The Reno Racing Engines

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REALLY ???? What is the tip speed of a turbo fan in a high bypass Turbo fan engine on a large jet liner????????????????????
ie "Proper power delivery" This is a thinking out of the box time.



"The fan turns at a maximum speed of only 2,550 rpm"
"The General Electric GE90-115B engine is an advanced ultra high bypass turbofan engine "
Hmmmm 128" diameter at 2550 rpm. Hmmm lets see pi x 128 is 402.123 inches, so that is 1025415. ish inches a minute so that is
85451 feet a minute, and that is 16.18 miles per minute now times 60 makes it 971.03 miles per hour, hmmm I'd say they are exceeding the speed of sound there.

And some good info here as far as tip speeds go.
http://www.airliners.net/aviation-forums/tech_ops/read.main/291319

And we haven't even talked about axial flow compressors yet.
In the 10,000 to 11,000 range rpm that is. And all a compressor is in a jet is a short tip. So something just don't make sense.
 
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You're missing the key facts when comparing jet engine compressor, turbine blades or fan blades to propellers - first two different animals - Fan/ compressor/ turbine blades ARE DESIGNED to turn and function at those speeds and produce no shock wave over their surface because in the case of compressor and turbine blades they are COMPRESSING air within a contained enviornment where operating temperatures allow them to compress air without making shock waves. With a turbo fan, a temperature rise at the fan prevents the airflow at the fan from becoming supersonic. There is also some air compression being accomplished there as well as the fan is contained within a shroud. Just the process of compression will prevent mach speed airflow to develop. Additionally guide vanes and in some cases variable guide vanes within the compressor section will also prevent any supersonic or adverse airflow from affecting the compression function. In addition to this supersonic air is kept out of the intake by either intake design or using cones, guide vanes or diverging intake flow to the front of the intake.

Info...

Components of jet engines - Wikipedia, the free encyclopedia

Here's a full discussion on this very subject....

compressors immune to mach? [Archive] - Physics Forums

And from the link you posted it is further explained...

"The air pressure goes up through the fan (not a tremendous amount of velocity change within the fan itself), causing a temperature rise. Higher temperature means higher sonic speed, so you get a Mach number drop through the fan. The rest of the fan duct converts that pressure rise to velocity, and you get the air coming out the back of the nozzle just below Mach 1."

So although you calculated a tip speed of well over 900 mph, because of the heat within the shrouded fan or within an engine (if we're talking compressor blades) and due to the compression process you're actual airflow speed won't be supersonic, again contained within an enclosure (compressor case in the case of compressor blades, Fan shroud for fans) that creates and operating enviornment where a small airfoil can go over 900 mph and create no supersonic shock wave due to the elevated temperatures within the Fan shroud, compressor or turbine case.


An aircraft propeller is operating in an open enviornment subject to temperatures and air densities that will enable it to become transonic and even supersonic. When that happens the shock wave going over the propeller will cause all kinds of nasty things to happen effecting efficiency, performance and in some cases adversely effecting the airframe. There's also a vibration and noise issue. It was tried and failed...

Republic XF-84H - Wikipedia, the free encyclopedia

The operating environment of a jet engine fan/ compressor or turbine blade be it axial or centrifugal flow is apples and oranges when compared to a propeller. True they are both airfoils but they are accomplishing two different functions, and because of the operating environment of the propeller, it is nearly impossible to efficiently operate it at transonic and supersonic speeds.

So with that said I stand behind my statement. You are not going to get much more out of any propeller driven aircraft with regards to speed regardless how much power you put behind the propeller.
 
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First I dont' know what your meaning by tip speed and heat of the engine??? I was talking the big fan on the front and tip speed. Second there is no apples and oranges here because I never said to use a propelller did I? You brought up the propeller topic not me. Nothing says a recip engine has to just turn a propeller, no reason it can't as well turn the same ducted fan the jet is turning. As I originally said this is a thinking out of the box deal. That means lets forget the old propeller stuff. Lets think new stuff.
Well if anyone starts using this, we all know who's idea it is.

I started reading the one link.
And its talking about airflow THROUGH THE ENGINE, we are talking tip speed not anything about airflow.
They completly ignore the major difference.

What the topic here is why can a jet fan spin at its major diameter way over mach 1 and not loose its air pumping ie thrusting ability, and a normal old propeller can not do that?
 
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engguy said:
First I dont' know what your meaning by tip speed and heat of the engine??? I was talking the big fan on the front and tip speed.
Click to expand...
Fan Blades - contained within a shroud - air passes over it, it is compressed, temp goes up, mach number goes down. Same thing happening within the compressor...

