Lift Requirements for Hybrid Airship

Question

so I am very interested in flying. I don't have any formal education in the topic so take my questions for what they are.

I was thinking about VTOL aircraft and the current state of such machines. A thought crossed my mind as I was pondering the topic. Would it be possible to produce a solid structure VTOL hybrid airship/airplane that is only slightly heavier than the air around it? It seems like this type of craft would provide for very long flights and "futuristic" landings. I understand this is no spaceship but the implications of building such a device seem like the "henry ford" moment of our generation. An interesting hybrid called the solarship was recently developed by some private company. That craft uses two different methods for generating lift (lifting gas and a wing). There is another method that we use to generate lift on helicopters. Could all three be combined with a craft slightly heavier than air? The mechanical motion required for lifting such devices is very low (little RPM required). The solarship is extremely small. I don't suspect we will develop personal airships. I was thinking more like larger commercial craft though both would be cool. I understand the craft would need to be made up of something very light, maybe a metal microlattice or a carbon body or even 3D printed plastic. It seems like such devices could benefit from hollow wings filled with lifting gas as well. Additional concerns would deal with punctures to the hull. Maybe a balloon inside the hull? There are solid structure airships already but those craft are easily damaged by wind and other extreme weather.

An additional question I have relates to the design of airships. Some recently built craft have deviated from the traditional blimp design. Why are there no vertical airships? I assume this is because of buoyancy or just the fact nobody has thought to build one. With airships the heaviest part will always be on the bottom. Even if we put the hull on top it would just flip over right? It seems like we could build some pretty cool designs with these considerations in mind.

Now don't get me wrong, I understand there are some major challenges associated with such an undertaking. Hydrogen is dangerous, helium is in short supply and hot air probably won't provide the necessary lift. Perhaps this will be more appealing once nuclear fusion is available. Though I think people will be more concerned with creating new thrust devices once fusion is a reality.

Thanks in advance for any helpful information. I do apologize if the question sounds stupid. Again, I am not formally educated in aeronautical engineering.

Answer 1

As with any aircraft an airship need to be able to generate lift equal to its weight to remain airborne and also some additional lift to be able to gain height.

Equally important is the ability to manoeuvre well enough to avoid collisions with terrain or other aircraft in a variety of reasonably foreseeable weather conditions. It is the latter point which has hampered a lot of lighter than air craft in the past.

It actually makes a reasonable amount of sense to have a marginally heavier than air craft which carries the bulk of its payload via buoyancy and used direct thrust for low speed manoeuvring and body lift for cruising. Indeed there have been several reasonably serious concepts along these lines which are potentially attractive as they combine the heavy lift capacity and range of a fixed wing with the versatility of a helicopter. slight negative bouyancy also tends to make the problems accociated with ground handling and trim/ballast.

It's certainly not that difficult to come up with a reasonably credible concept for something like this, after all even in the 1930s German zeppelins worked pretty well and the Hindenburg crash was in many way more notable as extremely unfortunate PR than highlighting any fundamental engineering flaw.

One of the problems was that a the outbreak of WWII fixed wing aircraft had more clear cut military uses and so huge resources were put into the development and so at the end of the war there was a reasonably mature technology and manufacturing base available for adoption for civilian use at a time when there was little spare cash available for developing speculative technologies.

In the meantime the civil aviation industry has become very conservative in the face of commercial, cultural and regulatory pressure to deliver very very high standards of safety.

In terms of lifting gas helium is indeed in short supply and likely to become more so as it is very important for cryogenic applications. Having said that hydrogen isn't necessarily that bad there are plenty of applications where flammable and explosive flues are routinely stored and transported and it is really just a case of mitigating the risk.

For propulsion ducted fans are quite attractive as they are compact in size relative to the thrust they generate and can be vectored to provide manouverability and lift (specifically a vertical thrust component) even at low speeds.

Answer 2

In college the graduating class (Cal Poly San Luis Obispo 2012) before us did the AIAA design competition for hybrid airships. I know one of the biggest limitations is the fact that these vehicles are efficient only in large sizes. This then creates a limitation in terms of locations to land and take off.

These vehicle are definitely feasible. I believe they used a Helium bladder for the buoyancy and then when compressed back down the ship was able to return to the ground.

My guess for the reason they haven't been created yet is this size limitation which also incurs a large cost for not enough benefit.