WesWorld

Reason I have kinda disappeared:



First Stage to Orbit launch vehicle. Designed to take a 5,000 lb second stage up to 100,000 ft. She's currently at around 40,000 lbs gross takeoff weight and about the size of a Dassault Rafale.

Interesting. Your senior project, I presume?

Yes, I made the mistake of being the team leader so its being very time consuming.

Quoted

Originally posted by Desertfox
Yes, I made the mistake of being the team leader so its being very time consuming.

Rule #1 of the Army (or anything): Never volunteer!

So true...



And yes the orientations are wrong

What sort of speed is it designed for at 100,000ft?

What sort of engines as well? Turbojets?

I think my general feeling would be to increase the fuselage length and pair the engines together on the centreline.

As a general design concept I might fancy a turbofan cruise engine for climb up to 40,000ft subsonic, then a liquid rocket engine for ballistic loft to supersonic speed and high altitude. Likely want a RCS for control at high altitude. Might end up being a smaller vehicle option, but really depends on what payload you're carrying.

Right now the plan is to launch at Mach 0.8 at 110,000 ft. Power comes from two turbofans similar to the EJ-200s, 20,000lb of thrust apiece on afterburner.

Flight profile is to go to 60,000 ft and Mach 2.1 then zoom climb to launch altitude. It will have RCS at high altitude.

Payload is currently 5,000lbs by 24ft long by 3 ft wide.

I'd advise you have a look at the MiG-31D and S variants which are pretty similar to what you're getting at.

In my experience I'd be skeptical that you can zoom climb from M2.0/60kft to M0.8/110kft.

Looking at the equation for energy height:

V1^2/2g + H1 = V2^2/2g + H2

M2.1/60,000ft gives a starting energy of 37823. A quick look at zero speed means that you should be able to zoom climb to ~124,000ft, however in practise it'll be less than that due to energy spent in the pull up and aerodynamic drag. Doing the calculations for 110,000ft and you can theoretically get to ~M0.98 as a maximum, but again this is discounting drag.

It's probably worth having a look at the NF-104 as well. With a similar zoom climb profile, but having a rocket engine to continue supplying thrust during ascent, those flights were maxing out at 110-120,000ft.

I think my general point is that it's probably worthwhile re-checking your performance calculations.

We looked at the NF-104, Streak Eagle, and Sukhoi P-42.

We are getting about the same numbers and you are right that no drag is included, however our engines are currently oversized and we have enough excess power to hit 150,000ft again with no drag. So there should be no issue with hitting alt 110k @ Mach 0.8.

I'd still be pretty skeptical based on real world performance. I wouldn't be convinced the engines are oversized with 40,000lbf for a 40,000lb vehicle. With a low bypass turbofan cycle the engines will be getting a little anaemic at 60,000ft and you won't get a great deal of thrust from them beyond that.

If you've got time I'd recommend doing some step by step performance calcs through the manoeuvre. Get some drag polars for various mach numbers, some thrust values against Mach and altitude, then you can simply set up lift/drag equations to find the resulting acceleration. Then step forwards in time. Excel should be fine for a rough answer, otherwise code it up and take Tg into account as well at each time step. I think you'll find that you bleed off quite a lot of energy during the pull-up, even if it's only 3-4g.

As an aside question, how have you been sizing the vehicle? Are the textbook relations for mass/drag etc. accurate for this class of vehicle?

Well it is a thrust to weight of 1 at max takeoff weight, and at Mach 2.1 @ 60k the plane's weight is closer to 33k.

Part of the team has been doing those calculations, thought I think they haven't considered the pull up maneuver yet.

Initial sizing was based on similar aircraft looking at midsize fighters. Then we followed Roskam's and Raymer's methods from there. Are you familiar with them? We have been following methods for fighter aircraft so they should be fairly accurate.

Raymer is fairly widely used and is one of the first books to go and have a look at. It's got good detail about how to go about the preliminary design process. The final answer is usually accurate within 10-20% but really it's just a good method of identifying trends.

As a concept design sizing problem, your launch vehicle has two stages; the vehicle and the rocket booster. It's possible to wrap the various correlations contained in Raymer (and elsewhere) into Excel or something and use it to rapidly produce entire vehicles sizes/masses/Cd etc. Then you can also put a solver around this to iterate the design in order to maximise some objective function (e.g. minimum weight and size of vehicle). This is a slightly more interesting problem as there's the two vehicles to consider separately. It'd be interesting to do a trade study into optimum launch conditions: high and fast launch requires large vehicle but small 2nd stage, lower and slower launch gives a smaller vehicle size but larger, heavier and draggier 2nd stage. You could get together correlation of vehicle sizes against launch altitude to see what conditions look best.

I haven't come across Roskam before. You rapidly find that once you move past the concept design stage the accuracy of open source data simply isn't good enough and so companies and governments generally operate with their own bespoke tools based on information available to them.

As far as the stages go, we are two separate teams. My team is designing the launch vehicle (and competing against another team) while a second team designs the rocket booster. The size and launch altitude were fixed since the beginning in the RFP we received. We had to launch at over 100,000 ft and the booster had to be under 5,000 lbs. Launch velocity was set as Mach 0.8 to give the most energy to the booster while avoiding shock waves.

While a trade study would have been nice we were not allowed to conduct one. I personally think launching a bigger booster at higher velocities (as long as shock interactions are not an issue) at a lower altitude would have been better.

Jan Roskam

I was just making some general musings on the design problem. It's a rather different area to what I've been doing recently and interesting to think about.

I'm not convinced about high speed and low altitude launch. Designing for supersonic speed leads to a very specialised design and many in service and certification problems. Personally, I think a stripped out Bombardier Global Express might be a good starting point. Should be able to get up to 40-45,000ft at M0.9 with a decent external payload. For more specialisation you really need engines that don't currently exist: somewhere between low bypass turbofans in fast jets and medium bypass jets in business jets. A bypass ratio of 4+ loses a lot of power at altitude. I think I'd aim to get up to 55-60,000ft to clear commercial traffic - but once you're there you can pretty much launch anywhere in the world.

Personally, I was thinking a stripped Su-27 could do the trick, launching at Mach 2+ at say 65k.

Definitely a unique and interesting problem. Ironically the third senior design team is working on a small UAV (fits in the RC category) to search for people in canyons at night. Talk about opposite ends of the spectrum.

The final product:



Finally done with her so now time to catch up with WW.

Remember that you have to wait at least 70 years before you can build a Wesworld version of it.

Awww...! Thought the payload on the WW version will probably be an ALBM designed to take out the Panama Canal expansion locks.

In the mean time, you will need a nice, shiny cargo ship with Filipinos aboard to take care of the Canal. The more Filipinos aboard, the bigger the KABOOOM.

Interesting how it's turned out. Those are some massive vertical stabilisers.

On a related note I recently found a similar air-launch system is currently being built by Scaled Composites. This is a subsonic high altitude design which is rather bigger - around 13.5t to orbit being the goal.

http://stratolaunch.com/index.html