Operational Performace Comparison: Viper, Beagle, and Stubby

Hello All,

I have received a lot of interest on this comparison, and it is honestly still going. Each aircraft has over 500 data points that must be looked up, cross checked, and calculated. Due to the time this is taking I figured I would go ahead and make the thread and let people know of my progress/limitations I am having.

Just to re-cap, I am comparing certain kinematic parameters for the Viper, the Viper with CFT, the Mudhen/Beagle/Strike Eagle, and "Stubby". All aircraft will have similar payloads (the F-35 will, when clean, have two fewer AAMs) and similar mission sets for both A2A and A2G. These missions are a 500nm CAP/Interdiction, in which loiter time will be measured, and Escort/Deep Strike, in which max range will be measured. Each mission will be calculated once with no external tanks, once with tanks retained, and once with tanks dropped. These again will all be calculated for both an Optimum cruise profile, in which cruise speeds and altitudes will be measured, and for an Operations Limited 20,000ft and 0.8M flight profile. In each case, the Structural G, Lift G, and Thrust (Sustained) G, available at the given cruise speed/altitude is calculated once at the 500nm point. The 0.8-1.2 level acceleration is also recorded to show excess transonic power available.

My calculations for the Stubby's performance is based on all the data that has been publicly released (most helpful of which was the statement of fuel burn at a given speed/alt), all data I have gathered over the last 14 years about dynamic trust, fuel burn, and wave drag, combined with my education as an Aerospace Engineer.

So Far my calculations show a few things to say I am on the right track, under the Op Limit case, Stubby has a radius of just under 600nm (remember, the range estimates are calculated using a "specific flight profile" among other assumptions) and an ability to sustain ~1.25M without Afterburner.

Currently my biggest logjam is decided where to put the Drag Divergence number for the Stubby as it greatly determines the Optimum Cruise speed. The F-16C and F-15E have a difference of ~0.06M when clean in this regard, with the Beagle being the higher of the two. The F-35 has a smaller frontal area than the Beagle, similar Mil Thrust, smaller wetted area, and when I look at all the various "bumps" on the F-35 I notice that as one decreases another grows trending to what is possibly a perfectly smooth (granted not the thinnest) area ruling.

More to come!

Hello All,

I have received a lot of interest on this comparison, and it is honestly still going. Each aircraft has over 500 data points that must be looked up, cross checked, and calculated. Due to the time this is taking I figured I would go ahead and make the thread and let people know of my progress/limitations I am having.

Just to re-cap, I am comparing certain kinematic parameters for the Viper, the Viper with CFT, the Mudhen/Beagle/Strike Eagle, and "Stubby". All aircraft will have similar payloads (the F-35 will, when clean, have two fewer AAMs) and similar mission sets for both A2A and A2G. These missions are a 500nm CAP/Interdiction, in which loiter time will be measured, and Escort/Deep Strike, in which max range will be measured. Each mission will be calculated once with no external tanks, once with tanks retained, and once with tanks dropped. These again will all be calculated for both an Optimum cruise profile, in which cruise speeds and altitudes will be measured, and for an Operations Limited 20,000ft and 0.8M flight profile. In each case, the Structural G, Lift G, and Thrust (Sustained) G, available at the given cruise speed/altitude is calculated once at the 500nm point. The 0.8-1.2 level acceleration is also recorded to show excess transonic power available.

My calculations for the Stubby's performance is based on all the data that has been publicly released (most helpful of which was the statement of fuel burn at a given speed/alt), all data I have gathered over the last 14 years about dynamic trust, fuel burn, and wave drag, combined with my education as an Aerospace Engineer.

So Far my calculations show a few things to say I am on the right track, under the Op Limit case, Stubby has a radius of just under 600nm (remember, the range estimates are calculated using a "specific flight profile" among other assumptions) and an ability to sustain ~1.25M without Afterburner.

I'm not too sure about your range estimates... depending on your assumptions, 600nm for a full heavy A2A load is incorrect. That's basically the same radius as the A2G load out with 4000lbs of bombs. The Radius with a light A2A load (only two missiles) is around 700~750 NM.

My calculations for the Stubby's performance is based on all the data that has been publicly released (most helpful of which was the statement of fuel burn at a given speed/alt), all data I have gathered over the last 14 years about dynamic trust, fuel burn, and wave drag, combined with my education as an Aerospace Engineer.

