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leinad

Joined: 19 Sep 2006
Posts: 283
Location: Central Virginia

Posted: Thu May 08, 2008 5:30 pm Post subject: Re: How many Gs are these maneuvers?

Sabrina,

That's almost impossible to say accurately because while you could estimate roughly 3 G from the apparent speed and how quickly he arrested the speed in one direction then add a G for normal weight, real world accelerations don't work like that, because of things like how gently the pilot applies stick pressure and air turbulence and other complicating factors.  The thing that struck me when I saw the video was that Richardo (God rest his sole) was an agricultural pilot and he was flying the plane as if it were a crop duster.



Could it be we haven't heard of any Corvair powered Zodiacs breaking wings because the Corvair folks know their engine won't take high G maneuvers so they fly their planes accordingly?   Of course it could also be because there are so few of us.



Dan



Dan

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n801bh(at)netzero.com
Guest

Posted: Thu May 08, 2008 5:51 pm Post subject: How many Gs are these maneuvers?

The pull up at the far end of the field is kinda hard to really see but I will guess 2.2- 2.5 G's. The last pass right in front of the camera is maybe 1.5 -1.8 at best and flown real smooth. Remember one can make some impressive manauvers and if kept smooth in control imputs it hardly reaches more then 1.5 G's.. Well within range of a +6, -3 airframe.. 

do not archive 

Ben Haas

N801BH

www.haaspowerair.com



-- "Sabrina" <chicago2paris(at)msn.com> wrote:

--> Zenith-List message posted by: "Sabrina" <chicago2paris(at)msn.com>



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planes_by_ken(at)bellsout
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Posted: Fri May 09, 2008 5:38 pm Post subject: How many Gs are these maneuvers?

Loops can be done in the 3g - 4g range.  The Decathlon I flew liked 

3.5g.  Any more I would run out of airspeed.  It depends on the pilot, 

aircraft and how aggressively flown.

Ken Lilja

do not archive



Sabrina wrote:

 	  Quote: 	
		   



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 http://www.youtube.com/watch?v=3X8GcFqTpYM





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grant.corriveau(at)telus.
Guest

Posted: Fri May 09, 2008 11:56 pm Post subject: How many Gs are these maneuvers?

G-force limitations on an airframe are determined according to particular formulae and there are a lot of maneuvers that can violate those presumptions.  For example, Ultimate G loads etc... are based upon a particular rate of onset.  If this rate is exceeded, then the momentary load limits can be exceeded.  Similarly a compound movement around more than one axis can cause outer wing panels to experience different G loading than the fuselage.



I'm just making the point that book numbers are just that - numbers.  If we fly the aircraft outside of the built-in presumptions, then we've entered the world of test piloting - bring your own parachute.  And I don't know about other countries, but in Canada my Zodiac carries a big placard that says: Aerobatics Prohibited.

Just my two cents worth.

Here's a good reminder - notice how slowly the loads are applied (yes - I know it isn't a Zodiac):

http://youtube.com/watch?v=fG96__plVFA



 [quote][b]

planes_by_ken(at)bellsout
Guest

Posted: Sat May 10, 2008 3:22 pm Post subject: How many Gs are these maneuvers?

Unfortunately, I would think that no aerobatics would be self evident.  But it is not.  Design limit g loads are misunderstood.  If the design ultimate is +6g -3g then usable is +4g -2g.  (1.5X safety factor)  For positive load limit factors, FAR 23.337 (a) (1) requires +3.8g for normal , (a) (2) requires 4.4g for utility category and (a) (3) requires 6.0g for aerobatic category.  For negative load factors FAR 23.337 (b) (1) requires -1.5g for normal, 1.6g for utility category and (a) (2) requires -3g for aerobatic category.  The airframe needs to withstand the force for 3 seconds.  Zenith has quoted +-6g and +6g -3g for ultimate limits.  Either way qualifies for NORMAL category.  A good number of light aircraft may be operated in utility category at reduced gross weight and at a narrower CG range.  It may be that production aircraft actually have a higher safety factor due to not trying to shave off that last pound.  The closer an airframe is designed to the limit, the less room we have for dumb pilot events.

 

 Ken Lilja     [quote][b]

leinad

Joined: 19 Sep 2006
Posts: 283
Location: Central Virginia

Posted: Sun May 11, 2008 8:52 am Post subject: Re: How many Gs are these maneuvers?

