RE: Hobby King 2.4 speckturn orange rx
[size=2]Many people using them here in Thailand with no problems.[/size] JIM
Posted on: 1/19/2011 3:10 PM by Author "Foxman" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=10274654

RE: Positive incidence
[size=3]When you put some packing under the leading or trailing edge what you are actually doing is changing the angle of the fuselage and stab. At a given speed and weight the wing will fly at the same angle whatever you do with the packing on the body. What you have changed is the angle that the body flies at. Adding weight to the nose to stop the nose up tendencies is probably the wrong thing to do. The elevator has to have more "up' dialled in which tends to make it climb even more as the speed or power is increased. Fly it inverted and see how much down you have to push in. Should only be a little bit. Get help with that. Getting the cg in the correct place is the only place it should be. Your other problems are due to it being designed as a trainer and should not be regarded as problems if you are a beginner. Find a good teacher, not a show off who wants to demonstrate "his" flying abilities with your model. Just because you fly good doesn't mean you teach good. Jim Fox
Posted on: 1/19/2011 3:02 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10274633

RE: Kit carwax mold release
I think the proper mold release wax is just carnuba the same. If you can save money that's good. The first coat is what does 90% of the wax impregnation, doing 6 doesn't add that much but if it works? I have used 1 coat and it worked ok. The secret is what goes onto the wax and how long it takes to go off. Jim
Posted on: 1/1/2011 8:14 AM by Author "Foxman" in the forum "Composites Fabrication And Repair"
http://www.rcuniverse.com/forum/fb.asp?m=10231601

RE: Laminate Thickness
I usually use 1 layer of 48 grm amd then 1 layer 200 grm. I don't use gel coat but just spray the paint into the mold and lay up on that. Saves weight. About 5 thin coats dusted on. Here in Thailand they make a paint that dries very quickly which is the secret to easy release. What really stiffens it up is a few lightweight bulkheads strategically placed for wing mounts, tail fixings etc. Better to use a few bulkheads than make the whole thing heavy. You can always use an extra layer of 200 around structural mounting point areas. Wings have to be a glass/foam/glass composite done with a vacuum. Then joined with the spars in place. Jim
Posted on: 1/1/2011 8:09 AM by Author "Foxman" in the forum "Composites Fabrication And Repair"
http://www.rcuniverse.com/forum/fb.asp?m=10231595

RE: Dihedral/anhedral effect on lift?
It is an interesting subject but why do you care about the dihedral when it's on a scale model. Surely you are making it as scale as possible so the dihedral has to be replicated exactly whatever it is. Apparently the Corsair had a very good fuselage to wing joint due to the anhedral and the circular fuselage so the angle was quite large, more than 90 degrees giving it lower drag than a conventional set up. Hope that makes sense? Jim
Posted on: 11/4/2010 7:52 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10115845

RE: my plane is ballooning
As High Plains says, a lot of the problem is a CG that is too far forwards. You are flying with some "up trim" in to compensate for the nose heavy airplane. As you open the throttle or fly faster the "up trim" becomes more effective and you climb. Every airplane exhibits this to some extent. My turbine Hawk climbed during high speed passes and moving the cg back cured it. I also had to give it a little more down trim to compensate for the CG move Your model is a trainer and is designed like this to get you out of trouble if you lose it. Cg is the biggest factor in this problem. I have had flat bottomed winged airframes that had no zoom climb. Changing the wing incidence actually means you are changing the body angle as the wing always flies at the same angle for any given weight and speed.
Posted on: 10/29/2010 9:24 PM by Author "Foxman" in the forum "Beginners"
http://www.rcuniverse.com/forum/fb.asp?m=10103379

RE: Extra 300S 60 Size balance
I can never remember which makes of radio are + and which are - to get expo the right way. A servos natural action gives an exponential movement of the surface the wrong way, i:e it moves it more around the centre and less at the end of it's travel. Adjusting in about 20% expo the correct way makes it linear. Jim
Posted on: 10/28/2010 8:01 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10100945

