Navigator Mains

[HausKatze 0]

Hello:

A question on PD's Navigator series:

I'm not jumping every weekend, and I am a few pounds heavier than I was 15 years ago... Looking at a huge Navigator canopy to be safe. I don't swoop, and I like a docile ride with a nice slow soft landing.

Their website says that Navigator canopies are ZP fabric plus "low porosity fabric."

When I was jumping a lot in the late 1990s, non-ZP canopies ("F-111"?) had a reputation of being very short-lived and wearing the f**k out much sooner than ZP ones.

I thought the industry had left non-ZP fabrics behind...?

So, are Navigators short-lived? I'm looking to buy a large main, one that's best for an occasional jumper who needs a forgiving canopy.

Should I be concerned about buying a main with a short service life? Is there another manufacturer of a 260sqft+ canopy that's entirely ZP?

Thx

It would appear that I am a tourist in my own youth.

[sundevil777 93]

The canopies that are a mix of fabric are ZP on the top skin only, with the small exception of some base canopies that might have ZP just near the leading edge of the top skin.

Like you, I like non-stressful, easy to execute, soft landings. I think a Navigator is actually not the best for what you want. There are many other canopies not specifically marketed for students that I think will likely provide better performance but are not intended as swooping machines.

I think that using non-zero porosity fabric on the lower skin does not result in lower performance over time.

When a wing is flying at high angles of attack (such as during a flared landing), it is very important that the airflow over the top of the wing stay "attached"/not separate from the surface of the wing. If air is leaking out through the top skin fabric too much, then I think it has the effect of separating the airflow. Conditions on the bottom skin of the wing are very different, with separation not being an issue, so leakage through non-ZP fabric on the bottom doesn't matter.

If it was possible to actually suck air into the wing through/from the top skin, then you get the ability to produce good lift at even higher angles of attack, as the airflow stays attached when it otherwise would not. This has been done on some experimental airplanes, including a Boeing 757 testbed that had part of the wing drilled with very tiny holes and a vacuum applied to suck air into the wing. So, air leaking out through the fabric matters a lot for the top skin, but not for the bottom, as long as it is not so much that cell pressurization suffers.

That's my theory on why non zp is being applied on bottom skins, and I think it makes sense. In my previous life I was a mechanical design engineer, even did such for the Boeing company.

edit- I believe some mfgs make canopies in larger sizes than advertised if you make the request.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[HausKatze 0]

sundevil777

Like you, I like non-stressful, easy to execute, soft landings. I think a Navigator is actually not the best for what you want. There are many other canopies not specifically marketed for students that I think will likely provide better performance but are not intended as swooping machines.

Thank you for the insights. Any suggestions as to a better option?

It would appear that I am a tourist in my own youth.

[gowlerk 1,903]

Navigators are not short lived. They are very well built and designed for long life as student canopies. The reason ZP lasts longer is that it does not become porous over its lifetime. Non-coated fabrics do. Making the ribs and bottom skin from non coated fabric is a compromise. It allows for lower bulk while at the same time the zp fabric on the more important topskin allows for better performance.

Sabre 2 is available as large as 260. So are Silhouettes, which are also hybrid construction. Navigators have Dacron lines and extra reinforcement for their role a student canopies. That makes them bulkier than other hybrids.

[JerryBaumchen 1,046]

Hi Haus,

Quote

Any suggestions as to a better option?

I have a very good friend; 72 yrs old - 7,000 jumps who needed to up-size. He had been jumping a Aerodyne Pilot 9-cell in all ZP.

He asked me what canopy he should get. I told him to try a Pilot7 in a hybrid. He had Aerodyne send him out a demo canopy &, after putting a number of jumps on it, he refused to send it back to them. So they sold it to him.

The Pilot7 is currently available up to 247 sq ft but you might contact them about a larger size.

Asking is always free, it is the answers that cost money.

Jerry Baumchen

[fencebuster 7]

I ran a DZ with Navigators for my students. They were docile for the students on .8 wing loading. I am a big guy and I jump a Sabre2 260 at 1.1. I have also jumped PD Silhouettes 210 and 230 and they were a nice ride as well. I changed my Sabre2 lines to Dacron to be easy on openings. As long as you fly around 1.0 WL any of the above as well as a Pilot will all allow you some fun and not be too much to handle.

Charlie Gittins, 540-327-2208
AFF-I, Sigma TI, IAD-I
MEI, CFI-I, Senior Rigger
Former DZO, Blue Ridge Skydiving Adventures

[sundevil777 93]

If you’re wanting lower than usual pack volume, the silhouette, pilot 7 or 9 cell in lpv or zpx versions, or firebolt. Many report 7 cell canopies are smaller packing than a 9 cell counterpart, so a spectre or other all zp could be a candidate. There are so many other choices from all the mfgs. Any canopy that is offered in sizes up to 210 might be available larger if special ordered. Don’t bother with those only offered up to a 170 or whatever.

