FLIEGERPFEIL ( Aviatordart ) WW 1

[Bellifortis]

This is a present of one of my elder clubmates who found it when sorting through his old toolbox. He did not know when and how it came to his family, only that it got there a long,long time ago. I start this new thread in this category, also I see the earlier discussions elsewhere under the heading Flechettes. In my opinion there is a big difference between a flechette and a Fliegerpfeil (literally translates as Aviatordart ). A Flechette is always explosively accelerated (fired, dispersed ), while the "Fliegerpfeil" is always just dropped, also their shapes and sizes can be nearly the same. Here now the technical data:
L. = 120,25 mm ; D. = 8mm ; W. = 20gr
I had a discussion with my mates about the velocity this dart will reach when dropped from an earoplane. I know that there is a maximum velocity a free falling body may reach. At a specific maximum velocity the braking power of the airdensity will cancel any further acceleration. There is a formula to calculate this, but mathematics and physiks have been my worst subjects in school. I wonder if there is anybody here on the forum who is able to give a scientifically founded answer ? What is the maximum velocity this dart may reach ?
Greetings,
Bellifortis.IMG_3236.jpg

[SdKfz251]

Yes - ANY free falling object regardless of size or weight or density will reach Terminal Velocity which is approx. 127mph. The time it take to reach this speed depends on the same three factors, so every free falling object takes a slightly different time. Hope this helps.

Regards

Marcus
PS - Know this as have done free falling parachute jumps many times in USA & around the world from 13,500 feet.

[Snufkin]

Bellifortis,

The basic equation for terminal velocity of an object is given by:

V = SqRt [ 2*m*g / r*A*C ]

where m is the mass of the object in kg; g is acceleration due to gravity = 9.81 m/s/s; r is the air density in kg per cubic m; A is the projected area of the object in square m; C is the coefficient of drag (no dimensions).

SqRt denotes the square root, * denotes multiplication and / denotes division.

For a long cylindrical rod, from tables, C = 0.8 approximately;
A = pi * .004 * .004 = 5E-5 square metre;
r = 1.3 kg per cubic m (for cold air);
m = .02 kg.

These figures give V = 87 m/s = 312 km per hour (195 mile per hour).

This is a ball park figure as air density can vary from 1.2 -1.4, and the drag coefficient will likely be affected by the presence of the in-line fins, so C between 0.75 and 0.85 - for simplicity the dart has been approximated as a pure cylindrical rod. Net result, it gives an idea that the dart will hurt if it hits you.

It is interesting that tests on the early British 12,000lb Tallboy bomb designed by Sir Barnes Wallis apparently revealed it to reach supersonic terminal velocity and so to wobble off target. But that's for another thread...


Barry ,

If you do the sums for a person free falling with arms and legs out, the terminal velocity is indeed around 127mph. Taking m = 100kg; A = .5 sq metre; r = 1.3; C = 1 for high resistance body, gives V = 55 m/s or 198 km per hour (124 mile per hour).

However, as you will have found when sky diving from 13,500 feet, sticking your head down, tucking your arms by your side and minimising drag, your terminal velocity will probably have touched 200 mph. Again, for m = 100kg, effective area now reduced so that A =.25; drag reduced so C = .8, we have V = 87 m/s = 312 km per hour (195 mile per hour). By coincidence, the same as the aerial dart.




T.

[Bellifortis]

Thank you very much T., thats exactly the kind of explanation i was hoping for.
Greetings,
Bellifortis.

[Snufkin]

Thank you very much T., thats exactly the kind of explanation i was hoping for.
Greetings,
Bellifortis.

Bellifortis,

What is the book or document that you have used as a background for your photo of the dart in your first post? I'd be interested if it shows examples of other air dropped items - such as grenades.




Tom

[Bellifortis]

Hi Tom,
it is the "Scientific Amercan War BooK", New York-1916 , Munn & Company,Icorporated ,which I mentioned in another post already. Another member here on the net found it online, nicely done , where you can turn the pages over like in a real book. I think it was google books.
Regards,
Bellifortis.

[SG500]

Nice Fliegerpfeil, are there any markings on it?
Dave.

[Bellifortis]

Hi Dave,
no there absolutely no markings. It is a very nice example of fine mashine work, that really surprises me for such a simple item. As you can see it is exactly the same as the one pictured in the 1916 US publication.
Greetings,
Bellifortis.

[Snufkin]

Attached is an excerpt from the "Scientific American War Book", concerning the anecdotes of an American volunteer pilot serving with the French air arm in 1914-5. Of interest as it describes the deployment of the darts, and markings put on some German copies - "Invented in France, but made in Germany".

There's been some debate about the veracity of such markings in a thread in Tip-offs (which has now disappeared), but the wording appeared to be in French (something like "design français - fabrication allemande") to add insult to injury, perhaps? Like many interesting things, fakes probably outnumber genuine surviving examples, but it would be good if any member has a known original dart with markings to show.




Tom.

[kz11gr]

I had a discussion with my mates about the velocity this dart will reach when dropped from an earoplane. I know that there is a maximum velocity a free falling body may reach. At a specific maximum velocity the braking power of the airdensity will cancel any further acceleration. There is a formula to calculate this, but mathematics and physiks have been my worst subjects in school. I wonder if there is anybody here on the forum who is able to give a scientifically founded answer ? What is the maximum velocity this dart may reach ?
Greetings,
Bellifortis.IMG_3236.jpg

Hallo Bellifortis

Hier ein Bild von einem frz. forum , wo man die Wirkung sehen kann .

Mfg von Paris

Hi, here a picture from a french ww1 forum, you can juge the strength of this weapon.