Ben,

I'd like to know how you estimated the G forces.

If I do some simple calculations, based on a guess of how fast the plane was going I get a much higher answer than your estimated 1.8 max during the second pull up.

The plane looks to be going about 200 feet per second.. or 137 mph, as the pilot traded altitude for speed and the plane is capable of that speed in normal cruise. (This is where I could be completely wrong)  He arrested all of that speed in the direction of the pass in 2 and half seconds.  That gives an average acceleration of -80 feet/sec/sec during the 2.5 seconds the velocity was bled off.  Dividing by 32 gives us 2.5 Gs if the deceleration were uniformly distributed through out the pull up, but much more likely there were almost no Gs at the end since the speed was almost gone, so the distribution of the force due to the pull up probably peeked near 5 G at the bottom, so that the average could still be 2.5.  You also have to add 1 G for the steady state level flight, as that is what the wings are normally holding up.  So there may have been a peek G at around 6 at the bottom of the final pull up.  And that only if the pilot put in perfectly smooth gradual input, and there were zero turbulence.

What struck me when I saw the video the first time was here was a very experienced agricultural pilot flying his 601XL like it were a crop duster.

[quote="n801bh(at)netzero.com"]The pull up at the far end of the field is kinda hard to really see but I will guess 2.2- 2.5 G's. The last pass right in front of the camera is maybe 1.5 -1.8 at best and flown real smooth. Remember one can make some impressive manauvers and if kept smooth in control imputs it hardly reaches more then 1.5 G's.. Well within range of a +6, -3 airframe.. 

do not archive 

Ben Haas

N801BH

www.haaspowerair.com



-- "Sabrina" <chicago2paris> wrote:

--> Zenith-List message posted by: "Sabrina" <chicago2paris>



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http://www.youtube.com/watch?v=3X8GcFqTpYM





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Gig Giacona

Joined: 10 Jan 2006
Posts: 1416
Location: El Dorado Arkansas USA

Posted: Sun May 11, 2008 10:22 am Post subject: Re: How many Gs are these maneuvers?

While it is true that many if not most basic aerobatic maneuvers  can be down with sub 2 G's one must remember that when the same aerobatic maneuver fails significantly more stress can be inflicted on the airframe. I have a friend that used to fly competition aerobatics at the international level. During a practice flight he had something come loose in the cockpit once that for a very short time jammed the stick. He pulled out of the simple loop but it took him 9 Gs to do it. Afterwords the entire plane was taken apart to check for stress failures.



I hear about a 601XL doing loops or other benign aerobatics I have to wonder if the pilot was trained in aerobatics or was "self taught." And if they were trained what was the extent of that training? There are lots of weekend and even one day aerobatic familiarization classes out there. When you come out of those your are NOT an aerobatic pilot. I know, I've taken two of them. And while I technically know how to do several maneuvers and could pull them off given the right aircraft I don't think of myself as an aerobatic pilot any more that I think of myself as a NASCAR driver because I've driven a few laps in a NASCAR auto.



When you see these videos of aerobatics in a 601 ask yourself, how many times did that pilot practice that maneuver before he had it taped and how many times did he botch it?



None of the aerobatic pilots I know would do this stuff in a 601 because that isn't what it was built for. An airplane is like any other tool. You don't use a hammer to drive a screw and those that do tend to break stuff.



 	  leinad wrote: 	
		  Remember one can make some impressive manauvers and if kept smooth in control imputs it hardly reaches more then 1.5 G's.. Well within range of a +6, -3 airframe.. 

do not archive

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601XL Under Construction
See my progress at www.peoamerica.net/N601WR

n801bh(at)netzero.com
Guest

Posted: Sun May 11, 2008 2:03 pm Post subject: How many Gs are these maneuvers?

Hi Leinad, First let me get this out, my guess is just that, A guess based on my past experiences while doing different flight maneuvers. You could be as correct as me but here is my reasoning... While is steady state flight like making a low pass before the pull up the G meter will read 0 G's. Not 1 like you propose. Any change in direction will influence the G meter either up or down or sideways. Your numbers of terminal velocity are probably real close and it is the only way to even get a realistic wild ass guess. If I were to amend my first guess I wouls add a G to the pull up at the far end because upon further viewing of the video it really looks like a pretty hard yank and bank. It is so far away that nobody will probably closely guess the true G force on that one. The second one in front of the camera is a very smooth pull up and bank. In my mind he didn't change course 90 degrees in either axis so your figures of deceleration is skewed, also his "speed almost gone"  concept is probably in error because to me he flew off at what looks like 70+ mph. Now if he really did a sharp pull up to a hammerhead stall in 2.5 seconds your numbers would be realistic. This is just my take and I could be entirely out to lunch...   I am putting my Flame suit on for this one too <G>...... 

do not archive..

