Raymond G wrote:
So, for a rocket/jet pack what would be the specifications? I can't speak for everyone, but can put out some thoughts of my own:
Configuration: Backpack. Something you can pick up and easily strap on your back!
Purpose: To Have Fun with something that some or several of us could build in our garages!!! Other uses are many, but would make other specs much harder to achieve, esp. flight duration.
Backpack Weight: Human portable, i.e. about 75-100 lbm, depending upon pilot weight. Probably 1/2 pilot wieght is max.
Thrust: Enough to be safe on a hot day at max gross weight i.e. 300-400 lbf. If multi-engined, enough thrust to land safely with one engine out.
Flight Duration: Enough to have some fun! 5-10 minutes min. Greater duration makes for more fun and more uses such as search and rescue, flying ejection seat, transportation, etc. but also makes design much more difficult. A wing may extend this greatly such as old Popular Mechanics design and Buz Lightyear.
Control: Highly stable AND simple design with intuitive interface. High thrust axis is one possibility, like the Williams, Gluhareff, and Bell designs. "Hollywood" designs with low thrust axis are probably unstable like Rocketeer, Buz Lightyear, and Minority Report. Spy Kids design offers an intriguing option to be able to roll in place with 4 vectored nozzles, but complex
Safety: Failsafe for VTOL flight, i.e. if engine fails, or runs out of fuel, can safely recover. Ballistic chute (as used on ultralights) would be an option.
I have some (possibly more realistic) notions about a PJ-powered "backpack":
1. The notion of a true backpack design is probably not feasible; the necessary dimensions to create the desired thrust (at a reasonable [low!] percentage of max thrust--for engine reliability) means that the combo of engine weight, ducting, fuel storage/supply and other ancillaries such as battery, ballistic parachute, etc.--is beyond the dream of a backpack concept.
2. The alternative is a "strap the pilot in" concept, which would have the power unit standing on its own legs, and the pilot would step into the assembly and strap himself in. I don't see a whole lot of difference in the result--except that the poor "pilot" wouldn't have to bear the weight of the whole thing before it gets off the ground.
3. Additionally, several refinements could be incorporated that would improve the quality of the product. These would include impact-absorbing "landing gear", increased fuel capacity, easy on-board start capability, (add your own list to the above).
I see the concept as a tripod, with a mast "backbone", which would be the structural center of the assembly; the engines would be attached to one side of the mast and the pilot would stand on a platform (or possibly sit) on the other side.
It is easy to divvy-up a weight analysis to provide the necessary items listed above. I estimate the total empty weight of the project at something like 200 lb., and the gross takeoff weight about 500 lb. including a 200 lb pilot and 20 gals of fuel--good for about 15-20 minutes of operation including start-up and reserves.
The engines necessary to make this a reality are considerably bigger than those possible for a backpack concept.
I would like to see a realistic concept that could be light enough to be a true backpack concept--but I really don't think it's possible to achieve with our pulsejets. The issue of thrust density prevents the dream of a backpack from being a potential reality.
Acoustic Propulsion Concepts