Introducing the 'EagleRay'

[Deskpilot]

As some of you already know, I'm prone to looking for something different. I recently came across a photo of the Stingray, a single seat version of John Dykes Delta, a 4 seat, plans built aircraft that has seen some success in the USA. Now the Stingray really caught my attention, but it didn't fit into the RAA rules, so I've designed my own.

 

So far what you see is all that exists but I'm well on the way to figuring out all the techie stuff like aspect ratio, surface area, mean aerodynamic chord, lift and drag coefficients etc, etc.

 

Still got to figure under-carriage placement which won't be easy. It's going to be semi-retractable and there's not a lot of room for the nose wheel. The wings will be de-mountable outside the main gear.

 

As for construction method, we'll see as we go but my thoughts are a mixture of wood, honey-comb F/G panels and maybe a F/G skin.

 

Imagine the wings to be aerodynamic, not faceted. I'm new to modelling.

 

I like it, what do you think?

 

 

 

 

 

 

 

 

 

[slartibartfast]

Lovely concept Doug.

 

If the engine is forward mounted and not a shaft from the rear, it looks like there will be a CofG issue. The horizontal stab surface area looks too small too.

 

Just impressions - I have no design experience.

 

The U/C looks like a hard task. Good Luck.

 

 

[Deskpilot]

Slarti, the 'horizontal stab' isn't a stab at all. It's a pitch trim tab. It's inclusion s to free the elevons to do their job properly. With a symmetrical wing profile, there is little or no movement in the center of lift, no matter what the AoA is. I'm not an expert in aerodynamics but I think I'm not far off. As I get on with more of the techie stuff, I'll be able to make adjustments, if necessary. My next task is to investigate the wing profile, bearing in mind that I have lengthened the cord to give a better slow speed performance. I will probably be contacting either Homebuiltairplanes or the Delta forum in America to get more answers. They certainly have more knowledgeable people over there who are happy to share knowledge or tell you where to find it. They just won't do it for you.

 

 

[Deskpilot]

Sorry for the split post but my 'puter froze?????

 

I'm not sure where the C o G is as yet and won't until I take the next step. Deltas are hard enough, double deltas more so. Add the symetry to it and I think you'll agree that I have taken on something that won't be sorted over night.

 

Stay tuned.

 

 

[slartibartfast]

Absolutely Doug. Very cool though.

 

Interesting about the pitch trim. I look forward to further development.

 

 

[skydog]

I would love to see this plane in our skies.

 

Reminds me of the feeling I got when I saw my first Rutan design, different , cool, fast I think, and sexy.

 

 

[Deskpilot]

Skydog, I'm not sure of what speed I'll get as the design has quite a large frontal area. This is partially due to the fact that I didn't want to go to a fully reclined seating posture. Too uncomfortable for long trips. I've reclined the seat by about 30 degrees and placed it as near the bottom of the fuselage as possible. NOT GOOD in the case of a heavy wheels up landing. Compromises all the way. If I get 100knots I'll be happy. It also depends on high light it can be built.

 

SEXY..........hell yes.

 

As you can see from the attached image (not good quality unfortunately) the Stingray was sleeker and more cramped. It apparently cruised at near 150knots I believe. It also had a rather high stall speed. oh, and it was powered by a Lycoming motor.

 

BTW it was made of wood and fiberglass and was way too heavy at 800lbs. I've corresponded the John Dyke and he reckoned it should have been around 500. It sure would have motored if built down to that weight. The plane flew for 30 years and is now in a museum.

 

I'll be adding more images explaining or showing the how's and wherefore's of dimension's etc as and when I do them. Maybe this can be an education for all of us. Some of it might sink in :hittinghead:

 

 

 

[Guest drizzt1978]

I gota know! Are you gunna do it, are you really going to build it! Or just thinking about it! With a project like this you could get helpers!!!

 

 

[Deskpilot]

Some dimensions to ponder.

 

OK, I haven't taken them all but here are a few basic dimensions. If you would like to know a specific dim', let me know and I'll try to let you know. In the final analysis, some, or all dim's will be adjusted to neat whole numbers. Problem is, Sod's Law says that won't happen.

 

Drizz, yeh that's the aim but it all depends on my finances at the time. We're a long way off from even contemplating it. If it doesn't work out for me, hopefully we'll end up with a set of plans that some-one else might like to take the risk and build. This will of course, fall into the Experimental category.

 

 

 

 

 

[Guest Maj Millard]

Very interesting, I would lengthen the wing span a touch, the tip thingos are too square but would look great if they were nicely curved like Slartis' wingtips. Fuselage would look better if a little longer too. I personally would not design and build a single seater again, but with that design it would not be too hard to engineer it into a two seater. I don't think the gear will be much drama as you have lots of storage area for gear.........................................Maj...