Ben Haas

N801BH

www.haaspowerair.com



-- "leinad" <leinad(at)hughes.net> wrote:

--> Zenith-List message posted by: "leinad" <leinad(at)hughes.net>



Ben,

I'd like to know how you estimated the G forces.

If I do some simple calculations, based on a guess of how fast the plane was going I get a much higher answer than your estimated 1.8 max during the second pull up.

The plane looks to be going about 200 feet per second.. or 137 mph, as the pilot traded altitude for speed and the plane is capable of that speed in normal cruise. (This is where I could be completely wrong)  He arrested all of that speed in the direction of the pass in 2 and half seconds.  That gives an average acceleration of -80 feet/sec/sec during the 2.5 seconds the velocity was bled off.  Dividing by 32 gives us 2.5 Gs if the deceleration were uniformly distributed through out the pull up, but much more likely there were almost no Gs at the end since the speed was almost gone, so the distribution of the force due to the pull up probably peeked near 5 G at the bottom, so that the average could still be 2.5.  You also have to add 1 G for the steady state level flight, as that is what the wings are normally holding up.  So there may have been a peek G at around 6 at the bottom of the final pull up.  And that only if the pilot put in perfectly smooth gradual input, and the!

re were zero turbulence.

What struck me when I saw the video the first time was here was a very experienced agricultural pilot flying his 601XL like it were a crop duster.

[quote="n801bh(at)netzero.com"]The pull up at the far end of the field is kinda hard to really see but I will guess 2.2- 2.5 G's. The last pass right in front of the camera is maybe 1.5 -1.8 at best and flown real smooth. Remember one can make some impressive manauvers and if kept smooth in control imputs it hardly reaches more then 1.5 G's.. Well within range of a +6, -3 airframe.. 

do not archive 

Ben Haas

N801BH

www.haaspowerair.com



-- "Sabrina"  wrote:

--> Zenith-List message posted by: "Sabrina" 



http://www.youtube.com/watch?v=LlpLeVvep7k&feature=related



http://www.youtube.com/watch?v=3X8GcFqTpYM





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leinad

Joined: 19 Sep 2006
Posts: 283
Location: Central Virginia

Posted: Mon May 12, 2008 4:03 pm Post subject: Re: How many Gs are these maneuvers?

Ben,

A wise man once said "those who live in a wooden house had best not throw flames. :)"

I stick by my contention that you have to add 1 G for steady state not withstanding how G meters are calibrated.  Of course if you are in orbit I take it back, certain hyperbolic flight paths can also result in zero G.  In level flight the weight of the aircraft (1G) is pulling down, and this is balanced by lift.  So while the ground holds the airplane up on the ground, the wings have to do it in flight.  

Another thing I disagree about is the idea that he didn't see those extremes because he still had 70 MPH of speed left.  The thing that matters is the change in speed in the direction he was going.  In fact the calculated acceleration would have a higher magnitude if he exited the maneuver in the opposite direction he started it.   Another way to think about it is that a change in direction IS a change in velocity.  So I've been sloppy when using the word "speed" instead of velocity.

I'm no scientist so I hope everyone is smart enough to take what I say with a grain of salt.

Off to Monday night chat!

Dan



[quote="n801bh(at)netzero.com"]Hi Leinad, First let me get this out, my guess is just that, A guess based on my past experiences while doing different flight maneuvers. You could be as correct as me but here is my reasoning... While is steady state flight like making a low pass before the pull up the G meter will read 0 G's. Not 1 like you propose. Any change in direction will influence the G meter either up or down or sideways. Your numbers of terminal velocity are probably real close and it is the only way to even get a realistic wild ass guess. If I were to amend my first guess I wouls add a G to the pull up at the far end because upon further viewing of the video it really looks like a pretty hard yank and bank. It is so far away that nobody will probably closely guess the true G force on that one. The second one in front of the camera is a very smooth pull up and bank. In my mind he didn't change course 90 degrees in either axis so your figures of deceleration is skewed, also his "speed almost gone"  concept is probably in error because to me he flew off at what looks like 70+ mph. Now if he really did a sharp pull up to a hammerhead stall in 2.5 seconds your numbers would be realistic. This is just my take and I could be entirely out to lunch...   I am putting my Flame suit on for this one too <G>...... 

do not archive..

