gear down speed: early vs. late skymasters

[gevmage]

Not a pilot yet, but I intend to be in a year or so. The Symaster design is interesting to me, so I've purchased a couple of Skymaster "Owner's Manuals" via ebay. I have manuals from the 1966 and 1974 models.

In comparing the two, I ran across a curious difference. Looking at the airspeed limitation charts in both books (page 4-2), the speeds line up pretty consistently, with the '74 model speeds slightly higher. There's one big difference, though, in the gear down speed. The '66 model lists:
Gear operation........160 mph
Gear Extended.........228 mph
(228 mph is also the "never exceed speed"). The '74 model says:
Maximum Speed, Landing Gear Extended....140 mph

That seems odd to me. is there some big fundamental difference between the extended landing gears of the two models that the safe operating speed with the gear down is hugely different? Or is just a change in regulations when the two models were certified, like the fact that the early turbo models were certified up to 28,000-odd feet, but the later ones were only up to 20,000?

Any thoughts?

[Mark Hislop]

I think you are confusing gear extended with gear operation.

When actually operating the gear (raising or lowering), the clam shell doors that house the main gear open up into the slip stream. They are very draggy, and a lot of load is imposed upon them. Therefore, the aircraft is limited to 160 mph when operating the gear, so as not to damage (or remove) the landing gear doors.

Once the gear is raised or lowered, the landing gear doors close back flush with the fuselage. At that point, you can fly the aircraft at any speed, up to Vne, whether the gear are up or down. The extended landing gear can easily withstand the loads imposed.

I have a 73 P 337, so I don't know for a fact that the 74 model is limited to 140 mph with the gear down. I find it hard to believe, since they are the same design. I think the 140 that you read is also probably 140 kts, since I think the last year they used "mph" was in 73. Somebody with a 74 or later 337 can elaborate.

You are also confusing the ceilings of the turbo models with the ceilings of the pressurized models. All pressurized models are turbocharged, but not all turbo models are pressurized. The turbo models can go up as high as 33,000. The P models are limited to 20,000 feet. This is due to limitations in the amount of pressurization supplied. The P models only have a 3.35" pressurization, which yields a 10,000 foot cabin at 20,000 feet. The aircraft will go higher (as a matter of fact, the single engine service ceiling is higher than 20,000 in many circumstances), but you can't do it legally.

I'm in Aurora, Il, not too terribly far from you. If you ever get up this way and want to go for a ride, let me know.

Mark

[Guy Paris]

Hi guy's, have my 77 G nornal aspirated POH in hand.

VLO (is) Max Landing Gear Operating Speed: 140 KIAS.
Do not extend or retract landing gear above this speed.

VLE (is) Max Landing Gear Extended Speed: 200 KIAS
Do not exceed this speed with landing gear extended.

guy, the old 72 driver....

[gevmage]

Originally posted by Mark Hislop
When actually operating the gear (raising or lowering), the clam shell doors that house the main gear open up into the slip stream. They are very draggy, and a lot of load is imposed upon them. Therefore, the aircraft is limited to 160 mph when operating the gear, so as not to damage (or remove) the landing gear doors.

I do understand that. I read someplace (talking about engine-out operations) the landing gear extended cuts single-engine climb by 100 fpm, but having it stuck half-extended cuts it by 240fpm. The doors being open create a lot more drag, and therefore, structural stress on the doors.

Oops--I just realized that I reversed the two entries. The '66 manual says "Maximum Speed, Landing Gear Extended.....140 mph", and the '74 says "Maximum speed/Gear Extended....228 mph". The '74 entry is consistent with what you two were saying, that the max with gear down is the same as V(NE). Perhaps in the first round of certification, flight with gear down had only been tested at low speeds, it wasn't yet certified for that, but between '65 and '73, additional testing and certification was done?

You are also confusing the ceilings of the turbo models with the ceilings of the pressurized models. ...This is due to limitations in the amount of pressurization supplied.

Oh yeah; yes I was confused about that. I didn't think of the pressure differential issue.

I'm in Aurora, Il, not too terribly far from you. If you ever get up this way and want to go for a ride, let me know.

I might just take you up on that if you're serious. Please contact me privately via:
http://www.craigsteffen.net/contact/

Thanks for the replies.

[kevin]

There is a difference in landing gear extended speed, but it has nothing to do with regulations, it is an actual structural difference. Earlier years had lower landing gear extended speeds because that saved weight for the extra structure. Starting in 1973, the basic airframe was the same for pressurized and unpressurized models, and the pressurized model needed a way to get the airplane down relatively fast in case of a cabin decompression. Cessna's solution was to make the maximum gear extended speed essentially the same as Vne (the red line, or never exceed speed). So on a '73 and later airplane, you have to slow down below 160 mph to extend (or retract) the gear, but once the gear is extended, you can push the nose over to red line (in smooth air) without exceeding design limitations (thereby getting a fast descent without excess speed buildup). You can't do this on the earlier airplanes.

Hope this helps.

Kevin

[Mitch Taylor]

I don't have the Dash one handy (maybe Oscardeuce can check his), but I don't believe there is a Vle listed for the O2. I remember looking for it, but I don't think I ever found one.

[gevmage]

Originally posted by kevin
...and the pressurized model needed a way to get the airplane down relatively fast in case of a cabin decompression. Cessna's solution was to make the maximum gear extended speed essentially the same as Vne (the red line, or never exceed speed)...
Kevin

Ah-ha! Yes, that was precisely the information I was looking for. That's interesting--they needed to have a way to add drag to lose altitude fast without overspeeding (to bleed energy, basically). Instead of adding something to do that (like a speedbrake), the gear and body were strengthened so that they could provide that function.

Learn something new every day. Thanks!

Craig Steffen

[kevin]

Mitch,

On the O-2A, my copy of the -1 shows a Vle of 139 knots. (Page 5-1, Airspeed Limitations).

Kevin

[OSCARDEUCE]

Sounds right Kevin,
I personally use 120kts as the old bird isn't a spring chicken, and I am not sure what loads were placed on her in combat., I don't know if Mitch feels this way or not, but with the old warbirds less airframe stress is better in my book!