Guest wecycle Posted July 24, 2015 Posted July 24, 2015 Some details similar to the Turner T-100D Mariah could simplify the design. Specifically the twin tail would allow raising the prop and eliminate the very costly and heavy drive system you would need for the prop. Have you determined the engine you intend to use? I have been looking at using a 2 cyl 2 stroke for powering a similar aircraft. The use of direct fuel injection to reduce the BSFC will improve the range significantly. Something similar to the BAT UAV from Northrop/Grumman would also sidestep some issues while adding concerns regarding stability and control. When do you expect to have a prototype flying?
Deskpilot Posted July 25, 2015 Author Posted July 25, 2015 Well this is a bolt from the blue. Hi wecycle, welcome to the forum. Did you notice that this thread sort of faded away back in 2010 or before. I'm still interested in the design but have moved on to more ambitious things........mostly just dreams. You refer to twin boom designs and that is not what was my intention. Note my signature: Dare to be different, think outside the square. So many aircraft are just modified clones of what has gone before and that's just not my choice. Note also my avatar, a design I'm currently working on. Not mine initially but I'm modifying it to my needs. Google Sgian Dubh by Hugh Lorimer. I did take the prop round the boom to a much more sophisticated design but the must be on another forum, HBA I think. I believe I over came most problems associated with the design with the exception of it being cheap. Search for Development of a Dream.
Guest wecycle Posted July 29, 2015 Posted July 29, 2015 Do you have a link to where the refined design is? On a related issue. The search for a suitable power plant continues. Most promising is an inline 2 cyl 2 stroke converted to direct fuel injection. For "out of the box" options take a look at the "Bat" UAV from Northrop/Grumman.
Deskpilot Posted July 30, 2015 Author Posted July 30, 2015 This should work http://www.homebuiltairplanes.com/forums/aircraft-design-aerodynamics-new-technology/5683-development-dream.html Every builder is searching for that most elusive animal..............the most suitable power plant. Lots of good ones available but we can all find problems with them, usually, cost, or in the case of 2 strokes, noise. Not into UAV myself but yes, I guess that is 'out of the box'.
SGIAN DUBH Posted April 22, 2016 Posted April 22, 2016 Well this is a bolt from the blue. Hi wecycle, welcome to the forum. Did you notice that this thread sort of faded away back in 2010 or before. I'm still interested in the design but have moved on to more ambitious things........mostly just dreams. You refer to twin boom designs and that is not what was my intention. Note my signature: Dare to be different, think outside the square. So many aircraft are just modified clones of what has gone before and that's just not my choice. Note also my avatar, a design I'm currently working on. Not mine initially but I'm modifying it to my needs. Google Sgian Dubh by Hugh Lorimer.I did take the prop round the boom to a much more sophisticated design but the must be on another forum, HBA I think. I believe I over came most problems associated with the design with the exception of it being cheap. Search for Development of a Dream. Deskpilot, I have just put the Sgian Dubh ( Yes the Hugh Lorimer Aircraft ) through the SSDR process in the UK & registered it as G-CJPK http://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=1&mode=detailnosummary&fullregmark=CJPK We hope to have G-CJPK in the air very soon, it will be a very moving event for me as I know how much Hugh has put into this Aircraft and it needs to fly so that Hugh can be happy that his dream will fly ( Hugh has a couple of other aircraft called the Quaiche & the Iolaire, these are Project 2 & 3 in my SSDR Portfolio at this time ) 1
rotax618 Posted April 23, 2016 Posted April 23, 2016 G'day Deskpilot, I think I may have made a comment on another forum concerning your "Prop around tail boom" design. As I see it the additional complexity and weight of having the prop rotating around the tail boom negates any perceived advantages (are ther any?). Have you investigated the weight of a 5-6 inch ID bearing capable of the thrust, side load (belt tension) at 3000 RPM. A conventional pusher with a high boom like the Streak Shadow is not the answer as it limits the prop diameter and therefore its efficiency, most pushers have a low boom, Sapphire, Boorabee, Drifter etc. If you want to think outside of the box, how about a dual ducted fan or prop on a pylon. 1
SGIAN DUBH Posted April 23, 2016 Posted April 23, 2016 Deskpilot, The link has now gone live http://publicapps.caa.co.uk/modalapplication.aspx?catid=1&pagetype=65&appid=1&mode=detailnosummary&fullregmark=CJPK So now you can see that Hugh's Project is very much alive & CLEARED TO FLY. The Construction number was assigned PJK 001 because of Liability in the Event of an incident, I gave Hugh a surety that by taking on the Sgian Dubh project I would absolve him from all liability. I am really looking forward to seeing G-CJPK take to the air ;-)
Deskpilot Posted April 23, 2016 Author Posted April 23, 2016 Hi Rotax, further investigation should lead to you to a newer design for the coaxial prop plane. I realised that the weight of those bearings would be a problem, let alone the cost. I went on with a cradle of small bearings in which the prop hub sat. This image has one side hidden to show the bearings. A top half would probably be needed but I stopped working on it. As to why the co-axial set-up. Why not? I would have preferred to go contra-rotating props for a straight airflow over the tail control surfaces. I'm not the first to use the system, the latest being on a Gyro-plane 1
AusFlyer Posted June 23, 2017 Posted June 23, 2017 Deskpilot, neat design. Yes it would need a top bearing or one could go with three bearings at 120 degrees. Four bearings would probably be easier to center and align. Did you have anything put together to take thrust and provide axial location? Remarkably similar to the bearing setup that held our previous washing machine tub in place and its belt drive. The current one is direct drive and havn't had to take it apart yet.
