Author Topic: Could the Spruce Goose climb out of ground-effect?  (Read 18901 times)

Offline undatc

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #15 on: February 16, 2010, 06:49:42 PM »
Correct AOI, been awhile since I messed with this physics stuff.
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Offline Baradium

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #16 on: February 16, 2010, 06:55:46 PM »
Honestly, I never had any doubts about whether it could fly.  The whole reason people asked about it when it was built was because of the sheer size of it in relation to anything else flying at the time.


Speaking of large airplanes, I got to see the AN-225 last week.   Just wish I could've gotten a look inside.
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Offline undatc

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #17 on: February 16, 2010, 07:07:16 PM »
Honestly, I never had any doubts about whether it could fly.  The whole reason people asked about it when it was built was because of the sheer size of it in relation to anything else flying at the time.


Speaking of large airplanes, I got to see the AN-225 last week.   Just wish I could've gotten a look inside.

So not fair!

I saw the 787 land last Saturday at BFI.  Just by dumb luck I was there when ZA002 touched down.

In the wiki article it says that the service ceiling of H4 is around FL200.  I dont see why it wouldn't get there.
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Offline Baradium

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #18 on: February 16, 2010, 07:09:39 PM »
Honestly, I never had any doubts about whether it could fly.  The whole reason people asked about it when it was built was because of the sheer size of it in relation to anything else flying at the time.


Speaking of large airplanes, I got to see the AN-225 last week.   Just wish I could've gotten a look inside.

So not fair!

I saw the 787 land last Saturday at BFI.  Just by dumb luck I was there when ZA002 touched down.

In the wiki article it says that the service ceiling of H4 is around FL200.  I dont see why it wouldn't get there.


It was dumb luck for me too.   I was sitting down enjoying some good sourdough pancakes when my friend said he'd read that the world's largest airplane was going to be in fairbanks for 12 hours refueling and getting ready to continue on it's way from Japan to Haiti hauling heavy equipment.
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline undatc

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #19 on: February 16, 2010, 07:20:07 PM »
http://en.wikipedia.org/wiki/NACA_airfoil

So there is the wiki article about NACA airfoils.  For the life of me, I cant figure out which series those NACA numbers are.  It seems as if we can figure that out, we should be able to then get the lift/drag ratios and prove it could fly.  Thou the more I read about the topic online, it seems that most everyone is in agreement that it is able to fly out of ground effect.
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Offline undatc

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #20 on: February 16, 2010, 07:21:06 PM »
Honestly, I never had any doubts about whether it could fly.  The whole reason people asked about it when it was built was because of the sheer size of it in relation to anything else flying at the time.


Speaking of large airplanes, I got to see the AN-225 last week.   Just wish I could've gotten a look inside.

So not fair!

I saw the 787 land last Saturday at BFI.  Just by dumb luck I was there when ZA002 touched down.

In the wiki article it says that the service ceiling of H4 is around FL200.  I dont see why it wouldn't get there.


It was dumb luck for me too.   I was sitting down enjoying some good sourdough pancakes when my friend said he'd read that the world's largest airplane was going to be in fairbanks for 12 hours refueling and getting ready to continue on it's way from Japan to Haiti hauling heavy equipment.

Nice, you were in Bethel right for awhile?  I was watching dirty jobs last week, and he was up there doing something with geese.  Probably shouldn't go much further than that  ::sick::
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Offline Baradium

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #21 on: February 16, 2010, 07:25:42 PM »

Nice, you were in Bethel right for awhile?  I was watching dirty jobs last week, and he was up there doing something with geese.  Probably shouldn't go much further than that  ::sick::

No, I avoided being based in bethel like the plague.    I flew through it a number of times, but I was one of the lucky ones that got to go back to town because it was always an out and back...
"Well I know what's right, I got just one life
In a world that keeps on pushin' me around
But I stand my ground, and I won't back down"
  -Johnny Cash "I won't back Down"

Offline Jupiter

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #22 on: October 29, 2010, 11:18:51 AM »
HAs anyone already been messing with these calculations? otherwise I might give it a try this weekend...
As for the remark on model airplanes being able to fly proving the real thing could fly: If you scale things, you change their aerodynamics. This because Mach and Reynolds numbers of the airfoil and their ratio change with scaling, resulting in different aerodynamic behavior...
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Offline Ragwing

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #23 on: October 30, 2010, 02:11:12 PM »
If you scale things, you change their aerodynamics. This because Mach and Reynolds numbers of the airfoil and their ratio change with scaling, resulting in different aerodynamic behavior...
Not only is the Spruce Goose made of wood (They did not use spruce), they did use screws to hold the wood together until the glue dried.  Then the screws were removed.

Howard Hughs had to make the Spruce Goose fly to received the government payments.
Just in case it crashed or broke apart, Howard had the pontoons and the body were filled with inflated beach balls.
Then he could put it together and try again.
RW

Offline Oddball

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #24 on: October 30, 2010, 06:32:56 PM »
I wonder if they would ever try again to fly it.
"You can teach monkeys to fly better than that!"and "spring chicken to sh**e hawk in one easy lesson"

Offline Jupiter

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #25 on: October 30, 2010, 07:12:03 PM »
With some simplifications, it shouldn't be too hard to calculate. Biggest problem will probably be finding a Cd0 for it. After that, a maximum climb rate should be calculatable. If this is around several m/s, it's feasible the aircraft would fly without ground effect. Maximum lift coefficients can be found by entering this profile in software like Javafoil etc.
@ Oddball: If they'd even think about flying it again, they'd probably be stopped by both the FAA and their budget. These aircraft cost a fortune to maintain and run (this thing had 8 engines of 71.4 Liters each), and the FAA would probably not like an unproven design take to the skies without an extremely costly full check, and of course a huge pack of paper and computer simulations proving this aircraft should be able to safely take to the skies.... It'd probably be cheaper and easier to build a replica with some modifications, than trying to fly this behemoth again...

