Decalage angle

Discussion in 'Aircraft Design / Aerodynamics / New Technology' started by Eugene, May 29, 2017.

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  1. Nov 17, 2019 #1421

    TFF

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    Just add another can of Cheese Wiz and keep sanding.
     
  2. Nov 17, 2019 #1422

    Doggzilla

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    I stopped getting alerts from this thread and assumed you just gave up.

    I’m glad to see you didn’t, and also glad to see how far you’ve come.

    As far as the wing AoA goes, if you require such a high AoA it means the wing is not developing properly lift.

    As we discussed a while back, having the front of the engine at the center of the wing will greatly interfere in efficiency.

    Mike Arnold set several word record, and he was adamant about keeping high pressure areas away from the center of the wing.

    Just look at the F4U Corsair and P-39 Cobra. They were both significantly faster than other aircraft with the same engines, but the only major difference was moving the cockpits away from the wings.

    Both are roughly 50mph faster than other aircraft which had cockpits over the center of the wing.

    The front of your engine is basically no different than having a cockpit in the same location. It will greatly effect wing efficiency.

    It’s far easier to add an extension on the nose of the engine to move the center of pressure than it is to change anything else.

    I highly suggest trying to move that pressure ahead of the wing instead of over it.
     
  3. Nov 18, 2019 #1423

    Eugene

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    Yes we talked about this and many other things. I would be lying to tell you that I do remember it all , or understand all of it, or agree with everything. I will do my best to put this concept on the paper and take a picture. Pictures work better for me. Then we all understand what we’re talking about.
     
  4. Nov 18, 2019 #1424

    Doggzilla

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    Okay, Ill try and put something together to explain it.

    But Im sure you have enough to keep you busy until then
     
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  5. Nov 18, 2019 #1425

    Eugene

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    Screen Shot 2019-11-17 at 22.53.25.png Screen Shot 2019-11-17 at 22.51.17.png

    This is 400 MPH aircraft. Are we sure that at 100 MPH cabin position in reference to the wing will have any effect at all?

    Screen Shot 2019-11-17 at 22.59.17.png
     
    Last edited: Nov 18, 2019
  6. Nov 18, 2019 #1426

    Doggzilla

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    Look up Mike Arnold. He holds many world records and made tutoring videos on the subject.

    He was able to get over 200mph on 60hp. His theories work extremely well even for low power levels.
     
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  7. Nov 19, 2019 #1427

    Eugene

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    Screen Shot 2019-11-17 at 23.06.40.png

    Reading russian sites about this airplane was very interesting. I had no idea about aircraft with engine behind pilot seat from WW2. I am in love with this machine already!!! So, thank you!

    But they think that aerodynamic efficiency has nothing to do with cabin position in reference to the wing. With engine sitting on CG = very skinny nose = near perfect fuselage shape + aft CG = efficiency.
     
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  8. Nov 19, 2019 #1428

    Aesquire

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    I did a rant on the P-39 in a myth history thread, then got distracted, & should get back to it. A very underrated plane.

    You can roughly divide WW2 planes as pre or post Battle of Britain. That's when the need for pilot armor & self sealing fuel tanks became obvious. ;)

    Pre Battle planes had to struggle with hundreds of added pounds and reduced fuel tank size, as they were uodated . ( the P-47 designer did forsee the need for future equipment and weight gain, and since he already had to build it big to fit the turbo supercharger ducting... which is how we got a fighter that fully loaded weighed as much as an empty DC-3. And did over 400 mph. )

    The Airacobra was the "smallest plane with biggest engine" approach, and had multiple strikes against it.

    The turbos weren't ready, so it lost high altitude performance without it, at the same time high altitude performance became vital.

    It was too small to absorb the extra weight of armor, etc. gracefully.

    It was an early pre war design that needed a major update, bigger wing, etc. But the company was low on cash at the time and the military demanded production at the expense of improvement. That attitude was an issue with many things, but you can understand the mind set. Rather have something now, than better later, or else we lose, now.

    The Russians had great success with the Airacobra in part because they used it at the lower altitudes of performed well at, & it was extremely maneuverable, sturdy, fast, had radios, and well armed. ( some Russian aces looked at the cannon trigger, a loop sticking out of the floor, said wth? and had their crew chief rig a switch on the stick )

    I admit the cockpit position looks like Mike Arnold had a say. ;)
    But it was probably more for visibility. OTOH the folk at Bell were pretty smart...
     
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  9. Nov 19, 2019 #1429

    Doggzilla

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    Don’t forget the P-63 King Cobra. Was much improved and had a much higher weight to allow for better equipment and fuel tanks.

    Soviets operated several thousand of them alongside the original Cobra. Over 3000 made.
     
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  10. Nov 20, 2019 #1430

    Eugene

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    Spend some time today reading about American help to Russia in WW2. Back in USSR at school they didn't tell us anything at all !!! Soooooooo sad!!!

    Screen Shot 2019-11-19 at 21.59.37.png
     
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  11. Nov 22, 2019 #1431

    Eugene

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    Screen Shot 2019-11-21 at 19.38.51.png
    On this picture Mike Arnold is telling us that he was disappointed to find out that elevator in flight not exactly inline with stabilizer. I see very similar picture in level flight on my horizontal tail. He is not explaining why this is happened to him. But I would like to know what was he thinking - wrong size or wrong angle? How did he fixed that?
     
  12. Nov 22, 2019 #1432

    rotax618

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    The elevator angle changes with speed and load distribution. The decalage is set for least trim drag at cruise and average load conditions (1/2 fuel, baggage, passenger loads)
     
  13. Nov 22, 2019 #1433

    Eugene

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    He said that he was disappointed to see elevator position like on this picture. So, he miscalculated stabilizer size? Or stabilizer incidence ?
     
