The Razorback construction thread

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by rtfm, Jul 11, 2008.

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  1. Jul 11, 2008 #1

    rtfm

    rtfm

    rtfm

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    Hi,
    Since the Razorback has morphed from a freewing design to a fixed wing design, and since the design process is now largely complete - it is probably appropriate to begin a new thread dedicated to the build process, and simply reference the older design thread for those interested enough in following the sometimes torturous path I've trodden so far...

    The design thread can be found here:
    https://www.homebuiltairplanes.com/forums/showthread.php?t=3799

    From now on, I'll devote my posts to discussing the actual build process.

    As of today (Frid 11 June):
    • I have erected a sturdy beam between two sturdy uprights
    • I've attached the 16" spinner bulkhead to one end of the beam
    • I've fitted a single seatback bulkhead
    • I have stretched 4.5mm glassfibre rods from front to back at regular intervals, forming a very uniform torpedo shape
    • I have begun attaching vertical "hoops" to tie all the longerons together. Each joint is currently loosely fastened with string, but will be bonded in place with a drop of epoxy when all rods are in place and the shape is perfectly uniform
    Photos will follow - except that my workshop is so small I can't get a decent photo of anything. This weekend I will add castor wheels to the stand, and wheel the entire lot out onto the driveway - both to facilitate work, but also to allow me to take some decent photos.

    Till later,
    Duncan
     
  2. Jul 28, 2008 #2

    Mac790

    Mac790

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    I was looking around and I found this
    [​IMG]

    Have you seen this plane it's similar to your design of course yours is better (prettier);).
    More details here.

    Seb
     
  3. Jul 28, 2008 #3

    rtfm

    rtfm

    rtfm

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    Hi,
    Wow - what a fascinating site. Isn't it so thrue that there is nothing new under the sun... There are some lovely little aircraft on this site - what a find. Thank you.

    It will be an interesting study to superimpose one of these little Fleas onto the Razorback...

    Cheers,
    Duncan
     
  4. Jul 30, 2008 #4

    rtfm

    rtfm

    rtfm

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    Progress so far:
    My approach of bending glassfibre rods front to back and then tying these together with vertical hoops has resulted in a perfectly symmetrical fuselage shape consisting of lovely curves. I am very pleased with this approach. My biggest problem with previous prototypes was getting the fuselage symmetrical - and I have now overcome this.

    What it has also allowed me to do is to rapidly arrive at a 3-D superstructure of the entire aircraft (it is very small - not quite ten feet in total length from prop bulkhead to tip of fuse). Seeing it take shape is both rewarding and instructive, because I have now been able to fit the underpinnings of the windshied to this glass rod latticework. I've had to re-do the angles a few times to get it right, but I've managed to use a flat polycarbonate sheet curved round the central brace in a simple curve, so there is no need to go to the time/trouble and expense of blowing a curved windshield. And it fairs into the aft fuse quite subtly. I've very pleased with the results so far. My next challengs in this area will be to design the doors. Probably only one door, since it is a single seater. But I want the door quite large, to make access and egress very easy.

    I am now working on the tail. As you can see from my avatar, the tail is raked back quite strongly. It is actually an extension of the underpinning strongback which runs under the pilot and acts as the engine mount also. Everything is attached to this strongback - including the landing gear and the wings.

    I have started laying scrim-cut 12mm foam strips over the underlying lattice work of glass rods, and I hope to be able to bond these strips into place very soon.

    I have fitted castoring wheels to the base of the stand which holds the fuse (like a rotisserie) but the base is so heavy, I am having difficulty moving it. When I get some help, I'll move the entire structure outside, and take some photos - both from a distance and some close-up shots of the glass rod detail.

    Till later,
    Duncan
     
    Last edited: Jul 30, 2008
  5. Jul 31, 2008 #5

    rtfm

    rtfm

    rtfm

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    First photos - Fuselage superstructure

    Hi,
    Well, I really don't have much to show, but here are a few photos of the first stage of constructing the fuselage.

