RE: [RCSE] porpoising solutions???
My experience has been that most FF models (this includes R/C sailplanes) are designed with too much decalage. I think the theory is: "better safe than sorry" - you can survive too much - not so too little. Or, maybe: "if a little is good, more is better." Flying stabs eliminates the problem. Regis -Original Message- From: Scobie Puchtler or Sarah Felstiner [mailto:[EMAIL PROTECTED]] Sent: Friday, February 16, 2001 5:52 PM To: Dave Seay; RCSE Subject: RE: [RCSE] porpoising solutions??? Dave writes: > I just took a close look at my LB2 and it looks like I definitely > have some > 'up' where I mounted the tail. Actually you do have to have SOME 'up', as you call it. That 'up' that you see IS the decalage angle. And SOME decalage is a fundamental requirement of ANY conventional glider, in fact that is the most basic purpose of having the horizontal tailplane: to keep the wing from diving (also can be thought of as: to keep the wing at some useful angle of attack). On all but the most carefully designed flying wing foils, a foil (your wing) producing lift also produces positive pitching moment, meaning the leading edge of the foil wants to go DOWN. Release any conventional glider without its horiz. stab attached and you will see this effect IMMEDIATELY,(don't actually try this, just trust me). A stab mounted at a NEUTRAL angle will give some very temporary relief to this problem, but until that stab is ACTIVELY holding the rear of the fuselage down by having it's trailing edge higher than its leading edge relative to the airflow, your glider is gonna dive bigtime. If it's mounted with too MUCH angle (Stab t.e. high) then your glider is going to constantly repeat one mild stall after another (porpoising).The trick is to have the RIGHT amount of this angle. Too much and you porpoise, Too little and you dive. Either problem can be crudely corrected by shoving weight all over the place and trimming the elevator like mad, but these are fundamentally bad solutions because they add, well, weight and drag, not to mention their effect on maneuverability. > How do you correct this w/o destroying the tail given the whole thing is > balsa? I guess I could try to cut the tail off. I am not familiar with the exact construction details of the LB2, but it MIGHT be helpful, depending on how it's put together, to remember that you can change the angle of the tailplane OR the angle of the wing. Is the wing mounted in such a way as to be shim-able in it's mount? If so, shim the rear of the wing up a bit and test (this will have the same effect as bringing the t.e. of the stab down. Remember, it's the relative angle BETWEEN these two surfaces that counts). Shimming the wing is actually a great way to experiment, if it is doable on your plane, because it's much more changeable than rebuilding your tail six times to get things just right. Good luck. Scobie in Seattle > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] porpoising solutions???
Just a couple things to check Dave . You shouldn't have to run noseheavy , I don't have an Xterminator but it's been my experience that recommended CG's are usually at least a touch on the conservative side . Something else is most likely wrong as you suspect . I would return to the recommended CG and look elsewhere for corrections . Is there anything loose in the fuse ? , more specifically is the battery secure ? Usually more often a power plane problem ( huge empty fuse for batteries to roll around in ) . But I had to ask . Variable CG make you chase the plane around the sky rather erratically stall/dive , stall/dive ... - usually can't be trimmed at any speed , changes every time the plane changes attitude . Loose servo mounts ? Control rod/cable bind ? Servo centering problem ? Bottom line - does the elevator/vtail surfaces return(center) to the exact same place when moved up full throw compared to down full throw . Don't rule out poor servo percision without first checking . That one will drive you nuts . If it looked OK mechanically then look to alignment .Can you trim it to fly level at a slow speed but it slowly porpoises at any faster speed (launch speed or dive) . Check your decalage - the relative alignment (incidence) of the wing and stab/vtail . If you notice your elevators are flying with some down trim at cruise speed then try to spacer up the trailing edge of the wing . 1/16" at a time until the elevator(s) cruise at level ( minimum drag ) . If this was (part of) the problem you should notice a wider speed range for a given trim setting now , and a longer glide . It's usually trainer type planes that are designed with extra positive incidence - that makes the plane sort of auto-recover from a dive . Then there's the dive test ... well it should be made stable before that ... Hope that made sense , Wayne RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] porpoising solutions???
