Trying to achieve turbonormalizing the home-built way

Discussion in 'Firewall Forward / Props / Fuel system' started by geosnooker2000, Aug 11, 2019.

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  1. Aug 16, 2019 #41

    pictsidhe

    pictsidhe

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    You should probably see how much power, boost you'll need and at what altitude first.

    I believe that the 601 flutteres inside its Vne to start with. The Cricket fluttered too. It is far from a safe bet that there is much more to be found from the 601. Increasing flutter speed is a task for people with considerable engineering acumen. I'd suggest picking a plane which does meet your goals.
     
  2. Aug 16, 2019 #42

    SVSUSteve

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    *takes bow*
     
  3. Aug 16, 2019 #43

    SVSUSteve

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    Louder for the people in the back.

    Literally the only structural issue that flat out scares me is flutter. Everything else I can figure out and reason my way through. That...I am designing to avoid, having the design reviewed by experienced folks, and then ground testing to be as sure as I can that it’s a risk that is reduced as much as possible.
     
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  4. Aug 17, 2019 #44

    geosnooker2000

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    A post or two has disappeared from this thread. One in particular I remember was someone said I needed to calculate what power I needed to cruise @ FL17 at what speed I desired. (BTW, I don't mind sticking to the 167 max cruise. That's the whole point of turboing an 0-320) I plan on doing some calculating on that, but where did those posts go? Did we get "moderated"?
     
  5. Aug 18, 2019 #45

    mcrae0104

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    No, I self-moderated. I asked (a second time) what your power need was for your intended performance at altitude. I decided it was redundant because TFF (in post 35) had essentially amplified the point I made earlier and it went unnoticed. I decided I wanted to step back from the conversation because 1) rather than heeding the point (you will be burning more fuel than you think), you basically said nobody was reading your posts, and 2) you didn't seem interested in answering questions, only stating what you believed to be facts. I'm not upset with you; I just decided I have better things to do with my time if nobody was playing ball.
     
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  6. Aug 18, 2019 #46

    geosnooker2000

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    No, I intend on answering your question. But that's not a question I can just answer off the top of my head. I've got to do some research.
     
  7. Aug 18, 2019 #47

    geosnooker2000

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    I'm sure this is not exhaustive, but it's a quick and dirty calculation to use as a starting point for you guys to correct me in my thinking in a more precise manor.
    Ok, so according to Andrew Gold's book 27 Years RV-ator, it takes 1HP to pull 2lbs of drag (page 410).
    Assuming the specs on the CH640 are correct, and a fully loaded plane @ 2200lbs gross powered by an 0-360 will cruise @ 75% power at 150mph @ 7000 feet,
    0-17000 feet = 50% drop in atmosphere so I assume that means a 50% drop in drag
    17000/50% = 7000/x ---- x = 20%
    So drag is 80% at 7000ft.
    so this means the 180hp 0-360 is pulling 360lbs of drag @ 7000ft.
    80/360 = 100/x ---- x = 450
    So drag @ sea level would be 450lbs
    450/2 = 225lbs of drag @ 17000ft.
    225lbs/2= 112.5hp

    But I want to go 167mph. Not 150mph. So,
    according to another formula on the same page of that book:
    X = (167/150)^3 x 112.5hp
    X = (1.11)^3 x 112.5hp
    X = 1.37 x 112.5hp
    X= 154 hp​
     
  8. Aug 18, 2019 #48

    pictsidhe

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    No, you do not get a drop in drag with altitude ata constant IAS. Reduce IAS, you reduce parasitic drag, but increase induced drag

    power = force * speed

    You will get much better answers if you calculate induced and parasitic drag seperately. You need a more advanced book. Better yet, a shelf full;)
     
    Last edited: Aug 18, 2019
  9. Aug 18, 2019 #49

    TFF

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    You really need a plane with a VNE of 200-220. Another part that comes into play is engine management descending from altitude. You don’t just let off the gas and come down. You don’t want to shock cool the engine. You reduce power but also pushing the nose over, descents tend to be fast. Add ATC control, the situation will have you bumping 200 in anything somewhat clean. The only other choice is to slow down as you climb. You have to reduce the indicated airspeed to not go over your true airspeed crossing VNE. Except for some fuel savings and possibly wind luck, you will not cover ground any faster at any altitude. Might as well stay low.

    For reference A Mooney M-20E has a VNE of 196. Push the nose over when you descend and it will rush right to it.
     
  10. Aug 18, 2019 #50

    Hephaestus

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    Fixed. Descent management is a critical skill in a mooney.
     
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  11. Aug 18, 2019 #51

    TFF

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  12. Aug 19, 2019 #52

    mcrae0104

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    Consider looking at this a different way. Pull out your E6B.

