Air launch capability

[scipt]

I have a similar problem. Do you find yourself having to stop yourself correcting people, to avoid looking like a nerd? I do :-( <div class="Discussion_UserSignature"> </div>

 

[PistolPete]

All of the time, except most of the time I don't even try to stop myself. Even I have to admit that it gets kind of annoying. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Do you find yourself having to stop yourself correcting people, to avoid looking like a nerd? I do :-( <p><hr /></p></p></blockquote><br /><br />You're mistaken.<br /><br />Oopppsss... sorry I did not stop myself in time...<br /> <div class="Discussion_UserSignature"> </div>

 

[vulture2]

Great links; Both the Space Launch and PanAero concepts are very interesting; as we so often say, to bad neither is funded. I am suprised PanAero felt a modified F-14 "carrier" plane could go supersonic with a large external load, but it was a versatile aircraft and they may be right. The DOD preference for an all-new carrier aircraft that could reach 60km (200,000 ft) for staging was perhaps to costly for a first attempt, and may have doomed the project. Does anyone know if the X-34 prototypes are still flyable?

 

[qso1]

The F-14 can go mach 2.2.<br /><br />Maybe it could go transonic (Mach .9 to mach 1.1) with payload aboard.<br /><br />Link to X-34.<br />http://astronautix.com/lvs/x34.htm <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[scottb50]

I think you miss the size a vehicle would need to be to get to orbit, even if it were released at mach1.1 and 50,000 feet, just the space to contain the propellant would require more area than the F-14, and that would be for a miniscule payload. <div class="Discussion_UserSignature"> </div>

 

[qso1]

Thanks for pointing that out.<br /><br />I just didn't explain my reply well enough. It was meant as more of a general answer. The F-14 would not be able to launch a manned payload for sure, and would be highly unlikely to launch an unmanned payload into space unless the payload was very small and even then.<br /><br />I was thinking about how supersonic jets could be greatly degraded in speed but still go supersonic with payloads such as bombs and missiles on board or better yet, an ASAT such as that tested years ago on an F-15. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[PistolPete]

<blockquote><font class="small">In reply to:</font><hr /><p>I was thinking about how supersonic jets could be greatly degraded in speed but still go supersonic with payloads such as bombs and missiles on board or better yet, an ASAT such as that tested years ago on an F-15.<p><hr /></p></p></blockquote><br />Going supersonic has more to do with aerodynamics than weight. The Mk 80 series bomb that the US military uses is actually designed to go supersonic. However, I think that Scottb50 is right about that F-14 concept. The rocket is just too huge. The ASAT worked because it wasn't that big. Also the ASAT didn't go orbital, it just whent straight up like a sounding rocket. <div class="Discussion_UserSignature"> <p> </p><p><em>So, again we are defeated. This victory belongs to the farmers, not us.</em></p><p><strong>-Kambei Shimada from the movie Seven Samurai</strong></p> </div>

 

[qso1]

I seem to have forgotten evry thing I once knew about aerospace...or maybe never knew it. <div class="Discussion_UserSignature"> <p><strong>My borrowed quote for the time being:</strong></p><p><em>There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened.</em></p> </div>

 

[halman]

propforce,<br /><br />All of the vehicles that you list experience max-Q at altitudes lower than 50,000 feet. If I understand you correctly, by launching at 50,000 feet, we will not be able to escape max-Q. However, won't the value of max-Q at that altitude and above be in the 4,000 mph plus range? <br /><br />According to Wikipedia, 72 percent of the atmosphere is below 33,000 feet. Therefore, the atmospherice density factor in the max-Q calculation decreases rapidly for altitudes above 33,000 feet. Also according to Wikipedia, the Apollo launches encountered max-Q at about 45,000 feet, though no velocity is given. However, I believe by then the launch vehicle was traveling at about 3,500 mph.<br /><br />A vehicle air launched at 50,000 feet is not going to encounter max-Q immediately, as its speed will still be very low. If it is capable of thrust factors of greater than 1 to 1, it can accelerate with the nose up sufficently to counteract the effect of gravity, so that it does not lose altitude while accelerating. The correct angle of attack will result in altitude being gained while velocity is gained, so that the region of max-Q keeps getting further away. This allows nearly all the propellant to be used for acceleration, instead of a large portion being used to counteract gravity. <div class="Discussion_UserSignature"> The secret to peace of mind is a short attention span. </div>

 

[scottb50]

