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bruce.smith(at)york.com
Guest

Posted: Thu Apr 06, 2006 3:59 am Post subject: Grumman strength

Gary, and fellow Teammates,



What is it that goes into determining the Vne of an airplane? Is it 

shear (brute?) strength alone, or aerodynamics, or a combination of 

factors. The Cheetah I fly has a Vne of 190 mph, where a Piper Archer is 

redlined at 174 mph.



Slow day again, so I thought I'd ask. Gary, any amusing annuals lately?



Thanks.



Bruce Smith

flyv35b(at)ashcreekwirele
Guest

Posted: Thu Apr 06, 2006 6:57 am Post subject: Grumman strength

Certified aircraft are required (FAR Part 23) to be dive tested (design dive 

speed) to 10% above what the manufacture sets as Vne.  For the Tiger that 

would amount to about 220 mph.  As far as I can determine this is and has 

always been based on IAS.  But read the article by Van's chief engineer 

about their "theory" that Vne is and should be based on TAS.  Quite 

interesting but I don't know if this has been subscribed to in any 

aerodynamic texts (Gary should be able to shed some light on this).



http://www.vansaircraft.com/pdf/hp_limts.pdf



This doesn't mean that flutter will automatically occur at the design dive 

speed, just that the plane was tested up to that speed and the controls 

excited and there wasn't any catastrophic flutter.  But don't forget that 

this was with a new plane with tight controls, cables adjust properly and no 

wear in the trim linkage.  And Lord knows I have seen a lot of Grummans with 

quite a bit of elevator trim linkage, much more than a new plane would have.



Cliff  A&P/IA



---

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Apr 06, 2006 12:34 pm Post subject: Grumman strength

In a message dated 4/6/06 7:57:57 AM, flyv35b(at)ashcreekwireless.com writes:

 	  Quote: 	
		   This doesn't mean that flutter will automatically occur at the design dive

 speed, just that the plane was tested up to that speed and the controls

 excited and there wasn't any catastrophic flutter.=A0 But don't forget that

 this was with a new plane with tight controls, cables adjust properly and=20no

 wear in the trim linkage.=A0 And Lord knows I have seen a lot of Grummans=20with

 quite a bit of elevator trim linkage, much more than a new plane would have.




	


OFF-THE-RECORD:   I know of one Cheetah that did a split-S at 12,000 feet and

leveled off at 3,000 feet.   At or near 200 indicated for a good portion of

the way down.   Smooth as silk.

_________________
Gary
AuCountry Aviation
Home of Team Grumman

923te(at)cox.net
Guest

Posted: Thu Apr 06, 2006 1:51 pm Post subject: Grumman strength

I thought you all might be interested in Fred Kokaska's comments when I ask 

him a similar question concerning Vne for teh 540 powered Tigers:



Fred:

"I went through the Vne part of certification at 100% of Vne for an AA5B 

(174 KIAS), There were two Part 23 objectives in this flight test (flown by 

FAA test pilot) of verifying the prop does not overspeed (above 2700 RPM) at 

Vne. .... The other was pitch and roll control and airframe vibration.



The test pilot started at 10 K feet and pushed over at full power to 

establish 174 KIAS, did some 30 degree left and right rolling maneuvers. He 

commented (and I looked out the right side) on the fact the ailerons were 

both about 2 inches above the normal even with the flap position in level 

flight from airloads. While this looks spooky, he noticed no binding or 

control input problems that he did not like."

I think the aileron flexing is a bit unerving.

Best Regards,

Ned

flyv35b(at)ashcreekwirele
Guest

Posted: Thu Apr 06, 2006 2:13 pm Post subject: Grumman strength

 	  Quote: 	
		   I think the aileron flexing is a bit unnerving.

 Best Regards,

 Ned

Apparently due to the high airflow over them and stretch of the cables or 
	


deflection in the system.  I guess that is the position they want to seek at 

high airflow.  Any flight at Vne can be a bit unnerving.



