EDIT: Please see post on page two for attachments of a more modern interpretation/analysis.

Prop hanging as a subject is currently being buried in the Pfalz thread. I think it is a subject worthy of its own thread and debate.

REAL video from the Valdez STOL competition. Wait till 56 sec mark and you will be amazed, if not amazed at the take offs leading up to it..
Apparently this is called a 'Harrier' rather than prop hang, but still relevant. Of course these aircraft have a much better thrust to weight ratio than out virtual crates and buses.

I do not believe for a second that the DVII could 'prop hang', but had a thicker airfoil (allowing higher angle of attack), with very low stall speed, and benign stall characterisitcs that made it APPEAR to prop hang. And yes, it would be a very stupid maneuver in any dogfight unless one-to-one, or otherwise vastly outnumbered your foes.

Say what you want. They were there, and we were not.



SE5a pilot John M. Grider, 85 Sqdn.

Good reading there..

OK, let's look at the important bits again:



The fact that the SE5a pilot, John M. Grider, was still turning to evade the tracer, which apparently kept following him in the turn, means the DVII was still maintaining airspeed in order to maneuver the SE5a into his sights, right? How else could the DVII pilot keep a stream of fire accurate on a moving target? I think there is some discussion of the "prop hanging" myth in the book "Three Wings for the Red Baron", I will transcribe relevant portions later once at home.

As far as being "witnesses to history", this is true, but witness accounts are notoriously unreliable and inaccurate. Take for example the case of the Flamming Onion 37mm anti-aircraft artillery (aka Lichtpucker LINK HERE ). Numerous RFC/RAF accounts testify to the flaming onion tracer rounds being chained or wired together. This is of course absurd on retrospect. Should we believe all historic accounts verbatim? Or should we interpret them with the knowledge we now have?

It would be well worth it to first define what you mean by "prop hanging." Otherwise, people will be talking about different things. The examples in the video of prop hanging all showed aircraft that still maintained some amount of airspeed.

What I think people think of when 'prop hanging' is mentioned.

As I said in my first post, some German aircraft with thick airfoils could attain high angles of incidence, low stall speeds, and had benign stall traits, all combined to give the impression they could literally "hang on their props". They were just moving slowly at the very edge of stall. If this is your definition of "prop hang", then I agree it is possible. If "prop hang" means stationary, I disagree.

Saying "the pilots who were there were wrong about prop-hanging, because this is how I define prop-hanging..." is an insipid argument.

Thanks for posting the STOL video, great to see !

Not completely OT, please also read further down about Fieseler: Another STOL plane from 1936:
The Fieseler "Storch" (Stork):

http://www.youtube.com/watch?v=VDcB0pSUYOI
(the narrator is wrong, the action to help Mussolini in Italy Gran Sasso was successful, it was not a "british mountain hideout")

Certainly not suited for bush pilots, since the freight load was very limited, but interesting to see how it is able to land without those big rubber wheels due to the ingenious gear arrangement. What you can also see is that this plane almost flies sideways, and can direct its nose anywhere at very low speeds.

And this brings me to a book written by Fieseler.

Back to the initial topic:
I tjink the D.VIIF was well able to fly at the edge of stalling, at very low speeds, and thus being able to fly sideways in a way and follow the SE5 in its curve like in the text by Grider, and at very high altitudes (for the time - DVII pilots also carried oxygen equipment with them)
I do not think it was able to hang on the prop like in the RC video, but it
a) was able to fly at a high angle of incidence, and slowly, without stalling
b) it was able to point its nose upwards indeed, and stay in this position longer than other planes without stalling. Even if it would fall back it wouls still be manoeuverable and not go into a spin.

Fieseler wrote a book "Meine Bahn am Himmel" where he describes his manoeuvers when he flew a Fokker DVII (he does not write about a "D.VII F" though) at the Saloniki front.
I had never thought that Fielesler also had been an "ace" in WW1 until i read that book b.t.w.

When he was asked to produce a plane able to land in very tight spots, with a short take-off distance he writes how his WW1 experience helped him to dsign such a plane (the "Stork"). WW1 planes had no slotted wings, but he writes that his DVII had been "able to hang on its prop" and how he transferred those properties into the Stork (!)

Thanks and greetings,
Catfish

Actually somebody asked (and rightly so) for a definition after the fact, so I provided a working definition for the sake of clarification, in fact I sort of provided two (in case my original assumption that people thought of stationary or nearly stationary as being prop hanging was wrong--I can admit I'm wrong). My discussion of the merits of historical accounts is an entirely separate issue. Care to start another thread?

I'm interested why don't you define "prop hanging" then? What do you think they meant by it in WWI? Is the airplane stationary or nearly so? Or is it balancing just above stall, but moving and being able to maneuver none-the-less?

