DFS 228, 2 prototypes flown , 904km/h(562mph).

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gabriel pagliarani
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Post by gabriel pagliarani » 18 May 2005 14:09

Topspeed wrote:Huck are you seriously saying a glider at 25 000 meters ( in the thin air ) has glideratio of 30-40 ? It has to carry the empty rocketsystem as well.
Plus Oxygen, cameras (....what kind of recce could be possible without cameras? Where are cameras in the drawings? 8) ) UHF/VHF radio-com, nav-aids, parachute & lifesystem. Try to add all at least 150 kg. more...
Huck wrote:...And by the way, Me 163 was not a particulary good glider....

Me 163B was the ONLY glider able to approach Mach1 without loosing the wings ever built during WW2, not a paper-tiger like this one.
Huck wrote:...There is nothing surprising that a glider goes for 900km if starts descending from 25000m.
I am so surprised that I cannot believe it, if the glider has a so high weight/wingspan ratio if compared to conventional gliders. (..the actuals, made in carbon fibers and kevlar and not of pine wood as you suggest us.. ) Any way high-speed = short wings and short-wings = short glide. Consequently short wings = short glide. Or you do you think that 900 km of east-ward glide over Germany (expecially in winter-time) is a "short glide"?
++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
And finally or at last but not least this is the reply of Mr. Dan Johnson to my own enquiry:
I hardly ever read that forum, but thanks for writing. There is no "LUFT46.com Forum", so I am not sure what you are talking about there. Thanks for writing...

Dan Johnson
Incident closed for me. Now I can dress my own ARMANI black shirt as usual. I feel so fashionable now ...
Last edited by gabriel pagliarani on 20 May 2005 12:14, edited 1 time in total.

Huck
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Post by Huck » 20 May 2005 01:42

Topspeed wrote:Huck are you seriously saying a glider at 25 000 meters ( in the thin air ) has glideratio of 30-40 ? It has to carry the empty rocketsystem as well.
gabriel pagliarani wrote:Plus Oxygen, cameras (....what kind of recce could be possible without cameras? Where are cameras in the drawings? 8) ) UHF/VHF radio-com, nav-aids, parachute & lifesystem. Try to add all at least 150 kg. more...
Sure it could. Optimum L/D remains the same for an aircraft regardless of load. This means that max glide range is the same for an aircraft, regardless of payload (once again I have to specify that I mean gliding without soaring; with soaring the range can be much bigger). This is different from the case of a powered aircraft where range is affected by payload. The explanation for this phenomenon is simple, but I will leave you the pleasure of discovering it ;) (cheating is allowed, even encouraged)

gabriel pagliarani wrote:
Huck wrote:...And by the way, Me 163 was not a particulary good glider....

Me 163B was the ONLY glider able to approach Mach1 without loosing the wings ever built during WW2, not a paper-tiger like this one.


Me 163, like any other plane, could glide, but wasn't very good at it. Me 262 had a glide ratio of 17, despite bulky engine nacelles mounted underneath the wings, compared with Me 163 which had a glide ratio of 13. This made Me 262 the better glider of the 2 planes, despite that critical Mach number was about the same for both planes. Unsurprisingly Me 262 had much higher aspect ratio wings than Me 163.

gabriel pagliarani wrote:
Huck wrote:...There is nothing surprising that a glider goes for 900km if starts descending from 25000m.
I am so surprised that I cannot believe it, if the glider has a so high weight/wingspan ratio if compared to conventional gliders.
Once again, weight plays no role in the range of a gliding plane.
gabriel pagliarani wrote:(..the actuals, made in carbon fibers and kevlar and not of pine wood as you suggest us.. )
Obviously I was talking about ww2 (training) gliders.
gabriel pagliarani wrote:Anyway high-speed = short wings and short-wings = short glide. Consequently short wings = short glide.
High speed does not equate with short wings (as long as you don't go faster than critical Mach). Think of U2 for example. Or airliners.
gabriel pagliarani wrote:Or you do you think that 900 km of east-ward glide over Germany (expecially in winter-time) is a "short glide"?
900km of gliding from 25km altitude is nothing special (though gliders flying at such altitudes are extremely rare and all are powered not towed). For a pure glider it is actually a very poor performance by today's standards.

