Tail Sitters: design project

In a similar vein to previous design challenges but with a twist: COLLABORATION.

Tail sitters are an interesting technology offering operational freedoms beyond conventional aircraft, typical VTOL aircraft and helicopters. They also have inherent weight limitations (shared by all vertical take-off system) because they must weigh less than the thrust.

To give us a design focus, let’s suppose that the role we hope to fill is close air support over the battlefield.

Let the squabbling begin!

PS. Catapult launched systems are a significant rival to tail-launched systems because they don’t need to have more thrust than weight. But they have practical weight/size limitations; the biggest air vehicle that is catapult launched, that I am aware of, is the Hermes 450 UAV which weighs about 450kg and is far too slow for credible low altitude close air support. To carry even two Brimstone anti-armor missiles (each 50kg) and travel at maybe 500mph you’d need a vehicle much heavier. Catapults are out.

PPS. Random thought:

I like the idea you could have this all over the place no need for airfields

I was doing an UAV CAS model so i did a quick conversion for these specs, any input?

Of course, this has already been done by the Nazis during WWII




[edit on 8-6-2006 by Aelita]

Aelita, a better example would have been the Bachem Natter, that tail sitter was actually built and flown, it was also used by Fairey in Britain as a reference for the design of the FD.1, intended as a rocket plus jet powered tail sitting VTOL Interceptor, the FD.1 ended up flying only as a jet powered CTOL research aircraft after a bloke at the Air Ministry realised the whole scheme was mental.

[edit on 8-6-2006 by waynos]

Ok, here are the obvious candidates for the power plant. I couldn't get reliable figures for the F-119 engine (F-22).


How should we decide which is best suited? - normally engine choice is political but we are of course unaligned and only playing at it anyway so we might as well just take the best.

Weight (lb) available for airframe, weapons and fuel at maximum afterburning thrust:

EJ-200: 17764
M88-2: 15027
F-414: 19718
RD-33: 15960
F-110: 25005


[edit on 8-6-2006 by planeman]

Which engine is the most efficient you would want an engine
that can get airborn on the least amont of fuel
so you have plunty for your mission and to land.
I no i cant spell

Just curious....
What software does everyone use ?

PS: planeman its long overdue but here is something you designed.

[edit on 9-6-2006 by imbalanced]

Dassault systems SolidWorks, It's an Engineering CAD software, not perfect for modeling, but best of the softs i have.

Originally posted by imbalanced
Just curious....
What software does everyone use ?

PS: planeman its long overdue but here is something you designed.

Thanks, that's awesome. My hope is to get the model put into some airflow software ("Computational Fluid Dynamics" ).

Originally posted by cylon555
Which engine is the most efficient you would want an engine
that can get airborn on the least amont of fuel
so you have plunty for your mission and to land.

A very good question but one we cannot answer very well because manufacturers don't have all the data.

The key figure here is called Specific Fuel Consumption (SFC) and is given as a weight of fuel per equivilent weight of thrust, i.e. an SFC of 1.67 means that it burns 1.67lb of fuel for every lb of thrust, per hour. These figures are normally (if ever) published for the SFC at maximum power which whilst a good indicator of engine efficiency, isn't the whole picture.

The Eurojet EJ-200 is sold as having "low fuel consumption". Although the official docs I've seen don't quote figures, the reputation is that it is extremely efficient. The health warning here is that the EJ-200 is marketed as a factor in the Eurofighter's supercruise capability so it actually has a quite high thrust without afterburner and because it is so light, particularly wet (figures we normally have are for a dry engine) it's thrust to weight ratio is the key factor.

One generally good site says:

" At its maximum dry thrust of 60kN (or 13,500lbf) the EJ200's SFC is in the order of 23g/kN.s. With reheat the engine delivers around 90-100kN (or 20,250-22,500lbf) of thrust with an SFC of some 49g/kN.s. [Comment: - note figures given per second not per hour] Compared to other engines these figures may actually seem relatively high, however such data must be used with caution and evaluated with all other performance data to be of any use. With reheat the engine weighs just 2286lb giving a Thrust to Weight Ratio of around 9:1." www.eurofighter-typhoon.co.uk...

From that we can run with SFC figures of 1.76 with full afterburner (?) and 0.82 at full military power (i.e. not afterburning).


The Snecma M88-2 has a SFC of 1.7 with full afterburner and 0.8 at full military power.

The General Electric F414 doesn't have a published figure for specific fuel consumption but assuming it is as good if not better than the F404 from which it was developed (used on Gripen, hornet etc), then it is at least 1.74 with full afterburner and 0.81 at full military power.

The Klimov RD-33 has a SFC of 2.05 with full afterbrner and 0.77 at military thrust.

The biggest engine, the General Electric F110-100 has a published specific fuel consumption of 2.06 at maximum thrust.