EDIT: on retrospect the discussion of prop hanging in the Pfalz thread may have lead me to incorrectly make assumptions. In that thread some maintained that prop hanging was nothing but a prolonged stationary moment of an aircraft at the apogee of a climb, followed by a stall. So a third definition. Which one should we debate?

PS: good stuff catfish, very interesting to compare that video with the STOL competition.

I would define prop "hanging" as just that - HANGING, as in zero forward momentum, with maybe some slippage.
I pilot with workable control surfaces, enough to follow a bandit above him anyway, is clearly not prop
hanging by that definition. I don't think "going very slowly, and moments away from a stall" is prop hanging
IMHO.

Amazing comments from such an expert.

Let's see-typical weight of a DVII is 1940 pounds. Max horsepower around 185 BHP on a good day.

That gives us a power to weight ratio of .09536082 which is SO far below one to one that it's not even funny. Apparently some folks think that you can "hang on the prop" at values less than 1 to 1.

Anyone who's actually flown a real aircraft knows that the ability of an airfoil to fly at high angles of attack and low airspeed DOESN'T mean the aircraft can "hang on the prop", it just means that the aircraft can still maintain a positive pitch attitude longer than other aircraft BEFORE IT STALLS.

The comments quoted are from people being shot at, who are trying to survive, and let's face it----didn't really know alot about aerodynamics as it was a new science. If you can't believe that, trust me to this day there are folks who are "professional" pilots who don't really get it.

Any aircraft can be pulled up into a zoom that will zero out the airspeed, then it will fall away UNLESS it has a power to weight ratio greater than 1 to 1 which the DVII or any other WWI aircraft CLEARLY doesn't have.

I've pulled three different models of helicopters to a near vertical attitude and held that attitude until the airspeed was zero,(a manuever referred to as "return to target") put in full right pedal, and changed my direction 180 degrees. No prop on the nose, just some old fashioned inertia. Funny how physics works.

Pretty basic really.

Discussion over.

Equally as amazing, is that a "copter driver" would compare the BHP of an engine to the WEIGHT of the plane....

...instead of the thrust of the propeller to the weight.


But I do get what you are trying to convey. We wont go into efficiency either, because your point still stands, you just got there a little funky.

Yes, that is funny Brian. Fwiw Copter, horsepower is a unit of power; weight is a unit of force. When they compare thrust:weight ratios for modern fighters, they make a big deal out of 1:1 because they are comparing one force to another.

Power = force * distance / time. If you can derive the thrust of a Fokker D.VIIF from the available prop and engine data, then you probably have a PhD in aeronautical engineering.

Also, 185hp is the German rating (who seem to have rated engines conservatively). The British rated the BMW IIIa at 230+hp.

Just a small data point. I sometimes fly a Steen Skybolt. It has an empty weight of 650 kg, which is less than that of the D.VIIF. It has a 260HP aerobatic engine with good lubrication and fuel flow in all attitudes, which is more than you can say about the D.VIIF. It has a modern constant speed propeller with very good thrust at low speeds. It is no way near being able to hoover.

Here is a relevant work up on the tactics and some aerodynamics behind "prop hanging" by Leon Bennett, author of "Three Wings for the Red Baron". Likely not enough aerodynamics details for some, leaving out the calculus for us regular types who only pretend at knowing more

To understand why prop hanging was desired, you have to understand the theory of what Bennett calls, "Anti-Gravity Drop Gunnery". If you find the sweet gunnery angle you can literally fire up at an angle to a higher altitude opponent with no deflection, no gravity drop to the bullet, and no backwards deflection, i.e. put the sights on target and the bullets will land THERE.

Both the British and Germans figured this out, but the Germans managed to make airplanes that could fly at that angle and achieve a technique called Stehenbleiben in der luft, or "hanging on the propeller" (Bennett references Luftfahrt, January 1919, page 21. I would love to see that reference, if anyone can find it and translate). The Dr1 could do it, and of course the DVII. Enough, read below...

This may be part (only part) of the reason that the AI is so good at those snap shots from below. They aren't "hanging", but they are likely achieving that sweet spot at the apogee of their climb, landing bullets with no deflection, before they stall away.

Get any of Bennett's books if you can, they are all superb reading and well researched including archived WWI era studies.

Now there seems to be a witness that the D.VII really does it :

http://www.southsearepublic.org/article/2473/read/fokker_dvii_


Here's apicture i found on a russian website:


(from http://flyingmachines.ru/Site2/Crafts/Craft25495.htm)

edit: Her's the original article from 1918, in the "Flight" magazine:
http://www.flightglobal.com/pdfarchive/view/1918/1918%20-%201310.html

" ...The evolution we have
on mind, and which was, we understand, originated by pilots
if Fokker biplanes at the Front, has become known as
"hanging on the prop". The title is very descriptive.
conveying as it does the idea that the machine is held up b
the propeller only. This would be exactly the impression
of another aviator watching from an aeroplane travelling at
ordinary speeds, although in point of fact it appears very
doubtful whether the machine is stationary. It is far more
likely that it is moving along, but at so comparatively slow
a rate that to an observer watching from another machine
moving along at a speed well above 100 m.p.h. it does indeed
appear to be "left standing." ..."