    I hope to take more photos soon, but the weather has been terrible, with repeated storms rolling over the country in a once-in-10-year severity. As you can see from the photos - very grey and foreboding.

    Photos 1 to 3 Various views of the fibreglass rods bent from front to back around a single bulkhead. The curves formed by doing this are extremely uniform and smooth. Notice that the first of the vertical rods are not yet in place. These are required to true up the curves. Notice the single rod curved over the top to give me a great template for the cabin roof and aft tail section.

    Photo 4 is of my workshop. Yes, I am really going to try build the fuselage in my half of a double garage. And please note, half a double garage width is quite a lot less than a single garage width. And don't forget the tools, the benches, the stuff piled along the walls. It's a tight fit...

    Final photo is of the Razorback with the windshield fitted. I've used a sheet of plastic for the initial sizing, but it does the job well enough for me to be able to take measurements. And if you look carefully, you can see the start of the tail. The tail will be integral with the strongback itself.

    It is amazing to think that what you can see here represents almost three years of work. Most of it in design and premature attempts, of course. But nevertheless, three years of hard and sometimes heartbreaking work. It certainly doesn't look like much... More photos later,

    Regards,
    Duncan

    Regards,
    Duncan
     

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    Last edited: Jul 31, 2008
  6. Aug 4, 2008 #6

    rtfm

    rtfm

    rtfm

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    Hi,
    Rainy weekend, so lots of building...

    This weekend I managed to fit the tail section of the superstructure. I had a few goes at it before I was happy with the results, but its amazing what (1) flat cardboard (2) MDF can do. First step: mock it up in cardboard. Then draw, cut, tape on extra bits (because you cut off too much). Step 2: transfer pattern to 3mm MDF Easy to cut and shape. Step 3: fit to rest of plane, stand back and admire. Call wife to admire together.

    I have also fitted another bulkhead at the widest point of the engine (I want to get this one right, if nothing else). Again, cardboard came to the rescue. Well, cardboard and masking tape.

    Finally, Mac790 took my 2-D drawings and rendered them into really nice 3-D views. Here are some of them... (Now I have an idea of what it is I'm actually trying to build... :gig: )

    Duncan
     

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  7. Aug 4, 2008 #7

    Midniteoyl

    Midniteoyl

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    Cool...

    Wow.. that really IS a big spinner.. )
     
  8. Aug 4, 2008 #8

    rtfm

    rtfm

    rtfm

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    Heh heh heh,
    Yep - If you're going to put a pointy bit in front of the prop, why not perfectly match it to the fise behind it? Well, that's my story, and I'm sticking with it...

    Duncan
     
  9. Aug 4, 2008 #9

    Midniteoyl

    Midniteoyl

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    Hmm... I was thinking 'compensating'... ;)
     
  10. Aug 4, 2008 #10

    rtfm

    rtfm

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    Heh heh heh. Don't be rude! :shock:
     
  11. Aug 6, 2008 #11

    rtfm

    rtfm

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    OK, serious question time...

    I have been collaborating with Mac790 on the design for the Razorback, and we have been thinking of making a few changes. Seb first was kind enough to render my 2-D drawings into 3-D, and the results were great (I've posted a couple of the results a little earlier). But it got me thinking that my REAL preference is for a low-wing configuration. So Seb has taken my basic design, redrawn it (in rough) and made a few suggested changes. But this has thrown up a few issues which maybe someone on the group could help us sort out.

    First picture is Seb's rough sketch, moving the wings to the bottom, changing the tail and h-stab, and making the nose more slender. I was immediately struck by the changes and thought they were really cool.

    2nd picture shows my version of his sketch, but with a change to the tail and h-stab. My reason for the change was to overcome the blanketing effect of the wing and h-stab in a stall. The commentary on my sketch explains the changes.

    Question 1:
    How serious is having the tail blanketed by the wing? Can one not use ailerons for spin control? (I suspect not, but I thought I'd ask).