You addressed By-pass Fan blade, compressor and turbine blade speeds... Your own words...

"REALLY ???? What is the tip speed of a turbo fan in a high bypass Turbo fan engine on a large jet liner????????????????????"

And we haven't even talked about axial flow compressors yet.
In the 10,000 to 11,000 range rpm that is. And all a compressor is in a jet is a short tip. So something just don't make sense.

I think its shown quite clearly why turbine engine Fan Blades, compressor or turbine blades (including their tips) can operate at speeds in excess of 900mph.

engguy said:
Second there is no apples and oranges here because I never said to use a propelller did I? You brought up the propeller topic not me.
Click to expand...
I brought it up because you didn't say anything about an alternative method of propelling the aircraft. My original statement addressed propeller speeds, look at post 40 - You responded, I answered your response.
So at that point you have a recip driving a ducted fan. OK - How much thrust/ SHP do you really think you're going to get out of it??? Also consider that the fans on Turbofans are agmenting thrust already being produced by the engine itself and are not really producing the majority of thrust. You're proposing a recip to drive a ducted fan, In essence you're back to square one as you're still driving a large fan for your primary source of thrust.

So going full circle here I doubt any current unlimited racer is going to see 550 mph at Reno.
 
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A dumb question. Is it the hot gases out the rear that create the most thrust in a jet? If so why have a "HIGH bypass fan? In another breath, the main goal nowadays with Turbo FAN engines, is to run the combustion process much cooler, to prevent NOx, so there goes some of those hot gases. So then is it the high pressure ratio from the compressor stages that creates thrust? What kind of fan do I have to hang on any motor to get thrust, this motor could be gas or electric. ?? Or is this high speed fanning only allowed in a gas turbine?

Back to square one? If a jet doesn't need it why have it?

I still don't understand why that huge fan can be spinning so fast and cracking the whip and still be an efficient air moving device.

I'd like to see a good link with photos explaining it.
 
Turbofans and turbojets, their effiiciency improve as energy/fuel/heat that is not wasted for heating all the propulsive airflow up to higher pressures and velocities more than needed to create propulsive power.
A bad but maybe reasonable anology would be; powerwise, turbojets are like sprinters, turbofans are like joggers, turboprops are like hikers.

The atmostphere isn't as perfect as a laboritory, CAD-CAM/CAP, testing and neither is our tech levels, abilities understanding too; but it was/still is enough to have worked since mid/late 1930's, it has improved since then, albeit at a slower rate of advancement, compared to that shown by home computers - of which they've have had since the 80's.
 
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It's about that. A one bladed propeller is the most efficent.

Don't be misunderstood there - the fan is still putting air into the compressor. It is shrouded and compressing air although some of that "compressed" air is bypassed. Although it acts like a propeller to a point, it is still being driven by the turbine engine and is part of the compression stage of the "Braton Cycle," so to say it's providing 80% of the thrust is a bit misleading.
 
Engguy,

The big fan in a high-bypass turbofan makes about 80% of the trust at low speeds and low altitudes, particularly when accelerating froma standing start on the runway. If either speed or altitude goes up much, the proportion of the trust produced by the big fan drops sharply.

Up at 30,000+ feet, where the 747's fly, the air is very thin and the turbojet part of the big turbofan produces most of the trust to keep the big bird moving in very thin air at jet speed. The big fan isn't producing much thrust at all at 34,000 feet and 600 mph ... the jet enging is doing most of the work. In climb, to GET to 30,000 feet or so, the big 747 is only climbing at 285 - 330 mph or so, and the fan makes pretty decent thrust ... up until it accelerates to jet speeds.

That's why a modern military jet almost always uses an afterburbning turbofan ... to get better low-speed acceleration. The old straight turbojets were fast, but didn't accelerte very well. The fan markedly improves the acceleration and the turbojet core maintains the high speed end. In fact, in the old Grumman F-14, the fan part of the turbofan was pretty much bypassed after about Mach 1.2 or so. In the SR-71, the fan (actually compressor part of the turbojet) was bypassed completely at mach 3 ... and it ran as a ramjet.

Another thing to keep in mind is reliability. A turbine is dead reliable if you keep feeding it fuel to the fire.

Big, high-strung pistons are not quite so relaible and, unless you want to spend a LOT of money for a racing airplane that can never win back the cost of the development, there is no market for a piston-powered fan anywhere in the people carrying for hire world. Relaibility is paramount when dealing with passengers these days.