Dave Seay wrote: > > I just took a close look at my LB2 and it looks like I definitely have some > 'up' where I mounted the tail. > > How do you correct this w/o destroying the tail given the whole thing is > balsa? I guess I could try to cut the tail off. Given that I've warped 'em before unintentionally, it is easy bend solid covered Balsa do by shrinking the covering more on one side than the other. Probably not the optimal solution, but I thought I'd toss it out there. P.S. Yes it is possible to get a C shape warp flat again *blush* -- Andrew E. Mileski RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] porpoising solutions???
I just took a close look at my LB2 and it looks like I definitely have some 'up' where I mounted the tail. How do you correct this w/o destroying the tail given the whole thing is balsa? I guess I could try to cut the tail off. Dave - Original Message - From: "Dan Borer" <[EMAIL PROTECTED]> To: "Dave Seay" <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]> Sent: Friday, February 16, 2001 4:44 PM Subject: Re: [RCSE] porpoising solutions??? > I'm no rocket scientist, but correcting the decalage on my > Gnome fixed it for me. > > Dan > > - Original Message - > From: "Dave Seay" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Friday, February 16, 2001 11:39 AM > Subject: Re: [RCSE] porpoising solutions??? > > > > I would like to hear the comments on this as well. > > I've got an Xterm parked on the runway waiting for the > wind to calm down but > > I noticed the same thing with my LB2. > > > > I initially had the LB2 balanced right dead on and it did > the roller coaster > > too. At first I added weight and it go it under control > but I did not like > > the increase in weight. I removed the weight and trimmed > in a little down > > and after doing this several times, I got a happy medium. > I have a little > > extra weight and a little down trim and I like the way it > handles. > > > > Dave > > - Original Message - > > From: "Daniel Boyer" <[EMAIL PROTECTED]> > > To: <[EMAIL PROTECTED]> > > Sent: Friday, February 16, 2001 2:20 PM > > Subject: [RCSE] porpoising solutions??? > > > > > > > I took my new Xterminator out for a test flight > yesterday evening (I found > > a > > > field with well packed snow that I could walk on)... > First off I have to > > > say that it floats like a dandelion (and this was in > VERY still air which > > > was giving me air times of ~12 seconds with my 11.5oz > Zagi THL)... The > > > first throw, it glided out nicely but started trying to > porpoise... I > > > brought it back to me and checked the CG... It was in > the dead center of > > the > > > recommended CG. I added pushed the battery pack to the > very front of the > > > nose (moving the CG forward about 1/8") and gave it > another toss... it > > still > > > porpoised so I brought it back and added a couple of > coins to the nose > > > (bringing the CG about 1/4" ahead of the recommended > CG)... gave it > > another > > > toss and it flew fine (although wasn't as responsive as > before. > > > > > > I added the weight to the front to correct the > porpoising, because in the > > > past when my planes have done this, everyone at the > field said to just add > > > nose weight. I always end up with my CG's in front of > the recommended > > CG's > > > because of the porpoising, but then I read about people > flying with cg's > > > behind the recommend placement. This has made me wonder > if moving the CG > > > forward is truly the correct correction for the > porpoising. Is there > > > another correction for this porpoising tendency other > than CG movement? > > > > > > Thanks, Daniel > > > > > > BTW: I only got to toss the Xterminator about 5 times > b/c on the 5th time > > I > > > decided to give the launch preset a try, so I switched > to the model memory > > > that I thought I had programmed with the latest launch > preset setup... > > Gave > > > it a toss, saw the plane starting to loop backwards so I > switch the preset > > > switch back in the opposite direction to which it > responded by doing a > > nose > > > dive (despite giving it full up elevator... I could see > that the elevator > > > was still showing down, so this was not a stall...) it > hit the ground and > > > cracked the fuse in numerous places (I have since fixed > it w/ about and > > hour > > > of work)... I assessed the damage and determined that it > wasn't anything > > > major, then I tried to figure out what happened... I > checked my mixing and > > > quickly realized that I had chosen the wrong model > memory and that the > > > switch had been having no effect, but instead my > throttle stick was in > > > control (I was apparently hitting the throttle stick in > my paniced state > > > causing the down elevator input). ie: ALWAYS DOUBLE > CHECK YOUR MODEL > > MEMORY > > > SELECTION!!! ;-) I'm going to try to give it another > try this weekend if > > > the snow holds off. > > > > > > RCSE-List facilities provided by Model Airplane News. > Send "subscribe" > > and "unsubscribe" requests to [EMAIL PROTECTED] > > > > > > > RCSE-List facilities provided by Model Airplane News. > Send "subscribe" and "unsubscribe" requests to > [EMAIL PROTECTED] > > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] porpoising solutions???