    Question 2:
    How much of the tail/rudder can be blanketed by either the wing or the h-stab before this becomes a serious issue?

    Final question:
    Does adding a ventral fin improve matters?

    Looking forward to your input. Thanks in advance.

    Duncan
     

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  12. Aug 6, 2008 #12

    Mac790

    Mac790

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    Please not that I'm a newbie here (I'm not deeply knowlegable) and it wasnt my intention, to respond to these questions, but because nobody else answered I did, I 'll be happy if someone correct me if I'm wrong.

    "Collaborating" sounds serious, I only help you with lofting and also with templates for the fuse.

    And I made a mistake, I didnt pay attention, I tried to keep your outside shape contour and I forgot some basic things.

    I did some research and I havent found anything about a tail blanketed by a wing in Raymer book, I believe that it's so obvious, that he didn't write about it or I missed it. I believe that the tail cant be blanketed by the wing, because blanketed area are useles and it sound serious.

    I've never found any information about aileron usage in the spin. In the spin the main wing is stalled so I think that the ailerons are useless.

    About 1/3 of the rudder area should be unblanketed. (Raymer again)

    I believe the best solution for you is to extend the fuse about 10-15in and maybe lower the tail a little bit, (if you extend the fuse you'll find extra space for a passanger).

    btw check out these 3 pictures it looks like the Ar-5 (pic3) top v-stab (tip) is blanketed by the wing, but two others are clear.

    My 2cents
     

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    Last edited: Aug 8, 2008
  13. Aug 6, 2008 #13

    rtfm

    rtfm

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    Seb,
    Hi. Sorry if I put too much emphasis on your help so far. I don't want you to feel "responsible" in any way, but your help is hugely appreciated.

    Your suggestion of lengthening the aft fuse to possibly accommodate a passenger is very interesting, since I quite like the idea of tandem seating. However, I think I went down this path previously, and found that making the CG behave itself was too much of an issue. And then there is the question of engine choice. I wonder how a two-seater is going to handle with only 60hp?

    But I will go home tonight and take another look at this.

    I figure that time spent on these details now will be well worth the extra effort in the end.

    Cheers,
    Duncan
    PS Nice selection of 3-views. Very intersetiong to compare each of them with the Razorback.
     
  14. Aug 7, 2008 #14

    Mac790

    Mac790

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    I dont know about 60hp but for example 80 is a lot. Have you heard about MC100 (pic1) (80HP almost 300km/h top speed) info here http://www.prekas.nl/dynaero/mrcolomban.htm

    That's a good idea, but don't hurry think about it few days, maybe even a week or two and after that make the final decision. What type of plane are you looking for. You need to find the answer to that. The price difference between a single and a double seater plane (i.e. materials cost for resin, foam, fabric etc) shouldn't be greater than 20/30%, even Orion has swapped his single seater design for a two seater one.
     

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    Last edited: Aug 8, 2008
  15. Aug 7, 2008 #15

    orion

    orion

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    Question 1: How serious is having the tail blanketed by the wing?

    If it happened it just might be serious but in all my years I've never heard of a situation where that has actually happened. The only instance where a blanketing effect was realized was in older Cessna 172s where the flaps could go down to 40 degrees +. When you did a forward slip in the Cessna, with flaps full down, you could actually blanket the horizontal to the point that you could move the yoke stop to stop and nothing would happen. The airplane is actually stable in that configuration so strangely enough, the situation maintains as long as the slip is maintained. However, as soon as you let up on the rudder, even a little bit, the control is regained.

    Keep in mind that when you enter a normal stall you are still moving forward, and doing so at a pretty good clip. As such, you still maintain a fairly good longitudinal flow component, even in an established stall. Furthermore, to realize the type of blanketing you see in the above pictures you'd have to be descending nearly vertically and flat.

    Can one not use ailerons for spin control? (I suspect not, but I thought I'd ask).

    No - to establish a spin you need the wing to be fully stalled. But you can use the ailerons through a partial stall, aiding the rudder in keeping you coordinated and thus, keeping the airplane from entering the spin. After all, a spin usually results from an uncoordinated stall.

