SM 2M Viper Jet thoghts, yet again
06-07-2011, 04:44 PM
#1
SM 2M Viper Jet thoghts, yet again
Fellas,
Let me apologize up front for writing yet another SM 2M VJ post. I know there have been lots, but I have some thoughts that weren't addressed in any of them, and since Levi begged me (ok, he just asked politely), I'll share some thoughts on the plane here. The standard disclaimer of 'these are just my thoughts' applies, so anyone that is offended or bothered, I once again apologize. My intent is that you hopefully can gain something and improve your plane, not to throw spears or anything else.
Background: I received the plane in December, and first flew it in April. Since that time the jet has attended both CA jets and Dixie jet rallies and currently has 46 flight on it. A normal day at the field is 6-9 flights, so I'm on track for 100+ the first year. I made several mods before it flew, and it has required several since. I'll post pictures to describe what I'm talking about to the max extent possible, and if you have further questions, I'll do my best to answer them. This is not my first turbine model, though it's the first one I've flown a fair amount (so it's safe to say, this is my first real experience with turbines-the others were flown off of roads in-between rice paddies in Asia).
Mine is equipped with a JR 12X tx, a 1221 rx, a Jetcat P-120SX, EQ-10 and 8411's on all the primary flight control surfaces, as well as NWS.
All the early issues listed below were brought to Patty's attention from BV (whom I ordered the plane from) and Anton in a PM. Patty was going to get back to me and got busy...I never heard from Anton.
Early problems:
-The plane uses the inboard-most rib in the stabs to mount the elevator servos. On the right stab, this worked great. On the left stab, the rib was in there so crooked that I had to shave in the neighborhood of 3/16" off of one side to get the servo mount parallel to the root rib.
-It looks like someone laid a solvent rag on the painted surface of the bottom of left stab (same stab as the rib problem). See pic
-The gear mounts were substantial, but their support wasn't. I ended up bolting/hysoling in some 90 deg aluminum angle in at both the inboard and outboard ribs for the front and rear plates that the gear mounts glue to. Now the load is better transferred to the ribs themselves rather than risking tearing out the gear supports (see pic). I've had zero problems with the mounts.
-The fuel tank hardware was something that I chose to replace. It came with rubber bungs that I was worries would eventually start leaking air. Simply a matter of opinion. See pic
-When I went to dry fit the rudder I noticed one of the pin hinges was broken. I thought that I may have sideloaded it in the fitting process so I drilled it out with a piece of brass tubing that I fit around the exposed broken hinge and replaced it with a Robart. I then hysoled the rudder in place. When I was setting up the radio, I cycled the rudder left and right and noticed more movement than I thought it should have (not deflection, but side to side). I found that another (read 2 of 3) of the hinges had broken, and now the rudder was hysoled in place. MUCH swearing and cutting later, I had the rudder free, the hinges all replaced and the rudder back on with zero problems since. I recommended asking them to drill the holes, but NOT install any of the rudder hinges at the factory.
V/R
Dave Evans
Let me apologize up front for writing yet another SM 2M VJ post. I know there have been lots, but I have some thoughts that weren't addressed in any of them, and since Levi begged me (ok, he just asked politely), I'll share some thoughts on the plane here. The standard disclaimer of 'these are just my thoughts' applies, so anyone that is offended or bothered, I once again apologize. My intent is that you hopefully can gain something and improve your plane, not to throw spears or anything else.
Background: I received the plane in December, and first flew it in April. Since that time the jet has attended both CA jets and Dixie jet rallies and currently has 46 flight on it. A normal day at the field is 6-9 flights, so I'm on track for 100+ the first year. I made several mods before it flew, and it has required several since. I'll post pictures to describe what I'm talking about to the max extent possible, and if you have further questions, I'll do my best to answer them. This is not my first turbine model, though it's the first one I've flown a fair amount (so it's safe to say, this is my first real experience with turbines-the others were flown off of roads in-between rice paddies in Asia).
Mine is equipped with a JR 12X tx, a 1221 rx, a Jetcat P-120SX, EQ-10 and 8411's on all the primary flight control surfaces, as well as NWS.
All the early issues listed below were brought to Patty's attention from BV (whom I ordered the plane from) and Anton in a PM. Patty was going to get back to me and got busy...I never heard from Anton.
Early problems:
-The plane uses the inboard-most rib in the stabs to mount the elevator servos. On the right stab, this worked great. On the left stab, the rib was in there so crooked that I had to shave in the neighborhood of 3/16" off of one side to get the servo mount parallel to the root rib.
-It looks like someone laid a solvent rag on the painted surface of the bottom of left stab (same stab as the rib problem). See pic
-The gear mounts were substantial, but their support wasn't. I ended up bolting/hysoling in some 90 deg aluminum angle in at both the inboard and outboard ribs for the front and rear plates that the gear mounts glue to. Now the load is better transferred to the ribs themselves rather than risking tearing out the gear supports (see pic). I've had zero problems with the mounts.
