Re-Engining Fighter/Strike Aircraft - considerations

[supersonic1861]

Does anyone know what issues/problems/safety risks might be encountered by re-engining an aircraft i.e. removing the engine out of the engine bay and upgrading to another engine?

Ive been asked to look into this as a fact finding mission at work so if anyone has any info stored up in their head on knows of some information in the public domain, I would really apprectiate some pointers

 

[CB90]

Does anyone know what issues/problems/safety risks might be encountered by re-engining an aircraft i.e. removing the engine out of the engine bay and upgrading to another engine?

Ive been asked to look into this as a fact finding mission at work so if anyone has any info stored up in their head on knows of some information in the public domain, I would really apprectiate some pointers

A million little things.

Seriously, assuming the performance characteristics like power and fuel consumption are already resolved, there's stuff like:
-Physical size. You don't want to mess with the fuselage if you don't have to
-Auxiliary requirements. Power generation, fuel lines, new ECU/FADEC compatibility with flight control software
-Center of gravity specs
-Changes to airframe stresses. More power is good, but maybe not if it wears the airframe out faster.

This would be pretty standardized stuff in checklist form for a big engineering/aerospace company or govt activity.

 

[supersonic1861]

Thanks for your reply CB90. Thats a good start, I think I need to start thinking about hypothetical problems or issues that could arise during the programme to install the new engines. As you say there are probably a million little things. There is some heritage in this area e.g. F14A upgrade with GE F110 engine, but little information exists (understabndably) in the public domain on problems etc encountered.

A million little things.

Seriously, assuming the performance characteristics like power and fuel consumption are already resolved, there's stuff like:
-Physical size. You don't want to mess with the fuselage if you don't have to
-Auxiliary requirements. Power generation, fuel lines, new ECU/FADEC compatibility with flight control software
-Center of gravity specs
-Changes to airframe stresses. More power is good, but maybe not if it wears the airframe out faster.

This would be pretty standardized stuff in checklist form for a big engineering/aerospace company or govt activity.

 

[2007yellow430]

Didn't the Israelis re-engine their F4s? I think they put much later engines in them, which greatly increased power. Don't have enough posts put up a link, but I'm sure you can find that information.

Google Boeing Super Phantom.

Art

 

[kronos319]

You will also have to consider the effects the new engine will have on the Avionics.

-Mission Computer software will need to be reviewed (which will cost ALOT of money if you want the OEM to make any custom changes)
-The aircraft will most likely have to undergo some re-certification, at least for Avionics from an EMI/EMC perspective
-Wire routing will need to be reviewed as some may now be exposed to excessive engine heat

There will also be logistical and training impacts which will take time to get right. However, the benefits from re-engining can be great:
-Greater performance
-Extension of lift of type
-Lower maintenance cost
-Greater capacity for future upgrades (especially if the generators can supply more power)

 

[the_big_m_in_ok]

Years ago, in AW&ST, it was speculated in the West and amongst American military analysts, that if the Russian wanted to upgrade their biggest and fastest jet interceptor, especially with the latest and biggest Tu-144 engines, it was concluded that serious airframe redesign issues were required to be negotiated to make it fly safely, but that if they could manage it, the resulting plane would be faster than the new F-22---and with vectoring engine thrust nozzles---more agile in the air, to boot.

--Lee

 

[StobieWan]

Strange then - they already had a *marginally* mach 2.8 capable interceptor in the air. The F22 isn't that quick flat out - I think the Eagle is still quicker if in a clean config for instance. I don't know what the outright top speed of an F22 is but the airframe and engines were optimised for supercruise, not for top speed.

I'll get worried when someone fields something that can outrun an AIM120D.

 

[My2Cents]

Didn't the Israelis re-engine their F4s? I think they put much later engines in them, which greatly increased power.

Never got past the prototype. Boeing was apparently worried the design would compete with F-18 sales.

 

[the_big_m_in_ok]

Strange then - they already had a *marginally* mach 2.8 capable interceptor in the air.

The Mig-25, originally, and the later -31 Foxhound follow-on. Right. I'd say even if the AW&ST piece was correct---and not Russian disinformation---and that Tu-144 engines were attempted to be fitted into the Mig-31 airframe, the air intakes would have to be made significantly larger; and that might as well require a whole new plane to be designed around the engines. A bigger plane usually means a higher wing loading, and that would reduce performance accordingly.

The F22 isn't that quick flat out - I think the Eagle is still quicker if in a clean config for instance.

I did see in the same magazine at a different time, a model of the Eagle follow-on with the biggest engines that would fit into the fuselage at that time. The twin tails were canted to outboard by, say, 10-15 degs, and I mentally estimated that the plane was capable of Mach 3 at altitude. It never made it past the drawing board stage, I suppose, so the program probably died for lack of funding? My speculation on that.

I don't know what the outright top speed of an F22 is but the airframe and engines were optimised for supercruise, not for top speed.

Yes, exactly. Stealth was also built into the airframe to some extent as well, I recall. I suppose the Max speed would have been Mach 2.5 @ 60,000+ ft.? More speculation from distant memory.

I'll get worried when someone fields something that can outrun an AIM120D.

http://en.wikipedia.org/wiki/AIM-120_AMRAAM

Well, the SR-71 was rumored to go Mach 5 at 100,000+ ft for at least 5,000 miles but that was what I heard. Who know what highly classified aircraft designs have been produced since then?

--Lee

 

[the_big_m_in_ok]

Never got past the prototype. Boeing was apparently worried the design would compete with F-18 sales.