« Last Edit: October 30, 2010, 07:13:52 PM by Jupiter »
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Offline Mike

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #26 on: October 31, 2010, 04:41:05 PM »
@ Oddball: If they'd even think about flying it again, they'd probably be stopped by both the FAA and their budget. These aircraft cost a fortune to maintain and run (this thing had 8 engines of 71.4 Liters each), and the FAA would probably not like an unproven design take to the skies without an extremely costly full check, and of course a huge pack of paper and computer simulations proving this aircraft should be able to safely take to the skies.... It'd probably be cheaper and easier to build a replica with some modifications, than trying to fly this behemoth again...

sadly, this very problem keeps a lot of people and companies from developing a new aircraft....
I just saw the History of the helicopter on the Military channel and it wasn't long until Sikorsky and Piaseki ran into issues with the FAA. Had we invented the helicopter now, it would never fly......


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Offline Jupiter

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #27 on: October 31, 2010, 08:00:38 PM »
hehe, true, but there is hope though. Things like the Terrafugia Transition etc do call for some new rules and revising of regulations...
Also, generally you can certify replicas of old aircraft on the basis of "it was OK then, so it is OK now" (at least, that's how we did it with ours...). The problem is that this aircraft was never fully certified, or even flown multiple times...
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Offline Jupiter

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #28 on: November 01, 2010, 03:40:07 PM »
Ok, bear with me:  (scroll down for conclusion)

Steady rate of climb (ideal climb situation, real values lie about 25-35% lower) is defined as the power available minus the power required, divided by the aircraft weight.

(Pavailable-  Prequired) / W

Available power Pa is known, 8 Wasp Major engines of 2640 [kW] each, results in total available power of 21.12 [MW]. If you assume a propellor efficiency of around 75%, this results in around 15.8 [MW] of power available.
The weight W can be guesstimated: assuming an MTOW of 180000 [kg], this is 180000 * 9.81 = 1.77 [MN]

Required power Prequired is not known here, but is defined as the drag force D multiplied by the airspeed V. Both of these values are also not directly known, but can be deduced with some assumptions. As wikipedia quotes a cruise speed of around 408 [km/h] or ~ 113 [m/s], a reasonable assumption of climbing velocity seems somewhere around 75 [m/s].

The drag D can be calculated by the probably familiar formula D = CD * 0.5 * rho * V2 * S. The air density rho can be taken at sea level to be 1.225 [kg/m3], the velocity V was calculated above and the wing surface area S is known to be 1050 [m2]. Now only the drag coefficient CD is unknown.
CD is defined as CD0 + (CL2 / (pi * A * e) ). The Aspect ratio A is defined as wing area divided by the square of the span, or 1050 / 96.9 = 10.8 [ ]. Oswald factor e is assumed 0.6 [ ], since it's not easily calculated and a relatively old design. 0-lift drag coefficient CD0 is assumed to be 0.025 [ ], a rather reasonable value since the aircraft has huge extrenal features like floats...
Lastly, the lift coefficient CL needs to be found, which can be done by entering the airfoil data in JAVAFOIL. I plotted the mentioned airfoil, but seeing the shape, I'm having a hard time believing this is what was used. The program gave me a maximum lift coefficient of 1.8, which is rather high, so a more reasonable value of 1.1 [ ] will be assumed.
This gives a drag force D of (0.025 + (1.12 / (pi * 10.8 * 0.6) ) ) * 0.5 * 1.225 * 752 * 1050 = 305 [kN].
Therefore, the power required Prequired will be 305 * 103 * 75 = 22.9 [MW]

This is larger than the power available, so the rate of climb will not be positive. This means the aircraft would not be able to climb, so certainly wouldn't be able to fly. What's bothering me is that this difference seems a little too large for my taste. Since I did make a lot of assumptions here, it could very well be there are some mistakes there...

If you spot any errors or have any theories on why this answer's resulting from this calculation, or have some better values for some of my assumptions, please let me know!
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Offline Franz

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Re: Could the Spruce Goose climb out of ground-effect?
« Reply #29 on: November 01, 2010, 06:51:28 PM »
I'd say you'll have to calculate the speed it could actually achieve by v max = (Pavailable/D)1/3, because it can only accelerate as long Pavailable > Prequired.
Using your figures I get v max ~ 66 m/s, assuming it has no drag from still being in the water.
The next step I think should be to figure out how much lift is generated at that speed [I'll see if I can figure out that JavaFoil-thingy]
and see if it's enough to get it of the ground.
Also, I would assume the weight to be something to between 150000kg (MTOW - one Sherman tank) and 90000kg (MTOW - 750 troops) because I think the using the projected payload is a little ambitious for a first prototype.

Now tear it apart while I go back to (not) studying physics . . .