-The fuel tank hardware was something that I chose to replace. It came with rubber bungs that I was worries would eventually start leaking air. Simply a matter of opinion. See pic
-When I went to dry fit the rudder I noticed one of the pin hinges was broken. I thought that I may have sideloaded it in the fitting process so I drilled it out with a piece of brass tubing that I fit around the exposed broken hinge and replaced it with a Robart. I then hysoled the rudder in place. When I was setting up the radio, I cycled the rudder left and right and noticed more movement than I thought it should have (not deflection, but side to side). I found that another (read 2 of 3) of the hinges had broken, and now the rudder was hysoled in place. MUCH swearing and cutting later, I had the rudder free, the hinges all replaced and the rudder back on with zero problems since. I recommended asking them to drill the holes, but NOT install any of the rudder hinges at the factory.
V/R
Dave Evans
06-07-2011, 04:58 PM
#3
RE: SM 2M Viper Jet thoghts, yet again
Here you can see the aluminum angle up under the gear mount, just to the right of the gear housing. You can see the bolt that goes through the gear mount, and the other (further to the right), that goes through the rib.
06-07-2011, 05:23 PM
#5
RE: SM 2M Viper Jet thoghts, yet again
Those are the early issues that surfaced. As I got further along with the jet, several more issues popped up:
-I have yet to come home from the field without at least one of the main gear door hinges broken. I think that the geometry was wrong on the right gear door cylinder, and it was putting too much stress on the door with the door in the open position (b/c the cylinder was not at its end of travel). I snapped several of the original white gear door hinges (VERY brittle), replaced them with Tam's HD hinges, and proceeded to snap several of these as well. I've now put in BV aluminum hinges and think my problem has passed. I'd HIGHLY recommend not ordering the plane with the gear/doors installed. I know, you're saying Dave is crazy and for $100 why wouldn't you? I'll tell you, I spent more time un-doing the hinges that were there and replacing them than I would have if I'd just installed the right hinges from the get-go. Additionally, I pulled the gear out, replaced all the gear tubing with a high quality replacement from Sin-City Jets (same stuff as Dreamworks I think) anyway, so I gained nothing by having the gear/doors installed. (see pic of the aluminum hinges on the forward portion of the doors. Aft hinges to be installed soon, I just ran out of time before taking the pic).
-I put my fuel tank vent in the belly skin just forward of the left gear door. I plug my taxi tank in there and then unplug it. The skin around the gear door is beginning to crack badly. It's occurring on both sides, but appears to be worse on the side with the tank vent being plugged/unplugged. I've since hysoled a craft stick in the belly just forward of, and parallel to the gear door line. (see pic for skin cracking)
-When I originally built the plane, I put three layers of ceramic paint inside the nozzle to protect it from the heat. It flew fine the first few times, but then began to bubble the paint. I've since made a template, laid in ceramic blanket, and then coated the blanket with aluminum tape. It still gets warm, but appears to be far less bubbled than before (see pic).
-The gear trunions have loosened greatly. I haven't had any horrible landings, though there have been a few Dukes of Hazard skidding post-landing episodes. I think it's just cheap aluminum trunions. I haven't sorted out a fix for them yet.
-I came up with clever way to strengthen the ventral fins. I drilled a hole immediately adjacent to the threaded studs through the surface that mounts to the fuse and injected hysol. That seemed to really tighten those mounting studs up and I haven't had any problems.
-The rear of the fuselage (just behind the wing) is very thin and was getting distorted from engine heat idling on the ground. To fix this, I put i a couple layers of ceramic blanket and some aluminum tape. This seems to have cured the problem.
-The bottom rear of the fuselage is VERY thin (see pic). It was cracking just from handling (again, not rough handling fellas, just normal moving a plane around). I laid in 2-3 layers of 1 oz cloth and you could play ball with it now.
-I added second control horns on all surfaces...no real need at the end of the day, just something I wanted to do.
-I have yet to come home from the field without at least one of the main gear door hinges broken. I think that the geometry was wrong on the right gear door cylinder, and it was putting too much stress on the door with the door in the open position (b/c the cylinder was not at its end of travel). I snapped several of the original white gear door hinges (VERY brittle), replaced them with Tam's HD hinges, and proceeded to snap several of these as well. I've now put in BV aluminum hinges and think my problem has passed. I'd HIGHLY recommend not ordering the plane with the gear/doors installed. I know, you're saying Dave is crazy and for $100 why wouldn't you? I'll tell you, I spent more time un-doing the hinges that were there and replacing them than I would have if I'd just installed the right hinges from the get-go. Additionally, I pulled the gear out, replaced all the gear tubing with a high quality replacement from Sin-City Jets (same stuff as Dreamworks I think) anyway, so I gained nothing by having the gear/doors installed. (see pic of the aluminum hinges on the forward portion of the doors. Aft hinges to be installed soon, I just ran out of time before taking the pic).