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Post by gabriel pagliarani » 20 May 2005 12:39

Huck, I think you are joking with us. If not you need further studies.

Ceiling 25000 mt (not ft) = H
Speed 900Km/h = 250 m/s = V
Descent rate 14 m/sec = d (your best option I argue)

Time of glide H/14 = 25000/14 = 1786 secs = 0, 5 Hours of flight
Landing after shut off = V*T = 250*1786 = 446.500 mt or 446,5 km NOT 900Km = END OF QUERELLE

If the glide ratio was 40 time of glide (your worst option I argue) was 25000/40= 625 sec hence the landing after shut off occurs after 250*625 =156250 mt or 156 Km only.

But I don't think this glider was able to land at the same gliding speed (904 km/h is too much for safe landings) thus there were some air-braking operation (opening flaps) to do in order to reduce at least 1:4 such speed (250 km/h as the Concorde) I hope you agree this was a necessary operation. The energy spent while reducing speed means a waste in distance (at least 100 km) so the plane glides safely in about 346 km not 446 km as per only kinetiks at glideratio 14. If glideratio was 40 the route was only 56 Km. (Strange! The same figures of Me163B 8) mumble... mumble... Huck!) And what kind of recce operations were possible in 1945 from 25000 mt? Gary Power's U-2 was hit when flying over SSSR at 17000 meters in 1962...This was the max ceiling for photo-spying till early 1960. And I have not yet seen your only-supposed-to-be-fitted camera, Huck.
Weight is not in the count but the ratio wingspan/weight yes and a ratio is a PURE NUMBER. Always.

Edited by Moderator Andy H

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Post by Topspeed » 20 May 2005 13:29

Huck wrote: 900km of gliding from 25km altitude is nothing special (though gliders flying at such altitudes are extremely rare and all are powered not towed). For a pure glider it is actually a very poor performance by today's standards.
Even with a 1/60 glideratio it ( 900 km ) would mean a starting altitude of 15 kilometres....now how do get a glider into 15 kilometrers ( 47 000 feet ) ?

I have a haunch that those glideratios are only valid at 1000-5000 ( 3000-15 000 feet ) meters altitudes.

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Post by Gespenst » 20 May 2005 13:59

Now i'm not sure if i'm lost in the simplicity of this, but for a glider to do a pure glide from 25 000 meters to the originally claimed distance of 105 000 meters requires a glide ratio:

105000 m / 25000 m = 42

Which means 42 meters of distance covered per meter of altitude lost.

And Topspeed,
Topspeed wrote: Even with a 1/60 glideratio it ( 900 km ) would mean a starting altitude of 15 kilometres....now how do get a glider into 15 kilometrers ( 47 000 feet ) ?
The thing was supposed to be towed or carried to 10 000 meters and then rocket to ~25 km altitude.

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Post by Topspeed » 20 May 2005 14:19

I was referring to a glider with 1/60 ratio. DFS design was far from it.

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Post by Gespenst » 20 May 2005 14:55

So i misunderstood your question.
It looked suspiciously like you were asking "by what means can a glider be placed to 15 km of altitude".

