Patriot XL--Are Retracts worth it?
02-11-2005, 03:16 AM
#1
Patriot XL--Are Retracts worth it?
Just like the subject line says, are retracts worthwhile in the Patriot XL? I suppose drag is reduced, but unless gear doors are used, is anything really gained? Retracts certainly add weight not to mention complexity, expense, and decrease durability. I'm certain its not worth it in 40 sized craft, but I'm not sure about 60 sized. Perhaps fixed gear with lightweight and thin wheels is actually a better choice. How would pylon racing wheels work in this application, are there any in the correct size? Would they even hold up to this use and what would the ground handling be like?
02-11-2005, 09:29 AM
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RE: Patriot XL--Are Retracts worth it?
Hi, welcome!
If you wish to save a few $$ and skip the retracts on the Patriot XL, there is no problem with that. It will fly just like any other sport plane, and it will perform well.
However, if you wish for the aircraft to be as fast as possible, you have to reduce drag and frontal area on the aircraft.
Retracts are almost always worth it, if the wing loading is not too far off. Weight is much more easily over come than drag.
The drag from wheels and struts is enormous, and far greater than the remaining wheel well in the wing. Even using "streamlined" or low profile struts and wheels, there is a bunch of drag. There is also a pitching moment created by the landing gear that has to be accomodated. Gear wells are in boundary layer most of the time. Sure they are turbulent, but the disturbance is only over a small section of lower surface wing area. If you want that extra 5 mph, then doors help - and then only if you have the thrust/hp to get you there.
You wouldn't imagine that a round 5/32 piece of wire is a lot of drag. I won't go into the theory here, but it is a great deal of drag. Pylon wheels are actually are actually pretty draggy. They are not airfoils. They are low frontal area and very light weight, thats about all that is gained. They are somewhat useless on soft fields, they absorb zero energy on landing, and have high rolling friction due to the tiny contact surface area and the weight beared. Those are not issues for pylon planes. But they are issues for a 6-7 lb sport plane. So I would not recommend them.
Weight wise, when you add up fixed gear mounting structure, steel wire strut weights, hardware, wheels, etc, you will be amazed. The retracts tend to add no more than 4-6 oz to an aircraft... including the extra servo. On a bigger plane, this is barely noticed. Yes, on something smaller, it is a significan part of the total weight, so it has to be accomodated properly.
Properly selected, and properly installed retractable gear is as durable (and in my experience sometimes MORE durable) as fixed wire strut/block installations. Loads tend to be distributed well by the gear mounting plates. I prefer good air retracts myself. Spring Air, B&D, in the past Rhom. There are a number of good mechanical gear systems out there too. The 'inexpensive' mechanical gear offered by Hobbico are ok, but keep in mind, as with anything else, you tend to get what you pay for.
I had someone write me about this recently, noting that the "pattern guys" stopped using retracts in lue of streamlined gear. Well, true reatracts are sorta out of favor. Reason being 1) the planes are too big for light weight retracts - very long struts with the big planes/big props - weight/structure and durability issues - big carbon fiber fixed gear, fuselage mounted rather than wing mounted, was simply easier 2) Pattern now relys on drag to help slow the planes down - as oppose to 1980 where speed = energy = vertical performance.
Anyway........ that was a bit longer than I intended !
Built the patriot XL. Its a nice ship either way. If you go fixed gear, just put regular wheels on it. Ask around here a bit.
Bob
If you wish to save a few $$ and skip the retracts on the Patriot XL, there is no problem with that. It will fly just like any other sport plane, and it will perform well.
However, if you wish for the aircraft to be as fast as possible, you have to reduce drag and frontal area on the aircraft.
Retracts are almost always worth it, if the wing loading is not too far off. Weight is much more easily over come than drag.
The drag from wheels and struts is enormous, and far greater than the remaining wheel well in the wing. Even using "streamlined" or low profile struts and wheels, there is a bunch of drag. There is also a pitching moment created by the landing gear that has to be accomodated. Gear wells are in boundary layer most of the time. Sure they are turbulent, but the disturbance is only over a small section of lower surface wing area. If you want that extra 5 mph, then doors help - and then only if you have the thrust/hp to get you there.
