Vne limit on CH 640

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MadRocketScientist

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Just saying that the Zenith folks did have flutter problems with two models of their airplanes, so they might still be very sensitive on the topic...
They also made a mess of the CriCri kits when they did them and made changes that caused flutter on those too! Killed at least one pilot. They don't like to talk about that much and pretend it never happened.
 

pictsidhe

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They also made a mess of the CriCri kits when they did them and made changes that caused flutter on those too! Killed at least one pilot. They don't like to talk about that much and pretend it never happened.
Is that related to Colomban designs not being avaialbe in the USA now?
 

MadProfessor8138

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It's my understanding that he will not sell to anyone in North America....PERIOD,DONT EVEN ASK !!!
Even though he had nothing to do with the design that killed the pilot,he was pulled into court and blamed for the incident.
He spent much time and money defending himself over an issue that someone else created by POORLY copying his design,without his permission.
Can't blame the man for having a resentment over the whole situation.

Kevin
 

pictsidhe

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This explains why I've never been able to find out why the Cri-Cri design was accused of being to blame. It wasn't...
You need to google Zenair Cricket, not Colomban Cri-cri.
 

MadProfessor8138

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That's right....they are 2 different designs.
The Cri Cri was not the plane that killed the pilot....the Zenair Cricket did.
But Mr.Colomban was pulled into court and sued over the issue that he had nothing to do with..
He spent huge amounts of time and money to clear himself of something that he had NO AFFILIATION WITH !!!
His design was copied,correction,his design was POORLY copied by Zenair without his permission and he got the short end of the stick out of the deal.
Zenair prett much walked away unscathed because of the attention on Mr.Colomban.
I can totally understand why the man will not sell to anyone in North America......would you ?

Kevin
 

Vigilant1

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I hadn't heard this story, thanks.
The account at this link (http://all-aero.com/index.php?option=com_content&view=article&id=2455:colomban-mc10--mc12--mc15-cri-cri-cricket&catid=59) indicates that M. Colomban and Zenair had a business relationship, and that Zenair's use of the design was authorized (which would be consistent with the similarity of name, Zenair's use of the designation "MC12", etc) Reportedly, Zenair's use a steel torque tube ( rather than the CriCri's aluminum one) caused the trouble. I'm sure the modification was a major issue in the trial.
 
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MadProfessor8138

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From what I remember ....from way back when....
Yes,he had a business relationship with Zenair but things started to go south after they started making changes to his design that weren't approved by him,and other issues I believe.
If my memory is correct,he walked away from Zenair but they continued on with their business plan anyways.
He was gone well before the incident happened but was pulled into court anyways.

That was a long time ago and my memory could be foggy but I believe I still have an article from the U.S. Aviator magazine laying the whole situation out.

Kevin
 

rdj

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Unlike Part 23 certificated planes, every homebuilt is unique, hence why Vne is 'subjective'. However, most kitplane manufacturers give Vc, and from FAR 23.335 you can get the minimum recommended Vd:
Normal: 1.40 * Vc
Utility: 1.50 * Vc
Aerobatic: 1.55 * Vc

These should be good numbers for a properly designed experimental (naturally, no guarantees though). With a minimum Vd, use FAR 23.1505 to establish Vne as 0.9 * Vd.

That's a good first approximation as to what you should CAREFULLY demonstrate during flight testing by actually diving your uniquely-built experimental aircraft to Vd and looking around to make sure nothing has fallen off. Vne is measured in TAS because the flutter considerations are related to the true speed of the air molecules over the surfaces.

Quick example: Vc for the Zenith 650 is 108 kts or 124mph. Multiply by 1.4 and you get 174mph. Multiply by 0.9 and Vne calculates to around 156mph. For comparison, Zenith lists 160mph as Vne for the 650 on their spec page:
http://www.zenithair.net/specs-ch650/

Note that the spec page shows that at 75% cruise at 8000 feet (about the most you can pull from a non-turbo IC engine at full throttle) you get 160mph TAS, which is right at Vne. In practice that's not a problem, because those numbers--like most experimental aircraft numbers--are "optimistic", and realistic non-firewalled non-fuel-guzzling cruise numbers aren't that high at 8000 feet. However, put a turbocharged Rotax 915 and a variable-pitch prop in a Zenith 650 and fly it up to 15000 feet, and I wouldn't be surprised at all if the wings fell off the first time you hit a bump. That's not the fault of the plane or the designer, but the fool who is trying to fly a faster and higher mission than the plane was designed for.
 

MadRocketScientist

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BJC

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The early Heintz designs were (my description) intended to be flown low and slow from farm land or open prairies, using minimum cost components such as wheelbarrow wheels and cheap VW engines. The were, by comparison to contemporary HBA, crude.

The designs may have been extrapolated too far.


BJC
 

BJC

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There goes the memory. Nice how that is the wrong Comanche in that picture.
It’s not clear to me if the NASA link is referring to the same flutter test flight as shown in the video, especially since the NASA article has a photo of a different airplane.


BJC
 

christos

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The flutter is a dynamic response problem. Flutter is a dynamic instability occurring in flight, at a speed called flutter speed.
You need an excellent aerodynamic and structural analysis background if you want to solve it. Stiffness of a wing is a wing geometry's and material's equation. So you can improve it without weight increase.
Flutter speed is an equation of weather conditions, fuel (in wings) and many others.
You need a really good boundary layer simulation to simulate it.


There is a lot of small aircraft without flutter analysis in their designs but these are fly without any problem because of these are quite stiff. Off course they make this stage of design in a sailplane's or a high-speed aircraft's case etc.
 

wsimpso1

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I wonder... was it really a steel tube, or was it a steel bar. Steel tubes are not known for their "tortional flexibilty".
Tube, bar, whatever. GJ/L is torsional stiffness, Tr/J is torsional stress. Generally, a tube is close to a solid bar on both stiffness and strength, with it mostly gaining weight when you fill in the center.
 
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