-I put my fuel tank vent in the belly skin just forward of the left gear door. I plug my taxi tank in there and then unplug it. The skin around the gear door is beginning to crack badly. It's occurring on both sides, but appears to be worse on the side with the tank vent being plugged/unplugged. I've since hysoled a craft stick in the belly just forward of, and parallel to the gear door line. (see pic for skin cracking)
-When I originally built the plane, I put three layers of ceramic paint inside the nozzle to protect it from the heat. It flew fine the first few times, but then began to bubble the paint. I've since made a template, laid in ceramic blanket, and then coated the blanket with aluminum tape. It still gets warm, but appears to be far less bubbled than before (see pic).
-The gear trunions have loosened greatly. I haven't had any horrible landings, though there have been a few Dukes of Hazard skidding post-landing episodes. I think it's just cheap aluminum trunions. I haven't sorted out a fix for them yet.
-I came up with clever way to strengthen the ventral fins. I drilled a hole immediately adjacent to the threaded studs through the surface that mounts to the fuse and injected hysol. That seemed to really tighten those mounting studs up and I haven't had any problems.
-The rear of the fuselage (just behind the wing) is very thin and was getting distorted from engine heat idling on the ground. To fix this, I put i a couple layers of ceramic blanket and some aluminum tape. This seems to have cured the problem.
-The bottom rear of the fuselage is VERY thin (see pic). It was cracking just from handling (again, not rough handling fellas, just normal moving a plane around). I laid in 2-3 layers of 1 oz cloth and you could play ball with it now.
-I added second control horns on all surfaces...no real need at the end of the day, just something I wanted to do.
06-07-2011, 05:25 PM
#6
RE: SM 2M Viper Jet thoghts, yet again
Here you can see the aluminum gear-door hinge. Additionally you can see the 24 oz smoke tank that sits perfectly across the fuse in between the inner gear doors. I have it mounted to a plywood plate that is then screwed into a bulkhead at the aft of the gear doors laterally across the fuse.
06-07-2011, 05:28 PM
#8
RE: SM 2M Viper Jet thoghts, yet again
The weak area of the fuse that I added a couple layers of cloth to is the area from the top of the white stripe around the bottom of the fuse. The gray area above the stripe was solid. Perhaps they just missed a layer or two in my plane?
06-07-2011, 05:36 PM
#11
RE: SM 2M Viper Jet thoghts, yet again
Just some interior layout pics. The servo extension and satellite antenna extension that seem out of place were added later when I had some extensions that stopped working. I have yet to bury them, again I just ran out of time before taking the pics...sorry.
06-07-2011, 06:12 PM
#12
RE: SM 2M Viper Jet thoghts, yet again
Ok, so now everyone is probably thinking: Dave you sound fairly upset by the build...how does it fly?
Short answer: great
Long answer: I really love the plane in the air. It has tracks straight on the ground, lift off and climbout are quite sedate (i.e. no popping into the air due to deck angle issues), and it is solid once 'on the step'.
My first few landings were awesome, and as the environment became more challenging (winds, sloped runways, etc), my landings became less consistent. Dan Avilla suggested I dial in as much crow as I could get. I tried it, and although I backed off from 'as much as I could get' (it made the ailerons feel sloppy to me in the base to final turn), I have found a true serenity with the plane. Now, with the added drag (I have my main gear doors close when the gear is up or down, so it probably has less drag than the average with the doors open) the approaches are consistent, rock solid, and I carry a bit of power to short short final...that feels much better to me. Coincidentally I tried the same thing on my Habu 32 with the exact same results. I'm a believer, at least for these two models. (see pic for deflections)
As far as speed...I haven't gotten a gun on it, but I'd guess in the 165-170 neighborhood straight and level (remember it's a 120SX). I wish it was faster (i.e. the limit of 200), but it works. I know Ali is a huge fan of the P-80 in the plane and he's got WAY WAY WAY more experience than I do, but the 120 does it for me. If the 80 and the 120 weigh the same and take up the same physical space, I'm glad to have the additional thrust for the low passes and long verticals (it'll climb out of sight, but isn't a rocketship like a Flash). I'd say the cruising speed (1/2ish throttle) seems to be 110-120 (again a total WAG).
The one thing my plane does that I do NOT like in the air is snap...and I mean a LOT. If it gets slow and I grab a handful of elevator (think trying to flop it over on its back at the end of a long vertical) the plane will execute a 360 deg snaproll with zero aileron/rudder input. It's always happened up high when I'm horsing around, but it goes through my mind each and every base to final turn. I've since, at the suggestion of my buddy Phil, mixed in a touch of up aileron when I exceed ~75% aft stick with the gear up. I haven't had a chance to try it, but I'm hopeful.
Other thoughts: I've found the recommended CG here in RCU (~12.5mm fwd of the middle of the main wing tube) to be quite nice. I have a slight up elevator deflection but inverted the plane holds a line quite well. I've increased the aileron throw rather significantly from stock. It just felt sloppy and slow on the roll before, now I'm happy (I don't have those measurements with me, but can look when I get home if anyone really is interested). I've also increased the flap throw in the landing config. Again, see pics for deflection.