 

 

[Deskpilot]

Hi Maj, if I make it much larger, I might as well build the original Dyke Delta and leave out the rear seat. I am in fact, thinking of making it smaller.

 

I previously stated that I'm a beginner when it comes to 3D modeling so you'll have to use your imagination re wing curves. My current thoughts are that the forward delta will remain knife edged in order to produce a vortex that aids in the laminar flow over the rear delta. To any aero-engineers tuned in, please correct me if I'm wrong. I'm learning as I go. I have Bill Whitney's cd and notes but his advice is to stay away from deltas. Therefore, my web search time is going up faster than this ship will climb ;-)

 

 

[Guest Maj Millard]

Deskpilot, I don't see you'r wing as being a true 'delta' more a stubby tapered wing, or for want of a better term a 'tail-less' aircraft. What Bill Whitney may be aluding to are the unique and sometimes dangerous capabilities that a delta wing can exhibit. Those are the potential tendencies for a delta to be mishandled, and then develop a pitch osicilation mode, which may be hard to control due to there being no tail to dampen it. The Mirage 111 for instance, which was a true delta, had automatic pitch dampeners. They were go/no-go items, and if not operating correctly the aircraft didn't fly. They were there to assist the pilot in controlling any unpleasant pitch mode divergances, which could quickly amplify in certain situations.

 

Additionally a Delta doesn't really stall, but instead achieves a high angle of attack with resultant high drag, resulting in a massive sink rate if left uncorrected. The Mirage if it lost the engine for instance, would eventually impact the ground at about a 60 deg tail down angle but technically it was still flying wing-wise, but with a massive stable rate of descent. Many of the later designed Deltas still in service.(Mirage 2000, Saab Viggen derivitives etc) use small moveable 'cunard' surfaces ahead of the main wing to augment pitch control. Your moveable pitch trim surface on the tail should do the same thing as long as it doesn't get blanked out by the main wing at high angles of attack............................Maj

 

 

[Deskpilot]

I understand where you're coming from Maj. Where does the change-over start? The Correct description is, I believe, a double delta with a forward swept trailing edge. No matter what we call it though, we cannot compare it to a Mirage, Viggen or any other modern fighter as they are all designed to be inherently unstable. Many computers are required to fly them and if they all go down, the pilot only has one option, BAIL-OUT. Even back in my day, the Lightning had auto-stabs without which, it couldn't be flown. (I serviced them, auto-stabs that is)

 

I don't know where you got your info from, but DD flyers have no problems with pitch oscillations. The pitch trim is there only to take a bit of pressure off the stick as per conventional aircraft. The only adverse flight characteristic reported so far, is that it takes a strong arm to deviate from level flight into a roll of any sort. This is something I have to take into account in my design as I want to go to side stick (less leverage) in order to allow the nose wheel to retract between my legs. Well, that's how the dreams goes.

 

Going back to your earlier post, I spent some time this weekend learning how to model rounded surfaces. Easy, but not easy. I can't get a smooth transition into the winglets. Somewhere in the process, I lost control of scale. the wings came out too deep. I'm still debating on whether to keep the knife edge on the forward delta.

 

I then got carried away with twin fins. I kinda like it.

 

It does look as though I'll have to move the pilot position about 1ft rearward, but that's down the track a little bit. I also have to figure out what airfoil section to use. JD developed his own and there's no info available that I can find. I might resort to asking one of the current builders to go and take some measurements for me. My model is a best guess thing. I downloaded the coordinates for the NACA0012 section but, hell there's a lot of them.

 

Unless I want to get into strife with the wife, I'd better put this to one side for now. We have a 7ft hedge out back that's currently reaching up to 9ft in places. Wifie's not impressed, nor I don't doubt, are the neighbours.

 

 

 

[Deskpilot]

Variation on a Theme

 

Since Maj's comments re curved surfaces, I've been busy learning to model a bit better. I'm still no expert but I think you'll agree, it's coming on.

 

These latest models have the sharp forward strake that produces a vortex that runs over the rear delta and aids slow speed flight without excessive nose up attitudes. I'm not totally happy with the single fin, it looks unbalanced somehow. I've got to remeasure everything and get a better idea of the C o G, which may lead to moving the pilot position rearward by about 1ft. What d'you think?

 

Oh BTW, remember that hedge, still not done.

 

 

 

 

 

 

[Guest Maj Millard]

Yes looking better now Doug, I think the double tail may be the way to go also. I recieved a small gift from a friend today and it was a gold pin of the new YF-23. If you look at it, it is very like your design in planform, with the additional tail-surfaces out the back. So the plan form you have must work. It looks like the inboard control surfaces on your wing might be for pitch control ?...or are they for both pitch and roll (elevons)...if not you may need additional ones more outboard for adequet roll control. I think if you made a model it would fly as it is now. Pity about the damn hedge............................................Maj...