RE: Extra 300S 60 Size balance
Determining the CG is very easy if the model is already flyable. Fly along and roll to inverted. Keep it level with the use of elevator. Get a friend to check the stick position if you can't tell. If you have to push a small amount of forward stick in to hold level flight then the cg is correct. Having to hold lots in means it's nose heavy. Having to hold none or very little means it's a bit marginal and should be moved forwards a bit. Small amounts at any one time. When you have this sorted you can then adjust the throws so that you can use full "up elevator" without it snap rolling. This is important. If you want to do snap rolls then fly on low rate for normal flight and high rate for your snap rolls About 20% expo will give a linear effect to the control feeling. The above advice applies to every aircraft I have ever flown but I haven't flown every aircraft.
Posted on: 10/26/2010 7:56 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10096363

RE: Nose pitch
If you bank an aeroplane you lose vertical lift so you need to use a balanced amount of elevator to hold a steady non diving turn. All aircraft need this to some extent. Has anyone with experience flown this model and commented on it.? Maybe you should ask someone else to fly it? Not knocking your flying abilities but it sounds normal to me. Jim
Posted on: 10/26/2010 7:40 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10096330

RE: Horizontel stab dihedral
Actually one very good reason the engines are underneath the wing on pylons is in case the engine falls off then it drops away from the wing. Engines have been known to seize up and shear off. The mountings are designed to do this. Jim
Posted on: 10/25/2010 7:44 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10093971

RE: Horizontel stab dihedral
Tall Paul, your answer confuses me. You say the C141, C5 has Anhedral because the engines are underneath???? Have you looked at any airliner nowadays? They all hang underneath. They usually have Dihedral so that part of your reply does not make sense. Then you say about the Harrier being "English" so it has Anhedral to make the wing tip U/C shorter, hhmmm Do you maybe think that having four jet nozzles that rotate may just have something to do with it having a high wing design so the Anhedral is to compensate for that? The way you write "English" makes out that we "English"do quirky things so who really knows why it's been done like that. You guys bought the Harrier design so it can't be too bad.
Posted on: 10/24/2010 7:24 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10091366

RE: Horizontel stab dihedral
I was pointing out that not all aircraft have Dihedral. All aircraft would prefer to have a midwing design but for many reasons it's not always possible. Passengers and cargo need to go somewhere. Undercarriage length etc etc. I used to fly a lot of pattern models and adjusting the dihedral on a low wing model was critical to stop it from rolling on the rudder. Too much dihedral and it would roll with the rudder, too little and it would roll against it. Cutting the wing in two and adjusting it was vital. A high winged aircraft with Anhedral is just an inverted low wing with Dihedral, and visa versa, if that makes sense? Mid wing aircraft as a rule don't have any or very little. Ask any pattern guy about Dihedral (or Anhedral on a high wing) and you will get a different answer to the average modeller who never uses it except for take off. Most modellers have no idea what the rudder is supposed to do. I thought this thread was about tailplane dihedral, sorry got off the subject
Posted on: 10/24/2010 8:02 AM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10090088

RE: Horizontel stab dihedral
My friend worked on the BAE Hawk which has Anhedral on the tailplane or stab. He told me it stops the buffet from the wings hitting all of the tail at the same time. There is always some of the tailplane in clean air. Dihedral on a tail would have the same effect. Someone commented earlier that with Dihedral on the wings the aircraft is self righting. So what about all the aircraft with Anhedral on the wings? Galaxy, Starlifter, Harrier . Having Anhedral does not mean they will roll over if left alone. These are not Free Flight models. One function of Dihedral or Anhedral is that it controls the rudder induced roll. Get it right and the aircraft only yaws on rudder. Jim
Posted on: 10/23/2010 6:34 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10089114

