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19 Jun 2021, 15:27 [ UTC - 5; DST ]


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 11 May 2021, 16:39 
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Username Protected wrote:
So if the untucked design is particularly draggy then 7-8 kts seems a little optimistic but not out of the realm of reason.

If there was that much drag to get rid of for 0.3 lbs of hub cap, Cessna would have done it.

Mike C.

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 11 May 2021, 17:04 
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It would be pretty easy to flight test the effectiveness of these hubcaps by any curious owner.

Pick a pleasant day where the weather, winds and temps are stable. Then perform a series of precision test flights which each cover the same range of angle of attack vs dynamic pressure, thusly:
  1. both hubcaps installed
  2. one removed
  3. both removed
  4. redo 1

Ideally aircraft should be equipped with an ADC, digital engine monitor and AoA of course.

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 11 May 2021, 20:47 
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A-B-A is all you need. Identical atmospheric conditions, you should be able to watch the performance go back and forth along with the change of hubcaps as often and as many times as you like.

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 12 May 2021, 20:53 
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A careful flight test is a lot of work if you want to see a couple of knots. >5 should be pretty clear without a lot of care - but you still need to fly under the same conditions, so A-B-A is good.

Fortunately hubcaps are easy to change up an back - can do the test in a day .

Trying to quantify say replacing the IO520s with IO550s in a baron is a BIG challenge. Very expensive, very slow to change, and unless you have two pairs of new but broken in engines you may not be doing a fair comparison. Obviously more HP -> faster, but determining how much is a very expensive proposition.


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 13 May 2021, 04:29 
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Here's an idea to reduce retracted gear drag with a device placed aft of the wheel well.

Patent write-ups are sometimes a great place to get an overview of a technology and an interesting discussion of the state of the art.

https://patentimages.storage.googleapis ... 7042A1.pdf


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 13 May 2021, 06:14 
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This patent (much earlier than the above patent application) also has an interesting discussion and specifically mentions smooth wheel covers and the perceived limitations thereof:

https://patentimages.storage.googleapis ... 410508.pdf

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 20 May 2021, 17:31 
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Peter,

Happy customer here! I have NOT done any CAFE type testing, but confirm the Rate of climb benefits. I consistently see 200-300 fpm increase for the same speed/power setting in a 421C.
Chad


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 21 May 2021, 15:41 
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Username Protected wrote:
Peter,

Happy customer here! I have NOT done any CAFE type testing, but confirm the Rate of climb benefits. I consistently see 200-300 fpm increase for the same speed/power setting in a 421C.
Chad

Clearly you're mistaken. Mike Ciholas said that kind of improvement is impossible with this mod. :lol:


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 21 May 2021, 16:01 
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I flew my 421C 1,100 hours without them and now 1,000 hours with them. There is a noticeable improvement.

I am a happy customer also.


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 28 May 2021, 11:20 
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I installed Hubcaps and Strakes on my 421. It was a HUGE improvement! See article I posted with flight data in Twin Cessna Magazine. Due to the success I also installed them in my 441. Drawback with my approach is I installed both strakes and hubcaps at same time, so it is hard to evaluate what helps most. But given that during climb the airspeed is low, angle of attack higher, I think the hubcaps were most important for climb - they made a significant difference.

Thanks Peter!

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2012 12 5 Strakes and Hubcaps on N2657N.docx


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 28 May 2021, 12:09 
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Username Protected wrote:
So if the untucked design is particularly draggy then 7-8 kts seems a little optimistic but not out of the realm of reason.

If there was that much drag to get rid of for 0.3 lbs of hub cap, Cessna would have done it.

Mike C.


I'm mostly in agreement with Mike here, but his statement reminds me of the economist who walks right past a $100 bill on the sidewalk. His buddy asks him why he didn't pick it up.

"If it were really there somebody would have picked it up already."

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 28 May 2021, 12:48 
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Its really strange Cessna would not have done this - the 421 seems to have had cruise speed as one of its design priorities.

Often mods have possible disadvantages (see the endless arguments over VGs) but lower drag hubcaps don't seem to have any downside.

Bizarre.

I'm not very familiar with Cessna twins. On Barons, I'm not aware of any mod that clearly improves cruise performance (other than larger engines of course). There is a lot of debate on winglets but no clear data that I can find


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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 28 May 2021, 13:57 
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Username Protected wrote:
Its really strange Cessna would not have done this - the 421 seems to have had cruise speed as one of its design priorities.

Often mods have possible disadvantages (see the endless arguments over VGs) but lower drag hubcaps don't seem to have any downside.


isn't it conceivable they simply underestimated the drag penalty? these planes were designed in the 1960's with a slide rule.

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 28 May 2021, 14:35 
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Joined: 01/24/10
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Location: Concord , CA (KCCR)
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Username Protected wrote:
Its really strange Cessna would not have done this - the 421 seems to have had cruise speed as one of its design priorities.

Often mods have possible disadvantages (see the endless arguments over VGs) but lower drag hubcaps don't seem to have any downside.


isn't it conceivable they simply underestimated the drag penalty? these planes were designed in the 1960's with a slide rule.




There’s no mystery, aircraft manufacturers are run by accounts not Enginers. If a product is outselling the competition 2 to 1 why improve it.

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 Post subject: Re: TWIN CESSNA WET WING SPEED MOD THAT REALLY WORKS
PostPosted: 29 May 2021, 14:21 
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Aircraft: Cessna 340A; C172
RAM has been selling 421 hubcaps for a long time. I am surprised they don’t make any performance claims, particularly since they evaluate most of their mods for performance improvements.


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