Ben Haas

N801BH

www.haaspowerair.com



-- "leinad" <leinad> wrote:

--> Zenith-List message posted by: "leinad" <leinad>



Ben,

I'd like to know how you estimated the G forces.

If I do some simple calculations, based on a guess of how fast the plane was going I get a much higher answer than your estimated 1.8 max during the second pull up.

The plane looks to be going about 200 feet per second.. or 137 mph, as the pilot traded altitude for speed and the plane is capable of that speed in normal cruise. (This is where I could be completely wrong) ï¿½He arrested all of that speed in the direction of the pass in 2 and half seconds.  That gives an average acceleration of -80 feet/sec/sec during the 2.5 seconds the velocity was bled off.  Dividing by 32 gives us 2.5 Gs if the deceleration were uniformly distributed through out the pull up, but much more likely there were almost no Gs at the end since the speed was almost gone, so the distribution of the force due to the pull up probably peeked near 5 G at the bottom, so that the average could still be 2.5.  You also have to add 1 G for the steady state level flight, as that is what the wings are normally holding up. ï¿½So there may have been a peek G at around 6 at the bottom of the final pull up.  And that only if the pilot put in perfectly smooth gradual input, and the!

re were zero turbulence.

What struck me when I saw the video the first time was here was a very experienced agricultural pilot flying his 601XL like it were a crop duster.

[quote="n801bh(at)netzero.com"]The pull up at the far end of the field is kinda hard to really see but I will guess 2.2- 2.5 G's. The last pass right in front of the camera is maybe 1.5 -1.8 at best and flown real smooth. Remember one can make some impressive manauvers and if kept smooth in control imputs it hardly reaches more then 1.5 G's.. Well within range of a +6, -3 airframe.. 

do not archive 

Ben Haas

N801BH

www.haaspowerair.com



-- "Sabrina"  wrote:

--> Zenith-List message posted by: "Sabrina" 



http://www.youtube.com/watch?v=LlpLeVvep7k&feature=related



http://www.youtube.com/watch?v=3X8GcFqTpYM





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rtdin

Joined: 16 Mar 2008
Posts: 46
Location: Florida panhandle

Posted: Mon May 12, 2008 6:32 pm Post subject: How many Gs are these maneuvers?

Guessing how many Gs another plane pulls is like reading tea leaves. Good luck. This was an Ag pilot. The so called "crop duster" turn is less G than you think. Ag pilots don't like to pull Gs for two reasons: Eight hours of high G is tiring and its foolish to do high G close to the ground with a heavy load. The loop is real slow over the top in a plane with wing loading less than 10 lbs per sq foot. (1320 lbs at t.o. with 132 sq ft) The big problem with looping a 100 HP plane is falling out of the top with inadequate airspeed. Low stress. Even more embarrassing is not even making it to the top and then back sliding. Stresses the control surfaces, could even "blow your flaps down," but otherwise low stress. If you are teaching a former military pilot, expect this because they always over estimate that puny 100 HP and try to make really big diameter loops. 

 Barrel rolls are low stress and are started like Chandelles and lazy eights. (Commercial maneuvers done in spam cans) Do a YouTube search for "Bob Hoover," turn up your volume and listen to his story about rolling a SabreLiner with a load of Generals. While he is talking, he is pouring iced tea into a tumbler on the glare shield. He is doing a barrel roll with his other hand. Like the prototype BO-707 did.

 Install a G meter or accelerometer. A cheap fish scale will do in a pinch. Get someone to show you how to do this stuff if you are going to do it. Start with a level 60 degree banked turn. Experience two Gs. Light a candle, don't curse the darkness. Remember, a 601 ain't a Pitts.

 

 Bob   Do not archive   

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rtdin

Joined: 16 Mar 2008
Posts: 46
Location: Florida panhandle

Posted: Mon May 12, 2008 7:12 pm Post subject: How many Gs are these maneuvers?

Another thing about steady state Gs. It is not zero but rather its one. I am looking at the Accelerometer, AKA G meter sitting above my fireplace. Its reading one as we speak.

 

 Bob Do not archive

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