My buddy Dave suggested mixing in a touch of wheel brake with full flaps so the plane begins slowing at touchdown. We've done that with good results as well.
For knife edges it needs a touch of mix, but nothing severe. A slight bit of opposite aileron and down elevator if I remember correctly.
Short answer: great
Long answer: I really love the plane in the air. It has tracks straight on the ground, lift off and climbout are quite sedate (i.e. no popping into the air due to deck angle issues), and it is solid once 'on the step'.
My first few landings were awesome, and as the environment became more challenging (winds, sloped runways, etc), my landings became less consistent. Dan Avilla suggested I dial in as much crow as I could get. I tried it, and although I backed off from 'as much as I could get' (it made the ailerons feel sloppy to me in the base to final turn), I have found a true serenity with the plane. Now, with the added drag (I have my main gear doors close when the gear is up or down, so it probably has less drag than the average with the doors open) the approaches are consistent, rock solid, and I carry a bit of power to short short final...that feels much better to me. Coincidentally I tried the same thing on my Habu 32 with the exact same results. I'm a believer, at least for these two models. (see pic for deflections)
As far as speed...I haven't gotten a gun on it, but I'd guess in the 165-170 neighborhood straight and level (remember it's a 120SX). I wish it was faster (i.e. the limit of 200), but it works. I know Ali is a huge fan of the P-80 in the plane and he's got WAY WAY WAY more experience than I do, but the 120 does it for me. If the 80 and the 120 weigh the same and take up the same physical space, I'm glad to have the additional thrust for the low passes and long verticals (it'll climb out of sight, but isn't a rocketship like a Flash). I'd say the cruising speed (1/2ish throttle) seems to be 110-120 (again a total WAG).
The one thing my plane does that I do NOT like in the air is snap...and I mean a LOT. If it gets slow and I grab a handful of elevator (think trying to flop it over on its back at the end of a long vertical) the plane will execute a 360 deg snaproll with zero aileron/rudder input. It's always happened up high when I'm horsing around, but it goes through my mind each and every base to final turn. I've since, at the suggestion of my buddy Phil, mixed in a touch of up aileron when I exceed ~75% aft stick with the gear up. I haven't had a chance to try it, but I'm hopeful.
Other thoughts: I've found the recommended CG here in RCU (~12.5mm fwd of the middle of the main wing tube) to be quite nice. I have a slight up elevator deflection but inverted the plane holds a line quite well. I've increased the aileron throw rather significantly from stock. It just felt sloppy and slow on the roll before, now I'm happy (I don't have those measurements with me, but can look when I get home if anyone really is interested). I've also increased the flap throw in the landing config. Again, see pics for deflection.
My buddy Dave suggested mixing in a touch of wheel brake with full flaps so the plane begins slowing at touchdown. We've done that with good results as well.
For knife edges it needs a touch of mix, but nothing severe. A slight bit of opposite aileron and down elevator if I remember correctly.
06-07-2011, 06:21 PM
#13
RE: SM 2M Viper Jet thoghts, yet again
Here's the bottom line guys: I love the looks of the plane as well as the way it flies; it sits on those tall gear looking majestic with the long wings and perfect winglets. I hated the build. I think for an extra few dollars here and there SM could have really improved the plane. I truly doubt the plane's durability if you plan on flying it 150 times a year.
If you're looking to take it out the field for 30 flights a year, I think you'll love it. If you're looking for it to fly day in and day out with little/no maint. on structural components, I think you'll be disappointed (yes, I know all complex pieces of machinery need constant TLC, but I'm basing my comments on the cracks, wobbly gear, wrinkled fuse, etc). Additionally, the fact that I sent Anton a PM with all of these problems and never received a response irks me. I didn't want to talk about the plane until I knew if I had an average plane or an anomaly, but I never found out.
For what it's worth, I've since ordered a Comp-Arf Ultra Flash. I've flown them and found their speed, aerobatic prowess, and durability to be amazing. I'll probably keep the VJ as a gorgeous show pony, but will use the UF as the war horse.
Again, none of this was meant to offend or upset. I want guys to make an educated decision, and then have the foresight to learn from my problems to make their planes that much better.
V/R
Dave
If you're looking to take it out the field for 30 flights a year, I think you'll love it. If you're looking for it to fly day in and day out with little/no maint. on structural components, I think you'll be disappointed (yes, I know all complex pieces of machinery need constant TLC, but I'm basing my comments on the cracks, wobbly gear, wrinkled fuse, etc). Additionally, the fact that I sent Anton a PM with all of these problems and never received a response irks me. I didn't want to talk about the plane until I knew if I had an average plane or an anomaly, but I never found out.
For what it's worth, I've since ordered a Comp-Arf Ultra Flash. I've flown them and found their speed, aerobatic prowess, and durability to be amazing. I'll probably keep the VJ as a gorgeous show pony, but will use the UF as the war horse.
Again, none of this was meant to offend or upset. I want guys to make an educated decision, and then have the foresight to learn from my problems to make their planes that much better.