The firebolt includes standard sizes up to 272.

Even though the pack volume is more, I’m glad I switched to Dacron lines on my pilot 210zpx.

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[HausKatze 0]

sundevil777

...Even though the pack volume is more, I’m glad I switched to Dacron lines on my pilot 210zpx.

Can you elaborate on that? Why?

P.S. I'm in Tucson. "Go Wildcats!" But I am not that bad, I married an ASU grad...

It would appear that I am a tourist in my own youth.

[sundevil777 93]

HausKatze

***...Even though the pack volume is more, I’m glad I switched to Dacron lines on my pilot 210zpx.

Can you elaborate on that? Why?

P.S. I'm in Tucson. "Go Wildcats!" But I am not that bad, I married an ASU grad...

Dacron absorbs some energy on hard openings. I haven’t had any hard openings since going to Dacron, perhaps because they have more friction against the slider. I also like that Dacron doesn’t get snagged on Velcro or sticks/brush or anything else like spectra does. Search on bill booth and Dacron to read more.

U of A beat ASU in their otherwise undefeated 1986 season when I graduated, but not this year!

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[mbohu 77]

Hallo HausKatze.

I really did not like how the Navigators were landing when I used to rent them and everything improved tremendously, once I started using different canopies: Sabre2, Storm, Spectre, all were much better as far as landings were concerned. (Storm was a bit tricky, as it seemed like all the flare power came in the last 2 inches of the flare.) It felt like the Navigator would react with tiny a time-delay to any flare-input and that made it extremely difficult to time the flares correctly. I got hurt on landings 3 times when I flew Navigators and never again after that. (Yes, it's true I had less jumps when I used them, but I felt a change immediately when I switched to other canopies, and whenever I had to rent a navigator again, because nothing else was available, I had the same landing trouble again.)

As far as soft and on-heading openings go, I LOVE my Spectre. My pack jobs look like sh... and it always opens nicely and on heading (literally: always), so if PD can make a 260 sqft Spectre I'd go for that (I have a 230 at 1.1 wingloading)

So: If you go with a Navigator, I'd first try one out and compare it to something else at a comparable size if at all possible--I don't think they are that great on landings and I had some semi-hard openings on them as well.

[skydiverek 54]

HausKatze

***...Even though the pack volume is more, I’m glad I switched to Dacron lines on my pilot 210zpx.

Can you elaborate on that? Why?


Check this on DACRON lines:

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=4706328;search_string=dacron%20booth;#4706328


.

[HausKatze 0]

skydiverek

******...Even though the pack volume is more, I’m glad I switched to Dacron lines on my pilot 210zpx.

Can you elaborate on that? Why?


Check this on DACRON lines:

http://www.dropzone.com/cgi-bin/forum/gforum.cgi?post=4706328;search_string=dacron%20booth;#4706328


.

A very good read. Thank you.

It would appear that I am a tourist in my own youth.

[HausKatze 0]

mbohu

Hallo HausKatze.

I really did not like how the Navigators were landing when I used to rent them and everything improved tremendously, once I started using different canopies: Sabre2, Storm, Spectre, all were much better as far as landings were concerned. (Storm was a bit tricky, as it seemed like all the flare power came in the last 2 inches of the flare.) It felt like the Navigator would react with tiny a time-delay to any flare-input and that made it extremely difficult to time the flares correctly. I got hurt on landings 3 times when I flew Navigators and never again after that. (Yes, it's true I had less jumps when I used them, but I felt a change immediately when I switched to other canopies, and whenever I had to rent a navigator again, because nothing else was available, I had the same landing trouble again.)

As far as soft and on-heading openings go, I LOVE my Spectre. My pack jobs look like sh... and it always opens nicely and on heading (literally: always), so if PD can make a 260 sqft Spectre I'd go for that (I have a 230 at 1.1 wingloading)

So: If you go with a Navigator, I'd first try one out and compare it to something else at a comparable size if at all possible--I don't think they are that great on landings and I had some semi-hard openings on them as well.

I think I'll be demo'ing a Saber2 260 with Dacron. I want something all ZP. I remember my old all F-111 canopy having the slowing power of a wet kleenex when I finally got rid of it in 2000.

Thank You

It would appear that I am a tourist in my own youth.

[evh 22]

HausKatze

I think I'll be demo'ing a Saber2 260 with Dacron.

It's always a good idea to form your own opinion on a canopy.

HausKatze

I want something all ZP. I remember my old all F-111 canopy having the slowing power of a wet kleenex when I finally got rid of it in 2000.

The Navigator is nothing like that. My dropzone switched from old F111 canopies to Navigators earlier this year. The difference is huge, and when I see students flare too early, too late or not at all, they keep surprising me with how soft the landings are. Also saw a few scary low turns that would have ended bad on the old canopies, but on the Navigators they were perfectly fine. So if you are looking for a big, slow, safe canopy, I wouldn't dismiss the Navigator without testing it.