I'm no rocket scientist, but correcting the decalage on my Gnome fixed it for me. Dan - Original Message - From: "Dave Seay" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, February 16, 2001 11:39 AM Subject: Re: [RCSE] porpoising solutions??? > I would like to hear the comments on this as well. > I've got an Xterm parked on the runway waiting for the wind to calm down but > I noticed the same thing with my LB2. > > I initially had the LB2 balanced right dead on and it did the roller coaster > too. At first I added weight and it go it under control but I did not like > the increase in weight. I removed the weight and trimmed in a little down > and after doing this several times, I got a happy medium. I have a little > extra weight and a little down trim and I like the way it handles. > > Dave > - Original Message - > From: "Daniel Boyer" <[EMAIL PROTECTED]> > To: <[EMAIL PROTECTED]> > Sent: Friday, February 16, 2001 2:20 PM > Subject: [RCSE] porpoising solutions??? > > > > I took my new Xterminator out for a test flight yesterday evening (I found > a > > field with well packed snow that I could walk on)... First off I have to > > say that it floats like a dandelion (and this was in VERY still air which > > was giving me air times of ~12 seconds with my 11.5oz Zagi THL)... The > > first throw, it glided out nicely but started trying to porpoise... I > > brought it back to me and checked the CG... It was in the dead center of > the > > recommended CG. I added pushed the battery pack to the very front of the > > nose (moving the CG forward about 1/8") and gave it another toss... it > still > > porpoised so I brought it back and added a couple of coins to the nose > > (bringing the CG about 1/4" ahead of the recommended CG)... gave it > another > > toss and it flew fine (although wasn't as responsive as before. > > > > I added the weight to the front to correct the porpoising, because in the > > past when my planes have done this, everyone at the field said to just add > > nose weight. I always end up with my CG's in front of the recommended > CG's > > because of the porpoising, but then I read about people flying with cg's > > behind the recommend placement. This has made me wonder if moving the CG > > forward is truly the correct correction for the porpoising. Is there > > another correction for this porpoising tendency other than CG movement? > > > > Thanks, Daniel > > > > BTW: I only got to toss the Xterminator about 5 times b/c on the 5th time > I > > decided to give the launch preset a try, so I switched to the model memory > > that I thought I had programmed with the latest launch preset setup... > Gave > > it a toss, saw the plane starting to loop backwards so I switch the preset > > switch back in the opposite direction to which it responded by doing a > nose > > dive (despite giving it full up elevator... I could see that the elevator > > was still showing down, so this was not a stall...) it hit the ground and > > cracked the fuse in numerous places (I have since fixed it w/ about and > hour > > of work)... I assessed the damage and determined that it wasn't anything > > major, then I tried to figure out what happened... I checked my mixing and > > quickly realized that I had chosen the wrong model memory and that the > > switch had been having no effect, but instead my throttle stick was in > > control (I was apparently hitting the throttle stick in my paniced state > > causing the down elevator input). ie: ALWAYS DOUBLE CHECK YOUR MODEL > MEMORY > > SELECTION!!! ;-) I'm going to try to give it another try this weekend if > > the snow holds off. > > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" > and "unsubscribe" requests to [EMAIL PROTECTED] > > > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
Re: [RCSE] porpoising solutions???
