Forum: Civil and General Aviation

Out of curiosity, why do most civilian jet aircraft not have a "afterburner"? (If for no other reason than just to have fun.) I was looking on-line at the Viper Jet and Javelin Jet and noticed that neither has an afterburner. Since these jets will be sold as "toys" wouldn't having an afterburner make them more marketable? I don't know anything about jet engines but based on the following, it doesn't appear to be a difficult process to add one (the Viper Jet will even use the J85 engine which I believe is the same engine used on the T38):

The big advantage of an afterburner is that you can significantly increase the thrust of the engine without adding much weight or complexity to the engine. An afterburner is nothing but a set of fuel injectors, a tube and flame holder that the fuel burns in, and an adjustable nozzle. A jet engine with an afterburner needs an adjustable nozzle so that it can work both with the afterburners on and off.

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Fuel, weight, and complexity.

I can tell you have never used a fork lift to raise an afterburner onto a trailer, as it's too heavy for two folks to manually lift.

I've taxied by a Demo Viper before at Marietta NAS with a busted AB. They are capable of breaking and require more maint.

They don't have the fuel to waste for the little gain offered. I can burn all my fuel in 12 minutes in burner, that's 6968 pounds, or I can burn it all using only burner for TO and 114 minutes doing a 900 mile cross country. We, nor can they, afford to spend $3,600 in fuel to only get a couple hundred miles and fly for 12 minutes.

JR, you're forgetting the possibilities of roasting marshmallows and hot dogs in the 'burner flame when the grill goes Tango Uniform at the airshow LMAO

!!!

In all seriousness, I think the fuel penalty and the fact that they're just not needed are the biggest reasons here. These are small personal jets that don't have to go supersonic - and going supersonic is TOUGH in the US as you have to either be on a DOD contract in an approved Supersonic Corridor, or you have to go out past the 12 mile limit over the ocean. Supersonic may be cool, but it ain't really practical for Civvie jets Wink

. Then there's that speed limit in US airspace below 10,000 feet - no faster than 250 knots indicated unless it's unsafe. JR and the Starfighters get to cruise around in the Zippers at 350 due to safety considerations - it's not as safe in the 104 to fly slower. Even once in IFR above 14,500 feet and under air traffic control, you can only go .99 mach max. So why waste the gas you don't have and can't afford?

I'll agree that it would be fun to have a 'burner for those times when an "unrestricted climb" would be useful to impress the new girlfriend in the back seat Twisted Evil

!

Well, then why do the T-38's and F-5's that Chuck Thorton refurbish come with an afterburner? Perhaps there is a safety reason however, I'm guessing its just to give the end civvie user the right to say that he has the power (kind of like the person who buys the new Corvette Z06. He doesn't need 500+ horsepower or a top-speed of 198 mph but he has it). A person who can afford $5M for a Javelin Jet will have no problem with a $3,600 fuel bill.

Spiker wrote:

Well, then why do the T-38's and F-5's that Chuck Thorton refurbish come with an afterburner?

Ummmm.....probably 'cause both of those models are ex-military jets and the military wanted AB on 'em? How many showroom-new civilian T-38s to ya see bein' built? The only engines that'll fit the bay are the original GE J85 series - that comes stock with AB. Does Thornton get to use AB? I'm tumbleweed but if so he's probably way restricted as to where and when.

Fact is, there's just no private sector market for an AB-equipped civvie jet.

One other reason that wasn't stated earlier: NOISE. Most civvie jets fly outta civvie airports and most of those get a little sensitive on the noise issue. John Wayne/Orange County CA (KSNA) is probably the most anal about it. So unless your a military driver doing a once- or twice-off airshow routine using the blower, chances are you'll never get a clearance for AB ops in the airport area even if you had one. So why bother?

"If it floats, flies, or f#cks, it's cheaper to lease"...

There has been, IIRC, one supersonic home-built jet ever made, the BD-10. The plane was a POS...hard to fly, hard to maintain, and expensive to operate. The flight test program was marred by delays and problems, and cost a friend of mine his life.

The BD-10 did not sell very well, and production ended after a very short run.

Beers and MiGs were made to be pounded!

Here is the response from the Viper Jet people: "The A/B is too heavy and long, the Viperjet will not handle the C/G difference."

That's why I mentioned...

Quote:

Fuel, weight, and complexity.