[riggerrob 558]

Most school canopies are made of two different types of fabric: ZP top skins and the rest F-111 (or a similar low-porosity) fabric. Since most of the lift (60%) is developed by the top skin, only the best fabric is sewn into top skins.
ZP flies great even after a thousand jumps.

Low porosity fabric makes it easier to squeeze air out, allowing quicker packing. Lopo fabric on bottom skins makes little difference to performance because bottom skins are pressureizd from both sides.

[sundevil777 93]

Quote

Since most of the lift (60%) is developed by the top skin

From where does this theory come?

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[riggerrob 558]

sundevil777

Quote

Since most of the lift (60%) is developed by the top skin

From where does this theory come?

————————————————————————————

Aeronautical engineering textbooks and pilot ground school text books.

[pchapman 261]

riggerrob

Since most of the lift (60%) is developed by the top skin,

I'll expand on what Rob mentioned:

Nobody should get hung up on a particular number. Various ones get bandied about. For a typical low speed cambered airfoil in skydiving, at moderately high angle of attack as in typical flight, it might be 80%, but that's just a guess. Based on having done undergrad aero engineering, but not having actually calculated anything for a particular situation & airfoil.

(Who knows, maybe 60% is better for an airplane at cruise, which is typically at a fairly low angle of attack, as airplanes tend to cruise much faster than their stall speed, so the wings doesn't have to work as hard to provide enough lift to keep the plane up. Less 'bite' into the air needed.)

It may be best just to say "most of the lift comes from the front, upper part of the airfoil", than quoting one number.

Since attachments can no longer be uploaded, I'll have to resort to links:

https://www.mh-aerotools.de/airfoils/images/velo6.gif

A reasonable example would be the airfoil in that link, which is at a moderate angle of attack. The graph shows velocity ratios from front to back on the airfoil, top and bottom, but that basically translates into pressure ratios. That is whether the pressures are higher or lower than the ambient pressure.

The difference between the upper and lower lines is the lift. The bottom surface has low speed, higher pressure air, so it does get a 'push' upwards. The top surface has higher speed, low pressure air, especially towards the front. Most of the area between the lines is above the value of v/V=1, so that's the contribution from the upper surface. If the angle of attack goes even higher, then that front upper surface line is even peakier, spiking upwards more. The front of the airfoil is working especially hard, up closer to the stall.

All that lift at the front top of the airfoil is why we use airfoils and not just flat surfaces. You can fly a barn door, but there's not nearly as much lift, and there's a ton of drag. Airfoils are the magical way to get a lot of lift for not much drag. (Things are a big different at small scale and low speed, so don't dump on insects for having simple flat wings. Viscosity & Reynolds numbers and all that.)

As an example of comparing angles of attack, see:
https://i.stack.imgur.com/f7wHm.png

It's a bit messy, but shows pressures on top and bottom for three different angles of attack.

At low angle of attack the wing isn't 'working hard' so the upper surface isn't providing much lift anyway. As the angle of attack increases, there's some more upward push on the bottom, but a lot of lift is added at the front of the upper surface.

[sundevil777 93]

To say that the upper surface of a wing provides any certain percentage, whether it is 60 or 80% or whatever, of the lift I think is misleading. I can understand it is convenient to describe it this way, but I still think it worthwhile to discuss how it is misleading.

I believe it is correct to say there is a pressure difference between upper and lower surface, and the pressure difference is greatest closer to the leading edge, and the pressure difference compared to ambient pressure is greatest on the upper surface. I believe it is correct to say the clean air flow on the upper surface is more important in creating this difference in pressure compared to clean air flow on the lower surface, but I think it is misleading to summarize this by saying the upper surface contributes 60 or 80 or whatever percentage of the lift.

To get back to the OP's original question...perhaps a lower surface that leaks air actually contributes to the higher pressure below the lower surface, so a non-zero porosity lower skin could increase lift? That seems like an important issue to discuss, no?

Perhaps my unease about this description is just an irrelevant point of semantics, but the engineering part of my brain seems troubled by it. Maybe this is something that should not cause me grief, as it reminds me of having beers with my friends after classes arguing why a beer bottle has a delayed foam-over when slapped on top by another beer. I also have a mechanical engineering background. I'm open to being convinced it is correct to say the upper skin contributes a certain percentage of the lift, but please consider what I've written, and understand I'm not intentionally trying to insult anyone.

Merry Christmas!

People are sick and tired of being told that ordinary and decent people are fed up in this country with being sick and tired. I’m certainly not, and I’m sick and tired of being told that I am

[mathrick 2]

However you want to word it, the reality is that the lower skin does not really matter for the wing's flight. This has been convincingly demonstrated by the creation of single-skin paragliders and speedwings. I don't claim to understand how it works, but it clearly does work just fine:

https://www.youtube.com/watch?v=tm6atN0AaFw


There are so many of them out there you can easily find comparison reviews.

"Skydivers are highly emotional people. They get all excited about their magical black box full of mysterious life saving forces."