I would like to hear the comments on this as well. I've got an Xterm parked on the runway waiting for the wind to calm down but I noticed the same thing with my LB2. I initially had the LB2 balanced right dead on and it did the roller coaster too. At first I added weight and it go it under control but I did not like the increase in weight. I removed the weight and trimmed in a little down and after doing this several times, I got a happy medium. I have a little extra weight and a little down trim and I like the way it handles. Dave - Original Message - From: "Daniel Boyer" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]> Sent: Friday, February 16, 2001 2:20 PM Subject: [RCSE] porpoising solutions??? > I took my new Xterminator out for a test flight yesterday evening (I found a > field with well packed snow that I could walk on)... First off I have to > say that it floats like a dandelion (and this was in VERY still air which > was giving me air times of ~12 seconds with my 11.5oz Zagi THL)... The > first throw, it glided out nicely but started trying to porpoise... I > brought it back to me and checked the CG... It was in the dead center of the > recommended CG. I added pushed the battery pack to the very front of the > nose (moving the CG forward about 1/8") and gave it another toss... it still > porpoised so I brought it back and added a couple of coins to the nose > (bringing the CG about 1/4" ahead of the recommended CG)... gave it another > toss and it flew fine (although wasn't as responsive as before. > > I added the weight to the front to correct the porpoising, because in the > past when my planes have done this, everyone at the field said to just add > nose weight. I always end up with my CG's in front of the recommended CG's > because of the porpoising, but then I read about people flying with cg's > behind the recommend placement. This has made me wonder if moving the CG > forward is truly the correct correction for the porpoising. Is there > another correction for this porpoising tendency other than CG movement? > > Thanks, Daniel > > BTW: I only got to toss the Xterminator about 5 times b/c on the 5th time I > decided to give the launch preset a try, so I switched to the model memory > that I thought I had programmed with the latest launch preset setup... Gave > it a toss, saw the plane starting to loop backwards so I switch the preset > switch back in the opposite direction to which it responded by doing a nose > dive (despite giving it full up elevator... I could see that the elevator > was still showing down, so this was not a stall...) it hit the ground and > cracked the fuse in numerous places (I have since fixed it w/ about and hour > of work)... I assessed the damage and determined that it wasn't anything > major, then I tried to figure out what happened... I checked my mixing and > quickly realized that I had chosen the wrong model memory and that the > switch had been having no effect, but instead my throttle stick was in > control (I was apparently hitting the throttle stick in my paniced state > causing the down elevator input). ie: ALWAYS DOUBLE CHECK YOUR MODEL MEMORY > SELECTION!!! ;-) I'm going to try to give it another try this weekend if > the snow holds off. > > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED] > RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
[RCSE] porpoising solutions???
I took my new Xterminator out for a test flight yesterday evening (I found a field with well packed snow that I could walk on)... First off I have to say that it floats like a dandelion (and this was in VERY still air which was giving me air times of ~12 seconds with my 11.5oz Zagi THL)... The first throw, it glided out nicely but started trying to porpoise... I brought it back to me and checked the CG... It was in the dead center of the recommended CG. I added pushed the battery pack to the very front of the nose (moving the CG forward about 1/8") and gave it another toss... it still porpoised so I brought it back and added a couple of coins to the nose (bringing the CG about 1/4" ahead of the recommended CG)... gave it another toss and it flew fine (although wasn't as responsive as before. I added the weight to the front to correct the porpoising, because in the past when my planes have done this, everyone at the field said to just add nose weight. I always end up with my CG's in front of the recommended CG's because of the porpoising, but then I read about people flying with cg's behind the recommend placement. This has made me wonder if moving the CG forward is truly the correct correction for the porpoising. Is there another correction for this porpoising tendency other than CG movement? Thanks, Daniel BTW: I only got to toss the Xterminator about 5 times b/c on the 5th time I decided to give the launch preset a try, so I switched to the model memory that I thought I had programmed with the latest launch preset setup... Gave it a toss, saw the plane starting to loop backwards so I switch the preset switch back in the opposite direction to which it responded by doing a nose dive (despite giving it full up elevator... I could see that the elevator was still showing down, so this was not a stall...) it hit the ground and cracked the fuse in numerous places (I have since fixed it w/ about and hour of work)... I assessed the damage and determined that it wasn't anything major, then I tried to figure out what happened... I checked my mixing and quickly realized that I had chosen the wrong model memory and that the switch had been having no effect, but instead my throttle stick was in control (I was apparently hitting the throttle stick in my paniced state causing the down elevator input). ie: ALWAYS DOUBLE CHECK YOUR MODEL MEMORY SELECTION!!! ;-) I'm going to try to give it another try this weekend if the snow holds off. RCSE-List facilities provided by Model Airplane News. Send "subscribe" and "unsubscribe" requests to [EMAIL PROTECTED]