Piston-powered ducted fans are made and marketed, mostly to the radio control aircraft world, and they work well. But if your RC quits, you can usually glide back to the airstrip because you are always within sight of it. If they marketed one for light aircrft, it MIGHT sell ... I think nobody knows.

So, it's possible to make a piston-popwered ducted fan for a light aircrft (or even a heavy one), but hasn't been done due to very uncertain market response to a very expensive development effort. In the light aircrft market, you'd be replacing the relatively lightweight and relatively efficient propeller with a big, heavy fan, adding weight and complexity, requiring more power. In a big application, turbines RULE for safety reasons.
 
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The old JM-2 pusher named "Pushy Galore" had a place perfect for a small ducted fan ... right at the propeller. I watched it race several times and it always accelerated away from Nemesis easily. Then Nemesis would slowly acclerate and about lap 2 - 3 would catch and easily pass Pushy Galore. I always thought the real problem for Pushy was the pitch of the propeller, not the design. But Bruce Bohannon never put a higher-pitch prop on Pushy and, soon after the last time I saw it race, it was donated to the EAA Museum (I think) and he started flying his Exxon Flying Tiger modification of a Van's aircraft.

However, the JM-2 was always described as being "not fun" to fly, so adding a heavy (relatively, compared with the prop) ducted fan at the stock prop location might not be possible, much less desirable. The Formula Ones were limited to a small Conteniental engine, and it might take a bit more power to get the same performance, much less more, from a ducted fan.

In the RC world, ducted fans take a high-horesepower engine that doesn't really produce a lot of thrust until the piston engine is screaming at very high rpm. I can't help thinking that the resulting gearbox, to GET to the high rpm, would add weight and complexity, the fan would be heavier than the propeller it is replacing, and the entire package might require more engine than the class allows.

I think they could allow a ducted fan class that would make good performance, but it would not be in the same class as any current class.

I might be wrong, but the added weight of a gearbox and the added weight of the fan unit would seem to take the new aircraft out of the Formula One specification. Just my speculation.
 
I'm still trying to grasp what makes the thrust? Is it heat or airflow? I would think its good old accelerated airflow out the back that does it. Because if you take a balloon and blow it up, let the temperature sabilize to ambient, then release the thing, it JETS away. So I guess my question is what is needed to, for better words blow up a balloon for my jet idea? The key must be the compressor stages? And a pressure ratio?
Yes turbines can be reliable, which is incredably suprizing, since there is alot of stresses going on inside them. Their short comming is filtering out such things as sand, volcanic ash and that kind of stuff. I don't see how they can operate in countrys that are very dry and dusty.
You mention that a piston engine is not reliable? There are many diesel engines that run nonstop for many months at close to rated power, I suppose theres some turbines as well.
Also there are many automotive engines that are very reliable, I don't like to compair them to aircraft engines though since auto engines are very lightly loaded,
and pretty much are run at 20 to 30 percent of rated power.
 
Hi Engguy,

Airlfow out the back cannot possibly produce thrust. What would it be pushing against? The air? If so, the air it pushes will simply move away. That does not produce thrust on an airframe.

In the fan part of the engine, the thrust is produced by lift on the fan blades, transmitted to the airframe through the engine mount. Same as a force produced by a propeller.

In the jet part, there is a lot of pressure in the combustion chamber, and there is an opening at the back where the pressure can escape. The high-speed escaping air brings Sir Issac Newtons Laws into play. For every action there is an equal and opposite reaction. The high-velocity air cannot accelerate unless it pushes against something; there is no acceleration without force. Recall F = ma, or force equals mass multiplied by acceleration. The something it pushes against is the jet engine turbine blades and exhaust case around the turbine blades ... the part facing forward. Sure, some force pushes up, down, and sideways but, since the exhaust tunnel is symmetric (mostly round, but not all), the sideways forces cancel each other and account for some inherrent inefficiency in jet engines. Like ALL engines, that cannot use ALL the energy produced. The net result is forward thrust. The turbine blades are firmly held in place by the thrust bearings. That's why they are called "thrust bearings." Again, the thrust is transmuitted to the airframe via the engine case and engine mount. In high thrust applications, the engine mount is designed so the engine case pushes against an integral stop, and the engine mount bolts just hold the engine stationary on the mount. That is, the thrust is acting against a metal stop and the bolts only prevent the engine from moving off the engine mount.

