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Quantum Leap test flight

#21
Oh, I've just realised you called him Rory, but his name's Roy Venton-Walters.
A guess/memory dredge on the name of someone whose wings don't really interest me...

I have a long list of hang glider/flexwing designer names to remember first...

Anyone from Felix Ruehle to Ian Grayland...

Pitch stability is not an optional extra...
 

BobH

Student Pilot
#22
There are of course many flexwings that have excellent pitch stability. The XL wing for one, which was a beefed up and scaled up copy of an American design that Brian Milton convinced British wing makers to make so that the British Hang Gliding team could compete successfully against an American team back in the 70s.

My XL wing is not easy to destabilise, and makes for quite hard work if you want to pitch up or down quickly.
 
#23
There are of course many flexwings that have excellent pitch stability. The XL wing for one, which was a beefed up and scaled up copy of an American design that Brian Milton convinced British wing makers to make so that the British Hang Gliding team could compete successfully against an American team back in the 70s.
The UP Comet, the world's first viable double surface/CFX glider, copied by Airwave as the Nimrod and Solar Wings as the Typhoon.
 

BobH

Student Pilot
#24
The Typhoon it was, and the wing used by Pegasus was the Typhoon XL for the two seater. I believe there was a Typhoon M wing used on a single seat trike. I remember seeing one once at Plaistows. Jay had the thing out and on the ground and then he attached it to the trike and tried to fly it. I can't remember if he managed to get off the ground. I don't think he did. I think there was a problem with the engine.
 
#25
Roy now lives on a farm not far from oshkosh now and incidentally has the raven (or had a couple years ago) that Eppo Numan used to cross the Atlantic stored In his barn. We had a good conversation about the design of the raven back in the day, he never intended it to have a 912 on the back or have mtow over 400kg and I could see that every time I carried a passenger. As you are single seat with a light trike underneath Bob your in the right window to get the most from it. I have some photos somewhere that he gave me from the initial testing phase and I'll see if I can find them, it had a refractive paint scheme so that competitors couldn't take photos if it.
Another interesting feature of the raven was the use of "granny's bloomers" between the top and bottom surface to allow the wing to billow easier, you can see Larry Mednick from evolution talk about using it in the revo wing as well, I'm sure it's on YouTube somewhere
 
#29
Lovely matching colours Bob!
That's the same colour wing that made my jaw drop when I was first introduced to flexwings, just thought to myself I would have a raven someday!
Yours looks like it's got plenty of washout and plenty safe in pitch
 
#30
Yours looks like it's got plenty of washout and plenty safe in pitch
The washout you see on the ground and loaded in flight will disappear at low angles of attack.

At or below the "zero lift" angle in a pitch test, most pitch stability will come from luff lines and tip sticks or washout rods.

Washout rods are most effective with larger areas of wing outboard, which is why the planform of modern hang gliders has changed.

With topless wings it all comes from the washout rods (sprogs in HG terms) unless there is reflex in the battens and it can be made to work rather than just blowing down with airflow from above.

Huge amounts of time and money has been spent on pitch testing, some of it on vehicles with dedicated test rigs on top.

None of this could have been done if it was possible to tell on a visual test, and as we know from experience, the Raven is borderline for pitch stability.

There have been no documented Raven pitch stability serious accidents, AFAIK, but you don't improve your odds of survival when you head into regions with marginal pitch stability.
 

BobH

Student Pilot
#31
randombloke,

It's a pity I no longer have any contact details for Roy Venton-Walters, otherwise you and he could have an interesting discussion regarding the design of the Raven wing. As for me, I can only go by my own experience of this wing, and my experience has been good. It's all a bit moot for me as well, because after straining my shoulders on FlyUK back in 2016, I've switched to flying 3 axis, so my flexwings are both just gathering dust at the back of the hangar.

With luck and a following wind next year might see us all allowed out to play with our toys once more in an unrestricted fashion, and if that happens I might be tempted to get both the flexwings out and try to sell them on to someone who might find a use for them. Meanwhile I think they're best kept where they are, out of the weather in my hangar.

I would continue with this post, but as it's dry outside I'm off up to the airfield to get my Spectrum out and fly it. Toodle pip!
 

BobH

Student Pilot
#32
Oh, one further thing I forgot to put in my post is that the Raven has washout rods just like any other flexwing, so there is some pitch stability imparted by them, and combined with the turbulators on the upper surface of the wing, they seem to do a good job.
 
#33
randombloke,

It's a pity I no longer have any contact details for Roy Venton-Walters, otherwise you and he could have an interesting discussion regarding the design of the Raven wing. As for me, I can only go by my own experience of this wing, and my experience has been good.
Hi Bob,

There would be no point me discussing Raven design with RVW. All the Ravens out there are not going to change.

That was not my intention. My intention, with some background in airworthiness, is to point out some of the fallacies I see in the microlight community about pitch stability. I have examples of aircraft that fitted your description in real life but went irrecoverably divergent on the test rig near the zero lift angle. That's a theoretical thing until you are flying in rough air...

However, we are all adults, we all make informed decisions, you obviously think I'm talking nonsense, that's your right, I just want to give the other side of the story so that others also make informed decisions. Then, if a problem occurs, the pilot has taken responsibility for his or her own actions.
 