 

 

[Deskpilot]

Maj, the original DD used only the in-board flying surfaces, referred to as elevons. Later mods include the pitch trim tab but that would be hard to incorporate with the twin fin set-up due to their angle. The 'mixer' control is quite interesting in it's operation. These are not my words but you should be able to work it out.

 

"The upright post pivots for and aft at the bottom.

 

The upright post twists from the bottom.

 

A pull on the main tube will pull the top of the upright post, and pull

 

both elevon rods.

 

A push on the main tube will push the top of the upright post, and push

 

both elevon rods.

 

A twist on the main tube will pull one of the upright post ears and push

 

the other using the linkage from the main tube's down extension. The

 

square channel is locked to the upright post, so it will pull one elevon

 

rod and push the other."

 

The 'twisting' referred to is not actually twisting the control column, but is a by product of push/pulling and leaning the stick at the same time. It had me guessing at first but becomes obvious as you study the images. It is not possible to roll the DD although I'd guess a large barrel roll would be possible. Seeing as I'm not looking for aerobatic flight, it doesn't matter anyway. Perhaps out board ailerons or even full length elevons would improve the roll capability but for the present, I'll stay as is.

 

Ah, the hedge. It's going to be 37* here today so it's not likely to get done...again. I am ready to go but I'm not ready to get fried.

 

 

 

 

 

[Guest Maj Millard]

That mixer set-up looks like a pretty well thought out piece of gear. I wouldn't go touching that hedge, hell you could fall off that damn ladder and that would be that. Far too dangerous mate................................................................................................Maj

 

 

[Skykid]

I agree with you, the twin fin looks a lot better!

 

For myself though I would go with a canard installation for better pitch control. But to rig it up to your mixer might be a bit of a hassel... (I haven't had time to go over the pictures you have posted) What about having a moving slab on the leading edge to help with slower speeds? Also it the added weight might mean you don't have to move the cockpit? Just an idea.

 

Maybe you should tell the wife that you need the EagleRay to reach the top of those hedges?!

 

 

[Deskpilot]

Maybe you should tell the wife that you need the EagleRay to reach the top of those hedges?!

Love it Skykid, love it.

 

BTW, the top of the hedge is now almost flat enough to land on. It also seems to be a lot wider now so if I include a swiveling u/c, I could land at an angle and not fall off the top.

 

 

[Downunder]

A Dyke Delta model plan (68 inch) can be found here. Mammoth Scale Plans

 

Might be something to play with............

 

Any ideas for engine size, HP?

 

 

[Deskpilot]

Thanks for the link Downunder, but I don't think I'll be using their plans. I'll model my own when I get to that stage. I'm still tinkering with other possibilities, even a two seater.

 

As for power, I'm hoping that I can keep it down to 80hp or less for the single seat version. Building real cheap would be to use a VW conversion of some sort.

 

 

[Guest Maj Millard]

Or pick up a cheap 80 hp 912............it'll be less hassle and more reliable, then you can go flying instead of playing with it.........................Maj...

 

 

[Deskpilot]

My Jabiru 2.2 in situ

 

I'm remodeling my plane and have just installed the 'Engine Block', suitably scaled down of course.

 

 

 

[Guest Maj Millard]

Sorry to hear about the hedge dying....damn.....now if you don't have to trim it all the time, you'll have all that time for other things !.................................................Maj...

 

 

[Deskpilot]

Update.

 

Been busy with visitors from the UK so, with others due to arrive over the Easter weekend, I though I'd up-date you with The Eagle-Ray.

 

I've decided to go with the twin fins and winglets just because I like the look. Arthur, I've restyled the winglets as per your suggestion and they look great. Bear in mind, this is a fun plane, not to be taken overly serious. I've changed the front delta, made it bigger and fiared into the main somewhat better. Moved the pilot back to a more 'looks about right' position. Now I've got to get to grips with the maths and figure it all out in reality.

 

I haven't found out how to model the complex shape of the cowl so it's a bit angular but you get the idea don't you. I'd like to make it longer and more pointed but that would mean having a prop shaft extension and associated torsional vibrations etc. Maybe best to KISS it. The fuselage looks better with the inward taper and will be blended into the wing surfaces to reduce drag. Still looking at using Honeycomb Fiberglass panels but they're not cheap, and that's something I've got to bear in mind at all times. To get the flat panel shapes I've got to revert to my sailing days. I'm hoping that I still have 'Small boat Design' books packed away somewhere. From them I can project the curved surfaces onto what ever material I eventually use.(talking Fuse' only here although it might work for the wings as well)

 

You'll see a lot of construction lines in the models. Unfortunately, if I turn them off, it's hard to see the various outlines(last image). I have hidden them on the cowl and wing upper surfaces only.

 

So, what do you think?