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Post by gabriel pagliarani » 20 May 2005 18:14

Gespenst wrote:Now i'm not sure if i'm lost in the simplicity of this, but for a glider to do a pure glide from 25 000 meters to the originally claimed distance of 105 000 meters requires a glide ratio:

105000 m / 25000 m = 42

Which means 42 meters of distance covered per meter of altitude lost..
I am not sure of this. Glideratio rules are linked to density of the air and in Tropopause air density doesnt decrease linearly while increasing height. Consider that at 25 km ceiling the plane is 10 km over Tropopause upper limit. Ballistics are more efficient while describing the descending route from 25km to 10 km height. Better to consider glideratio equivalent to average descending speed so glideratio 42 means 42 m/s and 14 means an average descending speed 14 m/s. Both values are perfectly allowable if you think that a parachute descending speed is 4-5 m/s.
Note I accepted both values as allowable in my own calculations without entering in the argument.

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Post by Gespenst » 21 May 2005 16:31

gabriel pagliarani wrote: Better to consider glideratio equivalent to average descending speed so glideratio 42 means 42 m/s and 14 means an average descending speed 14 m/s. Both values are perfectly allowable if you think that a parachute descending speed is 4-5 m/s.
Gabriel, could you please enlighten me how can you force the glide ratio number to be a speed of descent?
Do you mean that a plane with higher glide ratio descends faster than a plane with a lower one?

Glide ratio is an approximation for combined effect of other abilities that define the characteristics of the airplane,
such as lift and drag. When talking about a long glide from high altitude, the air density will of course play a major role.
Therefore it is valid to think the required glide ratio for that trip as a mean value.

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Post by gabriel pagliarani » 22 May 2005 02:58

Gespenst wrote: Gabriel, could you please enlighten me how can you force the glide ratio number to be a speed of descent?
Do you mean that a plane with higher glide ratio descends faster than a plane with a lower one?...
No, the contrary.I don' t forced the equation N/V = R/H simply because R = N*dt and V = H *dt and dt/dt =1. There is a reversed ratio (pls watch the sketches). Note I allowed an high descent speed and a low one. The corrected average value must be between these values. I pointed your attention on the fact that glideratio is allowable only in low atmosphere. A bolid moving at high speed in a so high ceiling (25 km) without further boost follows kinetik ballistic laws till re-entry in dense atmosphere. The problem is that tropopause limit is continuosly moving from 12Km to 15Km changing both the ballistic part of the course then the glided one. Also the effects of high speed jet-streams must be counted, but obviously in 1945 those atmospheric phoenomenons were totally unknown. Nice to watch the real original topometric mission profile of this plane: the guy who have counted 1000 Km of ballistic + glided descent never counted the fact that this plane was not able to trespass Mach 1 in any point of the course. Only a supersonic could do it, even if for a while. In this way the ballistic part of flight is dominant respect with the glided one: I have only shown you that a subsonic ONLY GLIDED course starting from 25 km height could not land after 900 Km. Not with those short wings....any way supposing it is possible an aerodinamical glide from 25 km height the DFS had to run 25Km/h as vertical speed or 6,9 m/s only. I don't think that the actual best gliders could perform this low vertical speed while frontward running 250m/s . Supersonic soaring is the only possible solution to this problem but DFS limit was 904 km/h.

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Post by Gespenst » 22 May 2005 15:58

Ok i will have a closer look at your presentation and digest it.
In the meanwhile i must point out that you assume the plane's speed to be a constant 250 m/s, while it is clear that when the plane would start the glide back home, it would have to have a much lower speed to begin with. That is because it has to do an U-turn.

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Post by gabriel pagliarani » 22 May 2005 16:21