    Question 2: How much of the tail/rudder can be blanketed by either the wing or the h-stab before this becomes a serious issue?

    Again, an unlikely scenario. But if you want to make sure, this type of qualitative "analysis" is just the thing a large scale RC model would be good for.

    Final question: Does adding a ventral fin improve matters?

    For what? For yaw stability - yes. For spin resistance - it depends but usually can't hurt. For spin recovery - not unless you also extend the rudder downward.
     
  16. Aug 7, 2008 #16

    rtfm

    rtfm

    rtfm

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    Thanks guys,
    It is easy to lose perspective on things like this - especially when one looks through the already narrowed lense of inexperience. This is one of the reasons I like this group so much - there are a number of very experienced eyes.

    Seb, I want to get this right, but I also don't want to spend more time on this than is necessary. I already have fully worked drawings of both a tandem and a side-by-side version. I need to sit down and carefully evaluate all options (single, tandem, side-by-side) to decide which one I'll build (first?).

    Regards,
    Duncan
     
    Last edited: Aug 7, 2008
  17. Aug 20, 2008 #17

    rtfm

    rtfm

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    Hi,
    Not much by way of new posts for a while, but in the background there has been some serious thinking, head scratching and changing of minds.

    Mac790 has suggested a number of improvements to my design, and I like them. So we've been cooking up a few variations. In the end, however, I think we've come back to basically his sketch above. I've tidied it up a bit, checked for h-stab and rudder blanketing and run the numbers as far as CG, and Static Margin are concerned. Passes with flying colours.

    Now I'm considering side-by-side rather than tandem. Mac790 is going to loft this and we'll take a look. This is getting to the serious end of the process, and very soon I'll have templates I can use to actually start building the fuse.

    I've taken a long hard and studious look at the superkr2 site, and have decided that laying foam "planks" over a series of male templates is the simplest and most reliable way to build the fuse. I'm placing the order for the Airex structural foam tomorrow. I'll be "gluing" the planks of foam together with aerosol spray foam, and attaching them to the templates with a touch of hot glue. Should work a treat.

    Pictures as soon as I have something to show.

    Regards,
    Duncan
     
  18. Aug 22, 2008 #18

    rtfm

    rtfm

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    Hi,
    Yes, I am getting down to the sharp end of this design phase. I had thought I was finished, but when Mac790 offered to loft my basic 2-D drawings for me, I began to explore some avenues I had avoided in the past because they were too hard.

    The design has now moved to a low-wing, side-by-side configuration, which Seb has kindly lofted for me. I have to say, I am extremely pleased with the design as it now stands. As far as I can tell, all the design bases have been covered, and the numbers stack up very nicely. The design is clean, visually pleasing and with the superkr2 construction method (and Seb's help in producing the required templates for the male formers) I hope to have a tangible fuselage reasonably soon.

    Here are some graphics of what the Razorback will look like. Power, BTW, will be via Aerovee (80hp, 167lbs ready-to-fly). Seating will be staggered, to put the passenger a little closer to the CG, and to make the most of the 42" cabin width. Fixed gear (not shown) will be steel spring, attached to the wings. Gas is in the wings. Instrumentation all digital.

    According to Raymers RDS software and cross referenced with the Da Vinci PDQ software, the performance figures should be in the region of:
    Stall: 45kts
    Cruise: 130kts
    Climb: 990fpm

    Dimensions: Length: 17.8ft (5429mm)
    Wingspan: 28ft

    Regards,
    Duncan
     

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    Last edited: Aug 22, 2008
  19. Aug 22, 2008 #19

    Midniteoyl

    Midniteoyl

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    Looks really good... and, your partner can go with you again :)
     
  20. Aug 22, 2008 #20

    Rom

    Rom

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    Dunkan,

    Nicely shaped; It should be a hot little airplane.
    Looks like you have come a long way.

    Mark
     

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