Turbofan

All I needed to do was look at this graph to figure out running airscrew propulsion on a craft where THE TOP SPEED IS FOURTEEN KNOTS would be stupid. If someone had to do any more math than that to figure it out then their analysis process was pretty inefficient.

 

Finally a correct answer, though not well argumented.

So it is not true that:

and it is true that:

Right, Franklin?

 

I'm not the mastermind who apparently wasted something more than a minute before he figured out fourteen knot top speed (human running speed) airscrew propulsion is idiotic.

 

Here's another newsflash <insult directed towards another member removed>

Those airboats that were "struggling" to get up a STEEP hill?

A good airboat prop develops about THREE POUNDS of thrust per horsepower.

A Top Fuel dragster only develops about 1.6 (ONE POINT SIX) POUNDS of thrust per horsepower.

The Top Fuel dragsters only LOOK efficient because of the 5g+ acceleration they have with 8,000 (EIGHT THOUSAND) horsepower.

 

< Insults/personal attacks have been removed from reported posts above. Let's please try and keep threads polite to other members and not escalate the insults and personal attacks. Thank you. >

 

Nobody on this thread, except for you, has tried to repeatedly imply that the air prop propulsion is suitable for what the OP was talking about.

Oh, by the way, did I forget to say that you are the one who wrote:

Because, you know, that was your point (repeated in two separate posts) before you changed it after Yellow jacket and I have shown it wrong.

Yeah, we might all be stupid. Sometimes we all probably are, and I for sure sometimes am. I have no problems admitting it.

But please, tell me, what do you call people like you, who write in rude manner and dismiss other persons with unprovoked insults?

 

How many channel crossings have been done with a huge hovercraft ferry driven by airscrew propulsion?

Plus, apparently, it took me a lot less time (like under two minutes) and A LOT LESS math than the people who say I'm wrong to figure out airscrew propulsion on a fourteen knot 600 ton craft is a dumb idea .

 

FranklinRatliff,

You are clearly a misunderstood, gifted, gifted individual.

My hat is off to your superior reasoning power and literary prowess.

Me, I am a simple, uneducated man but know talent and confidence when I see it.

You are the real Macoy.

Your stick-to-it-ivness with this unforgiving crowd blows me away.

How do you do it?

Where did you acquire your post secondary status?

Have you any books I could study.

Please, tell me more...

 

Actually, I AM a McCoy descendant on my father's side.

Good books to read? The Prophet by Kahlil Gibran, The Future of Flight by Leik Myrabo and Dean Ing, and How to Build a Flying Saucer by T.B. Pawlicki.

 

Calm down and read what I wrote, and not what you think I wrote. <insult directed towards other member removed>

What I said is that the weight of the car is close to twice the airboat. I'm figuring that the airboat with engine weighs about 1700 pounds (or less) The car weighs likely 3500 pounds so the boat is half the weight of the car. And since the airboat had a supposed 800 hp it had close to four times the POWER TO WEIGHT RATIO of the car. Twice the power, half the weight do the math...

A top fuel dragster, since you brought it up is an absurd comparison, simply because it is geared for much higher speed. That vehicle is limited by traction, more thrust can't be put to the ground, so there is no reason to increase the thrust. If they had more traction they would lower the gear ratio and produce much more thrust.

Let's use something more common. How about a simple Corvette. A C5 Z06 has a 10.157 drive ratio in first gear, 405 hp and 400 ft lbs of torque. Thrust at the 25 inch in diameter rear tire at maximum power is 3900 lbs, or 9.6 pounds of thrust for each horsepower. So actually the thrust per hp of a typical geared system is more than three times that of a typical propeller. Like I said, you need three or four times the power to produce the same thrust with a prop in air because of the poor propulsive efficiency.

And you can't calculate an acceleration without having the mass (remember that F=MA thing can't be calculated without a mass), but let's use a more common example for the propeller.

Typically if you get 3 lbs of thrust per hp that would be (in my airplane) a thrust of about 700 pounds. The airplane at gross weight weighed 3500 pounds. Initial acceleration was about .2 G, which is pretty leisurely to say the least. Now the power to weight ratio with that loading was 14 lbs/hp, but a car with that kind of power to weight ratio will have approximately three times the initial acceleration of my airplane.

Sorry if you just don't get it, but as I and others have pointed out, a propeller in air is a very poor way to push any vehicle at low speed due to the fundamental poor propulsive efficiency. Now if you absolutely can't push the vehicle any other way, you can use a prop in air, but it is horribly inefficient way to do it.

 

Yeah, I pretty much figured when challenged to do simple basic equations <insult directed towards other member removed>

 

How many channel crossings have been done with a huge hovercraft ferry driven by airscrew propulsion?

 

I never said it won't work, I'm just saying it's a poor way to do it. And I'm sure for every channel crossing by a hovercraft there have been 50 by conventional water propeller driven craft.

And finally, hovercraft are supposed to operate at higher speeds. If you can operate at 70 mph or higher you will get into the range where a airscrew could start to make sense, and some hovercraft run that fast.

 

And how many carried as much tonnage and traveled as fast as the hovercraft ferry?

 

I think you folks are using too much <insult directed towards other member removed> stuff. Every so often your posts are interrupted with <insult directed towards other member removed>, so when one sees the <insult directed towards other member removed>, this <insult directed towards other member removed> distracts attention from the real content of the post.
Unless, of course, the <insult directed towards other member removed> is the real point in your post.

Cheers

<insult directed towards other member removed>