Anyway 1050 km are 1050000 mt and not 105000 only. But 1050000/25000 = 42. You simply forgot a zero and glideratio is corrected. Pitch angle =arc cotg 42= arctg (1/42) = Downward (-) 1°21'50,14". Far small pitch reentry angle to be really controlleable. Somewhere among DFS data there must be written which was the real pitch angle when gliding: this information is obviously more important and believable than a supposed and badly & postoumosly calculated operative range. In Italy we say "liars have short legs" and in this case it is really true.
Gespenst wrote:Ok i will have a closer look at your presentation and digest it.
In the meanwhile i must point out that you assume the plane's speed to be a constant 250 m/s, while it is clear that when the plane would start the glide back home, it would have to have a much lower speed to begin with. That is because it has to do an U-turn.
250 m/s = 904 km/h is the max speed limit reported, but not a constant! i think it was very close to threshold structural limit before loosing wings and life. Your thought about "U" turn is acceptable if you consider a only ballistic climb to 25000. (..even if it was clearly better to approach backward the main target with the "rocket-mistel" just before launching DFS..) And the rocket-climb is the less impossible part of the whole stuff: DFS starting from his carrier at 8000 mt height had at least 3 minutes to reach top ceiling and 2 further minutes of full power boost to reach a " x" speed greater than 0 m/s. In fact a "low speed stall" at so high ceiling means a 100% loss of any aerodinamical control and the sequential loss of pilot's life after a "ded leaf" twist and crash. I have a theory about the horizontal speed DFS could really touch at 25Km height. If you want I can explain it, it isn't a tedious stuff!

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Post by Huck » 24 May 2005 20:16

gabriel pagliarani wrote:Huck, I think you are joking with us. If not you need further studies.

Ceiling 25000 mt (not ft) = H
Speed 900Km/h = 250 m/s = V
Descent rate 14 m/sec = d (your best option I argue)

Time of glide H/14 = 25000/14 = 1786 secs = 0, 5 Hours of flight
Landing after shut off = V*T = 250*1786 = 446.500 mt or 446,5 km NOT 900Km = END OF QUERELLE

If the glide ratio was 40 time of glide (your worst option I argue) was 25000/40= 625 sec hence the landing after shut off occurs after 250*625 =156250 mt or 156 Km only.

But I don't think this glider was able to land at the same gliding speed (904 km/h is too much for safe landings) thus there were some air-braking operation (opening flaps) to do in order to reduce at least 1:4 such speed (250 km/h as the Concorde) I hope you agree this was a necessary operation. The energy spent while reducing speed means a waste in distance (at least 100 km) so the plane glides safely in about 346 km not 446 km as per only kinetiks at glideratio 14. If glideratio was 40 the route was only 56 Km. (Strange! The same figures of Me163B 8) mumble... mumble... Huck!) And what kind of recce operations were possible in 1945 from 25000 mt? Gary Power's U-2 was hit when flying over SSSR at 17000 meters in 1962...This was the max ceiling for photo-spying till early 1960. And I have not yet seen your only-supposed-to-be-fitted camera, Huck.
Weight is not in the count but the ratio wingspan/weight yes and a ratio is a PURE NUMBER. Always.
Edited by Moderator Andy H

First you say that weight influences the glide range. Now you say altitude does the same thing. Then you come up with an acceptable by all parties :D sink rate of 14m/s, not knowing that sink rate varies a lot with altitude. Needless to say all your guesses are completely wrong.

Max glide range is affected solely by Lift/Drag ratio, aka glide ratio. Also Lift/Drag = Cl/Cd, the ratio between coef of lift and coef of drag. For a particular plane coef of drag varies (in subsonic range) only with angle of attack (as long as the aerodynamic config of the plane remains the same - one example of config being for instance flaps up, gear up). Coeficient of lift also varies with angle of attack.

There is an UNIQUE angle of attack for each plane in a particular flight config where the Cl/Cd is maximized. At this particular angle of attack maximum gliding range is obtained. That is as long as you keep this optimum angle of attack it does not matter the loading of the glider or the altitude at which it is operated, it will still have the same optimum glide ratio and will reach maximum gliding range (or more with soaring).

However, something does change with weight and altitude and that is gliding speed. But the changes are intuitive, at higher altitude the plane will fly faster that at lower altitude when kept at the same angle of attack. Also at higher weight the plane will have to fly faster in order to be kept at the optimum angle of attack. Another consequece of flying at the same angle of attack (preferable the optimum AoA) is that glide path always has the same angle with the horizontal, there are no such thing as curved optimum glide trajectories, like those pictured above by Gabriel, no matter if they are up in the stratosphere or down at 1000 feet.

