Torpedos with Wings - race plane

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Starman, Mar 14, 2014.

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  1. Apr 5, 2014 #181

    Aircar

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    Auto- I'd need to see the derivation of your table to even guess --it uses HP (imperial) feet ,m/s and is not 'transparent' -- I curled up in bed last night with my 20 year old Jane's and did some searching for 'ballpark' airliner powers and prop diameter (Jane's gives prop diameter for each entry) --the Friendship ( a good old Dutch design;) -has 12 foot 6 in dia props and around 2000 HP per side (full power --not sure of the height and speed that relates to) --the fact that their are Four blades and they are 'paddle type" (wide chord to the tip) tends to indicate that there is not a lot of margin to absorb much more power in that diameter . The biggest prop I found was 16 ft diameter --but the most power into a sub or around 15 ft was 2850 HP in the shin Mishewa flying boat . the 11000 HP quoted might be for the turboprop Tupolev and include equiv jet thrust but don't know . All I can suggest as a reality check is to figure the blade lift for a single blade as a rotating wing (integrating it over the whole blade with some tip loss )and the total power produced or the drag and power consumed to get some sort of order of magnitude (maybe working backwards from a known four foot diameter prop to get the net figures and then extrapolating ) simple comparisons like 1 lb of drag at 550fps equals I HP and ditto for thrust . ( I am in a public library /madhouse --there are screaming brats and slightly unhinged people talking to themselves or, maybe, concealed mobiles and nothing at hand to do any of the foregoing unfortunately . It just seems that the figure of 15000 HP into a 15 foot prop is itself way past the state of the art --someone could google the example used to establish this figure and post it here to settle the question I guess )
     
  2. Apr 5, 2014 #182

    Aircar

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    Looked up the Tu 114 and Tu 95 -- equiv HP = 14 800( implying possibly some direct jet thrust ?) but eight bladed contra rotating, The B 36 had 19 ft diameter for 3500HP and the Douglas Skyraider used an 18 ft diameter for 2800 HP --non of these are slouches and give some indication of actual practice
     
  3. Apr 5, 2014 #183

    autoreply

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    Included as an attachment, hope you can open it. I calculate thrust, for a prop with a given efficiency (the "prop l/d" figure). Then I calculate dV, assuming an even outflow, the resulting induced losses and the overall prop efficiency.
    Certainly. Because that design is designed for a speed of 80 mph. Take-off is the limiting case. It would have never gotten off the ground with two 4 ft prop.



    View attachment High speed prop.xls
     
  4. Apr 5, 2014 #184

    Starman

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    That makes sense, those planes are designed to have a short takeoff run so need maximum thrust at highway speeds, which calls for helicopter like propellers.

    On the other hand the A 400 M has 11,000 shp (notice the 's') and a 17' prop and it's also designed for short takeoff.

    1111.jpg

    searching for higher power examples.
     
    Last edited: Apr 5, 2014
  5. Apr 6, 2014 #185

    NoStealth

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  6. Apr 6, 2014 #186

    Starman

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    Thank you, that pretty much makes the case for direct drive on this racer. Actually I targeted 4000 rpm as a good power level for the big engine, which requires a three foot prop. A four foot prop would be limited to 3000 rpm, and it may limit the power output too much. It's been stated here before that all you need is 1000 hp to have a winner, and maybe one of those 1000 cu in engines would put out 1000 hp at 3000 rpm. However, I think it's best to go to 4000 for the higerh power output because these racers are long range two seaters and therefore bigger and heavier than minimum size.

    Here's the disc loading math I get for a three foot prop.

    Racer : 1500 hp into ~ 9 ft
    Airliner : 15,000 hp into ~ 130 sq ft

    power is ten times more and area is about 15 times more. so the prop loading on the airliner is 2/3 the prop loading on the racer.

    Here's the race rules again :)

    1000 cu in piston engine limit.
    comfortable seating for two tall people.
    must have enough internal fuel capacity to go 1000 miles at 400 mph but only needs to carry enough for a race.
    no standing start takeoff.
    ??

    The race rules can be variable but they must not do anything dumb like ensuring that the first plane to the first pylon blocks the others from having a chance. It could be some kind of circular course for spectator appeal, but it has to be a big enough course so the focus is on top speeds.

    So this race rewards straight line speed for two people
     
    Last edited: Apr 6, 2014
  7. Apr 7, 2014 #187

    Aircar

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    Snowed under for a couple of days -- I looked into the Tu 95 again -the props are 18ft 4 1/2 in diameter --it does "only"400 MPH at sea level but 575 MPH at something like 20 000 ft (forget the exact figure) so there is seemingly a lot of jet exhaust involved --the speed drops again above the ca. 20 000 ft height -- also the square of 18.25 is a lot more than 15 squared and the absorbed power less jet thrust might be also quite a bit lower than assumed -- I need to scour Roskram and others to get a handle on the blade loading limits . The Tu 95 is also contrarotating --do we double the 'disc area' to get a comparative figure ?
     
  8. Apr 7, 2014 #188

    Aircar

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    Auto -just opened that link and got a page showing the same figures but no idea of the method of calculation (and I think in imperial units rho = .00238 slugs per ft cu for example -who cannot like a 'slug'? ) I need to look at some dinosaur texts .....
     
  9. Apr 7, 2014 #189

    ultralajt

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    Maybe I dont understand here something...

    As far as I see, a discussion is going in direction about how much power can be squeezed trough a given propeller circle surface...

    It will probably be a good idea to start preliminary design with a given engine and incorporate it into a favorable plane layout.
    Then run calculations and see if results meet your goal.
    If not, then modify plane and powerpack in steps untill get the max result.

    If max. result is dissapointing, ther start all over again with another powerplant and layout features...
     
