My latest 'Want to build'

[Deskpilot]

G'day guys. You know that I love to dream and design new planes with the hope that one day I'll actually be able to build. Well, I've returned to my first off ever design and updated it. What do you think.

 

Introducing the DeMansfield Bolt Mk ?

 

 

Originally, this was to be a mid to shoulder wing but I've had to go lower to fit the wings. It will have a tricycle under carriage with a retractable nose wheel and differential brakes for ground steering. Probably be powered by a Jabiru for lightness, driving a specially made prop, around the tail boom. There's no contact between the prop and the boom. All control surfaces will be fake 'morphing' (shape changing) and not hinged as per normal. It will have extending and drooping leading edges, extending and 2 stag flaps, and hopefully, (nearly)seamless ailerons, elevators and rudder. Most of it is designed in my mind having spent countless hours working and reworking the details. Yes I know, morphing surfaces will be heavier and more complex, but due to their increased efficiency (no gaps), will be more efficient and therefore can be smaller. The boom and tail-assembly are removed in one piece and each wing is removable for towing purposes. It should all fit into a double horse box or similar trailer.

 

This is early in it's development and there's a lot of work still to do.

 

 

 

 

 

 

[skeptic36]

I love the visibility of those kind of designs. You would never keep a Jab cool enough as a pusher.

 

Regards Bill

 

 

[Deskpilot]

Bill, I already have cooling concerns, whatever engine I use. Air-cooled for lightness but, top draft or bottom. Intuition tells me to use normal convection theory and go for a low inlet, high outlet and let heat rise. The problem I see with that is heat from the exhausts will impinge on the cylinder heads and cause a problem there, regardless of engine make. If there happens to be a motor that has the exhausts on the top however.................

 

As for where intakes are placed, it seems to me that on the bottom is best and leave the upper fuselage clean for aerodynamic purposes. This would mean a lot of internal ducting and airflow losses. Like I said, lots of work to do.

 

Re the cockpit, yes, I to like a clear view. For access, the canopy will hings to the right, together with a minimalist inst' panel. The screen will be a one piece wrap round poly type. Construction is wood and fibre for the fuselage, and alloy and fibre for the wings. The canopy may have an alloy tube running around its periphery to add some stiffness.

 

 

[turboplanner]

I like the very clean design, but have two questions.

 

1. Too much prop masking? or do you have that covered?

 

2. If a bearing overheats/locks up, or the prop's thrown etc. which happens from time to time, you could be left with a flying wing. I know you've done previous work on that concept, is there a contingency or previously successful design?

 

 

[turboplanner]

I know this is changing the design too much, but how about a ducted fan down low (slight rear bulge below bottom of fuse) and boom up higher, so the fan is clear of it?

 

I notice quite a few ducted fan RC models, haven't looked closely but the fan diameter seems a lot smaller than a similar RC prop. There would be hobby shop guys who've sold engines with both prop and ducted fan, and may be able to give a rough idea of the thrust variation.

 

 

[Bob Llewellyn]

G'day guys. You know that I love to dream and design new planes with the hope that one day I'll actually be able to build. Well, I've returned to my first off ever design and updated it. What do you think.Introducing the DeMansfield Bolt Mk ?

 

[ATTACH]27027[/ATTACH] [ATTACH]27028[/ATTACH] [ATTACH]27029[/ATTACH] [ATTACH]27030[/ATTACH] [ATTACH]27031[/ATTACH]

 

Originally, this was to be a mid to shoulder wing but I've had to go lower to fit the wings. It will have a tricycle under carriage with a retractable nose wheel and differential brakes for ground steering. Probably be powered by a Jabiru for lightness, driving a specially made prop, around the tail boom. There's no contact between the prop and the boom. All control surfaces will be fake 'morphing' (shape changing) and not hinged as per normal. It will have extending and drooping leading edges, extending and 2 stag flaps, and hopefully, (nearly)seamless ailerons, elevators and rudder. Most of it is designed in my mind having spent countless hours working and reworking the details. Yes I know, morphing surfaces will be heavier and more complex, but due to their increased efficiency (no gaps), will be more efficient and therefore can be smaller. The boom and tail-assembly are removed in one piece and each wing is removable for towing purposes. It should all fit into a double horse box or similar trailer.

 

This is early in it's development and there's a lot of work still to do.

For what it's worth - (1) the HS is too small for stability. Yes, the pusher prop has a small stabilising effect with power on, but it doesn't have much arm in that position; and yes, gapless controls are 5~15% more efficient than a 0.5% chord unsealed gap; but control efficiency contributes naff all to stability.