In another forum, there was a guy named Gaston who postulated there was something called a "thrust column" that magically somehow moved an aircraft of the piston propeller variety forward. We were never quiote able to convince him of the truth, that when the air coming back from the propeller hits an aircraft surface, it can only produce two effects: drag (backwards force) or lift (about 90° away from the direction of the air velocity). The only forward force comes from the lift on the front side of the propeller blades, and that gets transmitted to the airfame via the engine mount. Once the air departs the airframe, it can no longer interact with the airframe since there is nothing against which to push. Once the air moves past the airframe, it is gone ... and gone forever, as far as the airframe is concerned. Yes, there may well BE a moving volumn of air ... but it does not interact with an airframe that is already past the moving air, so the moving air just becomes an artificial breeze. If you dump smoke into the that air, you can see wake turbulence and white smoke from exhaust. Go watch a Blue Angels show (ot Thunderbirs, Snowbirds, Red Arrows, etc.) and you can see the exhaust trail. But it doesn't make thrust ...

There is no magic, only Physics. We could never quite get Gaston to actually read a Physics textbook. At least, if he ever did, the information didn't "take." I have to admit his arguments were inventive and entertaining, but not rooted in physical reality. He might make a great fiction author, sort of like E.E. "Doc" Smith's spindizzys in science fiction.
 
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The upper camber of any airfoil accelerates airflow, creating an area of low pressure relative to the angle of attack. The bottom of the airfoil receives high pressure airflow as the secondary component of lift (or thrust). When a propellor spins in level flight thrust is in equalibrium. When you climb, the descending blade is pushing more air backwards than the ascending blade which causes the aircraft to yaw left (american aircraft) and causes a need for right rudder, and its just the opposite when you dive, you are pushing left rudder. The engine is mounted rigidly to the airframe. The combustion process turns the crankshaft transmitting energy directly to the propellor or through a series of gears to the propellor. Airflow from the propellor around the airframe is thrust backwards overcoming drag and creates forward motion. Airflow spirals around the airframe hitting the left side of the rudder yawing the airframe to the left. Most aircraft have rudder offset built into the airframe for this reason. It is most noticable at slow speed. The spiraling airflow from the propellor creates, for lack of a better description, a wake behind the aircraft. This, combined with wingtip vortices, really makes a mess of the air behind an aircraft, again, more noticable behind a slow moving aircraft when lift generation is at its greatest. Teaching formation and aerobatics, especially in the T-6, really brings these factors home real time. There are more elements involved in the big picture of "P factor" but this is the basics of propellor dynamics.

jim
 
Thanks jimh. Good explanation. I didn't want to get into twisting airflows, just wantred to explain that the force driving the aircraft to accelerate acts through the engine mount.

If I am not mistaken, there is one manufacturer out there, Pilatus, who markets a really neat propeller-powered jet trainer, the PC-21. It has automatic yaw-roll damping, and thus mimicks a jet becuase it accelerates straight under power even with your feet flat on the floor. The rest of the pilots in accelerating piston-powered aircraft stomp on one rudder or the other, depending on which way the propeller rotates. More propeller aircraft are fitted with automatic yaw dampers, maybe even yaw-roll dampers, but I beilieve the PC.21 mimicks a jet the best, according to many flight tests.

Not knocking any other aircraft in the slightest. Just mentioning the PC.21 as an example of how you can use propeller-driven aircraft to train for jet aircraft. No other agenda.
 
Not correct! The balloon does not create lift in the front due to a negative pressure. Nor does a rocket, using either solid or liquid propellant.
If you take for example a screw, any screw. And there are screw drives as well, (swamp crawlers etc View: https://www.youtube.com/watch?v=zBjlSJf4274). They do not create a low presure area to travel they dig in and actually there would be positive pressure from that action. Especially if that screw happens to be a tap in steel. It is bitting its way in to the medium. A propeller can do its job just fine with zero airfoil shape (ceiling fan), and even with the air foil curvature on the oppposite side ( a reversable cooling fan in a tractor), whats important is the twist direction just like the screw, as it works the exact same way except the medium is air which allows slippage, and thus an attempt to improve the grip so to say using an airfoil surface. A propeller does its thing by the air impinging on the side towards the engine and being directed back, and like said above in a climb that angle is steeper and thus more thrust on that side of the prop disk. Its really pretty simple mechanics. Saying that there is lift to make a prop work is like saying that a turbine blade works by lift. If that were the case the discharge should be directed on the backside more than in the bucket. Not the case.

Air can be accellerated out the back of a multi stage centrifugal or vane type compressor and produce thrust. Gee guys take a high pressure washer or even a normal garden hose and the water accellerates from it and produces thrust. And anyone that says the air or gas comming out of a jet of any sort has to push on something is totally incorrect. A rocket in space has nothing to push on.

I'm a pilot I know about P factor.