  14. Nov 22, 2019 #1434

    Eugene

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    9E3EDE20-3D80-47B4-A5E7-44C1E9CEB2A5.jpeg

    Looks like I have another question. This is obviously very successful engine and they made so many of them. I wanted to know why did we start going backwards right after war ended and start building air cooled engines? I realize that there was no use for 12 cylinder thousand horsepower engines anymore. But four-cylinder 300 hp would work perfectly in airplanes like Bonanza.
     
  15. Nov 22, 2019 #1435

    BJC

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    He might have missed the design condition (where the elevator would be aligned with the stabilizer) by missing one or more factors, including C.G., total aircraft pitching moment (driven by wing moment, fuselage contribution, center of drag location, engine thrust or thrust line), actual speed / Reynolds number, size of stabilizer, lift slope of stabilizer, etc.

    He wasn't off very far, but at record low drag values, every little bit is important.


    BJC
     
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  16. Nov 22, 2019 #1436

    Eugene

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    Yes, yes, yes, thank you, this is corresponding to what I was thinking as well. I’m starting to think pretty smart about myself by now!!! What was his plan for fixing it? Changing angle on stabilizer? or increasing its size? If we decide to change stabilizer angle to fix our mistake, how much is OK to do? Is there normal mark like about 4°? And if that still not enough - you need bigger tail? Like never turn it down to 8°or so. I can't seem to find that kind of information in my books.
     
    Last edited: Nov 23, 2019
  17. Nov 22, 2019 #1437

    Aesquire

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    We didn't "go backwards" to air cooled engines, they kept right on using the already being made ones. The basic flat four was developed before the War and used in observation planes throughout.

    That ignores the millions of air cooled radials used in transports, bombers, fighters & observation planes. And the inline & V, Ranger, Argus, Hirth, etc.

    Liquid cooling, like your 912, has it's advantages & costs. Exactly why the air cooled Continental and Lycoming ( and Walter and ... ) became the dominant power plant is complex, power, weight, simplicity, cost & availability.
     
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  18. Nov 23, 2019 #1438

    Eugene

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    For many years I was only dreaming about getting my pilot license. There was no money for anything else and only enough money for dreaming and one-day ticket to Oshkosh.

    So, I was stopping at local airport, spending some time with pilots/aircraft owners, pretending to be one of them and listening to all kind's of stories. Stories about rebuilding engines, cracked blocks, broken valves, and on, and on, and on. And money they spend to keep this air cooled engines going was absolutely unbelievable to me!!! And it was much more unbelievable to my wife!!!

    And all this time my 15 years old Honda Civic didn't need anything at all!!! Mobil-1 oil change every 15000 miles and no pre heating engine start on 20°F below.

    When I started flying C-172 with my instructor we had engine failure on Lycoming H-engine.

    That is why it feels that Lycoming and Continental didn't get to 21-st century yet. But Rotax with 912 engine did.
     
  19. Nov 23, 2019 #1439

    TFF

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    Don’t worry, if you mistreat the 912, it will shell out. A friends AirCam had to have both engines top overhauled with about 350 hours from new. The certified parts for the 912 can be significantly more expensive than the homebuilt. My friends air cam has had constant ignition problems. I replaced the stator in one of the engines. They built the AirCam in the 2000.

    You are really comparing apples to oranges, and missing the brilliance of the air cooled. No pump to drive or radiator to cool the engine, lighter than same size engine with water jackets, no prop drive gears that require above average engineering or machining, power is matched to the prop direct drive, stand alone modular ignitions, if equipped with fuel injection, it is very simple. Very simple engines, and remember Rotax is German.

    Sure you can improve stuff, but there is no money in it. If you changed ever GA engine in the world today with new engines, great. At current airplane engine build rate, it would take stockpiling engines about 20 years to do that. That’s one day production if adding all the auto manufacturers together.

    The lawyers have made Lycoming and Continental expensive. CYA is what they build into the price. If Rotax had equal flight exposure here in the US, a 912 would be a $60,000 engine. If you were flying a 320 H2AD, Lycoming, that is a terrible engine. Lycoming is trying to erase that thing like Russia would do. They will not claim to have built it and they make no replacement parts for it. It’s actually different than any other Lycoming. But even if it was a different model engine, a flight school engine probably has 8000 hours on the components; it can be overhauled with infinite time. Those lawyers made it expensive to the point that using 8000 hr parts is required to be economical. Field overhauled. Now if you can afford for Lycoming to overhaul, they will throw away the 8000 hr parts. The data tag might be original, but in their best interest they send out equal to new when they overhaul. It does cost. Of the non turbo engines I have run, not one required work to make it to TBO. Of the turbocharged engines, three cylinders were required repaired out of ten engines. I’m not saying you can’t have a bad engine from Lycoming, there is always a percentage, but if you have a true overhauled engine like they do, they run a long time.

    I don’t know what the Allison TBO is, but the Merlin was around 500 hours. They were highly strung war engines. A combat planes expected life was less than 100 hours.
     
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  20. Nov 23, 2019 #1440

    Eugene

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    Our local mechanic was telling me that 912 engine is much more reliable then anything out there.

    But my own engine have seen 3 different gear boxes already in only 1000 hours.

    So, that is why I was wondering, if they build reliable 2700 rpm water cooled engines already 80 years ago. Why they didn't stay with it in smaller engines!!?? We would have by now aviation engines that just as reliable as Honda Civic!
     

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