LaGG-3 Series 35

[LLv34_Flanker]

S!

 

 Thanks for the input on flutter Crump and Sternjaeger

[Crump]

No Crump, you're confusing two different things. 

When your control surfaces start fluttering you don't experience vibration, it whips the wings and SHAKES the airframe, and it can be a relatively common occurrence. Whilst it is advisable not to reach flutter speed, there are several stages to it, more or less safe to "explore", and the intensity and frequency increases with the airspeed.

 

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

 

 

note that wing flutter is peculiar to the wing/surface design, so it doesn't occur on the same airspeed for all aircraft of course.

 

I think it's safe to say (and others will probably confirm) that the 575km/h shaking in a dive that the manual refers to describes flutter speed.

 

 

I am not confusing anything Sternjager.

 

You are showing Piper's testing  of the Pa-30.  The film showing the elevator flutter is greatly slowed down.

 

 

 

 

So what is the “flutter” in flutter testing?

 

Flutter phenomena are seen when vibrations occurring in an aircraft match the natural frequency of the structure.

 

 

 

 

If they aren’t properly damped, the oscillations can increase in amplitude, leading to structural damage or even failure. A similar problem occurs in bridges and brought down the Tacoma Narrows Bridge in 1940.

 

In the video above, astronaut Fred Haise is piloting a Piper PA-30 Twin Commanche during flutter tests NASA conducted with general aviation aircraft in the late 1960s. Once the vibrations are introduced into the tail of the aircraft, in this case a stabilator, the flutter increases dramatically causing tremendous oscillations in the horizontal surface making the stabilator flex as if made of rubber.

 

 

According to NASA, Haise said of the experience, “I’m fearless, but that scares me.”

 

http://www.wired.com/2010/03/flutter-testing-aircraft/

 

By definition, flutter is a vibration. 

 

In order to have flutter, the harmonics must align which means the natural frequency of the aircraft and the control surface are equal.  That leads to the energy being released in the form of amplitude changes to the in control surface. 

 

The Hawker 800 winglet STC has a AD issued on it based several reported incidents. 

 

 

SUMMARY: We are adopting a new airworthiness directive (AD) for certain

Hawker Beechcraft Corporation (Type Certificate Previously Held by

Raytheon Aircraft Company) Model BAe.125 Series 800A (including C-29A

and U-125), and 800B airplanes; and Model Hawker 800 (including variant

U-125A) and 800XP airplanes modified in accordance with a certain

winglet supplemental type certificate. This AD requires revising the

Limitations section of the airplane flight manual (AFM) and installing

placards on the instrument panel. This AD was prompted by reports of

several instances of severe vibration and wing/aileron oscillations. We

are issuing this AD to prevent vibration and wing/aileron oscillations,

which could cause structural damage or lead to divergent flutter, and

result in loss of integrity of the wing, loss of control of the

airplane, and in-flight breakup.

 

 

It is NOT divergent flutter on that film!!  In other words, while dramatic, scary for the people on board, it is not the same subject.  Different animal completely.....

 

 

We are issuing this AD to prevent vibration and wing/aileron oscillations, which could cause structural damage or lead to divergent flutter, and result in loss of integrity of the wing, loss of control of the airplane, and in-flight breakup.”

 

http://www.gpo.gov/fdsys/pkg/FR-2013-06-17/html/2013-14247.htm

 

Hawker engineers are investigating it but they have not reached any conclusions.  They will rebalance the ailerons as part of the investigation.

Edited May 17, 2014 by Crump

[Sternjaeger]

First of all let's try and keep it civilised, don't want this to be yet another case of thread locked because of silly arguments.

 

Having said that, flutter is not perceived as a vibration, it's a violent oscillation which is triggered by aileron excitement (hence the importance of having balanced control surfaces)

 

http://youtu.be/aZQlmxrmjXQ?t=1m36s

 

vibrations are normally caused by other resonances, flutter is a shaking experience of the worst kind

 

[LLv34_Flanker]

S!

 

 Crump and Stern, points made by both of you. Let's not get this into a trench war     Topic: LaGG-3 and it's performance.

[Crump]

 

First of all let's try and keep it civilised, don't want this to be yet another case of thread locked because of silly arguments.

 

 

There is nothing to discuss or argue about.  

[Sternjaeger]

There is nothing to discuss or argue about.  

 

I wholeheartedly agree. 

[LLv34_Flanker]

S!

 

 And then some more info on the LG-1 in question. Enjoy! http://mig3.sovietwarplanes.com/lagg3/lg1/lg1.html

[LLv34_Flanker]

S!

 

 And here some more info from impressions LG-1 caused when sent to LeLv 32..

 

 

 Air Force General Staff department SPK 8194, Index N:o 3090

 

19th of March 1943

 

I hereby report LeLv 32 first impressions of the LaGG-3:

 

1) The long runway of Nurmoila air base is enough for the plane.

2) Pilots' first impressions are less enthusiastic, but

3) Speed greatly surpasses the CU(Curtiss Hawk 75A), on the deck about 450km/h and at 4km about 580km/h. Numbers not fully accurate.

4) Withstands 750km/h dive speed and is stable

5) Performs normal aerobatic moves quite well, therefore

6) Pilots grew to like it after flying the plane more, especially due the high speed and good armament. I therefore request to expedite the repairs of the next LaGG-3 so it could be transferred here before runway gets soft.(Ha/Le.V have supposedly  left it unfinished due a Fiat). More detailed test reports and statements will be sent on paper.

