Forum: Civil and General Aviation

Going to multi-engines together, in juxtaposition, there is a vortex generator placed between the two engines to separate turbulent flow.

On the F-15, the problem was the thrust from the engines were blowing off the "turkey feathers" so they took them off. That was due to a vacuum between the engines sucking off the feathers. Then again, converging/diverging nozzles are an engima when placed close together due to those "turkey feathers" coming off because of the thrust from the engines creating a vacuum in between each other.

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Thanks for the kind words AP! Lordofbunnies is still in school, I came to school on this forum!!!!!!!! Still learning myself, there are a lot of knowledgeable people around here, yourself one of the foremost may I add! I value your perspective.

Lordofbunnies is asking the kind of questions that I would ask if I had more time! I cant believe I have 100+ posts up already having said that Very Happy

Keep asking questions `bunnies, you have some very good ones. Several engine manufacturers have small jet engines, how does the Williams effort compare in price I wonder?

The VC` does have two engines in tandem. The XB-70 had 6 engines together called the "6 pack". I wonder if the XB grouping experienced thermal problems like heat soak?
There have been more than a few aircraft with tandem engine configs`. I would imagine they would be well insulated from each other. Do jet engine casings get particularly hot?

The Williams effort I don't know about, I'm sure on the XB-70, the heat sink problem was certainly worked out the same way it would worked out on the B-1, F-117, and F-4 Phantom. It's not that big of a deal, I will research the William's effort, don't know anything about it, never heard of it.

The major thing about the Williams engine is that its so light and produces a fair deal of thrust for what it does. It's about 12 inches (30 cm) across and it can do all that. If you want something interesting look up the NASA SATS program. They are trying to basically make a move at personal air vehicles. I could go on a speel about what I'm doing with my professor in the lab, but most people wouldn't be all that interested and there are some very biased and ticked off people at NASA. Anyway, they are doing a small tail fan aircraft. It looks goofy but the design (at least from what I can see) is very good.

There are a few small engine manufacturers out there, P&W Canada is making some for the class of Very Light Jets that are coming out. Williams is another one. The biggest thing of is GE IS TEACHING HONDA. What Honda did for cars, GE is hoping they'll do the same for jet engines and aircraft in general. If you're really bored, look up the Honda Jet.

Thanks Bunnies - will do. Wow, a personal jet! What a life!

Yes, it's true, NASA people are very biased and ticked off! They must be looking for a few "Pe'od people", sort of like the Marine Corp.

Just a thought about civil engines..... I took a flight once to Germany with HLX airlines, a German carrier. I got aboard a Fokker 100. I was seated right at the back of the aircraft, right between the engines. The noise from them was TERRIBLE!!!! The cabin crew had a bag of ear-plugs! I had to wear them for the whole flight. You couldn`t hear the person next to you without the plugs.

How did Fokker get away with producing a commercial plane that deafens its passengers!!!!!! I dont know what engines propelled the beast but I wont be sitting in the tail section again!!!!!!!!!!!!!!!!!!

Synpa - I do believe the Fokker is equipped with turbo-jet engines, just like the Caravel (a French design, going back to the 60's I believe). They are classic noise makers. I do remember flying in the Caravel in the front of the fuselage and the crew were indeed handing out earplugs!

Ahhh, turbo-jets! thanks for that AP! Praise the lord for turbofans!!!
In that Fokker 100, they took out the windows between the engines and put thick soundproofing in their place....It didn`t work!!!!
Wonder why they haven`t upgraded the engines. I guess that`s why HLX can offer flights between the Uk and Germany for five dollars!!!!-return! Was the Caravelle THAT uncomfortable too? I guess civil airliners are a luxury compared to the noise a millitary jet makes!!!!

Snypa777,

You are more likely to get those prices from a turbofan operating airline. I would imagine, like with any airliner, you have your power plant options on the Fokker 100. I think it is highly unlikely it had turbojets for many reasons. Turbofans can be very noisy too, especially if you are sandwiched between them…

Pat - Your post says "turbofan engines", in the first sentence. I think you're right. The Fokker 100 is a relatively new aircraft vs the operational status of a turbo-jet. And another thing about price, the turbofan engine is extremely economical vs the turbo-jet. The Caravelle I flew did however have turbo-jet engines.