Where did you get the fuel burn rate data? The only number I've seen was a comment on a blog post saying ~4600lb/hr at 30k and Mach .75 with a 2500lb weapons load, but it doesn't mention fuel load (or better gross weight), so I don't know how useful that is. A clean ~28klb viper with a full tank will consume something like 1/3rd more fuel/distance at optimum cruise than the same viper at 21klb about to flame out. With a much larger internal fuel fraction, I would imagine that figure varies much more for the F-35 than it does for the F-16C.

Castlebravo, I used the data you listed along with the publicly released figures of the airframe and engine to estimate both the drag, and thus the weight, of the aircraft as there was also the KEY statement of that being the max endurance point.

hb pencil, a mud moving load of ~4700lb or a full 6AAM A2A load of ~2100lb is a difference of ~2600lb on an airframe that is weighing roughly 50,000lb mission starting weight, a mere 5% difference. Since the drag is essentially the same minus the added lift drag the radii for a mud mover and its escort is very small. Also remember that the range figure I gave is for the constrained sub-optimal flight profile (and is in the ball-park of the "official" figure), the optimum profiles are giving numbers in the 700+ range like you state.

Thank you both for you input, I always like to see people thinking critically.

I have Preliminary data for the F-35 (unless I decide through input here to change the drag divergence mach number from the lowest value to a higher value) completed, F-16C completed, F-16C w/CFT and F-15E are about 30-40% done.

Castlebravo, I used the data you listed along with the publicly released figures of the airframe and engine to estimate both the drag, and thus the weight, of the aircraft as there was also the KEY statement of that being the max endurance point.

What was the gross weight you ended up with for 4600lb/hr cruise?

about 39,000lb

Sprts. Can't wait to see this, by the way, what Stubby model are you using? I have a hunch its the A, I'd be happy to see the C model as well, in my oppinion the A and the C models should rival each others Kinematics in different ways.

better T/W ratio vs better W/L,

"A" may have better IST Turn rates and G handling while the C may get better STD Gs esp at higher altitude, similar to the claim that Eagles are more maneuverable than vipers above 30K feet, or something like that

also watching an old JSF documentary, I remember it was the Navy that required more maneuverability which gave Boeing designers a headache with their less maneuverable X-32 design.

The docu didn't say if the AF had any such requirements, I guess they didn't since at the time they thought they would have 300+ insanely maneuverable F-22s anyway.

So i'm guessing they were happy with X-32 class agility, but the docu did say that LM had no problems with the increased performance requirements of the Navy.

'zero-one' not quite sure what you mean by this quote (from an old documentary?):

"...also watching an old JSF documentary, I remember it was the Navy that required more maneuverability which gave Boeing designers a headache with their less maneuverable X-32 design...."

Lots of things give people headaches these days. However it is clear to me that the USN F-35C requires good manueverability at the required minimum/maximum carrier landing approach KIAS and weights. The weight/speed combination is set in stone for the current capacity of arrestor gear. There are no ifs or buts for the maximum required bringback weight and the airspeed combination otherwise the arrestor gear breaks. The KPP is 145 knots for the required F-35C bring back weight KPP (thrown in are the required fuel levels to achieve other criteria accounting for weather etc.).

Is this what you mean?

Classic 'Bowman' quote re USN KPP:

Scorecard: A Case study of the Joint Strike Fighter Program
Geoffrey P. Bowman, LCDR, USN — 2008 April - pages 10-11

"...The Navy has added approach speed as a service specific key performance parameter. The threshold for approach speed is 145 knots with 15 knots of wind over the deck. This must be possible at Required Carrier Landing Weight (RCLW). The RCLW is the sum of the aircraft operating weight, the minimum required bringback, and enough fuel for two instrument approaches and a 100nm BINGO profile to arrive at a divert airfield with 1000 pounds of fuel. The minimum required bringback is two 2000 pound air-to-ground weapons and two AIM-120s. The Navy further requires that the CV JSF be capable of carrier recovery with internal and external stores; the external stations must have 1000 pound capability on the outboard stations and maximum station carriage weight on the inboard."

Source: http://www.f-16.net/f-16_forum_download-id-14791.html (PDF 325Kb)

zero-one, I am doing the A model for this go. I will have to make a few assumptions to create a model for the C to properly account for how the big wing will impact form drag and wave drag. WRT turning, the data I am seeing now is that under most operational scenarios the C will have better instant and sustained turn rates as the F-35A is lift limited under these conditions. What the F-35A will have that I do not expect the C to have is the M1.25 max speed in Mil. But I will do the C comparison against the F/A-18E.