V/R
Dave
06-07-2011, 06:51 PM
#14
RE: SM 2M Viper Jet thoghts, yet again
Fun cockpit pics. My daughter gave me the Barbie for the backseat, and after I'd cut her legs off, glued her in, and covered her top with masking tape...demanded her back. Sorry hunny, Barbie's on a mission!!
06-07-2011, 07:45 PM
#15
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RE: SM 2M Viper Jet thoghts, yet again
Blah, blah, blah....
The bigger questions is....when is the next Dino-burning session?
Seriously, good write up, hopefully the info saves others some pain.....
The bigger questions is....when is the next Dino-burning session?Seriously, good write up, hopefully the info saves others some pain.....
06-07-2011, 09:41 PM
#16
My Feedback: (2)
RE: SM 2M Viper Jet thoghts, yet again
+1, thanks a million! I love the Vipers looks but the "snap" she is famous for has bit me before and now I stay away!
Shaz
Shaz
ORIGINAL: InboundLZ
Blah, blah, blah.... The bigger questions is....when is the next Dino-burning session?
Seriously, good write up, hopefully the info saves others some pain.....
Blah, blah, blah....
The bigger questions is....when is the next Dino-burning session?Seriously, good write up, hopefully the info saves others some pain.....
06-07-2011, 10:23 PM
#17
RE: SM 2M Viper Jet thoghts, yet again
Legend Dave. Great info mate. Will save me heaps of hassle on the build and flying. I wish every new jet came with a detailed analysis like that.
Cheers
Levi
Cheers
Levi
06-08-2011, 02:26 AM
#19
RE: SM 2M Viper Jet thoghts, yet again
Shaz/Levi,
No worries!
I'm hoping that little bit of up aileron makes the difference with the snap. I'm afraid to put any pull on the poll during the final turn. It really only goes apes**t when I haul on it, so it'd probably be fine, but with no altitude...
Dave
No worries!
I'm hoping that little bit of up aileron makes the difference with the snap. I'm afraid to put any pull on the poll during the final turn. It really only goes apes**t when I haul on it, so it'd probably be fine, but with no altitude...
Dave
06-08-2011, 03:12 AM
#20
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RE: SM 2M Viper Jet thoghts, yet again
I so dont want these comment to come across as negative, or aggressive in anyway. So please read them in a helpful context.
The Snap..
I have found that every jet has an ideal weight. I have flown a few jets where they are just too light and floaty for the given wing area. However. I have flown many more that have been on the heavy side for the given wing. The most obvious and apparent effect of this is an increase in stall speed, and usually a more aggressive and pronounced tip stall.
I have done a fair bit of flying with the 2M Viper, and have really enjoyed each and everyone. I have found the behaviour in and around the stall to be as friendly as I could ever expect a jet of its type to be. By that I mean a semi scale jet with a swept and fairly narrow chord wing. I am sure the stall could be made even slower and even less likely to drop a wing, but I fear that to do this, some of the smooth and precise elements of the VJ's flight would be compromised. ( I have flown some jets with a wide chord and think section wing, and while they do slow down a treat, they dont have a patch on the viper when at flight speeds for smoothness and locked in feel)
I think for a softer flying jet, with a slower stall than the VJ the Boomerangs and the such fill that slot perfectly well. The VJ is an ideal stepping stone onto something larger, or more scale jets. I can think of quite a few scale jets that will bite you, far quicker/ sooner than a VJ would.
Having said all of this. I think weight is really important. From the offset I tried to push that I thought the VJ's great handling was allot to do with its wing loading.... Sometimes you just get that feeling that a jet is sweet and light, and just the right sort of weight. A good sign of this is when you can feel the difference in performance at the start and at the end of the flight. ( Full fuel, and empty)
I managed to convince most of my customers who ordered a VJ to go with the paint in mould option. My fear was that the extra weight of the paint finish would effect the way thew plane flies. Having flown a few now which have been painted, it is for sure noticeable the difference that extra weight makes. This also goes for other aspects of the build as well.
A painted plane is for sure going to need more nose weight to balance, as the majority of the painted area is behind the C of G. This also increases the chances of ending up with a tail heavy model, which of course will exaggerate the stall tendencies even more... Its all a sort of knock on effect in a way. All leading toward a model getting to a wing loading where it starts to become unfriendly.
A few weeks ago I was flying a VJ2M and really taking liberties with it on and around the stall. The only way I could get the wing to depart, anywhere near what has been reported was by massively excessive elevator inputs that would induce a high speed stall.. Other than that, I really could not see how anyone would want a softer stalling jet ( Other than a boomerang )
To be fair. I have never got to 100 flights on a VJ. I guess my most has been 50 or 60.
I cant say I have ever had a problem with a trunion. I did once crack a gear mount on one wing when I caught the edge of the runway on a dead stick approach. Even then the trunion survived. I guess that the power slide to stop landing and roll outs are putting enough side load to open up the claws. Without seeing how hard the side loads are, I guess its a toughie to know..