(2) the HS is either in the wrong place, or needs to be MUCH BIGGER, for power-off stability - on final at flight idle, the propellor stagnant wake will be dragged down by the wing wake, completely masking the tail surfaces. Look at the size of the Seabird Seeker tailfeathers, and study one in the flesh - particularly the directional control system. (3) the fuselage bum just fwd of the prop will separate, causing turbulent flow into the prop, strong vibrations, prop fatigue, and extra drag - see Cessna 336 / 337. (4) The rear fuselage boom will either weigh a ton, or have a very short life - the empennage is being flogged by the shed vortex system from the propellor (if a wing is interposed between the prop & empennage, it acts as a flow straightener and turbulence damper to a great degree); and the full up-elevator at Va, at full power (ie extra dynamic pressure from the slipstream) case will superimposed rather substantial quasi-static loads onto the prop-induced vibrations. (5) The boom joint will be a nightmare - as discussed, the boom base is about the most highly stressed and fatigue-loaded item in the structure, exactly the wrong place to put the stress concentrations of a joint (particularly non-permanent). (6) the stall handling will be, er, challenging - normally pre-stall buffet is produced by premature separation in the wingroot-fuselage junctions (low wing), but you have a propellor vacuuming that nasty separation away; so the initial stall will be one wing, outboard of the prop, generating a healthy wing drop.

 

Have a close look at the Taylor Mini-Imp / Micro-Imp; that layout raises none of the above issues, which is partly why Molt chose it.

 

By the way, how do you mass balance "morphing" controls? If it's doable, a two-stage morph, or variable camber surface, would definitely have applications...

 

Apart from that, looks nice. Oh, what kind of energy absorbtion in the U/C?

 

 

[Deskpilot]

Thanks for your comments guys. Now the come back.

 

TP, yes too much prop blanketing and I intended for a more pointy rear end but ran into two problems. First was that I've been experimenting with a new addon to Google SketchUp called Curviloft. This program adds a skin to per-constructed 'formers' or stations. It sounds easy but in reality, if you don't get the stations right, the skin takes on all sorts of weird forms. I lost control quite a few times and my design suffered somewhat. I'll be trying for a better shape shortly. The second reason, and more believable is that, for mechanical reasons, I don't want a long prop hub. Therefore I'm stuck with close proximity of prop to fuselage. As you say in your second post, a ducted prop etc is too far away from what I want so no, not going that way.

 

The possibility of losing the boom and tail assembly has been raised in many discussions on this configuration and my basic answer is,

 

a) build it strong, even at the expense of weight and speed. Choose bearings that will be under running their normal speed and load specs.

 

b) Fit a ballistic cute. As far as I know, there's no previous design using the bearing method that I've designed. Most mid prop systems had a small bearing on a thin tube which necessitated one or two extra stay to hold the tailplane. Again, not what I want.

 

Bob, yes my boom and feathers was too small. When I first set out on this redesign, this assembly was the first to be completed. I was working from "this looks right" point of view. Later, the fuselage turned out bigger than I thought and I never really looked closely at the comparable sizes. I see now where you're coming from so I've scaled up the rear end and, I've taken 10 degrees dihedral (anhedral? not in dictionary) from the horizontal stabs. I knew that the 120 degrees between surfaces was wrong but, being pig headed.............

 

Re shaping the fuselage will help re vortex separation etc. In a perfect would, I would go as far as a pair of contra-rotating props to cure many concerns. I personally think that c/r props should be allowed if on the same axis. Just call it a single 'Propulsion system' not 'twin props'. Yes I know, hellish heavy, expensive and complex..........but doable.

 

As for the stall comments, I don't think it will be as bad as you intimate. the prop only covers about 16% of the total wing span and most of that is that section through the fuselage. Actual wing surface would be about 7%. I have more concerns about the same area having a negative influence when the flaps are lowered. Note that I have a 3 bladed prop so only one blade affected at any moment in time.

 

I have looked at Taylor's Mini-imp but even he had trouble, mainly in the long drive shaft required. Again, I'm not looking for a clone.

 

Would morphing control surfaces need mass balancing? Birds don't have them Guess that's going to be a wait and see type of thing. A more considered answer is that most control surfaces are hinged on a central axis and need some form of dampening from time to time. My system can't flutter as it's driven from both top and bottom simultaneously, side to side in the case of the rudder, and will be much stiffer than conventional. To appreciate that statement, take a piece of paper and fold it in half. Hold the open ends to form a control surface and then push/pull to activate the curve. That's the basis of my design. There is one big drawback however. The surface must have a constant X-section which negates tapered depth wings and tail plane surfaces. Looks particularly ugly on the tail surfaces unfortunately.

 

Under-carriage will probably be wood and fiber-glass composite. Why do you specifically ask that? Ah, thinking of prop strike in the case of a hard landing perhaps. The idea is not to land hard

 

Bearing in mind that all things can change, does this look better?