    Premise 1: 150 mph TAS @ 7,000 ft (assume satandard temp) is 135 IAS.
    Premise 2: a 180 hp O-360 running at 75% is 135 hp. (We can come back to that 2 lb/hp you mentioned in a minute)
    Premise 3: you can fly the same IAS at any given altitude for the same power (if you can make the power up there)
    Premise 4: 135 mph IAS @ 17,000 ft is 175 mph

    Conclusion: if you can produce 135 hp at 17,000 ft (standard day) then you can make 135 mph IAS and therefore 175 mph TAS

    I don't have the SFC figures for a generic (carbureted?) O-360 at hand, but referring to a 172S POH, and doing the math, the IO-360-L2A is right about 0.45 lb/hp/hr. Multiplied by 135 hp and divided by 6 lb/gal, this yields a fuel burn of 10-ish gal/hr.

    Now you will need to ask yourself 1) what pressure ratio you will need to produce 135 hp at 17,000 ft, and 2) will you be running as lean as a normally-aspirated, fuel-injected 360 when running at that pressure ratio? (It seems reasonable that in order to avoid detonation, you will be running different timing, reducing CR, running richer, or some combination of the above, all of which would increase your SFC. Also it is likely you will need to consider charge cooling, which would increase drag somewhat.)

    My earlier instinct that you would be running higher burn rates may have been wrong--but it comes down to the answers you find to #1 & #2 above. Further, it may depend somewhat on your mission (anticipated leg length) to determine whether a 17,000 ft climb is worth it to you. (The DA was 8,000-something feet at the airport when I took of this afternoon, and I'm not sure I'd have the patience to grind all the wayup to 17k even if the ol' girl would make it up there).

    SIDEBAR: Horsepower is in units of lb x ft / sec. This is work (force x distance) divided by time. To equate 1 hp to 2 lb of drag is a non sequitur. It is true at a given speed (you can do the math and find out the speed at which that is true), but otherwise it is not meaningful.

    Although I am contemplating a turbocharged engine myself, I hope Ross or someone who has experience with turbo 360s will chime in about how much power you can reasonably expect at 17,000 ft.
     
  13. Aug 19, 2019 #53

    rv6ejguy

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    You can get as much power a you need at altitude within reason and within cooling limits which is usually the limiting factor on air cooled engines.
     
  14. Aug 19, 2019 #54

    pictsidhe

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    Premise 3 is wrong.
    At a constant IAS, the drag is invariant with altitude. At a constant IAS, power increases in proportion to TAS.
    At a given indicated airspeed, dynamic pressure (0.5*rhoV^2) is constant. Keep IAS constant, induced drag and parasitic drag and therefore total drag (excluding mach effects) is constant, as well as CL.

    If you need 135hp for 135mph IAS at 7,000, you'll need 158hp in the thinner air at 17,000. If the engine is 180hp at sea level, you are looking at somewhere over 10psi boost, depending on how well aftercooled the charge is. I'm not sure I'd like to cruise at Vne, though. Any hiccups, and you can easily sail past it.

    How much power you can get is likely to be cooling limited. The thinner air up high does not cool as well. You can blow more volume through the engine to compensate, but your cooling drag will increase.
     
  15. Aug 19, 2019 #55

    mcrae0104

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    Not sure I follow. I am happy to be corrected and learn if you would be patient enough to explain. I agree that total drag is the same for a particular IAS regardless of altitude but I am not following why one would need more power at higher altitude if total drag is the same.
     
  16. Aug 19, 2019 #56

    pictsidhe

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    You fly a higher TAS at altitude.
    Power = Drag * TAS
     
  17. Aug 19, 2019 #57

    geosnooker2000

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    This article https://www.boldmethod.com/learn-to-fly/performance/vx-vy-altitude-and-where-they-meet/
    suggests (as well as pictsidhe) that as you climb higher, there are less molecules to create lift (in addition to less parasitic drag), so that while parasitic drag reduces with altitude, induced drag (the drag that keeps you in the air) increases as a matter of need. That's because you must fly at a higher angle of attack to produce the needed lift to maintain the same altitude at a given speed. However, it only makes sense that if you increase your TAS, you shallow your angle of attack -thereby negating some if not most of the increased induced drag. Sort of like a boat planing out on the water after you "send it".
    But the prop becomes less effective the higher you go, hence the need for a VPP, but not necessarily more power.
     
  18. Aug 19, 2019 #58

    TFF

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    Angle of attack gets worse the higher you go. Yes you are going faster because of less density, but you have less lift because of less density. They are just not linear. Physics can’t be different from the propeller which is increasing pitch as you go faster to maintain its max thrust but it changes more because less density. Probably the best choice for comparison would be studying the SR-22 Cirrus. Forget the fancy stuff, the airframe comes in both turbo and non turbo. There has to be enough operating details written for a good comparison.
     
  19. Aug 20, 2019 #59

    PW_Plack

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    No, you're not. Vne is expressed as indicated airspeed (and marked in red on the airspeed indicator) because it, like stall and other V-speeds, scales with decreasing density. Vne is a specific IAS no matter what the current TAS may be.
     
  20. Aug 20, 2019 #60

    pictsidhe

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    Flutter depends on TAS. Vne is generally defined as TAS for that reason.
     

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