probationary second string substitute apprentice relief bloggers’ helper in training john hare
Everybody that reads my posts knows that I think most people get way too complicated with launch assist platforms. In my post last week I suggested a really inexpensive platform that was a flying wing powered by a pair of very large cage Jets. I didn’t justify how I felt it would be such low-cost. I’m going to try to do that in this post.
The cage Jets I suggested would be on the order of 60 feet in diameter. This large, they would have an RPM on the order 600. This large, they would be of a size useful to power plants. If they were useful for power plants, then there would be enough production to get the cost down. It is ironic that the larger the engine of this nature, the easier it is to maintain clearances and margins.
The blades would all be a single profile which could be extruded, cut, and locked into the wheels. By making the blades and all the other parts very simple, cost comes down. By making it very large, inspection is by people walking around inside the engine checking for problems. Maintenance is mechanics with large wrenches and not technicians with superhigh tech computer-controlled gadgets.
Other than the high thrust to weight of these engines which is critical, and potential very low cost, the major advantage a for launch assist platform is that power can be pulled from any part of the circumference of the engine. This means that during takeoff and landing some air can be bled into the plenum chamber of the hover landing system. Some thrust can be straight down from the nose when rotating for liftoff. During low-speed flight a large quantity of air can be directed from the wingtips for an air curtain virtual winglet of very large size. This is to allow the low aspect ratio wing to operate with any efficiency approaching that of a medium aspect ratio wing.
Construction of the aircraft that is the launch assist platform was more or less hand waved in the last post. I do not specify exact construction techniques other than to say it should be something simple cheap and easy for the available construction force and supply chain.
In the cartoon above is a quick sketch of the vehicle from the rear. I see it as a truss layout in both directions big enough to allow construction workers to walk inside and out of the vehicle while under construction. The circle on top being the launch vehicle.
My mental picture was of it being an aluminum structure assembled in a manner similar to the steel buildings we see go up every day. Semi trucks would deliver large truss assemblies that cranes and forklifts would place in the designated area to be bolted together by a construction crew. With good design a construct this size could be assembled by modest crew in well under a month. Then I see sheeting coming in again on semi trucks, with cranes and forklifts lifting it up to be riveted or screwed onto the main structure.
As I said in the original post however, construction should be whatever is most comfortable and familiar with the designer and crews available. George suggested wood and fiberglass. That is certainly feasible as the Mosquito bomber of World War II was made of wood and capable of well over 400 miles an hour. We’ve had 70 years to improve on that wooden technology. It is possible the vehicle would be best made out of plain steel with steel trusses and sheeting assembled by workmen used to dealing with that material. The skin could even be corrugated metal as in the Fokker Tri motors and most famously by the Junkers JU52. When we’re only looking for 400 to 500 miles an hour, there are many construction techniques that might work. The controlling factors not get so high tech and overdesigned that the cost goes through the roof.
The direct material cost using aluminum, steel, wood, or even fiberglass would be under $1 million for this very large vehicle. With proper design, labor cost for assembly could be under a million also. The cost of the basic structure would be dwarfed by the cost of the engines, crew modules, and control systems. The way to hold the cost down would be to build a subscale model first, and test it out not only for flying capability, but also for ease of construction and the cost thereof. If there is a glitch in the small UAV, you address it by building another UAV of similar small-scale to address the problem. Once problems are handled is that scale, you can build a quarter scale model that could possibly launch a rocket vehicle capable of one ton payloads to orbit. Only after that works out the you begin construction of the larger vehicle.
It may turn out that the smaller vehicle is profitable enough that you don’t need the larger vehicle for quite some time. It also may turn out that you become internally funded to the point that you do not have to go begging for vulture capital funds. It is also possible, that the entire concept is found to be flawed, in which case you can stop before investing enough money to sink your company.
A follow on for later that would be a bridge too far today, would be a supersonic launch assist platform. If the cage Jets have the capability that I suggest that they do,Mach 3 to Mach 5 is eventually attainable. If it becomes desirable to have this capability, then it may be that an incremental upgrade is a way to attain it.