Ok, speed maybe still 20 or so mph, so no real standstill, but as good as -

and:

" ... assumes a position so near the vertical, but when preparing
the drawing it was found that if the angle was less,
the drawing did not convey the impression desired but
rather one of a modern high power machine climbing at a
steep angle.
From what we can gather from pilots who have seen the
Fokker go through this evolution it appears that this machine
is able, not only to assume this attitude, but to maintain it
for long periods, the latter being the feature of the stunt
which impresses pilots most. It is, we think, generally agreed
that the majority of machines, if placed in such an attitude,
would be very prone to come out of it in a side slip or a tail
slide. This does not appear to be the case with the Fokker
which, as already pointed out, seems to be able to maintain
this extraordinary position practically indefinitely.
As to the advantages of this stunt, these would appear to
be a steady platform from which to fire, and the ability of '
firing up at a machine passing overhead, i.e., in a position
where it is precluded from returning the fire. ..."



By Fred Berg, Fokker D.VII net:

" ... Page 5

That is why the allies in WW I complained about the new German plane that can hang on the prop and shoot at you from below you, Reinhold Platt was the designer of the plane. Mr. Platt liked the big hollow box spars because the spars produced wings that were full cantilever. They did not need any bracing wires between the wings. N shaped struts were placed between the wings so that if in combat one wing was damaged the other wing would support it. Now thick wings give tremendous lift especially at low speeds. This is why the plane has such remarkable flying characteristics. I am not sure that all this was understood at that point in time. When l lost the propeller in flight I was at less then 1,000 feet altitude. I flew over to and followed William Floyd Parkway in a northerly direction crossing Jericho Turnpike. There was no traffic. Suddenly the four lane parkway divides into two lanes north and south with trees in the divider. Two lanes produce a runway too narrow to land on. I am now perhaps at one hundred and fifty feet altitude. I made a sharp turn going south over the parkway. I land just short of Jericho turnpike. All this time I was gliding at 50 mph.After losing the prop I felt that I must have traveled five miles. How many airplanes can travel that slow and make sharp turns safely? When the U.S. government gave Suffolk County their military airport in the Hamptons I was invited to the celebration. Since I do not have radio equipment in the plane I contacted the tower and was told that they would give me a green light when they wanted me to land. Given the signal I came into the landing pattern, lined up with the runway an landed at a nice safe 50 mph. Everybody behind me cursed me out because they had to go around the pattern a second time because they could not fly as slow as I could.

There is a drawback with the low stall speeds. If you taxi to fast with the tail down there is a tendency to jump into the air stalled and then you can't control the plane. This occurs when the air flowing over the control surfaces does not have enough pressure to make them work. It is as if you were in a balloon. It happened to me once. I drifted all over the place and just kept the nose up, hanging on the prop until I picked up speed and then could lower the nose. Once you have air speed you are safe. It is a frightening experience. I know of two cases where this happened and the plane was lost. To take off safely get the tail up as fast as possible to kill the lift and when you hit 50 mph the plane starts to float up into the air and is very responsive to the controls. Again when landing at slow speed, the ailerons in the upper wing are not effective at all. If a gust of wind rolls the plane you must rely on the rudder to straighten it out. Simultaneously give the engine more throttle and kick the rudder on the side corresponding to the high wing. The increased engine power will send a blast of air over the rudder so that the rudder will respond and the plane will yaw such that the high wing will move rearwards losing lift and the low wing will move forwards gaining lift. The lift is dependent upon the relative air speed over the wings. When the lift is equal on both sides of the wing the wing will level off. Then kill the power and proceed to land or go around once again. The last flight was at Oshkosh Wisconsin in 1975. Teaching responsibilities and family problems forced me to abandon the Fokker for what I thought would be short time. In 1976 my father died. I built a house across the street from the farm so that my mother could come to live with me. I placed the Fokker in the basement and it has been there ever since.

Everything said in this report is true. I hope you enjoyed reading it and perhaps learned a thing or two.
Fred Berg..."


I remember a discussion at "The Aerodrome", where a 1922 test was mentioned, testing the D.VII for its prop hanging. If i remember right the result was a flight at 4000+ meters of altitude, at an angle of 60 degrees. No helicopter effct but an almost (!) upright very slow flight, without losing altitude.



After having read Fieselers reports re the "Stork", the descriptions in the "Zuerl" and those others, it is now my belief that the Foker D.VII was indee able to "stand" in the air / hang on the prop / whatever you call it, almost upright. Imho, but having done quite some research.

