Hehe.. Let's do a thought experiment.
Take a stock, Lycoming O-540-B2B5 235 hp powered Piper Pawnee D235
Empty Weight 1450 #
Gross Weight 2900 #
Take a towed Grob 103a Twin II
Assume loaded to Gross 1300#
3 different cases.
Case 1.) 200# pilot 150# Fuel
Case 2.) 200# pilot 150# Fuel 1100# Hopper
Case 3.) 200# pilot 150# Fuel 1300# Towed Grob 103
Stall, Best rate of climb, Rig Weight
Case 1.) 46 kias, 1400 ft/min, 1800 #
Case 2.) 61 kias, 500 ft/min, 2900 #
Case 3.) 46 kias, 1200 ft/min, 3100 #
Questions
1.) How can you have more total weight being lifted into the air at a greater rate of climb using exactly the same amount of available horsepower?
2.) Does this affect range?
3.) Why
4.) Which of these two birds has a polar more similar to the Raptor?
5.) How much more similar?
6.) As you transition from one end to the polar spectrum (Pawnee to Grob) to the other are the effects linear?
7.) Why not?
8.) What are the implications of that for performance of the Raptor in regards to...
a.) Take of roll
b.) Stall speed
c.) Best Climb
d.) Service ceiling
e.) Best cruise speed
e.) Range
f.) Is the effect linear for all of the above as weight is added?
g.) Which is not linear for?
g.) Why? (see 4,5,6, and 7 above)
h.) What are the implications for performance at given IAS, CAS, and TAS speeds?
i.) Are they all affected equally?
j.) Why not?
k.) Which of the above (IAS, CAS, TAS) integrate mass vs velocity?
l.) Why does this matter?
Final thoughts.
1.) Aircraft polars MATTER!!!!!
2.) The effects are non linear. (They are geometric because lift and drag increase at the square of velocity.)
3.) Boundary area laminar flow and induced friction drag (which is the constant used to determine total friction drag (not induced drag from lift!!!) is an order of magnitude less than the amount of induced friction drag resulting from turbulent flow. i.e. See 1 above. This difference is then SQUARED when computing induced drag and friction drag. So you have one that is an order of magnitude greater than the other, THEN the product (Total drag) is squared as velocity is increased. This has a MASSIVE effect on total drag as speed increases.
4.) The mass of an object DOES NOT AFFECT boundary area induced friction drag.
It often helps to tackle problems by inversion.
To understand this dramatic effect of polar's and non linear effects in powered flight at high rates of speed and altitude (and see it demonstrated both mathematically and practically) watch (better yet go fly) a glider flying at high speed in ground effect.
If these videos leave you in any way unsettled, once you understand what is going on intellectually from a physics perspective, and see the beauty and safety of it, I would submit you will see the Raptor in a whole new light.
https://www.youtube.com/watch?v=L-xOZ2luGZANotice (watch and listen) the spoilers are cracked (Too much energy) at 2:08 in the video when he still seems impossibly far out.
Also "listen" to when he enters ground effect in the 20 seconds before he cracks the spoilers.
Not the low frequency howling from the cockpit vent...
The hiss.
Notice the change in volume in the very high pitched hiss that sounds like , oh I don't know, high velocity water in turbulent water flow??? :-) (Think of what water sounds like coming out of a hose when it is in laminar or plug flow (Nearly silent) versus when you put your thumb over the end... Same exact phenomenon.)
And the force you have to exert via your thumb to do so is equal to the drag being imparted to the water necessary to make it phase change from laminar to turbulent flow?
And this drag or force is exactly the same slowing an airframe down or not?
Yes indeed they are.
https://www.youtube.com/watch?v=s8xglwbRfW8Watch the stick movements (or lack thereof once in ground effect.)
Now consider these videos both occur at massively high speed where the polar of these ships falls off a cliff. And yet still this performance? How? Think!!!!!
You can hear the difference in induced drag due to lift in ground effect. And you can feel the momentum change when you fly into it.
If these videos give you a sickening feeling, I would suggest you refer back to that feeling before commenting on the Raptor.
The more thoughtful among the community will understand the implications quickly even if they did not before.
Others with start to ask thoughtful, probing question from a posture of humility. It is the low gate we must all crawl under to learn and gain entrance to the garden of enlightenment on the other side.
Still others still, those so psychologically possessed of their misguided and counterfactual idioms will continue to make strong statements which will not bear the load of scrutiny.
It took me until I was 50 to actively avoid the third class of folks professionally. I could have done better.
My natural instinct when I was much younger was to seek out and be like the first class of folks.
That practice stood me well through my decade long competition sailplane and hang glider flying.
All of the folks I flew with when I was younger, who were of the 3rd class, are to a man dead.
Fly Raptor Fly!!![/quote]
You should take an intro to Aerospace Engineering class. You obviously have an interest in the topic.
In the mean time, look up the formula to get from engine hp to thrust hp. This is where you see why as TAS increases with increased altitude you need more engine hp to maintain the same IAS.
Also, research BSFC of typical modern diesels and the most efficient diesel cycle engines, using the weight per gallon of jet A, estimate what kind of engine hp you think he can achieve at the proposed fuel flows.
Research the speeds, weights and engine hp of the slickest Reno racers in various classes. Estimate their drag coefficients. Do the same for Lancairs Velocity’s and other slick experimental and certified aircraft. Plot the data to get an idea of what has been achieved by others with better training, better experience, and better resources. Where is the Raptor likely to fall? Why?
If you do the above and still believe in the Raptor’s numbers, then you may want to consider the possibility that it is you who is in your third group clinging to strong statements that will not bear the load of scrutiny, nor survive the brutal reality of flight testing.[/quote]
Friend, I have what might be considered more than a passing interest in the subject.
1.) The polar on the slickest Lancair will look like a dog compared to this ship at speed.
2.) The reynolds number for the combined prop pitch and prop airfoil (and resulting torque) which is the PRIMARY determinant of shaft horsepower to final thrust is well understood at these altitudes.
3.) The ONLY issue with diesel is can he get enough oxygen to it to keep it lighting off efficiently. With the turbo I thinking that will be a resounding yes. That science was also solved back in the 40's as well. (i.e. The Mustang Merlin/Supercharger combo)