You wouldn't imagine that a round 5/32 piece of wire is a lot of drag. I won't go into the theory here, but it is a great deal of drag. Pylon wheels are actually are actually pretty draggy. They are not airfoils. They are low frontal area and very light weight, thats about all that is gained. They are somewhat useless on soft fields, they absorb zero energy on landing, and have high rolling friction due to the tiny contact surface area and the weight beared. Those are not issues for pylon planes. But they are issues for a 6-7 lb sport plane. So I would not recommend them.
Weight wise, when you add up fixed gear mounting structure, steel wire strut weights, hardware, wheels, etc, you will be amazed. The retracts tend to add no more than 4-6 oz to an aircraft... including the extra servo. On a bigger plane, this is barely noticed. Yes, on something smaller, it is a significan part of the total weight, so it has to be accomodated properly.
Properly selected, and properly installed retractable gear is as durable (and in my experience sometimes MORE durable) as fixed wire strut/block installations. Loads tend to be distributed well by the gear mounting plates. I prefer good air retracts myself. Spring Air, B&D, in the past Rhom. There are a number of good mechanical gear systems out there too. The 'inexpensive' mechanical gear offered by Hobbico are ok, but keep in mind, as with anything else, you tend to get what you pay for.
I had someone write me about this recently, noting that the "pattern guys" stopped using retracts in lue of streamlined gear. Well, true reatracts are sorta out of favor. Reason being 1) the planes are too big for light weight retracts - very long struts with the big planes/big props - weight/structure and durability issues - big carbon fiber fixed gear, fuselage mounted rather than wing mounted, was simply easier 2) Pattern now relys on drag to help slow the planes down - as oppose to 1980 where speed = energy = vertical performance.
Anyway........ that was a bit longer than I intended !
Built the patriot XL. Its a nice ship either way. If you go fixed gear, just put regular wheels on it. Ask around here a bit.
Bob
02-11-2005, 09:34 AM
#3
RE: Patriot XL--Are Retracts worth it?
Think about this, Your flying around and everything is going fine and for whatever reason, your engine quits. Now lets say your a good pilot and don't get to bent out of shape over it. You instantly realize you are not going to make it back to the runway and will have to ditch somewhere.
Propjets have a high wing loading and don't glide very well and need a bit of speed on landing. You put that thing down anywhere but the runway with the gear down (retracts or not) and the chances of you ripping it all out and taking the bottom of the wing with it are very good.
Leaving the gear retracted will greatly reduce any damage to the plane, maybe just dirt or ripped monokote. Thats my main reason for using them, the second is struts look stupid.
Coomonly , most pilots think the gear is going to protect the fuselage from damage when landing out in north 40. Once in a while you may get away with it. but more often than not, the gear is about 20 feet behind the plane. Its a major fix.
Propjets have a high wing loading and don't glide very well and need a bit of speed on landing. You put that thing down anywhere but the runway with the gear down (retracts or not) and the chances of you ripping it all out and taking the bottom of the wing with it are very good.
Leaving the gear retracted will greatly reduce any damage to the plane, maybe just dirt or ripped monokote. Thats my main reason for using them, the second is struts look stupid.
Coomonly , most pilots think the gear is going to protect the fuselage from damage when landing out in north 40. Once in a while you may get away with it. but more often than not, the gear is about 20 feet behind the plane. Its a major fix.
02-11-2005, 09:50 AM
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RE: Patriot XL--Are Retracts worth it?
ORIGINAL: Snoop Doggy Bag
Leaving the gear retracted will greatly reduce any damage to the plane, maybe just dirt or ripped monokote. Thats my main reason for using them, the second is it really looks stupid.
Leaving the gear retracted will greatly reduce any damage to the plane, maybe just dirt or ripped monokote. Thats my main reason for using them, the second is it really looks stupid.
I ran my P-51 out of fuel one day last season.... brought the plane around, got it lined up, put the gear down just before the end of the runway with the plane about 3 feet up. They locked down about 6" before touchdown. Some guy came up and stated something along the lines that it looks cool to put the gear down just at touchdown. I told him it wasnt a cool thing. You always keep the gear up until you are 100% you are sure you are going to make the field. Less drag for the glide, and the last thing you need are the twigs hanging down if you come up short in the weeds.
Oddly enough, my very first retract installation was in an old Curare. It had fixed gear. I tore the gear from the wings coming up short on a dead stick. Damage from the blocks being pulled out was a big hole in the foam wing... looked like about 3/4 of a wheel well. A friend talked me into installing a set of Rhom air gear. Took less time to do that installation than it would have been to fix and reinforce the damaged installation, and I never had an issue with the gear after that.