View: https://www.youtube.com/watch?v=1uynmApjhWI
another screw drive system.
 
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Engguy,

Swamp crawlers don't create thrust in a gas (air). They push against water, mud and dirt.

A rocket in space? The thrust comes from the pressure at the front of the combustion chamber. The low pressure is at the rear, where the opening lets the pressure escape. The thrust comes from the difference between the pressure in the front of the combustion chamber and the presure at the exhaust. Have you ever read a textboook on rocket engine design? How do you think they contol thrust termination in a solid fuel rocket in space, when they insert something into orbit? They blow out the side of the combustion chamber with det cord, so there is no pressure in the chamber anymore. The fuel keeps burining but, since it doesn't have containement, there is no pressure differential and the thrust stops immediately.

Flat plates CAN make a fan and produce some airflow. The reason why they usually have good airfoil shape is to maximize the efficiency, not because it the only shape than can produce an airflow. The total thrust comes from the lift on the prop blade front surface and the mass of the air moved backward pushing on the back of the prop blade. Usually, with good design, the air mass force is much less than the lift on the front surface of the propeller. This is the same as the lift of a wing, the totality of which is the sum of the top surface lift ad the puch from the bottom as the air mass is accelerated downward by angle of attack. Again, proper design means the main force os from the upper surface.

This is beginning to sound like a familiar argument here ... and I already had it with Gaston; repetition is not the order of the day. For someone who says he is a pilot, you aren't making the right arguments. I decline to continue.

Good luck with your theories.
 
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I refuse to get into internet arguements but I defy you to your local airport and find a propellor that does not have an airfoil shape. The root word of propellor is propel...not fan. LOL A ceiling fan moves air with a minimum amount of thrust, it's purpose is not to fly a house just move air around space. A propellor is not screwing itself throught the air...AirBp is doing that well enough. A propellor is creating lift, just like a wing, an area of low pressure in front the blades and high pressure on the behind the blades. The "twist" of the blades evenly distributes the angle of attack of the blade along its length, like a wing, it can stall if its critical angle of attack is exceeded.

I'll be the first to admit I know very little about jet engines, I flew an L-39 once and it didn't blow my whistle. I do know that a jet gobbles huge quantities of air, compresses it, heats it and accelerates it out the back...its pretty simple. The heated air is used to turn the turbine and mix with cooler compressed ducted air to be exhausted through the nozzle as thrust. The turbine blades look like a ceiling fan to me...just alot more of them A garden hose is actually a good example of a jet engine. When you turn on the spicket water flows out, put your thumb in the stream on the exit point and you have created a nozzle accelerating the flow of water. Water is substituted for air. The next few Flight Reviews I give are going to be interesting!



To further this and stay on topic the limiting factor at Reno is the propellor. Merlins, R-3350s, R-4360s, and even the little Continental 0-200 guys are squeezing every bit of horsepower out of thier engines but are up a against a wall of air that can't turn into more efficient thrust. Rare Bear ran a big prop for a few season with some luck but it has since turned back to the 60 year old design it came with. Propellor driven aircraft hit thier peak during WWII, 70 years ago. If thier were more efficient props out there the guys at Reno would be running them. The key is the airframe. Tsunami was on the right track to potentially dominating the sport. Galloping Ghost had the right combination of airframe refinements to also dominate. Lighter, smaller (less draggier) airframes are the key. John Sharp figured that out and was unstoppable. Barrow can still build you his version of a "mouse motor" but a good airframe can win with a slightly stock engine.

jim

ps...is draggier even a word??
 
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I just have a problem with illogic. And pressure in a combustion chamber in a rocket is whats pushing it is nonsense. Its the velocity out the rear. Even a 1st year rocket scientist knows that.
The airfoil shape works in reverse. As in reversing the prop for slowing down, reverse thrust. Also an aircraft can fly upside down. The airfoil is like mentioned for effciency only. A propeller works exactly like a screw. It would be interesting to see what the actual pressure on the front face is at a P51 like speed, I bet its more positive than thought. Its the deflected to the rear air velocity that does the work, just like the jets huge fan and compressor blades do.

Ion thruster - Wikipedia, the free encyclopedia : AND NOTE THERE IS NO PRESSURE IN THE COMBUSTION CHAMBER.

Text book or rocket engine design? Written by who?
Some books are written by not so intelligent people. I had a tech class teacher that wrote a book. He tried to tell us all that it was the flux that carried the heat to the joint when soldering. If he couldn't get that right how do we know how much else in his book was correct? I've seen many mistakes in tech books of all sorts.
 
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