BobH

Student Pilot
#34
randombloke,

I don't think you're talking nonsense at all. I think that there might possibly be a bit of a dichotomy of views between yourself and RVW over wing design. But then again, he wasn't designing for slow speed. I believe he wanted to get the fastest wing he could, given the design constraints at the time. The fact that a Raven 503 will still outdrag a Quantum 582 in straight and level flight (I know this because I was the passenger in the Raven 503 at the time when we left Rob G and his passenger in their Quantum 582, in our slipstream!), and can cruise at Quik type speeds even today, is testament to his design genius at the time.

However, things move on, knowledge is expanded, and people begin to realise that speed at the expense of divergent behaviour is not really an acceptable compromise. Also, the actual rules have changed somewhat since the Raven wing was designed. I believe RVW would have made a much smaller wing if he could have, but at the time the microlight rules were based on wing loading, so big wings were necessary for two seaters, and as far as I know the Raven has always been a two seater.

I'm sure today's wing designs are much better all round than the Raven ever could be, but it would be interesting to ask RVW what he'd do differently if he was designing the equivalent of a Raven wing now.

Best regards,

Bob H

P.S. I know you're mainly an HG man, but have you ever flown a Raven wing yourself?
 

BobH

Student Pilot
#35
Oh, just one other thing, I remember in an earlier post you said about luff lines. The Raven has luff lines, three per side if memory serves correctly, so when the wing does go negative, the luff lines pull up the rear of the wing to create reflex and prevent the wing from continuing on over into a forward roll.

When I had my sail mended after I managed to rip it (Doh!) I was going to have the luff lines detached from being sewn to the rear of the wing and instead I wanted to put something like hoops and small carabiners in, so that I could dismantle the wing more easily. However, I was warned against this by my inspector (he has a Raven!), who told me that when a wing was made at Medway, Chris had to measure each luff line, and sew it to the rear of the wing at a specific length, so mucking about with them was a definite no no.
 
#36
Oh, just one other thing, I remember in an earlier post you said about luff lines. The Raven has luff lines, three per side if memory serves correctly, so when the wing does go negative, the luff lines pull up the rear of the wing to create reflex and prevent the wing from continuing on over into a forward roll.

+

P.S. I know you're mainly an HG man, but have you ever flown a Raven wing yourself?
I didn't say the Raven lacked luff lines. Luff lines are not sufficient, some sweepback is needed. As HG wings started to push nose angle to the limit, some of then needed small tails (late 1990s, early 2000s) ended up with tails to help in extremis. This is why, to some extent, flexwings are limited in nose angle and you don't see them with 180 degree nose angles, mid 130s is about the usual limit.

In order to provide an argument which people would accept or reject, I had to outlines the case, that's all.

I haven't flown a Raven, as one of my mentors died in pitch stability accident so I have stronger views on it than most. There is no point ignoring an accident report that makes harrowing reading, as someone dies over 45 minutes on a hillside with a ruptured aorta.

We all make choices. I have flown through a thermal that made me completely weightless on exit, and my feet touched the keel. The side wires went slack and twanged hard on reloading. That is not where you want to be with something with marginal pitch stability.

Divergence you might be able to ease out of, but a low speed tumble is game over. When I had that "twang" in Spain, as the side wires went tight again, I had a reserve, and I was 2,500ft above terrain, and I could have thrown the reserve if need be.

Not true in most trikes.

I asked you a few posts ago if you felt lucky, and I can answer that question for myself in that I don't feel lucky. So, I do what works in my opinion to reduce the odds against me. It's only my opinion.

YMMV.
 

BobH

Student Pilot
#37
I don't feel lucky either, and I now only fly 3 axis.

I agree that it must have been a very harrowing experience finding out about your mentor. I take it he was flying a Raven when he died?
 
#38
I take it he was flying a Raven when he died?
No, I said:

There have been no documented Raven pitch stability serious accidents, AFAIK, but you don't improve your odds of survival when you head into regions with marginal pitch stability.
It was on an Airwave K2.

They went on the test rig, failed, and came back with two serious mods.

As did the Goldmarque Gyr.

Both had luff lines, but found themselves post mod with tip sticks, as in the case of the Gyr, only close to the zero lift angle did it go completely pitch unstable.

As one or two microlight designers have mentioned, there's a big trike underneath and pendulum helps.

We could also look at the Flash 2 as a study... and Guy Gratton did...
 

BobH

Student Pilot
#39
Oh yes, the Flash 2. Nuff said!

I've been told a lot about the Flash 2 and it's various handling querks, but I was also told that most of these were because the wing parameters could be adjusted by the owner/pilot. The F2A was designed to prevent this, and was a safer wing, if a little slower I believe.
 
#40
Oh yes, the Flash 2. Nuff said!

I've been told a lot about the Flash 2 and it's various handling querks, but I was also told that most of these were because the wing parameters could be adjusted by the owner/pilot. The F2A was designed to prevent this, and was a safer wing, if a little slower I believe.
The difference is that the pitch characteristics of the Flash 2 are very well documented, as is the set up for the correct amount of pitch stability.

From memory, it went on the testing rig, both for the manufacturer and for Guy Gratton's PhD thesis, where it was tested in more than one configuration.

There are also SBs with exact documentation of standard settings and also how to restore luff heights (as opposed to luff line lengths, as sail stretch adversely affects the height above the datum) to the correct dimensions.

I was in a Flash 2 syndicate for a while, and had a few flights in it. Fast, light in pitch, but somewhat heavy in roll.

Exactly the same planform as the Solar Wings Ace, which I also owned at the beginning of my time hang gliding. Same 100% double surface at the tips... but with washout rods.

I think that's one of the main differences between the F2 and F2A, tip sticks. There are other differences too...
 

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