So, my guess of which are are most efficient, with full afterburner:

Joint 1st. General Electric F414 & Snecma M88-2
3. Eurojet EJ-200
4. Klimov RD-33
5. General Electric F110-100




GENERAL CORRECTION ON MY PREVIOUS POST: The diagram shows the F414 engines as P&W when it is actually made by GE.





[edit on 9-6-2006 by planeman]

There are a ton of CFD software !
Have any preference ?

en.wikipedia.org...

Actually, while I would not choose /any/ of the current engines (Blk.52 F-16C is powered by a P&W F100-PW-229 or 232 btw.) there are a few interesting things to be said for tail sitters.

1. Motive power source can be placed at almost any position from a midbody Triebflugel centerpoint to a forward mount XFY-1 Pogo to a tail position as with the Vertijet or the Coleopter _without taking the lift vs. lift-cruise out of axis_ as a function of either vectoring (heavy) or thrustline orientation (useless). Or compromising engine cycles with cold pipe takeoffs and 'fan in front' VTOL thrust to weight requirements.

2. With the current emphasis on LO, a tail sitter almost requires a large faceted area to close off the fanring, this can be warped and blended to form a fair lifting body. Furthermore, by blocking off a straightline 'slice' out of the sides of the triangle (that is the faceted fan duct), You can typically insert HUGE system volumes either within the fuselage proper or through misson pods scabbed to it. At the same time, the center column (on which the cockpit pod and engines are mounted) can act as a central fuel tank and/or possibly an internal ladder/lift to ease crew access. If the engines are podded at the back, they can also be potentially drop-replaced as entire units (assuming the transmission is centralized).

3. Weights for airfoil mounted systems and indeed structural stiffening overall can remain highly 'directional' (along the longitudinal axis) for thickness and stiffness without a complex system of longeron and frame point workaround for broken load paths (landing gear, inlets etc.)

Now, t'wer me, I would look at a pyramidal or double cone (with midbody secondary faceted lift ring) so that I could effectively fenestrate a turboprop at either the tail or midbody with the potential for a second (much smaller= much more fuel efficient) turbojet 'cruise mode' propulsion back of it (something in the J60 thrust range would be fine). All using the same inlet system without the complexities of variable cycle in one engine and _without the failure mode_ problems of 'start up/shut down' at a critical point of transition. Since the cruise systems can be contributing to fan thrust at all times.

Done properly, you should be able to create a blended wing-body shape that has the ability to function as a lifting body (assume canards assisting fan vector paddles and maybe a short-span mid wing like a Starfighter) during primary flight and to both cruise at very low speeds (150-200 knots) and sprint to 300-500 or so because the fantips are _enclosed_ in a giant blisk-like monoring and can achieve very high efficiencies at rotational velocities well beyond those of uncontained rotor/prop systems (assuming you don't feather and go with a pure jet cruise mode).

THE KEY is going to be having a high efficiency secondary lateral control system (Tandem Fan coupled shafts come to mind), high enough up the body to give good positioning control and probably some augmented lift during tipback and settle onto the primary lift column. Together with (in manned versions) either excellent visionics or possibly a tilto-whirl bangseat that gives the pilot a 'seated' horizon perspective (window in belly) that is intuitive for rate vs. altitude when settling through a hover cushion. Obviously highly sophisticate attitude hold modes would be a necessity but the potential also exists to go Skyhookish and abbreviate the overall landing sequence to the extent that a biased nose-point angle could be coupled with a vertical grapple (on a crane) to rapidly take over vehicle letdown in heavy winds using stabilizer pads on the flat fuselage bottom. This could be seen as similar to a tanker hookup (follow the lights) and might remove the requirement for a lot of 'piloteering' from either onboard the airframe or a remote operator station.


KPl.

I like the mobility of the idea, but the practicality is obviously not very time worthy. However, since this is ATS, indulgence of our fantasies is whats important here...: ).

Ever since tailsitters have been around, the biggest problem hasn't been the aircraft design, the storage and transporting, or even the launching of it, but the recovery is the most critical part; cuz what's the point of making it, if its one time use. Let's just not forget the whole picture and get stuck on the part that makes the most noise, whether its the takeoff or the crash (my favorite part eitherway: ).

So would the group rather it be manned or unmanned? Manned being the heavier and generally more costly but is more self sufficient, or the unmanned which can be more mobile but requires more tech and off site support, ie satillites or other aircraft for control signal relaying.

What about the use of RATO? Giving the advantage of heavier TO weights, then after releasing ordinance and using fuel could land vertically.

Anyone thought about the convoy? the launcher/carrier of the aircraft, fuel truck, radar/flight control truck, habitation/crew quarters truck, and a couple light gun trucks. how's that sound?

Like i said, not very practical when compared to conventional AC, but a great concept: )

[edit on 11-6-2006 by ioogy]

[edit on 11-6-2006 by ioogy]