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  #61  
Old 04-27-2006, 12:26 PM
ShaleDC ShaleDC is offline
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If you are serious about the performance advantages of retracts on our aircraft, use the data from the Velocity. According to their data, retracts improve cruise speed by 15kts / 8.99% and range by 111 mn / 12.32%.

There's no denying that retracts on high speed aircraft significantly improve cruise and range performance. If you don't like them for other reasons, that's a PERFECTLY VALID decision, but here's the data:

Cruise Speed @ 75% power:[/
Velocity SE w/IO-320 FIXED GEAR: 155 ktas
Velocity SE w/IO-320 RETRACTS: 170 ktas (9.68% faster)

Velocity SE w/IO-360 FIXED GEAR: 172 ktas
Velocity SE w/IO-360 RETRACTS: 187 ktas (8.72% faster)

Velocity XL w/IO-540 FIXED GEAR: 175 ktas
Velocity XL w/IO-540 RETRACTS: 190 ktas (8.57% faster)

Range @ 65% power:[/

Velocity SE w/IO-320 FIXED GEAR: 1160 nm
Velocity SE w/IO-320 RETRACTS: 1240 nm (6.90% greater range)

Velocity SE w/IO-360 FIXED GEAR: 930 nm
Velocity SE w/IO-360 RETRACTS: 1000 nm (7.53 % greater range)

Velocity XL w/IO-540 FIXED GEAR: 816 nm
Velocity XL w/IO-540 RETRACTS: 1000 mn (22.55% greater range)
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  #62  
Old 04-27-2006, 12:54 PM
rutanfan rutanfan is offline
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Quote:
Originally Posted by Richard Riley
In the specific case of the Infinity gear, very few people understand

How many hours it takes to install, including debugging
How little speed there is to gain
What the flights risks are - both of retracts in general, and this one in particular
That there is very little if any roll over danger with the original fixed gear (Pazmany notwithstanding)
Historically, JD takes years to deliver.
How JD has behaved toward other members of the homebuilt community - specifically Bing Forbing and Shirl Dicky.
Richard.

You’ve personally given me a lot of good advice, so I take your opinion to heart. The Cozygirlzzz have already mentioned this, but I’ll say it for my sake as well. You’re conclusions regarding retracts, and specifically the Infinity, are presented in black and white. There are quite frankly pros & cons with both. Your suggestion that a “properly” faired gear yields a 99.5% advantage is hard to swallow. I think the accurate term would be “perfectly faired.” It reminds me of a joke that my professor told in my arrow dynamics class, where engineers & scientists were commissioned to improve a racehorse’s speed. I forget the majority of solutions, but the physicist’s solution was to make the horse spherical. My point being that the tire, sticking out of the gear, is far from perfect. Not to mention the down pitching moment created by a tire 36" from CL versus a 3" transponder antenna… or the holes drilled to cool the brakes. My field is at 5,000 ft and I routinely fly into Salt Lake Intl. Try riding those brakes for a quarter mile after a 110 deg density alt. landing. There’s also gear spread and shimmy problems with the stock fixed gear, or reduced FOD with a wider stance. (All of which are easily fixed, yet still worth considering.)

There’s also the fact that the two most outspoken individuals against retracts both have them. It reminds me of all those “Don’t Do Drugs” public service announcements by rocks stars in the 80’s.

Finally, it is easily discernable, from both your and Lynn’s posts, that you both abhor J.D. Certainly you’re at liberty to dislike anyone of your choosing. But on this subject, your opinions come across as a vendetta rather than objective opinion… Just my two cents.
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  #63  
Old 04-27-2006, 01:07 PM
Ben Ben is offline
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Note to any newcomer to this website:

"Infinity gear" refers to a specific brand of retractable gear, not to the fact that this gear discussion goes on into infinity.
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  #64  
Old 04-27-2006, 01:11 PM
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Also of note on the transformation of the long - i think the standard gear legs are not well faired - doesn't Klaus (considered by many as a speed king) sell gear leg fairings for the long?
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  #65  
Old 04-27-2006, 02:43 PM
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Quote:
Originally Posted by Dust
Also of note on the transformation of the long - i think the standard gear legs are not well faired
True. It does look like Bill made an effort though. See the image here:
http://ourworld.compuserve.com/homep...s/stormlak.htm

-dave
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  #66  
Old 04-27-2006, 02:59 PM
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Great pic of the old hangar in the background.

wheel to leg looks good, no it looks great - leg still looks too stubby front to back to have been faired to perfection

Been thinkin bout this - i do have a dog in this race - i have fixed gear and am probably justifying my decision, to one degree or another.
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  #67  
Old 04-27-2006, 09:01 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Richard Riley
And I keep saying it's a 5 to 7 mph gain.
And with respect to Bill Theeringer's aircraft, with the claim of 19-23 mph difference, it's fairly obvious from looking at the pics at:

http://ourworld.compuserve.com/homep...s/otherpho.htm

That he didn't have pressure recovery wheel pants and didn't have gear leg fairings, which, for the relatively narrow L.E. gear legs, makes a HUGE difference in drag.

