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22 May 2025, 00:35 [ UTC - 5; DST ]


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 16:53 
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It would just look faster and better with the wheels up. No practicality implied
Imagine a fixed gear Spitfire ? :roll:


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 16:54 
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Username Protected wrote:
It has to be more than 5 knots going from fixed to retract. I went from a 180HP Cherokee to a 180HP Arrow, and my cruise speed is 15 knots faster.


A bit apples and oranges. Look carefully at the design of the fixed gear on the Cherokee compared to the fixed gear of the SR22/SR20. There's a big difference in the aerodynamics between the two.

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:08 
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Username Protected wrote:
The gear is also quite important in a landing under parachute. There have been very few significant injuries from chute landings, but one of the significant ones was from a guy who landed in water where the gear had no shock absorber function.
Given the choice, I think I'd rather land on the Bonanza gear.


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:10 
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Username Protected wrote:
The gear is also quite important in a landing under parachute. There have been very few significant injuries from chute landings, but one of the significant ones was from a guy who landed in water where the gear had no shock absorber function.
Given the choice, I think I'd rather land on the Bonanza gear.

Vertically?
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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:18 
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Username Protected wrote:
Given the choice, I think I'd rather land on the Bonanza gear.

Vertically?
Well, at the same rate of descent. Don't you think it's pretty robust? I'm basing my opinion on anecdotal accounts of rough landings.

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:26 
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Chad,

The shock struts on a Bo offer a few inches of travel before they bottom out and your spine takes the rest. A springy gear, IMO, would be much more forgiving when dropped in. My experience above in the Cirrus was surprising to say the least.

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:27 
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Biggest thing I've learned from this thread is that a fixed gear design may allow a more efficient wing than otherwise possible. In that setting the usual fg vs rg comparisons really don't hold.


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 17:36 
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Username Protected wrote:
Biggest thing I've learned from this thread is that a fixed gear design may allow a more efficient wing than otherwise possible. In that setting the usual fg vs rg comparisons really don't hold.


I don't believe that's entirely an accurate statement. Comparing efficiency of wings is more about comparing airfoil designs, wing taper, flap design, wing loading, etc. The Cirrus has an efficient wing primarily due to it's laminar airfoil and high lift flaps.

The impact of a retractable gear on wing design is simply designing the wing root to be deep enough to allow for the gear. This is not that difficult to do and not a huge determining factor on wing efficiency. The bigger impact is as it relates to fuel volume since the retracts take up a considerable space that could otherwise be used to store fuel. Weight, cost and complexity are the bigger factors.

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 18:38 
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Curiously lancair came to the same conclusion about gear. So did cessna with the NGP project. Whatever the reason it must be compelling to have three separate teams reach the same solution to a problem that had previously uniformly been solved with RG.


The Columbia/Corvalis was originally lofted to accommodate an RG mechanism with the main gear folding much like they do on the Lancair IV planes into the fuselage. The metallic structure that mounted the gear legs could be easily changed (design-wise, not retrofit!) to have the legs pivot. There were loose plans to make 200 and 300 HP versions as well RG and turbo. Fixed gear, 300 HP was chosen first to beat the Cirrus SR-20 in performance while keeping everything as simple as possible. Of course the company struggles precluded developing the other versions after the turbo... and modern sales figures for all piston singles show an extreme bias towards the higher HP versions if there is a choice, so IMO releasing a 200 HP variant would have been a losing proposition.

I agree with the assessment that the juice just isn't worth the squeeze for this class of plane, and that the speed difference would be in the neighborhood of 5 knots at equivalent weight when considering well-faired fixed gear. I also agree that fixed gear looks silly on a high performance plane, but it is what it is! :D I'm happy with the my relatively simple retractable gear in my Mooney.

Don C's post right above me is excellent too.


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 18:42 
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I like the "whine and clunk" sound my gear makes when it swings in and out.

Perhaps Cirrus could just include another audio file in the aural features of its aircraft that mimics the "whine and clunk" when the pilot pushes a button just after takeoff and just before landing.

Prolly would cost no more than a pair of high-quality assless chaps and not induce any drag or limit fuel capacity. ;)

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 18:44 
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Username Protected wrote:
The impact of a retractable gear on wing design is simply designing the wing root to be deep enough to allow for the gear. This is not that difficult to do and not a huge determining factor on wing efficiency. The bigger impact is as it relates to fuel volume since the retracts take up a considerable space that could otherwise be used to store fuel. Weight, cost and complexity are the bigger factors.


I'll add a couple more points to the impact of RG design, especially in relation to composite airframes and especially wings. If the gear folds into the wing cavity AND the pivot points/mounting structure is in the wing as well, then the very high and discrete loads from the gear mounting have to be accommodated in the wing spars and this becomes a substantial issue with composite structure. Composites generally suck at handling fastener bearing loads when compared to metallic materials. To absorb the gear loads in the shear web of a wing spar, for example, you would have to add a lot of extra thickness to the shear web that otherwise isn't needed for wing loads, or spread the load over a large area with lots of fasteners, or a combination of both. This contributes to the weight gain with RG, and often the design space for doing this is fairly small inside the wing.

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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 18:55 
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The retract adds a lot of cost...

Tim


Tru dat.

I've just had my gear motor rebuilt and the mechanic has told me my transmission is leaking, prolly needs a rebuild. :doh: :bang:






(Maybe it's a good thing I didn't buy the $34k factory reman, I'd really be done...)


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 19:07 
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All things being equal, I wonder how much less insurance would be on a fixed gear.


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 19:09 
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Username Protected wrote:
I'll add a couple more points to the impact of RG design, especially in relation to composite airframes and especially wings. If the gear folds into the wing cavity AND the pivot points/mounting structure is in the wing as well, then the very high and discrete loads from the gear mounting have to be accommodated in the wing spars and this becomes a substantial issue with composite structure. Composites generally suck at handling fastener bearing loads when compared to metallic materials. To absorb the gear loads in the shear web of a wing spar, for example, you would have to add a lot of extra thickness to the shear web that otherwise isn't needed for wing loads, or spread the load over a large area with lots of fasteners, or a combination of both. This contributes to the weight gain with RG, and often the design space for doing this is fairly small inside the wing.

Premier 1?

Lot's of composite RG aircraft out there besides Cirrus.


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 Post subject: Re: Retractable Gear Cirrus
PostPosted: 09 Jan 2014, 19:25 
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Jason,

The Premier I is composite fuse and metal wing....

BTW, Scott didn't say it couldn't be done with composites, he just pointed out it comes with a weight penalty.

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