Cliff

---

A1ynk(at)aol.com
Guest

Posted: Thu Apr 06, 2006 3:01 pm Post subject: Grumman strength

The aileron flexing is in the torque tube. It is meant to flex. That is how 

you get the 15 degrees up travel and 7.5 down. The aileron hits the stop and 

then the torque tube flexes alowing the other aileron to go up and hit that stop.

Bill Hatton 

N9965U

gilalex(at)earthlink.net
Guest

Posted: Thu Apr 06, 2006 8:48 pm Post subject: Grumman strength

Don't forget the one that had aileron flutter at Van Nuys....

The photo of the 'bent' wing was quite scary, but nice to see the spar 

could bend without breaking.

They lost their counterweights in wake turbulence while on downwind.

It was on a FAA poster at WJF - I'm sure Gary remembers it.... I think it 

got the aileron AD started....

gil in Tucson

At 01:31 PM 4/6/2006, you wrote:

 	  Quote: 	

In a message dated 4/6/06 7:57:57 AM, flyv35b(at)ashcreekwireless.com writes:

 > This doesn't mean that flutter will automatically occur at the design dive

 > speed, just that the plane was tested up to that speed and the controls

 > excited and there wasn't any catastrophic flutter.=A0 But don't forget that

 > this was with a new plane with tight controls, cables adjust properly 

 and=20no

 > wear in the trim linkage.=A0 And Lord knows I have seen a lot of 

 Grummans=20with

 > quite a bit of elevator trim linkage, much more than a new plane would 

 have.

 >

OFF-THE-RECORD:   I know of one Cheetah that did a split-S at 12,000 feet and

leveled off at 3,000 feet.   At or near 200 indicated for a good portion of

the way down.   Smooth as silk.

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Apr 06, 2006 10:26 pm Post subject: Grumman strength

In a message dated 4/6/06 4:02:18 PM, A1ynk(at)aol.com writes:

 	  Quote: 	
		   The aileron hits the stop and

 then the torque tube flexes alowing the other aileron to go up and hit that 

 stop.

 Bill Hatton

 


	


Not true.   To go past the stop on the left side you are actually stretching 

the cables so the right aileron hits its stop and vice versa.

_________________
Gary
AuCountry Aviation
Home of Team Grumman

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Thu Apr 06, 2006 10:28 pm Post subject: Grumman strength

In a message dated 4/6/06 9:49:39 PM, gilalex(at)earthlink.net writes:

 	  Quote: 	
		   Don't forget the one that had aileron flutter at Van Nuys....

 

 


	


Well, it did NOT have aileron flutter.   And, it happend a LONG time after 

the AD came out.   



I looked at that Tiger to do an estimate on repairs.   The ailerons had been 

installed wrong.   The long bolt that goes through for the aileron stop had 

been installed outboard of the stop.   Thus, (don't you just love that word) the 

aileron stop could not act as a stop.   The plane had encountered (or so the 

pilot said) wind shear from a jet landing on an adjacent runway.   As the 

story goes, the pilot tried to correct for the roll and the aileron ripped out.   

Funny, but the aileron stop was still there and intact.   The other aileron 

was still on the plane and the aileron counter-weight had made a mark in the 

wingtip where it had gone way past the design limit.



Gary

_________________
Gary
AuCountry Aviation
Home of Team Grumman

bruce.smith(at)york.com
Guest

Posted: Fri Apr 07, 2006 3:43 am Post subject: Grumman strength

Cliff, Gary,

So, Vne is calculated, and then tested, right? Based upon spar strength, 

fuselage material strength?

Did the factory ever do a static test to destruction? It would be 

interesting to learn what the ultimate load factors were, just for 

conversation and bragging rights.

Gary, OK how much is the Cheetah annual costing right now?

