Introducing HDwing 4 - my motor-glider for high altitude balloon (HAB) launch

Some who have followed my blog posts will know that I have been working on my HDwing design series for a return-to-launch glider concept using ArduPilot Mega.  Everything I have revealed so far has been based on relatively conventional flying wing ideas. Till now...

This forward-swept flying wing concept was inspired by the work of Justin Ammon (EdgeRC / birdofprey) that I spotted on www.rcgroups.com  A period of spreadsheet analysis and messing about with various X-plane simulations over te Christmas/New Year break demonstrated to me that, whilst unlikely to be a walk in the park, a forward swept wing could be made to work and would yield some worthwhile advantages over a mainstream flying wing.

A bunch of CAD work and several iterations later, based on an acceptably flying X-plane model, I came up with this design and I am now committed to bringing it to reality.

One of the difficulties with the forward swept design, especially as a pusher, has been to establish a workable centre of gravity position.  This necessitates the use of a protruding fuselage (a deviation from the pure flying wing) but offers an advantage of placing a payload area virtually right on top of the CoG.  Thus the design can accept a wide variation in payload mass and still be (X-plane) flyable.  How this translates into real world usefulness is yet to be seen, but it bodes well.

The drag-based yaw stablity of a conventionally swept wing also no longer works with a forward swept design, so the addition of a vertical stabiliser fin is required.  Bad for stealth, I know!

The nose cone has been sliced off at an angle to yield a removable camera pod as well as a large access aperture for working on the interior of the airframe.  I am designing in a removeable avionics tray so that the majority of the avionics and payload can be mounted on a lightweight demountable chassis to aid bench testing, modification and repair.

The location of the battery at just ahead of the CoG will allow me to increase its capacity with minimal adjustment to balance.   It is also is attached to the avionics tray for ease of complete systems-level bench-testing.

Personally, one of the attractions of the forward swept wing is that, similar to a canard design, all of the wing surface is lifting to produce pitch stability.  The lift distribution isn't the most theoretically efficient, but at higher speeds and lower C_L, this is not such a huge penalty.  The X-plane simulation shows a best L/D of about 19:1, which is not so bad for such a stumpy, low aspect ratio craft.  My earlier HDwing designs didn't get this far and they had the advantage of winglets and a lift distribution closer to the theoretical optimum.

The forward swept wing layout does come with some compromises but also offers compensatory advantages to exploit.  There is a whole host of detail design work to be done, but hopefully a worthwhile UAV airframe will result.  Time will tell.

 

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Comment by Christiaan van Vollenstee on March 16, 2012 at 6:41am

This looks awesome I would defnitly buy something like this.

Comment by Jonathan Lussier on March 16, 2012 at 9:06am

Hi Andrew, looks interesting but I wonder about the motor?  Why do you need it if all you're doing is returning (gliding) back from high altitude?


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Comment by Vladimir "Lazy" Khudyakov on March 16, 2012 at 9:25am

Lokk nice, but it's only drawing...

For last 5-6 years I'm experimenting with different swept-forward FW. And what I say...

1. Only tractor, any pusher

2. Positive V

3. Big arm for vertical tail

http://diydrones.com/profiles/blogs/mamadu-my-last-project

And this one still in modification

 

Comment by Andrew Rabbitt on March 16, 2012 at 4:17pm

@Jonathan, I first considered a pure glider, but I added a motor for several reasons.  Firstly, it allows easier testing of the prorotypes.  Secondly, I can use it for landing positioning and potentially a non-landing recovery method I'd like to try.  Thirdly, it makes the craft more multi-role, which may be useful in the future.  I can make a pure glider derivative if I need to.

@Vladimir, I respect your skepticism - it can be the sign of a good engineer!  It is a little more than a drawing though.  I have done a fairly extensive series of hand calculations and experimental simulations using X-plane.  I take your point that tractor is easier, but it doesn't permit forward-looking cameras, which is one of my requirements.

The 'positive V' comment I take to mean dihedral.  In my X-plane experiments, I played with dihedral from positive through to negarive (anhedral) and discovered that anhedral improved stability markedly. 

I agree I can always use more tail volume too, but both the pusher configuration and balance requirements limit how much tail area and how far back I can push it.  I look at your Mamadu airframe and estimate where your CoG is and I think your tail volume wouldn't be too much greater than mine as it stands.  I'd be happy to do the calculations to compare them?  I guess it's really the ratio of tail volume to yaw inertia that is important too.

@cvancollenstee - I need to get it flying successfully, but if it works well, I will consider commercialising it.

 

Comment by Dez Socks on March 16, 2012 at 4:50pm

Great work.

This design reminds me of the Deep Flight Challenger.The project is part of a mission to dive deeper than before into the depths of the ocean.The inverted wings/hydroplanes allow the submarine to dive downwards,at a controlled steady speed.

Comment by Andrew Rabbitt on March 16, 2012 at 5:36pm

Thanks Dez!  Wow, I didn't know submersible flying existed till I googled about the Challenger, but it sounds a very cool idea.  Thanks for the info!

@Jonathan - one more thing I forgot to add regarding the motor/propellor.  I found that it adds a useful degree of pitch (and possibly yaw) stability due to gyroscopic rigidity. 


Moderator
Comment by Vladimir "Lazy" Khudyakov on March 17, 2012 at 7:19am

Dear Andrew...

I have > 20 years practical experience with build & flew RC models...Believe me, you gonna wrong way...

Comment by Dez Socks on March 17, 2012 at 12:39pm

Fair play, you didn't have to spend millions to come up with the concept.They also say that water can be teated as air from certain engineering points of view.Maybe borrow some ideas there

Comment by Andrew Rabbitt on March 17, 2012 at 4:39pm
Thanks for your concern Vladimir, but I'm not prepared to just accept the advice of someone who says "trust me, I know best" but can't take the time to expound the reasoning behind his position. Engineering is science, not religion.

Moderator
Comment by Vladimir "Lazy" Khudyakov on March 18, 2012 at 1:23am

@Andrew

Sure. Build it, flew it, engoy it. :))))

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