Being sandwiched between two turbo-jet or turbo-fan engines is nerve racking; ie early 727's. The MD-80 is however very quiet, very smooth. I did work on engine procedures on the MD90, the Rolls Royce V2500 engine. Never had an opportunity to fly in it, great theory and design, but the airplane never flew well. There were no wiring harnesses between the pylons and engines, all electrical input from the PLA's were relayed through the pylon to the engine via EMF. What frequencies? I really don't remember, however I can imagine once the aircraft was flying, it was pretty quiet.

Synpa - another Rolls Royce design, super engine. Three spools, of course and a ratchet locking system that sensed vibrations of the turbine and when this occured this ratchet system incorporated into the N1, N2, and N3 cranks, would lock up the engine with a wire that would twist its way around the shafts and cease engine RPM. Pretty sneaky design that kept the engine from spitting turbine blades when times were getting fatiguing on the engine. It also incorporated Full-Authority-Direct-Engine-Control (FADEC) just like GE or Pratt, another unique system whos' origin I do not know. Any questions about the FADEC system, just post and we'll talk about it. I did much work on the FADEC system.

Most of the noise that you hear on the ground and for the most part in the air, on jet fighters, occurs from the intakes. The F-16 and T-37 were loud, the F-4's engines were quiet, however, when the speedbrakes were deployed, there was a loud, but such a cool whinning sound that came from the airframe on downwind, really loved to hear that thing pop-out! Very Happy

Fellas, the Fokker 100 engines were turbofans after all. Rolls Royce Tay 620-15`s. Later ones use the Tay 650`s. The 100 was the last airliner Fokker ever built before they went bust. They were owned by Daimler Benz.

I know the Tay is a high-bypass engine, most of the bypass duct is made of carbon fiber. It is said to be reasonably quiet! I would hate to fly on the Fk-100 with engines that made MORE noise!
Is intake noise most of what you hear on the ground on civil jets? Does the fan make all the noise? The earliest analogue FADEC that I can recall was used on Concorde Olympus 593 engines, waaaay back. That is the earliest use I can think of. SNECMA and ROLLS could have come up with that system jointly.....Unless they sub-contracted out the work.
Didn`t NASA produce the first digital systems?
Sorry, so many questions!!!!!!!!!!

Synpa - I didn't know the Concorde and Rolls Royce had incorporated FADEC, so, I am assuming you know all about the system. Thats an awful lot of knowledge that you've acquired the last several months. Boy, I need to go there.

As far as digital, I would guess to say with accuracy that NASA did indeed create it. Wouldn't know exactly when, however.

As far as intake noise, thats all you'll hear when you have a military aircraft coming at you, (just about) as it travels past you, you hear what is known as "exhaust shear". It's the relative wind that cuts through the static air that causes the "roar", also if you are in burner, with the aircraft on the ground and standing just a few feet away from the nozzle of an F-16, you can feel your internal organs vibrate. It is awesome none-the-less. I am fortunate to have been an F-16 Crew Chief. Very Happy

AP, the Concorde system is an analogue system so ...really cannot be called a FADEC, rather, it was the grandpappy of the FADEC. It was not a fully integrated system, ie one system controlled fuelling and the primary nozzle, a separate control system ran afterburner fuelling. The system was very complex. A maintenance nightmare I have been told!
I am hungry for knowledge! Aviation is just an avid interest of mine. I am looking at aerodynamics and engine design right now. My background is in automotive engine control systems, fully integrated digital jobs!
Understanding FADEC systems on aircraft comes a little easier than aerodynamics to me!
Having your internal organs "shook" can`t be good for you! Certain very low frequencies can actually cause damage to the body over the years!!!

I have just read up on the origins of the digital FADEC, it was indeed NASA, with Pratt & Whitney who jointly developed the first civil/millitary FADEC equipped aircraft. The F-100 and PW2000 units being the first FADEC engines.

Active Member Joined: Jan 10, 2005 - 07:58 AM Posts: 137

Is it better from a failure standpoint to have FADEC or DEEC in your aircraft?

The DEEC systems are the forerunners of newer FADEC systems. FADECS can be fully integrated into flight control systems, like in vectored thrust aircraft. I think the early DEEC systems had good redundancy like FADECS. The HDDEC systems developed by NASA? were even more flexible. In the event of failures both systems can default to modes which allow use of hydrodynamic/ cable, redundant mechanisms. I suppose it depends on how reliable the stuff is and the overall system/integration/design. For which system is actually better, I would refer you to Roscoe or AP for anything definative... Wink

Forum: Civil and General Aviation

Aircraft Engines - Civil and Military