Gear door hinges... These are a nightmare. I had similar issues on my early VJ's. I remember breaking one on the bench just doing a gear cycle and I used too much pressure. I spoke with Skymaster about this and to be fair, the last 4 VJ2m's we have been supplied have all come with a fibreglass reinforcement on the hinges. Basically two GRP plates that sandwich the original hinge plastic and make it allot stronger.
I dont use a taxi tank often, but if I do. I try to put the nipple somewhere where its nice and solid. The underside of the VJ fuselage is a very light lay up, and I dont even like putting the fuselage down to rest on it ( I make a simple cradle) So the thought of pushing on, and tugging off a vent fitting each time that is fixed to that area, does not fill me with joy.
Looking at your photos.. Your set up is running damn hot. The Paint discolouring on the underside ( Remember heat rises so imagine how hot the top of the fuz is getting) suggests that something is not right. Our current VJ2m is P120 powered and suffers no such issues. It may be worth looking at turbine placement/ tail pipe set up to see if anything can be improved
A bit of crow ( Up aileron) With full flap will help you slow down, and will help somewhat with the wing departing. Just be aware that there is a speed where that wing will stop working, and that model will stop flying. No matter of set up will get round this. Although "Grabbing a load of elevator" will do you no favours.
The landing with pre set breaks is something that I have seen used in the states quite a bit. Just be aware that if you get it wrong and set the breaks too aggressively then there is a hell of a load on that U/C by putting all the landing loads onto a locked or held wheel.
Hope these comments are of help?
regards Al
The Snap..
I have found that every jet has an ideal weight. I have flown a few jets where they are just too light and floaty for the given wing area. However. I have flown many more that have been on the heavy side for the given wing. The most obvious and apparent effect of this is an increase in stall speed, and usually a more aggressive and pronounced tip stall.
I have done a fair bit of flying with the 2M Viper, and have really enjoyed each and everyone. I have found the behaviour in and around the stall to be as friendly as I could ever expect a jet of its type to be. By that I mean a semi scale jet with a swept and fairly narrow chord wing. I am sure the stall could be made even slower and even less likely to drop a wing, but I fear that to do this, some of the smooth and precise elements of the VJ's flight would be compromised. ( I have flown some jets with a wide chord and think section wing, and while they do slow down a treat, they dont have a patch on the viper when at flight speeds for smoothness and locked in feel)
I think for a softer flying jet, with a slower stall than the VJ the Boomerangs and the such fill that slot perfectly well. The VJ is an ideal stepping stone onto something larger, or more scale jets. I can think of quite a few scale jets that will bite you, far quicker/ sooner than a VJ would.
Having said all of this. I think weight is really important. From the offset I tried to push that I thought the VJ's great handling was allot to do with its wing loading.... Sometimes you just get that feeling that a jet is sweet and light, and just the right sort of weight. A good sign of this is when you can feel the difference in performance at the start and at the end of the flight. ( Full fuel, and empty)
I managed to convince most of my customers who ordered a VJ to go with the paint in mould option. My fear was that the extra weight of the paint finish would effect the way thew plane flies. Having flown a few now which have been painted, it is for sure noticeable the difference that extra weight makes. This also goes for other aspects of the build as well.
A painted plane is for sure going to need more nose weight to balance, as the majority of the painted area is behind the C of G. This also increases the chances of ending up with a tail heavy model, which of course will exaggerate the stall tendencies even more... Its all a sort of knock on effect in a way. All leading toward a model getting to a wing loading where it starts to become unfriendly.
A few weeks ago I was flying a VJ2M and really taking liberties with it on and around the stall. The only way I could get the wing to depart, anywhere near what has been reported was by massively excessive elevator inputs that would induce a high speed stall.. Other than that, I really could not see how anyone would want a softer stalling jet ( Other than a boomerang )
To be fair. I have never got to 100 flights on a VJ. I guess my most has been 50 or 60.
I cant say I have ever had a problem with a trunion. I did once crack a gear mount on one wing when I caught the edge of the runway on a dead stick approach. Even then the trunion survived. I guess that the power slide to stop landing and roll outs are putting enough side load to open up the claws. Without seeing how hard the side loads are, I guess its a toughie to know..
Gear door hinges... These are a nightmare. I had similar issues on my early VJ's. I remember breaking one on the bench just doing a gear cycle and I used too much pressure. I spoke with Skymaster about this and to be fair, the last 4 VJ2m's we have been supplied have all come with a fibreglass reinforcement on the hinges. Basically two GRP plates that sandwich the original hinge plastic and make it allot stronger.
I dont use a taxi tank often, but if I do. I try to put the nipple somewhere where its nice and solid. The underside of the VJ fuselage is a very light lay up, and I dont even like putting the fuselage down to rest on it ( I make a simple cradle) So the thought of pushing on, and tugging off a vent fitting each time that is fixed to that area, does not fill me with joy.