Originally quoted from post #8 and also referring to it:

I recall turbofans were fitted into the fuselage of an F-4, but the resulting performance wasn't something spectacular, so they went the way of the dinosaur.
LATER REEDIT:
Okay, here it is...

http://enwikipedia.org/wiki/List_of_McDonnell_Douglas_F-4_Phantom_II_variants

...under the Super Phantom heading near the bottom of the page. Never got past the theoretical stage. That project was cancelled. The IAI Super Phantom was built and demonstrated to go Mach 1+ without afterburners, but sales of this plane would have indeed competed against the F-18, so that much is true.

--Lee

 

[StobieWan]

Well, the SR-71 was rumored to go Mach 5 at 100,000+ ft for at least 5,000 miles but that was what I heard. Who know what highly classified aircraft designs have been produced since then?

--Lee

Max IAS recorded on an SR71 was something like M 3.4 for a few minutes over Libya while evading an SA-5.Max alt I can't speak to but no-where near 100,000 feet as far as I understand, since the engines are air breathers. Generally the 71 was limited by intake temperature to M3.2 Anyone told you M5, they were teasing.

Neither does the 5,000 mile range figure *unrefuelled* make any sense - those things were always just about to tank, had just tanked or looking for their next tanker at the speeds they were moving at.

 

[swerve]

Originally quoted from post #8 and also referring to it:

I recall turbofans were fitted into the fuselage of an F-4, but the resulting performance wasn't something spectacular, so they went the way of the dinosaur.
LATER REEDIT:
Okay, here it is...

http://enwikipedia.org/wiki/List_of_McDonnell_Douglas_F-4_Phantom_II_variants

--Lee

The British-built Phantoms had turbofans back in the 1960s. The engines delivered more thrust (both wet & dry) except at high altitude, & were more fuel-efficient - but drag was increased, & they performed worse high up. Top speed, & acceleration & climb rate at high altitude suffered, but take-off performance (important on small RN carriers), acceleration & climb rate at low to medium altitudes, & range all improved. I don't think top speed at low altitude was much, if at all, different, but it could be sustained longer.

That's sometimes portrayed as worse performance overall, with no mention of the areas where it was better.

 

[the_big_m_in_ok]

The British-built Phantoms had turbofans back in the 1960s. The engines delivered more thrust (both wet & dry) except at high altitude, & were more fuel-efficient - but drag was increased, & they performed worse high up.

Right, I agree with the high altitude performance being poorer. The 'fan' in a turbofan moves more air mass and gives greater thrust at the cost of a lower exhaust velocity. At altitude, this translates to lower speeds. Taking out some fuel to compensated for the loss in high altitude thrust and thus lower fuel consumption further may give less-than-adequate returns in performance. Thrust augmentation is a plus, though. 10%-20% more by proportion to turbojets. SFC suffers with more fuel consumption, as well.

--Lee

 

[koxinga]

Does anyone know what issues/problems/safety risks might be encountered by re-engining an aircraft i.e. removing the engine out of the engine bay and upgrading to another engine?

Ive been asked to look into this as a fact finding mission at work so if anyone has any info stored up in their head on knows of some information in the public domain, I would really apprectiate some pointers

Republic of Singapore Air Force | A-4 Skyhawk Association

"1984 to 1989:
The RSAF conducted a Skyhawk service life extension program. The 8,400-lb-thrust J65 engines were replaced with 11,000 lb. thrust F404-GE-100D turbofans. Other upgrades included modified engine air intakes; new structural mounts to accommodate the F404 engines; installation of new refrigeration, hydraulic pumps, air turbine starters, and oil coolers; new sensors, cockpit instrumentation, and state-of-the-art avionics; engine and environmental control systems; higher output electrical generators; and improved air-to-air and air-to-ground ordnance carrying and control capability.
In 1986 a upgrade program for the A4S-1/TA4S-1 fleet was initiated by the RSAF. This included a new engine, a non-afterburning General Electric F404-GE-100D turbofan. Engine inlet changes were made to accomodate the new engine. Other improvements were and turbine starter, improved hydraulics, improvided air and oil cooling. , Singapore gave the new model the designation A4S-1/F404, but it was sometimes referred to as the "A-4U". Later the aircraft's avionics package was upgraded, which included a Ferranti 4510 HUD, and a laser seeker."

 

[koxinga]

If you are willing to pay AUD 33, you can get this

Informit - Australian Aeronautical Conference, 1989: Research and Technology, the Next Decade, Melbourne, 9-11 October 1989; Preprints of Papers, The - F404 Engine Upgrade on the A4 Skyhawk (Engineering Collection)

Australian Aeronautical Conference, 1989: Research and Technology, the Next Decade, Melbourne, 9-11 October 1989; Preprints of Papers, The

F404 Engine Upgrade on the A4 Skyhawk

Abstract: The A4 Skyhawk was designed by Douglas Aircraft Company in 1952. Early production models were powered by the Curtiss Wright J65 engine and later models by the Pratt and Whitney J52 engine. The fitment of the J52 engine was a new production design.

In 1985, the Republic of Singapore Airforce (RSAF) initiated the first re-engine programme on the A4 Skyhawk. The old J65 engine that powered the RSAF A4 was replaced by the non-after burning F404-GE-100D engine made by General Electric of USA. The modifications involved in fitting the F404-GE-100D engine on the A4 are briefly described. The engineering considerations and constraints encountered in matching the new systems to the old airframe are elaborated. The experience gained from the re-engining of the RSAF A4 shows that re-engining is a viable process, provided the constraints resulting from the different operating and maintenance concepts of the old and new systems are understood early in the programme.