19-23 mph is NOT the difference between optimal wheel pants, optimal gear leg fairings, and retracted gear.
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  #68  
Old 04-27-2006, 09:48 PM
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Quote:
Originally Posted by Marc Zeitlin
19-23 mph is NOT the difference between optimal wheel pants, optimal gear leg fairings, and retracted gear.
Absolutely and completely true. I agree 100%. Bill took an average (aerodynamically) plane and did the conversion, which is why I found it so interesting.

[nomex]
Bill's plane looks a lot like the majority of EZs I've seen, which makes the speed and GPH rate comparisons much more realistic in terms of the existing fleet of aircraft (what I'd call the 75th percentile, Canardians are pretty careful as a rule), as opposed to holding up a few folks who have done amazing work on their planes (the 95th to 99th %ile).
[/nomex]

Yes, someone who is willing to go to very high levels of aerodynamic optimization will get the same or more out of a FG plane as Bill did with his RG conversion, no question. Klaus is a shining example of this and his Vari is a wonder. It does make RG look more attractive to builders who know they can't or won't be attaining that level of craftsmanship and slippery-ness WRT the cooling and the optimization of the FG parts though, and I think that's a big reason why it keeps coming up.

-dave
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  #69  
Old 04-27-2006, 09:51 PM
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Quote:
Originally Posted by Richard Riley
Maybe something involving the high drag coefficient of unfaired small diameter cylinders? Or maybe intersection drag of multiple structures joining at an acute angle? I'm just asking here....
If you mean the 2M amateur radio antenna on the winglet, I doubt that would account for all of it. Yes, it'll add drag, but not 20mph worth.

-dave
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  #70  
Old 04-27-2006, 09:53 PM
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MarbleTurtle MarbleTurtle is offline
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Also keep in mind that the retracts vs. fixed aircraft listed for comparison do NOT completely close the wheel wells with the retracted gear. Big half moon open cutouts on the underside of the wing are not exactly good for smooth airflow...
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  #71  
Old 04-27-2006, 10:14 PM
Ben Ben is offline
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Quote:
Originally Posted by Richard Riley
Klaus has contributed a lot with his pre-molded leg fairings.
All other things equal, what kind of gain would one expect from the fairings alone?
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  #72  
Old 04-27-2006, 10:51 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by Richard Riley
Maybe something involving the high drag coefficient of unfaired small diameter cylinders? Or maybe intersection drag of multiple structures joining at an acute angle? I'm just asking here....
Crap - didn't see those antennae :-). You're right - that's got to be 3-5 mph easy right there, if not more.
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  #73  
Old 04-27-2006, 10:57 PM
eracer113 eracer113 is offline
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Richard
I have question for you. Are there any FG 540 Berkuts and if there is, what kind of airspeed are they seeing. That would be a very good indication of the differences , be it small or large. I am still looking for an answer and maybe Mark could chine in on this. Does the drag difference between FG and RG widen as airspeed increases, say above 225 kts, or does the differential stay about the same. I have a hard time beleiving that well faired FG would still show only 5 to 7 MPH slower over RG at say 250 kts.

Jack
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  #74  
Old 04-27-2006, 11:33 PM
Marc Zeitlin Marc Zeitlin is offline
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Quote:
Originally Posted by eracer113
Does the drag difference between FG and RG widen as airspeed increases....
Yes. Don't think about "drag" - that's a force that's proportional to the drag coefficient and the velocity squared (as well as a few other things, like the density of the air and the area of the thing being measured).

Think about the drag coefficient. The power required to go a certain speed is proportional to the drag coefficient and the velocity CUBED (since power is force x velocity) to a close approximation, especially at higher speeds and low AOA's, so the induced drag is very low.

If you assume that power is constant, than the relationship between velocity and drag coefficient is one of the inverse cube root - this means that with everything else (like power and area) held constant, a decrease in the drag coefficient of a factor of "X" will give you a factor of "X^(1/3)" increase in speed. The faster you go, the faster the FACTOR will get you. If you decrease your drag coefficient by a factor of 2, you'll get 2^1/3 = 1.26 times your previous speed - if you were going 100 mph, this would be 26 mph - if you were going 200 mph, it would be 52 mph.

This is all rough, but gives you a basic idea of what's going on.

Quote:
Originally Posted by eracer113
I have a hard time beleiving that well faired FG would still show only 5 to 7 MPH slower over RG at say 250 kts.
Well, since 250 is 25% faster than 200, if the RG was 7 kts faster at 200 kts, then it would be ~9 kts faster at 250 kts. About.

This is why 100 mph planes don't spend a lot of time and effort reducing drag :-).
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  #75  
Old 04-28-2006, 12:32 AM
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So basically what you are saying is.... that I need a jet engine that pushes me to 300kts so people will then stop telling me it is stupid to put retracts on a Long? Ignoring the obvious issue of flutter.
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