Bruce

TeamGrumman(at)aol.com said the following on 4/6/2006 4:31 PM:

 	  Quote: 	

 In a message dated 4/6/06 7:57:57 AM, flyv35b(at)ashcreekwireless.com writes:

> This doesn't mean that flutter will automatically occur at the design dive

> speed, just that the plane was tested up to that speed and the controls

> excited and there wasn't any catastrophic flutter.=A0 But don't forget that

> this was with a new plane with tight controls, cables adjust properly and=20no

> wear in the trim linkage.=A0 And Lord knows I have seen a lot of Grummans=20with

> quite a bit of elevator trim linkage, much more than a new plane would have.

>

>     

 OFF-THE-RECORD:   I know of one Cheetah that did a split-S at 12,000 feet and

 leveled off at 3,000 feet.   At or near 200 indicated for a good portion of

 the way down.   Smooth as silk.

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 4:46 am Post subject: Grumman strength

Agreed.  The torque tube is pretty rigid and deflects very little.  And the 

amount of deflection upward after the opposite aileron hits its stop seems 

to vary from plane to plane and appears to be less than the difference in 

travel between the two (7.5 degrees), although I haven't measured it 

specifically.  Due to tolerances in travel and rigging there can be quite a 

difference here.



Cliff

---

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 5:05 am Post subject: Grumman strength

The aileron got started years ago off the east coast, on a plane coming back 

from the Bahamas I think.  I understand that it consisted of a mild 

amplitude oscillation of a couple of cycles per second, probably the same 

phenomenon that many owners have experienced at times when flying in rain 

and otherwise.  Initially, the FAA wanted to truncate all the ailerons at 

the trailing edge as a solution and the AYA and owners interceded and 

allowed the alternate solution of the 100 hr inspection which most everyone 

has opted for since.



I bought a really nice 79 Tiger from an insurance company years ago that was 

declared unairworthy primarily due to this oscillation by an owner who 

wanted to get rid of the plane and he found a young new IA who was ignorant 

and agreed to go along with the idea.  The insurance adjusted never came out 

and look at the so-called damage!  The story is a bit more involved but the 

bottom line was I flew the plane after installing all new aileron bearings 

and adjusting the cable tension and the oscillation still existed just 

before the stall buffet while creeping up on it slowly from a slow flight 

condition.  It is nothing serious to worry about.  Later on after removing 

and balancing the aileron to dead on (it was within tolerance before) the 

oscillation completely disappeared.  I sold the plane a year later after 

flying it all over for 100 hrs for $26,000 more than I paid for it!



Cliff  A&P/IA

 ---

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 6:14 am Post subject: Grumman strength

Gary probably knows more about this than I do, but I think that Vne is more 

based on the aeroelasticity of the control surfaces and their attachment 

structure that it is on ultimate strength.  Factors such as balance, control 

surface and system rigidity and design of the control surface itself are 

more important than brute strength.  Of course you also want the strength in 

adverse situations such as rapid aileron deflection, maybe to the stops, at 

reasonable speed.  That doesn't mean that you can go to Vne or almost and 

then do maximum aileron deflection at the same time.  This would add a lot 

of load to the wing with the down aileron, not to mention the forces on the 

aileron itself.  This is exactly what has happened with the T-34 Beechcraft 

during the mock combat flying during a dive and rolling severely while 

"chasing" another plane.  The plane was never designed for these 

"combination" loads at the extreme edge of the envelope.  Full aileron 

deflection is not all that hard to do for a short time, even without doing a 

roll, by starting in a steep bank one direction and rolling the other way 

with full opposite aileron for about 3 seconds.  Don't try this at speeds 

above maneuvering speed.



Don't know what the factory did regarding static load testing.  I'll bet 

they never went to failure on the wing.  My concern with overload would not 

be with the wing but with the tail, especially on the AA5A and B.



Cliff  A&P/IA



---

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 6:21 am Post subject: Grumman strength

This makes me believe that the critical part of the aileron system and 

inspection per the AD79-22-04 is the integrity of the balance weight and the 

outer aileron bracket.  Both of these areas can be inspected pretty well on 

even a preflight with a good strong flashlight if you know where to look. 