 

Colonel V.Rekola

[Crump]

 

Withstands 750km/h dive speed and is stable

 

 

Which is the 600 kph IAS.....depending on the altitude.....

 

 

What was the altitude the speed was measured at Flanker?

 

BTW,  Here is a history of flutter research.  It might help understand the state of affairs at the time the Lagg was designed.  The Resonance (vibrational frequency) method used today to separate flutter from other aeroelasticity effects was not developed until 1935. 

 

It was only used by a few countries during World War II.  

 

Historical development of aircraft flutter.pdf

[Crump]

Any altitude over 11,500 the Lagg 3 can easily attain 750 kph reading 600 kph IAS on the stock airspeed indicator.

[LLv34_Flanker]

S!

 

 That is only the document sent by the officer of LeLv 32 to General Staff so it did not contain anything special and therefore held the note of the reports to be sent later. We are currently trying to dig up information on the LG-2 as well So far it seems we had LG-1 that was Series 5/7 because of the bulges for light MG's. Light MG's were removed by Finns to save weight. LG-3 was Series 35 and those reports are here already. LG-2 remains a bit of a uncertain, but I recall it being from Series 28/29 or something. But give us a bit of time and we will find it Thanks for the documents Crump

[Sternjaeger]

Any altitude over 11,500 the Lagg 3 can easily attain 750 kph reading 600 kph IAS on the stock airspeed indicator.

What? Seriously?

[MiloMorai]

What? Seriously?

 

Afaik, the ceiling was 9600m.

[Crump]

S!

 

 That is only the document sent by the officer of LeLv 32 to General Staff so it did not contain anything special and therefore held the note of the reports to be sent later. We are currently trying to dig up information on the LG-2 as well So far it seems we had LG-1 that was Series 5/7 because of the bulges for light MG's. Light MG's were removed by Finns to save weight. LG-3 was Series 35 and those reports are here already. LG-2 remains a bit of a uncertain, but I recall it being from Series 28/29 or something. But give us a bit of time and we will find it Thanks for the documents Crump

 

 

Well, Sternjager's post indirectly sparked the possibility that that TSAGI might also have misidentified the issue with the Lagg-3 series.  Does anyone have a similar paper detailing the state of TASGI's flutter research at the time?  It would be interesting to see where they were at in comparison.

 

To me it sounds like they were doing actual flutter flight testing long before the Western Allies or Germany.  Wonder if that is the result of research or desperation?

Edited May 18, 2014 by Crump

[Sternjaeger]

my 2 cents is that they were trying to do a rather pragmatic and somewhat crude flight envelope testing to understand the capacities and limitations of the design, flutter was a known issue with all aircraft designs, they just knew not to go there because it always ended up in tears. 

 

I get your point about indicated airspeed readings varying according to altitude, but I think that it doesn't really pertain to this specific aircraft, because of the aforementioned ceiling. What I think might be questionable is relying on the readings of instruments which of course might be inaccurate for other reasons (quality of components, vibrations, installation of pitot etc..)

 

Again, I always think of this sort of reports as interesting to give you some decent ballpark figures, but are they very accurate? Nope, especially because they don't take into account different loads, temperatures, altitudes etc..

Edited May 18, 2014 by Sternjaeger

[LLv34_Flanker]

S!

 

 As JtD clarified on the Klimov VK105PF engine's so called boost or take-off setting. It had no significant effect on speed(~5km/h) so the Finnish tests seem to be pretty accurate with the 2600rpm setting used. New things learned every day.

[snowsnipersnow_sniper]

Hi every body

 

found this info about lagg-3 what do you think about ?: 

 

flaps which cover 56% of the scale and have only two positions 15 ° and 50 ° (Nothing to do with the gradual deflection of LaGG3 in BoS ?) 

 

The wing is equipped with internal slots. Only series 22,34,35 and 66 receive automatic slat ( have you see it in BOS ? only on the 109 isn't ?.

 

The train is hydraulic folding inwards. It is only on the series 35 and 66 that the rear wheel is retractable and partially Series 28.

 

(H.Leonard Soviet Aircraft - Red Star - VVS Fighters)

[LLv34_Flanker]

S!

 

 Any info found is welcome, of course!

[Tab]

 

Hi every body

 

found this info about lagg-3 what do you think about ?: 

 

flaps which cover 56% of the scale and have only two positions 15 ° and 50 ° (Nothing to do with the gradual deflection of LaGG3 in BoS ?) 

 

The wing is equipped with internal slots. Only series 22,34,35 and 66 receive automatic slat ( have you see it in BOS ? only on the 109 isn't ?.

 

The train is hydraulic folding inwards. It is only on the series 35 and 66 that the rear wheel is retractable and partially Series 28.

 

(H.Leonard Soviet Aircraft - Red Star - VVS Fighters)

 

 

that's true, because we have 35th series in BoS, which had the gradual adjustion in steps of 3° and max deflection of 60°

 

In russian: http://pro-samolet.ru/samolety-sssr-ww2/istrebiteli/60-istrebitel-lagg-3?start=1

The earlier (or later?) versions might have had the 2 fixed positions. Does the book says anything about production series or year?

[LukeFF]

 

 

that's true, because we have 35th series in BoS, which had the gradual adjustion in steps of 3° and max deflection of 60°

 

It's the Series 29 being modeled. 

[LLv34_Flanker]

S!

 

 Found a tidbit about Soviet plane speeds measured by themselves. Enjoy.