cessna retracs and drag in motion

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Brad W

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watching planes at lunch today....
cessna 337 taking off.....sparked a thought I've wondered about a fair bit.

with the cessna retracts (not just the 337) the mains sorta flap around down there with the wheels sideways to the relative wind for quite a while. Seems to me they might be making more drag right when you need it the least... down very low...than they do when down and locked
I know the nose sucks up quick, so maybe the net is better...but I wonder if it might be better to leave the wheels streamlined till just a bit higher up....
 
I have been told that the POH in relevant aircraft states the gear should be left down until obstacle clearance is achieved.

You can see in this Youtube video that the main gear is carried almost perpendicular to the airflow until the end of the gear swing. And at least on this Cardinal, the nose gear isn't a great deal faster than the mains retraction. So... Follow the POH! -Skip

 
It is common for the gear retraction/extension sequence on any aircraft to increase drag. You often have doors opening or closing, along with changes in the interference drag of the airflow over the gear bays and gear legs.

Just look at the nose gear door on a C-130, looks like a big airbrake being extended.

 
Skip Miller said:
I have been told that the POH in relevant aircraft states the gear should be left down until obstacle clearance is achieved.

You can see in this Youtube video that the main gear is carried almost perpendicular to the airflow until the end of the gear swing. And at least on this Cardinal, the nose gear isn't a great deal faster than the mains retraction. So... Follow the POH! -Skip

Click to expand...
It's even worse with the C-337 and pre-1979 C-210s, where just about the whole bottom half of the airplane disassembles and gear doors open up everywhere.
 
Makes the manual Mooney seem so elegant
 
Skip Miller said:
I have been told that the POH in relevant aircraft states the gear should be left down until obstacle clearance is achieved.
Click to expand...
yes, that's what I recall from flying them a long while ago... I've flown R172, 177RG, and R182
but what does clearance really mean? I basically remember all the instructors teaching me to bring them up after no more runway remaining for the most part.
On a very very long runway that puts you a good bit higher, but on a short runway....or for those that practice sucking them up once positive rate is established.... yeah, kinda not so much.
I'm thinking a better approach might be to hold till high enough for gliding options...such as 1,000 ft which is a oft cited number for turning back, etc...
just thinking out loud.... If I had access I think I might try to do some testing to see if it makes any notable difference
 
Tantalum said:
Makes the manual Mooney seem so elegant
Click to expand...
This! You can easily suck them up or hang them out in under 3 seconds.

As for drag, my only Cessna retract time was in a 172RG. If you pulled the power with the gear out, that plane would glide like a toolbox. Since the mains of the RG (when they're down and locked) are essentially the same a fixed gear 172 with no wheel pants, I have to think the lion share of the crappier (than fixed gear 172) glide performance was coming from the nose gear.
 
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Brad W said:
yes, that's what I recall from flying them a long while ago... I've flown R172, 177RG, and R182
but what does clearance really mean? I basically remember all the instructors teaching me to bring them up after no more runway remaining for the most part.
On a very very long runway that puts you a good bit higher, but on a short runway....or for those that practice sucking them up once positive rate is established.... yeah, kinda not so much.
I'm thinking a better approach might be to hold till high enough for gliding options...such as 1,000 ft which is a oft cited number for turning back, etc...
just thinking out loud.... If I had access I think I might try to do some testing to see if it makes any notable difference
Click to expand...
Obstacle clearance means you have passed the obstacles that you were climbing at Vx to not hit.
 
Brad W said:
but what does clearance really mean? I basically remember all the instructors teaching me to bring them up after no more runway remaining for the most part.
Click to expand...

You are combining two different factors or techniques. Obstacle clearance means you have enough altitude that you aren't going to hit the trees, powerlines, hills, etc. off the end of the runway. Depending on where you are, that may not mean a lot, or that could mean a max performance Vx climb for quite some distance.

The no more remaining runway is another technique, which would allow for you to make a dead stick landing on the pavement with the wheels down if the engine quit just after lift off. The downside to that is accepting reduced initial performance in exchange for reducing damage to the aircraft if the engine quits. That isn't that big a factor in my decision making. If performance is the question, I'll take the risk of a belly landing in the event of an engine failure.
 
MauleSkinner said:
Obstacle clearance means you have passed the obstacles that you were climbing at Vx to not hit.
Click to expand...
yeah, i know.... I meant more in a rhetorical sense.
that tree at the end of the runway is the obvious thing...but I was thinking like maybe the 'obstacle' might be the altitude required to have options.... to glide to a suitable place... or maybe to turn to make the runway
oh well.... it's elementary I suppose...only a few seconds in transit I suppose in the big scheme of things opposed to many other variables such as not hitting the airspeed or whatever it is....
 
The swing of the gear on the Navion is pretty straight up so you don't get any MORE drag in transit. What you do get, however, is that one of the mains will come up slightly before the other (this is just how the hydraulics work, more flow goes to one side until it is on the stop and then the other one gets its flow). This results in a little tail wag that you see most Navions do on takeoff as the drag is asymetrical.
 
Skip Miller said:
I have been told that the POH in relevant aircraft states the gear should be left down until obstacle clearance is achieved.
Click to expand...

This is true for the Mooney POH. It clearly states to leave the gear down and flaps at takeoff and fly Vx until the obstacle is cleared, then retract gear and flaps in that order.
 
I have a fair amount of 172RG time, and my recollection is that gear retraction only takes a few seconds to complete. On the other hand, I once forgot to raise the gear until I got to about 7000 AGL, and I wondered why it was climbing so poorly! So my guess is that delaying gear retraction is going to be a net negative.
 
Wow! At least I figured it out before the enroute phase...
 
'79 T210N is very similar to the Cardinal, although the nosewheel comes up sooner. My habit is normally to raise the gear and reduce power at around 1000 feet AGL. From below that altitude I would rather not be thinking about the landing gear if I have to land in a hurry. I too have made the mistake of leaving the gear down in the climb. It sure is a noodle scratcher when you get to around 4,000 or 5,000 feet, and then you feel like a real idiot.

 
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