This allows nearly all the propellant to be used for acceleration, instead of a large portion being used to counteract gravity....<br /><br />The problem is you want that acceleration beyond where the atmosphere creates a problem and you have to get to that point first. Using the Shuttle as an example it uses a lot of thrust to initially accelerate against gravity until it is above the atmosphere then descends to build speed. As long as it stays above the atmosphere it becomes a matter of changing orbits. The OMS burn then raises the orbit from around 80 miles to a sustainable orbit.<br /><br />Max-Q is simply the shock wave moving across the vehicle, the Concorde went through slow enough that it presented little problem, with higher acceleration the aerodynamic pressures can pile up because of the different structures the air has to get around, which can create excessive loads at different points. <br /><br />Either way it is a transitory problem, once Shuttle gets through the region it can resume acceleration. I wonder about your figures for Apollo launches though, that seems awfully high, though the mass of the Saturn was huge 3,500mph at 45,000 seems a little low.<br /><br />Either way Max-Q will be encountered anywhere below 200,000 feet or so no matter where you start from. <div class="Discussion_UserSignature"> </div>

 

[barrykirk]

So, if launch occurs at 54,000 ft with the same<br />acceleration profile, then the same velocity would be<br />reached at 108,000 ft. What is the difference in pressure between 54,000 ft and 108,000 ft?<br /><br />I would image it would be an extreme difference so the Max-Q would be substantially lower. Orders of magnitude different.

 

[scipt]

SG - which part of the shuttle do you work on? You know about all of it in a hell of a lot of depth. <div class="Discussion_UserSignature"> </div>

 

[j05h]

> All of the vehicles that you list experience max-Q at altitudes lower than 50,000 feet. If I understand you correctly, by launching at 50,000 feet, we will not be able to escape max-Q. However, won't the value of max-Q at that altitude and above be in the 4,000 mph plus range?<br /><br />I think Prop's point is that any rocket flight in atmosphere experiences a point of maximum pressure. It is a meeting of speed and the air. Plowing through the lower atmosphere creates a higher Max-Q, launching above most of the atmosphere @50k makes for a much lower value of Max-Q. The different craft all experience it differently, but it's a function of flying. For rockets, it's simple: get above the atmosphere as fast as possible. <br /><br />We'll see some great example of this if Airlaunch really flies.<br /><br />Josh <div class="Discussion_UserSignature"> <div align="center"><em>We need a first generation of pioneers.</em><br /></div> </div>

 

[ua_vt_ae]

Here's my 2 cents.<br /><br />I think in metric units, so<br /><br />at 16 km (52, 493 ft) density is ~ 0.166 kg/m^3<br /><br />and at about 32 km density is ~ 0.0136 kg/m^3.<br /><br />Since q (dynamic pressure) is 0.5 * rho * (V^2), the dynamic pressure ratio between these two altitudes (at the same velocity) would be rho_32/rho_16 = 0.0819.<br /><br />Of course, with the same thrust profile, the acceleration of the two flights would be quite different.

 

[ua_vt_ae]

Here are some public domain plots of the Saturn V. The first shows max q and the second shows the flight profile. As stated above, you certainly want to get out of the atmosphere as quickly as possible and then pitch over quickly to achieve orbital (or escape) velocity.<br />

 

[ua_vt_ae]

Here's the max q plot:

 

[propforce]

<blockquote><font class="small">In reply to:</font><hr /><p>Also the Max Q value was 700 pounds per square ft. (The Shuttle max Q is around 400 ) <p><hr /></p></p></blockquote><br /><br />Hi S_G,<br /><br />Please review the shuttle max Q with the following link below. It's quoted the shuttle max Q is around 690.<br /><br />http://www.aerospaceweb.org/question/aerodynamics/q0025.shtml <div class="Discussion_UserSignature"> </div>

 

[propforce]

I understand. But the shuttle usually only go 2 places in orbit <img src="/images/icons/smile.gif" /> <div class="Discussion_UserSignature"> </div>

 

[scottb50]

Max Q is the maximum dynamic pressure.....<br /><br />Of the shock wave moving across the vehicle. The faster it moves the higher the pressure, the more gradual the lower the pressure. <div class="Discussion_UserSignature"> </div>

 

[ua_vt_ae]

Can I ask an honest question?<br /><br />When are we going to stop using English units and start using metric?

 

[mrmorris]

<font color="yellow">"When are we going to stop using English units and start using metric? "</font><br /><br />My bet is on when Hades reaches 0 degrees Celcius.

 

[rocketman5000]

My company, Ingersoll Rand uses metric units on products not used by the American consumer. Ie our construction equipment.

 

[edkyle98]

The answer is that we will stop using them when we stop. I've already stopped, as much as possible, by using metric units in my message board postings. I find it much easier to compare worldwide launch vehicles that way.<br /><br /> - Ed Kyle

 

[propforce]

<font color="yellow">"When are we going to stop using English units and start using metric?" <br /><br />in my next life. </font><br /><br />When I first started in the aerospace industry, I was mentored by a senior guy refering the metric unit as the "communist unit".<br /><br />This was back in the cold war era then. <img src="/images/icons/smile.gif" /><br /><br />BTW, a slug is something in my backyard! <div class="Discussion_UserSignature"> </div>