 

 

 

 

[Bob Llewellyn]

Thanks for your comments guys. Now the come back.TP, yes too much prop blanketing and I intended for a more pointy rear end but ran into two problems. First was that I've been experimenting with a new addon to Google SketchUp called Curviloft. This program adds a skin to per-constructed 'formers' or stations. It sounds easy but in reality, if you don't get the stations right, the skin takes on all sorts of weird forms. I lost control quite a few times and my design suffered somewhat. I'll be trying for a better shape shortly. The second reason, and more believable is that, for mechanical reasons, I don't want a long prop hub. Therefore I'm stuck with close proximity of prop to fuselage. As you say in your second post, a ducted prop etc is too far away from what I want so no, not going that way.

 

The possibility of losing the boom and tail assembly has been raised in many discussions on this configuration and my basic answer is,

 

a) build it strong, even at the expense of weight and speed. Choose bearings that will be under running their normal speed and load specs.

 

b) Fit a ballistic cute. As far as I know, there's no previous design using the bearing method that I've designed. Most mid prop systems had a small bearing on a thin tube which necessitated one or two extra stay to hold the tailplane. Again, not what I want.

 

Bob, yes my boom and feathers was too small. When I first set out on this redesign, this assembly was the first to be completed. I was working from "this looks right" point of view. Later, the fuselage turned out bigger than I thought and I never really looked closely at the comparable sizes. I see now where you're coming from so I've scaled up the rear end and, I've taken 10 degrees dihedral (anhedral? not in dictionary) from the horizontal stabs. I knew that the 120 degrees between surfaces was wrong but, being pig headed.............

 

Re shaping the fuselage will help re vortex separation etc. In a perfect would, I would go as far as a pair of contra-rotating props to cure many concerns. I personally think that c/r props should be allowed if on the same axis. Just call it a single 'Propulsion system' not 'twin props'. Yes I know, hellish heavy, expensive and complex..........but doable.

 

As for the stall comments, I don't think it will be as bad as you intimate. the prop only covers about 16% of the total wing span and most of that is that section through the fuselage. Actual wing surface would be about 7%. I have more concerns about the same area having a negative influence when the flaps are lowered. Note that I have a 3 bladed prop so only one blade affected at any moment in time.

 

I have looked at Taylor's Mini-imp but even he had trouble, mainly in the long drive shaft required. Again, I'm not looking for a clone.

 

Would morphing control surfaces need mass balancing? Birds don't have them Guess that's going to be a wait and see type of thing. A more considered answer is that most control surfaces are hinged on a central axis and need some form of dampening from time to time. My system can't flutter as it's driven from both top and bottom simultaneously, side to side in the case of the rudder, and will be much stiffer than conventional. To appreciate that statement, take a piece of paper and fold it in half. Hold the open ends to form a control surface and then push/pull to activate the curve. That's the basis of my design. There is one big drawback however. The surface must have a constant X-section which negates tapered depth wings and tail plane surfaces. Looks particularly ugly on the tail surfaces unfortunately.

 

Under-carriage will probably be wood and fiber-glass composite. Why do you specifically ask that? Ah, thinking of prop strike in the case of a hard landing perhaps. The idea is not to land hard

 

Bearing in mind that all things can change, does this look better?

 

[ATTACH]27097[/ATTACH] [ATTACH]27098[/ATTACH]

Yessly. The Seabird ended up needing a couple of auxiliary fins out near the ends of the HS, although it's fin LOOKS big enough.

Re stall, if the initial stall doesn't happen in the 5% of wing adjacent to the fuse, it'll drop a wing fairly enthusiastically. Not necessarily a prob - Doolittle used to flick roll P-38 lightnings, which do the same thing stallwise...

 

Taylor solved the 'shaft with a French invention, the shot coupling - as used on the Riley motorblanik. not heavy or hard to do.

 

The 19m Kestrel fluttered the pilot to death with no control slop at all; aeroelastic resonance is a high-energy phenomenom. Good luck!

 

Glass U/C tends to shear between the fibres in an embarrasingly short time; if you sketch the kinematics of the curved bit, you will see that the shortening of the inner fibres causes a transverse tension, on top of the shear forces. I suggest spring steel, or (for gentle landings) aluminium. A properly designed steel springleg for a 600kg LSA I wot of, weighs about 10kg with wheels, tyres and brake discs...

 

For the tailfeathers, a prop brake for engine failures and some kind of dive brake so you can land with a little power on will make a perfectly acceptable aeroplane, although you won't Type Certify it like that!

 

 

[Deskpilot]

Was never thinking of type certification Bob. This is a one off for sure.

 

 

[Bob Llewellyn]

Was never thinking of type certification Bob. This is a one off for sure.

no worries! However, if I give advice, I am meant to be guided by any relevant Product Safety Standard - which for erringplanes comes under Certification. So, I am indicating that I have been so guided, and consider them of little relevance to getting your creation off the ground. Or we could just kill all the lawers... (Shakespear)