Greetings,
Catfish/Wels

OK, I get it now after reading the last few posts.
I can see how my definition of "prop hanging" was a bit too stringent.

Catfish,

You are painting an incorrect picture ( pun intended ) by the choice of words you leave out of that quote.

But since English is not your first langauge, I'll cut you some slack.

In conjunction to that image, as it relates to that image, the full text from the same article reads:

"In the accompanying sketch we have endevored to convvey
an expression of the attitude which the Fokker biplane assumes
when performing this new "stunt". As a matter of fact,
it may be doubtful whether the machine actually...

... assumes a position so near the vertical, but when preparing
the drawing it was found that if the angle was less,
the drawing did not convey the impression desired but
rather one of a modern high power machine climbing at a
steep angle."

...so it only shows the steep angle to convey their expression. Had they posted tha ACTUAL angle, it would have merely looked like a modern ( as in November, 1918 modern!!) plane climbing at a steep angle.

[EDIT:] In other words, they exaggerated the sketch to illustrate the point

Yeah, and I'm sure that the propeller airfoils created by the engineers in the war years were soooo efficient-I mean heck, I'm sure that they just crunched the NACA numbers in their trusty IBM-oh wait, not there yet.

The last aerobatic airplane I flew was a Pitts S2A, yeah I know, kinda old. Very small airplane, big engine, couldn't come close to "hanging on the prop".

If the nose of the airplane is still "up" it means that it hasn't stalled yet or it's at the top of an energy zoom.

Yes, I think we all agree that they were able to "hang on the prop", but...

There I disagree. If the angle of incidence was "almost upright", the wings would generate minuscule lift especially at just above stall speed, and the power to weight ratio is just not there. Even the 60 degrees you mentioned/remembered from another article is likely impossible to be maintained in a prop hang. IMHO, the angle of incidence portrayed in Bennett's figure (above) is more realistic.

So perhaps we are now just debating the details. Also, I haven't tried to do this in the DVII yet, anyone else successful?

I just had to check that my recollection is correct, and indeed, the D.VIIF is very controllable deep deep into the stall. With full power, I can control a descent with approx 30 degrees nose up attitude, and an airspeed so low that the anemometer doesn't register anything. It's difficult to judge the angle of descent, so I can't say if AoA is 35 degrees or 45 degrees, but it's probably in that range. It's steep enough to wreck the plane if you follow through all the way to the ground. You have to be very careful with the aileron in that region of flight, but careful adjustments with the rudder makes it remarkably controllable.

Hi,
yes the sketch is exagerrated in showing the plane hanging at some 80 degrees, while it must have been around 60 degrees in reality. Also please note that "Flight" is "a bit biased" as well, the tone is often underestimating, and belittling - so the drawing might be actually right but they would never admit it. They also find it "hard to believe" elsewhere, that Mathy indeed intentionally tried to bomb harbour installations, and not babies in a hospital.

The text from Fred Berg also says that the plane was trying to get "airborne stalled" from the ground, and that it was frightening to hover all over the place without being able to really control it. Seems it is indeed a powerful plane ..

From every report, the Rhinebeck demonstration and the test peformed in 1922 the Fokker was obviously able to hang at 60 degrees for a long time, without falling. Those texts with those i read in Zuerl have indeed convinced me. If reports of Entente pilots, reports from german pilots like Fieseler and others, a demonstration at Rhinebeck aerodrome, the test from 1922 and the report from Fred Berg do not convince you, i guess nothing will.


Edit @ Swingman: Do yo fly a real D.VII/Replica ??!
They recently built a 1:1 replica with an original D.IIIa"ue" Mercedes engine in the Netherlands, a friend at the "Aerodrome" told me about it

Greetings,
Catfish

@Catfish: No, I don't fly a real D.VII or a replica of one. I just checked in RoF. I wish I could fly one, but the few who own and operate these rare birds are a bit possessive about them ;-)

A WW1 engine is very different from a modern engine of similar power - the thrust available is much higher due to the huge diameter, and the relatively low inflow velocity for the same power.

Bear in mind that power:weight is not directly relevant - the important value is thrust:weight, which must indeed be 1:1 to indefinitely hover.

As a note, the Power:Weight of the 170hp DVII is .149 kW/kg, 185hp DVIIF is .163 kW/kg, modern helicopters range from .19 to 0.39 kW/kg, with most towards the lower end. While the disc loading of the Mercedes is higher than most helicopters, it is close to that of the V22.

I don't consider that the engine and airframe will support indefinite flight at these high attitudes and very low velocities, but the duration may be significant before the loss of speed &/or altitude forces a recovery, with reasonable control by rudder and elevator due to prop-wash, even though the ailerons are ineffective due to low speed.