'zero-one' not quite sure what you mean by this quote (from an old documentary?):

I think the title was "Battle of the X planes"

sometime in early development it said that the Navy increased the maneuverability requirement for the JSF

Which was one of the considerations (Im sure there were more) for Boeing changing the design from a heavy Pure delta to tailed delta like the F-22/35, which for a time was being considered to be a Pelikan tail design

zero-one, I am doing the A model for this go. I will have to make a few assumptions to create a model for the C to properly account for how the big wing will impact form drag and wave drag. WRT turning, the data I am seeing now is that under most operational scenarios the C will have better instant and sustained turn rates as the F-35A is lift limited under these conditions. What the F-35A will have that I do not expect the C to have is the M1.25 max speed in Mil. But I will do the C comparison against the F/A-18E.

Wait hold on! the C will have better IST turns than the A?

I thought Smsgtmac said the A will have better ist Turn performance

'zero-one' I think my explanation accounts for the doco comment. IT is important that the F-35C lands on a carrier as required in the KPP - otherwise?

'zero-one' I think my explanation accounts for the doco comment. IT is important that the F-35C lands on a carrier as required in the KPP - otherwise?

Possibly, all they said was, "The Navy wanted a more maneuverable fighter"

then Boeing changed their final design, but pushed with the prototype.

Since the F-35 is billed by many to have Hornet like Agility, and the X-32 is less maneuverable than the X-35, then it could be that the X-32 was expected to have less than the F/A-18's performance.

I guess the Navy simply didn't want a step backwards in performance

Again all these are just guesses

Just as one speaks of the devil.... youse can hear the chains rattle - or synchronicitical co-incidence? The long running thread about the MILLStones at where ever will have a test pilot comment about the F-35C Manuver ABilitity. I'm not spellin' well today am I?

viewtopic.php?f=57&t=15767&p=274976#p274976

Here is the quote there:

"......Another major test programme currently under way at VX-23 is high angle-of-attack (AoA) envelope expansion. Initial envelope expansion and intentional departure testing, which required the use of a spin recovery chute, was conducted with F-35B BF-02 and F-35Cs CF-01 and CF-05. The ITF then conducted initial low-speed departure resistance testing, high AoA loads testing, and high AoA buffet testing with F-35B BF-03 and F-35C CF-02 to prove the recovery characteristics of each variant from uncontrolled flight.

“The ‘B was not expected to be much different from the ‘A because the wings are a similar shape, the tails a similar shape, but the mass properties distribution differs because the propulsion systems are different, and each variant’s fuel load is carried differently. Fundamentally the aerodynamic shape of the ‘B and ‘A is broadly similar, whereas the C has a different wing and a massive tail. While the B is turning out to be very nice, the C is the most remarkable, it’s absolutely awesome at 50 alpha and very controllable,” said Peter Wilson STOVL lead with the Pax F-35 ITF...."

zero-one, I am doing the A model for this go. I will have to make a few assumptions to create a model for the C to properly account for how the big wing will impact form drag and wave drag. WRT turning, the data I am seeing now is that under most operational scenarios the C will have better instant and sustained turn rates as the F-35A is lift limited under these conditions. What the F-35A will have that I do not expect the C to have is the M1.25 max speed in Mil. But I will do the C comparison against the F/A-18E.

Wait hold on! the C will have better IST turns than the A?

I thought Smsgtmac said the A will have better ist Turn performance

Under some circumstances he is correct. Two things limit an planes ITR: Lift and Structure. Generally only one limits at a time and which one is dependent on speed.

Below Corner Velocity a planes turning is limited by how much dynamic pressure it can put on the airframe at Max Lift Coefficient. Dynamic pressure it determined by air density and airspeed. At 30-40kft and subsonic most aircraft are lift limited as the dynamic pressure for corner velocity will be well into the supersonic region.

Above corner velocity a planes turning is limited by the structural loads imposed by the lift limit (in the case of the F-16 we are talking the neighborhood of 234,000lb, or 9G at 26,000lb). At Sea level this occurs between 350 and 500 knt and the speed only goes up as air density goes down.

So, as you can see the 9G F-35A will have the advantage in a super sonic fight or transonic at low altitude, but the F-35C with an extra 50% wing will hold the advantage at lower speeds.