Deskpilot Posted June 24, 2017 Author Posted June 24, 2017 G'day AF, nice to see my design is still intriguing someone other than myself, not that I've worked on it for several years now. I've just had a look at my SU model and can't find an answer for you re thrust bearings. I imagine the easiest way to do it would be to lean the bearings on a 45% face, both for and aft. That would lock the hub longitudinally and axially. The bearing cage is fixed to the airframe. The tail boom assembly can be slipped out from the airframe by itself leaving plenty of access to the prop and hub assemblies. I may get back to this design after I've finished restoring my Thruster.
rotax618 Posted June 24, 2017 Posted June 24, 2017 Prop rotating around the boom is a complex solution looking for a problem. 1
Deskpilot Posted June 24, 2017 Author Posted June 24, 2017 Prop rotating around the boom is a complex solution looking for a problem. Rubbish! It just has to engineered right. The normal way people think if doing this is to have bearings on the boom itself and this leads to problems like torsional vibrations. My system leaves the boom completely from of contact with the prop assembly. For AF's info, I've been re-looking at my bearings today to provide fore and aft thrust restraint. Now I'm not an engineer but I think something like this would work. Whilst not modeled, tho outer bearings are mounted to the airframe in a 2 part cage (top and bottom assemblies). The hub & propeller assembly is trapped between the 12 bearings. The boom and tail assembly slides in through the hub (with about 5mm clearance all round) and is fixed directly to the airframe and should behave as any other boom type design. Control rods run through the tube and have no direct linkage to the airframe part of the control system. How? don't ask, it's all in my head. Your probably thinking something like "does he think he knows more than a certified engineer", well know, I don't, but I do as my signature says, and think outside the box. Actually I'm going to change that to sphere as I think in true 3D,. all around. It will be most interesting to hear/read comments when I publish my morphing control surfaces. Now that's a really interesting subject.
rotax618 Posted June 24, 2017 Posted June 24, 2017 Prop around the boom can and has been done BUT for what gain? The engineering complexity in a half ton MTOW sports aircraft makes no sense. The prop drive bearing is only a small part of the solution - Since the prop is driven by a belt the the engine vibration cannot be isolated from the boom by rubber mounts. Propellers are not turbines and have their own modes and vibration frequencies, all of this is being transferred to a thin walled boom tube and amplified by the length of the boom to the tail cluster, this can induce flutter and fatigue.
geoffreywh Posted June 24, 2017 Posted June 24, 2017 Put the prop in the front. No, Really!, it makes so much more sense. I'm sure that the engine can stay where it is if needs be. And add some stub wings that will unload the rotor above certain speed.
Deskpilot Posted June 25, 2017 Author Posted June 25, 2017 -Since the prop is driven by a belt the the engine vibration cannot be isolated from the boom by rubber mounts. Propellers are not turbines and have their own modes and vibration frequencies, all of this is being transferred to a thin walled boom tube and amplified by the length of the boom to the tail cluster, this can induce flutter and fatigue. Rotax, you seem to have missed my point. My engine, hub and propeller are not in contact with the boom what-so -ever. Therefore, whilst your assertions are correct for the commonly accepted method of co-axial props is correct, it is not so with mine. No engine vibrations can reach to boom, nor can prop influences other than airflow over the tail surfaces. If it was legal, I would put contra-rotating props on to reduce swirl effect as well.
rotax618 Posted June 25, 2017 Posted June 25, 2017 I stand corrected, hope the extra effort gives the design some advantage in weight and thrust. Still seems more complex than bolting the prop onto the flange of the engine and hanging the tail from either a low boom or twin booms.
AusFlyer Posted June 25, 2017 Posted June 25, 2017 Tractor does make a lot of sense. Probably the reason why so many are designed and built! But doing something because one wants it done that way also has a place. Darkpilot's design idea does solve a couple of problems - vibration coupling, getting away from twin booms, and additional boom loading. There is a lot to be said for unobstructed view, and shape. Personally I'd be happy with a Sadler Vampire or Winton Grasshopper (showing my age, here).
AusFlyer Posted June 25, 2017 Posted June 25, 2017 And came across this while surfing: Ring Around the Tail Boom - Sustainable Skies Weight of the hub and vibration into the boom can't be too much of an issue if these are able to be installed on gliders?
Deskpilot Posted June 25, 2017 Author Posted June 25, 2017 Nice one AF, with no pulses as from an ICE, I "guess" there won't be TV problems.
pylon500 Posted June 26, 2017 Posted June 26, 2017 If it was legal, I would put contra-rotating props on to reduce swirl effect as well. If you could keep this in 95:10, you can have as many props/engines as you like. As for contra-rotating, just a quick scribble... As I say, only a quick scribble, probably a lot of little details to sort out, but you get the idea... 1 1
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