 engine build in to get this low fuelconsumption.

Edited January 27, 2020 by MagicD

[AeriaGloria]

but the jf17 dont not have a curve. it is linear

 

As tested between 383 MPH GS and 557 MPH GS. This is not its entire useful speed range but only the high cruise portion, which I’m sure many engineers would want to make a flatter cruise curve for a wide range of speeds, just like you see with A-10.

 

As for MiG-29 I don’t know what you mean. Aside from the engine similarity, what are you trying to say in respect to Fulcrum Hornet and Eagle? That the JF-17 should have a cruise graph like MiG-29?

Edited January 27, 2020 by AeriaGloria

[MagicD]

if you want to flatter the cruise curve ..than you have to build a plane with wings like A10 or an civil airliner.

[MagicD]

with the fuelconsumption of Klimov RD-93 engine (show in video post #1 it is possible to get this farry ranges...but the "power curve diagramm" of the jf17 looks not real

[AeriaGloria]

if you want to flatter the cruise curve ..than you have to build a plane with wings like A10 or an civil airliner.

 

The Super Hornet sized LERX lower wing loading and cambered root don’t count for helping it in cruise? Less washout then F-16 also:)

 

And what if the slower and higher speed portions of the graph were extended, maybe it would show a more obvious curve, who knows. It is only testing high speed cruise 383mph-557mph GS, hardly indicative of the entire power curve. The site you linked shows the bell shaped power curve starting at stall speed, I think you would need to extend the cruise curve in this test to lower speeds atleast if you want to show it’s linear and completely unlike a “proper” power curve

Edited January 27, 2020 by AeriaGloria

[AeriaGloria]

At very slow speed and high AOA it certainly does take an increase in power to maintain altitude, I guess you haven’t flown it, but it does happen. You would certainly see a curve if the test was extended to more then 200mph of cruise.

 

I checked the NASA Mach calculator(https://www.grc.nasa.gov/www/k-12/airplane/sound.html) and this post by a dev(https://forums.eagle.ru/showpost.php?p=4045960&postcount=13) with best cruise speed. The best cruise is listed as Mach .8 and 36000 feet. Caps test is at 32500 feet, and 383mph-557mph is Mach .571-.83. This is likely the very bottom left half of the cruise curve

Edited January 27, 2020 by AeriaGloria

[MagicD]

ok ..thx for testing :)

[MagicD]

i think..the best way is to do some wind tunnel or fluid simulation of the shape jf17 model to get the true charateristic.

[Shiz]

Why do you even compare f16 and jf17, they seem to have totally different airframes, airfoils, weights, centre of masses, configurations and aerodynamics, etc.

And there is no mig-21 comparison, that would make a bit more sence, since jf-17 is a deriviative of mig-21.

And the graph is too choppy and undetailed. Too few measurements were taken to see any curves to judge of any suttle behavior changes based on airspeed, we need a better more detailed test anyways.

Perhaps the curve function is there, but you do not see it, since you look only at 4 choppy measurements for 300+, instead of like 20 measurements of 100-300. Or it could be of measurement error... whatever...

Edited January 27, 2020 by Shiz