Looking at your photos.. Your set up is running damn hot. The Paint discolouring on the underside ( Remember heat rises so imagine how hot the top of the fuz is getting) suggests that something is not right. Our current VJ2m is P120 powered and suffers no such issues. It may be worth looking at turbine placement/ tail pipe set up to see if anything can be improved
A bit of crow ( Up aileron) With full flap will help you slow down, and will help somewhat with the wing departing. Just be aware that there is a speed where that wing will stop working, and that model will stop flying. No matter of set up will get round this. Although "Grabbing a load of elevator" will do you no favours.
The landing with pre set breaks is something that I have seen used in the states quite a bit. Just be aware that if you get it wrong and set the breaks too aggressively then there is a hell of a load on that U/C by putting all the landing loads onto a locked or held wheel.
Hope these comments are of help?
regards Al
06-09-2011, 11:37 PM
#22
RE: SM 2M Viper Jet thoghts, yet again
ORIGINAL: Ali
I so dont want these comment to come across as negative, or aggressive in anyway. So please read them in a helpful context.
The Snap..
I have found that every jet has an ideal weight. I have flown a few jets where they are just too light and floaty for the given wing area. However. I have flown many more that have been on the heavy side for the given wing. The most obvious and apparent effect of this is an increase in stall speed, and usually a more aggressive and pronounced tip stall.
I have done a fair bit of flying with the 2M Viper, and have really enjoyed each and everyone. I have found the behaviour in and around the stall to be as friendly as I could ever expect a jet of its type to be. By that I mean a semi scale jet with a swept and fairly narrow chord wing. I am sure the stall could be made even slower and even less likely to drop a wing, but I fear that to do this, some of the smooth and precise elements of the VJ's flight would be compromised. ( I have flown some jets with a wide chord and think section wing, and while they do slow down a treat, they dont have a patch on the viper when at flight speeds for smoothness and locked in feel)
I think for a softer flying jet, with a slower stall than the VJ the Boomerangs and the such fill that slot perfectly well. The VJ is an ideal stepping stone onto something larger, or more scale jets. I can think of quite a few scale jets that will bite you, far quicker/ sooner than a VJ would.
Having said all of this. I think weight is really important. From the offset I tried to push that I thought the VJ's great handling was allot to do with its wing loading.... Sometimes you just get that feeling that a jet is sweet and light, and just the right sort of weight. A good sign of this is when you can feel the difference in performance at the start and at the end of the flight. ( Full fuel, and empty)
I managed to convince most of my customers who ordered a VJ to go with the paint in mould option. My fear was that the extra weight of the paint finish would effect the way thew plane flies. Having flown a few now which have been painted, it is for sure noticeable the difference that extra weight makes. This also goes for other aspects of the build as well.
A painted plane is for sure going to need more nose weight to balance, as the majority of the painted area is behind the C of G. This also increases the chances of ending up with a tail heavy model, which of course will exaggerate the stall tendencies even more... Its all a sort of knock on effect in a way. All leading toward a model getting to a wing loading where it starts to become unfriendly.
A few weeks ago I was flying a VJ2M and really taking liberties with it on and around the stall. The only way I could get the wing to depart, anywhere near what has been reported was by massively excessive elevator inputs that would induce a high speed stall.. Other than that, I really could not see how anyone would want a softer stalling jet ( Other than a boomerang )
To be fair. I have never got to 100 flights on a VJ. I guess my most has been 50 or 60.
I cant say I have ever had a problem with a trunion. I did once crack a gear mount on one wing when I caught the edge of the runway on a dead stick approach. Even then the trunion survived. I guess that the power slide to stop landing and roll outs are putting enough side load to open up the claws. Without seeing how hard the side loads are, I guess its a toughie to know..
Gear door hinges... These are a nightmare. I had similar issues on my early VJ's. I remember breaking one on the bench just doing a gear cycle and I used too much pressure. I spoke with Skymaster about this and to be fair, the last 4 VJ2m's we have been supplied have all come with a fibreglass reinforcement on the hinges. Basically two GRP plates that sandwich the original hinge plastic and make it allot stronger.
I dont use a taxi tank often, but if I do. I try to put the nipple somewhere where its nice and solid. The underside of the VJ fuselage is a very light lay up, and I dont even like putting the fuselage down to rest on it ( I make a simple cradle) So the thought of pushing on, and tugging off a vent fitting each time that is fixed to that area, does not fill me with joy.
Looking at your photos.. Your set up is running damn hot. The Paint discolouring on the underside ( Remember heat rises so imagine how hot the top of the fuz is getting) suggests that something is not right. Our current VJ2m is P120 powered and suffers no such issues. It may be worth looking at turbine placement/ tail pipe set up to see if anything can be improved
A bit of crow ( Up aileron) With full flap will help you slow down, and will help somewhat with the wing departing. Just be aware that there is a speed where that wing will stop working, and that model will stop flying. No matter of set up will get round this. Although ''Grabbing a load of elevator'' will do you no favours.
The landing with pre set breaks is something that I have seen used in the states quite a bit. Just be aware that if you get it wrong and set the breaks too aggressively then there is a hell of a load on that U/C by putting all the landing loads onto a locked or held wheel.