As for DFS 228, it could have anywhere between 25 and 30+ glide ratio. With a glide ratio of 25 it would have to use a couple of rocket thrust dashes to pick up speed, then glide again. At 30 glide ratio it could glide from 25km for 750km. With the slow down from rocket powered flight to gliding and some soaring (which is just impossible not to be able to do in such a long glide) it could easily reach 900km to complete the flight profile.

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Post by Huck » 24 May 2005 20:24

This open canopy DFS glider from the 30s had an aspect ratio of 10 (just like DFS 228) but much more primitive construction and finish, still it had a glide ratio of 21. I see no problem for DFS 228 to have anywhere between 25 and 30+ glide ratio.


Image


Compare the above with DFS 228:

Image

Image

gabriel pagliarani
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Post by gabriel pagliarani » 24 May 2005 20:50

Huck wrote: First you say that weight influences the glide range. Now you say altitude does the same thing. Then you come up with an acceptable by all parties :D sink rate of 14m/s, not knowing that sink rate varies a lot with altitude. Needless to say all your guesses are completely wrong.
This is what you have understood. But I wrote a different thing related to the ratio WEIGHT/WINGSPAN (Wing charge? How do you call it?. Ratios aren't weights :roll: (2nd time I say you that ratios are pure numbers..evidently this evidence is up to you.)
Huck wrote: ...Max glide range is affected solely by Lift/Drag ratio, aka glide ratio. Also Lift/Drag = Cl/Cd, the ratio between coef of lift and coef of drag. For a particular plane coef of drag varies (in subsonic range) only with angle of attack (as long as the aerodynamic config of the plane remains the same - one example of config being for instance flaps up, gear up). Coeficient of lift also varies with angle of attack..
Your figures please. Physics are numerical proven not "declared".Lift/drag ratio are the opponents of gravity (9.81*mass) and air drag force (-Cx*velocity) and Lift = Cz.
Huck wrote: There is an UNIQUE angle of attack for each plane in a particular flight config where the Cl/Cd is maximized. At this particular angle of attack maximum gliding range is obtained. That is as long as you keep this optimum angle of attack it does not matter the loading of the glider or the altitude at which it is operated, it will still have the same optimum glide ratio and will reach maximum gliding range (or more with soaring)..
If there is an OPTIMUM there is also a NON-OPTIMUM and your UNIQUE figures (never shown) now are 2.Sillogistic thought the yours.
Huck wrote: However, something does change with weight and altitude and that is gliding speed. )..
No. Density of air increases linearly the drag force (F =-b*v) so it could change, in the while gravity is a constant (G= -9.81*m) I remember you the 1st law of motion= "a body moving at fixed speed without any external force (air drag and gravity in this case) continues its motion undisturbed" Year 1546 author Galileo Galilei. Known also as Principle of Inertia.
Huck wrote: But the changes are intuitive, at higher altitude the plane will fly faster that at lower altitude when kept at the same angle of attack. Also at higher weight the plane will have to fly faster in order to be kept at the optimum angle of attack. Another consequece of flying at the same angle of attack (preferable the optimum AoA) is that glide path always has the same angle with the horizontal, there are no such thing as curved optimum glide trajectories, like those pictured above by Gabriel, no matter if they are up in the stratosphere or down at 1000 feet.
As for DFS 228, it could have anywhere between 25 and 30+ glide ratio. With a glide ratio of 25 it would have to use a couple of rocket thrust dashes to pick up speed, then glide again. At 30 glide ratio it could glide from 25km for 750km. With the slow down from rocket powered flight to gliding and some soaring (which is just impossible not to be able to do in such a long glide) it could easily reach 900km to complete the flight profile.
This is the oniric part of your dream, Huck. I don't follow your argue.... Edited by Moderator Andy H

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