  10. Apr 7, 2014 #190

    Starman

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    The engine choice is pretty simple, and there isn't much room for changing the layout of the plane defined as a torpedo with wings, Race rules for sports class allow 1000 cu in, so about the only possibilities are one Hemi Mopar celebrates 50 years of the 426 Hemi engine | Hemmings Daily running a reduction gear or one of the new800 - 1000 cu in monster motors I learned about recently. The Hemis actually are more powerfuyl and reliable for ultimate power, but a monster motor allows the enticing possibility of running it direct drive and using a propfan.

    So the only thing to do is build it and it will win =)


    I had no idea it snowed so much in Melbourne.

    No, disc area means how much area that the prop goes through in order to get 'traction'. The two prop discs are working on the same air so it counts as one disc area. The main thing that contrarotating gets you is it takes the swirl out of the air and uses it for thrust so it's roughly the same as putting anti swirl vanes in front of the prop.
     
  11. Apr 7, 2014 #191

    Jay Kempf

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    I think it would be a good idea to look at optimizing a small propeller around a direct drive V8 at high HP settings and higher RPMs and see if there is a sweet spot somewhere above the normal 2500 RPM giant prop design point that is so well represented. Of course this sort of thing requires a very low drag and very light airframe to make it work and probably only off of very improved surfaces but that is what the subject of the thread is in the end. Starting with the highest speed cruise optimization and then working backwards could be an interesting investigation.
     
  12. Apr 8, 2014 #192

    Autodidact

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    Another thread prompted me to do some looking at F1 (auto) racing in the late 70s early 80s; according to wikipedia, these compressed (turbo charged) 1.5 liter engines made something like 650hp/liter with 900hp/liter used in qualifying and trashing that engine to use another one for the race. They weren't all that low tech either, with things like hydraulic valve springs, sophisticated metallurgy, and very accurately built. They also made their power at relatively high rpm. But lets say we use technology that doesn't require the full financial and engineering weight of a BMW or Honda behind it, i.e. pushrods and lower rpm possibly, but advanced enough to make 350hp/liter. Unlimited wants a large airframe, so why not build an engine that displaces, say 24 liters or 1464 ci. 350hp/liter is roughly 5hp/ci, so this engine could possibly produce 7320hp. The prop fan technology would be a must, I would think. Of course, if the above is valid, then a 1000ci engine could make 5000hp... I think a v12 would be better for a couple of reasons, better instantaneous torque signature, and lower frontal area per displacement - could be exciting.
     
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  13. Apr 8, 2014 #193

    delta

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    Bury the engine in the fuselage with a positrack type differential to the fans and kiss some drag goodby. It might be faster with prop fans instead of ducted, but if they don't have rules about after burners yet...
     

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  14. Apr 8, 2014 #194

    Jay Kempf

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    A brand new engine is going to require the budget you don't want to access in your paragraph above. But using existing blocks and heads and relatively off the shelf parts is not. Boosting a big block and tuning the boost to the RPM band you want to enhance is probably the way to go. Use more than one if you don't get enough HP out of one engine. Put them through gearbox and drive counter-rotating props. The gear box could provide some reduction. That's a lot less of a project than building a new engine for thousands of cubic inches for no reason. If the crank to prop flange joint is too weak then just reengineer that one part with a splined adapter and a bolt on bearing housing to support the weak link in the chain.
     
  15. Apr 8, 2014 #195

    Autodidact

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    For an air racing team, yes, it would cost too much. But for and engine builder, it could be profitable because the engine would be useful for more than just air racing, especially boats...
     
  16. Apr 8, 2014 #196

    Doggzilla

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    You would think that would be aerodynamic, but all of the advantages of that design would be for supersonic flight, and it would have some significant disadvantages in normal flight speeds. Lately, the most aerodynamic designs have been sailplanes and tandems.

    Since you are interested in such a groundbreaking design, Im interested to see what you would build after taking into account the advances made my sailplanes and touring sailplanes.
     
  17. Apr 8, 2014 #197

    Starman

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    31286d1396963309-torpedos-wings-race-plane-sst-df.jpg

    Something like that could definitely be a winner. Since Autoreply was suggesting a relatively big wing of around 100 ft I was thinking the best way to combine big wing and high speed is low AR delta. All you need to do to make that into a winner is remove the ducted fans and put a single prop fan sticking out the back right in the middle of the vertical fin. The wing would protect the prop from debris, and you could have the world's shortest landing gear on it. If you could make that change to the drawing, it would be neat to see it.
     
  18. Apr 9, 2014 #198

    Starman

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    Or better yet, the one foot spinner on that one should go behind the wing, a foot or more behind the TE but higher, not centered, and an AR somewhere between what it looks like you have and a Vulcan

    So the racer would look just like this, maybe with a little lower AR, I think the bigger paddle style wing tips are better than straight tapers or pure deltas.

    XH558-Charles-Toop_2367278b.jpg
     
  19. Apr 9, 2014 #199

    delta

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    You'd have to keep the duct or perhaps go counter rotating to keep the prop wash from hitting the elevons at a side angle. There was a recent discussion about that and a crunched a delta pusher.http://www.homebuiltairplanes.com/f...ting-body-kits-not-dyke-delta.html#post210896
     

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    Last edited: Apr 9, 2014
  20. Apr 9, 2014 #200

    Starman

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    Originally I was envisioning the prop disc back up there but behind the trailing edge, and didn't know your wing was so big in the back center part.

    The racer will be about the same size as this model since it has a twenty foot wingspan (~ 100 ft sq area); but with a longer and higher fuselage, with the prop mounted where the tail cone is.

    hqdefault.jpg

    I know it's difficult but try to imagine that model with a big V8 in it and you'll see why, experts agree, it'll easily beat the unlimiteds.
     
    Last edited: Apr 9, 2014

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