Hope these comments are of help?
regards Al
I so dont want these comment to come across as negative, or aggressive in anyway. So please read them in a helpful context.
The Snap..
I have found that every jet has an ideal weight. I have flown a few jets where they are just too light and floaty for the given wing area. However. I have flown many more that have been on the heavy side for the given wing. The most obvious and apparent effect of this is an increase in stall speed, and usually a more aggressive and pronounced tip stall.
I have done a fair bit of flying with the 2M Viper, and have really enjoyed each and everyone. I have found the behaviour in and around the stall to be as friendly as I could ever expect a jet of its type to be. By that I mean a semi scale jet with a swept and fairly narrow chord wing. I am sure the stall could be made even slower and even less likely to drop a wing, but I fear that to do this, some of the smooth and precise elements of the VJ's flight would be compromised. ( I have flown some jets with a wide chord and think section wing, and while they do slow down a treat, they dont have a patch on the viper when at flight speeds for smoothness and locked in feel)
I think for a softer flying jet, with a slower stall than the VJ the Boomerangs and the such fill that slot perfectly well. The VJ is an ideal stepping stone onto something larger, or more scale jets. I can think of quite a few scale jets that will bite you, far quicker/ sooner than a VJ would.
Having said all of this. I think weight is really important. From the offset I tried to push that I thought the VJ's great handling was allot to do with its wing loading.... Sometimes you just get that feeling that a jet is sweet and light, and just the right sort of weight. A good sign of this is when you can feel the difference in performance at the start and at the end of the flight. ( Full fuel, and empty)
I managed to convince most of my customers who ordered a VJ to go with the paint in mould option. My fear was that the extra weight of the paint finish would effect the way thew plane flies. Having flown a few now which have been painted, it is for sure noticeable the difference that extra weight makes. This also goes for other aspects of the build as well.
A painted plane is for sure going to need more nose weight to balance, as the majority of the painted area is behind the C of G. This also increases the chances of ending up with a tail heavy model, which of course will exaggerate the stall tendencies even more... Its all a sort of knock on effect in a way. All leading toward a model getting to a wing loading where it starts to become unfriendly.
A few weeks ago I was flying a VJ2M and really taking liberties with it on and around the stall. The only way I could get the wing to depart, anywhere near what has been reported was by massively excessive elevator inputs that would induce a high speed stall.. Other than that, I really could not see how anyone would want a softer stalling jet ( Other than a boomerang )
To be fair. I have never got to 100 flights on a VJ. I guess my most has been 50 or 60.
I cant say I have ever had a problem with a trunion. I did once crack a gear mount on one wing when I caught the edge of the runway on a dead stick approach. Even then the trunion survived. I guess that the power slide to stop landing and roll outs are putting enough side load to open up the claws. Without seeing how hard the side loads are, I guess its a toughie to know..
Gear door hinges... These are a nightmare. I had similar issues on my early VJ's. I remember breaking one on the bench just doing a gear cycle and I used too much pressure. I spoke with Skymaster about this and to be fair, the last 4 VJ2m's we have been supplied have all come with a fibreglass reinforcement on the hinges. Basically two GRP plates that sandwich the original hinge plastic and make it allot stronger.
I dont use a taxi tank often, but if I do. I try to put the nipple somewhere where its nice and solid. The underside of the VJ fuselage is a very light lay up, and I dont even like putting the fuselage down to rest on it ( I make a simple cradle) So the thought of pushing on, and tugging off a vent fitting each time that is fixed to that area, does not fill me with joy.
Looking at your photos.. Your set up is running damn hot. The Paint discolouring on the underside ( Remember heat rises so imagine how hot the top of the fuz is getting) suggests that something is not right. Our current VJ2m is P120 powered and suffers no such issues. It may be worth looking at turbine placement/ tail pipe set up to see if anything can be improved
A bit of crow ( Up aileron) With full flap will help you slow down, and will help somewhat with the wing departing. Just be aware that there is a speed where that wing will stop working, and that model will stop flying. No matter of set up will get round this. Although ''Grabbing a load of elevator'' will do you no favours.
The landing with pre set breaks is something that I have seen used in the states quite a bit. Just be aware that if you get it wrong and set the breaks too aggressively then there is a hell of a load on that U/C by putting all the landing loads onto a locked or held wheel.
Hope these comments are of help?
regards Al
Kind Regards
Levi
06-10-2011, 12:50 AM
#23
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RE: SM 2M Viper Jet thoghts, yet again
Anytime.. Glad to be of help.
Your set up will go fine I am sure. We have one flying here in the Uk that us painted on the outside, all the options and powered by a P-70!! [X(]
Just booking my tickets to Kentucky jets today.. Looking forward to it.
Regards Al
Your set up will go fine I am sure. We have one flying here in the Uk that us painted on the outside, all the options and powered by a P-70!! [X(]
Just booking my tickets to Kentucky jets today.. Looking forward to it.
Regards Al
