So if you want to loose a little weight....

You should exhale and not inhale and you could loose those extra pounds that I have been trying to get ride of. :p
And for God's sake I am never going to drink any more water. :eek:

Kent
 
dont do the math

just think about how stuff works. do you know any object that if you toss it out the window of a 747 at 35000 feet it will be going 550mph when it hits the ground. if you find one and i dont think you will compare it to a rv7. the rv is light for its size and has a huge prop on the front. i am not saying that it couldnt overspeed the engine. but if it didnt then no way would it go 550mph
 
I feel like being a geek today . . .

burgundyja said:
just think about how stuff works. do you know any object that if you toss it out the window of a 747 at 35000 feet it will be going 550mph when it hits the ground. if you find one and i dont think you will compare it to a rv7. the rv is light for its size and has a huge prop on the front. i am not saying that it couldnt overspeed the engine. but if it didnt then no way would it go 550mph
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A bullet or the X-1 though X-15 would reach 500mph. Even some of higher speed (~0.85M) business jets would probably make it.

Being light has nothing to do with it given the universal law of gravitation discussed above. Its all about the drag coefficient at transonic speeds. The RV's drag coefficient is going to rise rapidly as it approaches 0.6M.
 
light does have somting to do with it. if you take a lead ball and drop it and then a empty ballon of the same size they will fall at diffrent speeds. in a vacum they will fall at the same speed. rvs are light for there size/drag. compared to a biz jet.
 
burgundyja said:
light does have somting to do with it. if you take a lead ball and drop it and then a empty ballon of the same size they will fall at diffrent speeds. in a vacum they will fall at the same speed. rvs are light for there size/drag. compared to a biz jet.
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I meant relative to an object making it to the terminal velocity calculated using the equasion earlier in the thread that, of course, depends on mass.

The reason an RV won't make it (ignoring the whole structural thing) is that it will have a severe drag rise due to compressability. Any object designed to move at transonic or supersonic speeds will have a lower drag rise, and get closer to the terminal velocity calculated with that equasion. For light objects like your balloon, the topic of compressability doesn't matter since the terminal velocity is very subsonic.
 
You just need max L/D and best glide speed

A quick look. Short version. L/D max = 10 at best glide speed of 85 mph. TV = sqrt L/D max X best glide speed. Then double L/D, keep 85.
TV = sqrt of (10 or 20) X 85 = 270 to 385 mph
plug in the correct values for your airplane

Long version. Start with L/D max of 10 at best glide speed of 85 mph. For L/D, L=W and for TV, D=W, so starting with the drag at the max L/D speed, D has to increase by a factor of 10 (L/D max) to equal W which you get by increasing speed by a factor of (sqrt 10). Keep all things the same (configuration, stick position?.), then TV = sqrt (L/D max) X best glide speed, or =sqrt 10 X 85 (or about 3 times best glide speed). Of course the wing would have to produce 10 Gs at an L/D of 10 and would separate before reaching TV. That would count as a change in configuration. So lets look at zero lift even though there is still no guarantee that the wings would stay on. Since cd=cdo+cdi and at max L/D and best climb speed, cdo=cdi or cd= 2 X cdo. A zero lift situation gives a cd = cdo or ? the D in the 10 L/D noted above. With ? drag, our L/D would double. We?ll cheat here a little bit. Just plug 20 into the L/D max knowing that L is 0, keep the 85. So a zero lift TV = sqrt 20 X 85 (about 4.4 times best glide speed). Therefore, TV by calculation is 272 pulling 10 Gs or 385 pulling 0 Gs.

Sometimes all we need to know is what the answer isn?t. It isn?t likely that we can fly our RVs at 272 pulling 10 Gs or 385 at 0 Gs, so we don?t need to be very precise since we are now dealing with a theoretical speed.

Also, the speeds are indicated rather than true. At altitude, you would need to convert to true. Just think, a TV at 20,000 feet is 37% greater than TV at SL. It is good to know that once reaching TV, you would be slowing down when you hit the ground at 385 mph. That is when you would experience terminal acceleration. Terminal acceleration is more of a social or physiological issue rather than an engineering issue, so I won?t try to explain that one further. ;)
 
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No drag

If you could climb to 1,246,719 feet you could go about 18,000 mph with out any problem. :rolleyes: (actually you would need to do 18,000 mph to not fall out of orbit and burn up in re-entry.)
 
i think the question is what is tv at sea level? i still think around 270 to 300mph with idle and windmilling prop.
 
gmcjetpilot said:
If you could climb to 1,246,719 feet you could go about 18,000 mph with out any problem. :rolleyes:
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You can call me for your clearance when you're ready to head up there George.... :p :D

Paul
 
Geeks

As long as we are being geeks, it should be noted for this discussion that the ultimate terminal velocity that can be achieved due to earth's gravity is about 25,000 mph. This is the speed a rock (or an RV) would reach if dropped to the earth from about Pluto (can we still capitalize Pluto now that it isn't a planet?) or beyond. It is the absolute limit of speed achieved due to falling into earth's gravity, and is more commonly known as escape velocity, as it works both ways.

Of course, the last 80 miles or so would be a problem.
:p
 
I don't have a flight simulator version of an rv, but it would be interesting to see what happens and compare to all the calculations discussed. Anyone?
 
In the May '07 issue of Sport Aviation at page 64, there is new numbers for us. Wetted Area for RV-6 is said to be 410 sq. ft and Cdwet would be around 0.0045. Numbers are from CAF? foundation test flights and adjusted so that there would be no landing gear. Anyone willing to try math with these? My work day is about to be over so I'm heading home now...
 
escape velocity = [(seriousness of the crime)*(cost of repairs)]^craziness of wife

terminal velocity = escape velocity being 1mph slower than your wife
 
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