Any crack in the radius of the aileron bracket or in the weld joint of the 

balance weight is cause for immediate replacement.  I have seen a few outer 

aileron brackets cracked but no balance weights.



Cliff  A&P/IA

---

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Fri Apr 07, 2006 10:22 am Post subject: Grumman strength

In a message dated 4/7/06 4:45:14 AM, bruce.smith(at)york.com writes:

 	  Quote: 	
		   Gary, OK how much is the Cheetah annual costing right now?

 

 Bruce

 


	


let's just say that the prop had crackes in the hub, an ADF was removed, the 

dorsal fin was replaced, the windshield was replaced, a top overhaul with new 

Lycoming/Lycon prepared cylinders, painted firewal, lots of powder coating, 

JPI with fuel flow, new hoses, new engine mount isolators, complete annaul, new 

brakes, repair of brake line, two wheel bearings, and lots of odds and ends.   

So far, it's almost 70% of the cost of the plane (he bought it in Nov 05.)

_________________
Gary
AuCountry Aviation
Home of Team Grumman

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Fri Apr 07, 2006 10:26 am Post subject: Grumman strength

In a message dated 4/7/06 7:15:20 AM, flyv35b(at)ashcreekwireless.com writes:

 	  Quote: 	
		   Don't know what the factory did regarding static load testing.=A0 I'll bet

 they never went to failure on the wing.=A0 My concern with overload would=20not

 be with the wing but with the tail, especially on the AA5A and B.




	


I had heard that the Cheetah that encountered the thunder storm was tested

and it took something like 16 to 20 g to bend the wings.

_________________
Gary
AuCountry Aviation
Home of Team Grumman

GrummanDude

Joined: 15 Jan 2006
Posts: 926
Location: Auburn, CA

Posted: Fri Apr 07, 2006 10:28 am Post subject: Grumman strength

In a message dated 4/7/06 7:29:10 AM, flyv35b(at)ashcreekwireless.com writes:

 	  Quote: 	
		   This makes me believe that the critical part of the aileron system and

 inspection per the AD79-22-04 is the integrity of the balance weight and the

 


	


How about an aileron bracket that uses the same bearing as the one inside the 

outboard flap bracket?   That would eliminate a good portion of the wear on 

the outer aileron torque tube.

_________________
Gary
AuCountry Aviation
Home of Team Grumman

bruce.smith(at)york.com
Guest

Posted: Fri Apr 07, 2006 10:36 am Post subject: Grumman strength

So, you're preparing a "Better Than New Cheetah" for him or her.



TeamGrumman(at)aol.com said the following on 4/7/2006 2:20 PM:

 	  Quote: 	
		   

 In a message dated 4/7/06 4:45:14 AM, bruce.smith(at)york.com writes:

   

> Gary, OK how much is the Cheetah annual costing right now?

>

> Bruce

>

>     



 let's just say that the prop had crackes in the hub, an ADF was removed, the 

 dorsal fin was replaced, the windshield was replaced, a top overhaul with new 

 Lycoming/Lycon prepared cylinders, painted firewal, lots of powder coating, 

 JPI with fuel flow, new hoses, new engine mount isolators, complete annaul, new 

 brakes, repair of brake line, two wheel bearings, and lots of odds and ends.   

 So far, it's almost 70% of the cost of the plane (he bought it in Nov 05.)

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 11:35 am Post subject: Grumman strength

Like I said, I wouldn't worry about the wings.  Maybe the tail isn't of any 

concern either.

Cliff

---

flyv35b(at)ashcreekwirele
Guest

Posted: Fri Apr 07, 2006 11:37 am Post subject: Grumman strength

That would be an improvement and preclude the expense of installing the 

stainless steel wear sleeve and oversize bearing.  There is plenty of room 

for a wider bearing it seems to me.

Cliff

---

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