I can tell you have never used a fork lift to raise an afterburner onto a trailer, as it's too heavy for two folks to manually lift.

Maybe not for a J85, but it's taller than normal humans for the J79!

Even if it could fit and the weight and balance worked, what percentage of your fuel would you use up in mere minutes??? If an F-14 can go through its entire fuel load in seven minutes in burner, how long would you have before you're bingo in a Javelin????? Not long. So even if you can pay for the gas, you can't carry enough to make it worth while Wink

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Avtechgroup claims the following on their website "Since performance is a key requirement, the Javelin uses next generation engines. Two engines, which combine to produce a thrust-to-weight ratio greater than the supersonic T-38 Talon." I assume the Talon has a greater thrust-to-weight ratio when in afterburner?

Merely having afterburners does not necessarily improve your thrust-to-weight ratio over a non-afterburning jet. Will explain in a moment...

Anyway, you got me curious, so I had to do the metric conversions, just to get this right. Wink

The Javelin weighs just over 2,500 lbs. The two FJ33 high bypass turbofans put out 3,400 lbs of thrust.

The T-38's max takeoff weight is 12,093 lbs. Its two J85s put out 2,050 lbs. of dry thrust and 2,900 lbs. with AB. Thrust after the Propulsion Modernization Program has been upgraded to 2,200 lbs. of dry thrust and 3,300 lbs. with AB.

The Javelin's two big advantages are its two high bypass turbofans (making AB redundant and unnecessary), and its low weight.

The T-38 has a higher weight, and has low bypass turbojets, making AB necessary for supersonic flight. The Javelin will do nearly .92 Mach without burners! Now, how's that for smoking? Cool

Beers and MiGs were made to be pounded!

ok, stupid question...if the Javelin is lighter and has more thrust than the T38 in afterburner (3,400 vs. 3,300) why is the Talon faster (or why can't the Javelin go supersonic)?

Spiker wrote:

...if the Javelin is lighter and has more thrust than the T38 in afterburner (3,400 vs. 3,300) why is the Talon faster (or why can't the Javelin go supersonic)?

While I'm still waitin' on ATG's website to load (over 5 minutes now) so I can view some specs, I'll repeat my point that the Jav wasn't designed to break the Mach on a regular basis whereas the F-5/T-38 was, T/W ratios not withstanding. Can the airframe go supersonic in certain situations? Possibly. It certainly looks slick enough. Cool

But the inlet geometry may not be able to slow the airflow down far enough to keep the FJ33s out of their stall envelopes. The greater thrust in the Jav may also have been a function of it's balanced runway spec (3900').

The Jav may have future military applications involving supersonic speeds which may require some airframe/powerplant redesigns to a mil spec, but the baseline commercial version of the Jav was designed using a set of market parameters that didn't include being able to go above the Mach.

Maybe JR007 ("Mr. Zipper") can expand on this, but I believe for a civilian to be able to merely fly supersonic-capable aircraft you have to have a special high-performance certificate from the FAA saying you're qualified to do so. It's possible that most of the potential civilian Jav buyers didn't want to go to the extra training, expense, and re-cert requirements to maintain that certificate. So the Jav designers just didn't include supersonic performance in the jet.

LinkF16SimDude wrote:

Maybe JR007 ("Mr. Zipper") can expand on this, but I believe for a civilian to be able to merely fly supersonic-capable aircraft you have to have a special high-performance certificate from the FAA saying you're qualified to do so. It's possible that most of the potential civilian Jav buyers didn't want to go to the extra training, expense, and re-cert requirements to maintain that certificate. So the Jav designers just didn't include supersonic performance in the jet.

Most of US airspace has restrictions against going supersonic so there's no point in putting the feature on a US civil aircraft. It scares the general public and the Government gets sued. In fact during 9/11 two Vipers went supersonic over Dayton trying to get to the airliner that went down near Pittsburgh. The sonic booms caused such a panic in Dayton that people thought the town was being bombed. We live in a land of scared sheep....

Elite 1K Joined: May 26, 2005 - 08:39 PM Posts: 1496

I'd guess the lack of sonic booms over the US contributes to the ignorance. People hear a loud bang, they think bomb. Sonic booms over the US are so rare that it's no wonder people don't have a clue.

Forum: Civil and General Aviation

Afterburner