RE: 156
Have you thought about using a medium strength vertical web spar and utilizing the wing skins for the strength? I make composite wings and the spar is used as a spacer for the skins which take nearly all the loads. A lightweight I shaped spar which has carbon at the top and bottom with vertical grain balsa between. Saves a lot of weight. Only my 2 cents worth or Thai bahts worth. Jim
Posted on: 10/20/2010 6:58 AM by Author "Foxman" in the forum "Composites Fabrication And Repair"
http://www.rcuniverse.com/forum/fb.asp?m=10080547

RE: kf Airfoil questions
My model club is awash in models with this KF section, they mostly seem to fly ok so what can I say. I doubt competing aerobatic pilots would use it but for a simple electric trainer it seems to be ok. The wings are not very rigid but I have not seen any cases of flutter yet. They don't seem to glide very far either. I am not knocking it but I am intrigued as to why people use it? Is it just because it's simple to build? Jim
Posted on: 10/17/2010 11:23 AM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10074159

RE: kf Airfoil questions
Maybe it works and maybe it doesn't but it sure looks ugly. If it flies inverted then what's the point of the step? I guess it's a cheap and easy way to make a wing which is it's main advantage. What happens if there is a step top and bottom?
Posted on: 10/16/2010 8:39 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10073111

RE: Wing snapping when too much elevator given
I noticed recently a couple of full size Red Bull air racing aircraft snap roll due to too much G being used. One crashed into the water and another hit the water but got away with minor damge. It happens to us all modellers and full size. Jim
Posted on: 10/16/2010 8:34 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=10073099

RE: TF Spitfire build
Hello Roger, no I realise it is not your 6 degrees but it was your quote. There seem to be rather a lot of differing views on the actual degree angle. I am making some new molds for an 1/8th scale Spitfire. I fly electric now and that is about the biggest size I can transport on my motorbike. Trying to get it right with the flat centre section and correct dihedral makes all the difference to the look. I will be doing it as an all composite kit eventually but not in any great quantity. Lot's of ideas going through my head and emerging problems. Motor cooling is going to be one. Might use the carburetor intake and duct the air to the motor, then use the hollow wing as an outlet taking the hot air to the radiator. If I shape the inside like a venturi it will have a slight depression and the air should get sucked through. Sounds ok in theory. hhmm Could maybe let it out of the exhaust stacks, sounds easier. Hope there will be enough airflow to cool the lipo as well The spinner is 3 inches in diameter so no chance of cooling air from anywhere else, not that its ever cool here in Thailand. Everything starts at 30 degrees c.
Posted on: 10/8/2010 8:41 PM by Author "Foxman" in the forum "RC Warbirds and Warplanes"
http://www.rcuniverse.com/forum/fb.asp?m=10056717

RE: TF Spitfire build
Hi, no not trying to start an arguement. My main question was that I found a number of different degrees quoted for the dihedral but I have gone with your 6 degrees and it looks correct. Thanks. Jim
Posted on: 10/8/2010 1:13 PM by Author "Foxman" in the forum "RC Warbirds and Warplanes"
http://www.rcuniverse.com/forum/fb.asp?m=10055874

RE: Avoiding Flutter on Byron F-16
Hi, if you are worried about the stab flutter you could mass balance them. Just add a little weight into the leading edge till they balance on the pivot. They will not flutter even if the link came off. Yes do away with the rudder, it's useless. I had one and I put some mass balance weight on the leading edge of the rudder in front of the hinge point and never had any problems with flutter although it was still useless. Jim
Posted on: 10/8/2010 1:06 PM by Author "Foxman" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10055864

RE: Effect of wind speed on EDF thrust
What the last couple of posts say is correct. Imagine swimming in a river that is flowing. If you closed your eyes you wouldn't know the water was moving. This is what the model experiences in moving air. There is no difference in thrust upwind or downwind. A fan unit does not unload in flight it actually loads up slightly because the airflow increases and the fan has more work to do. Cover one intake up and the revs increase. This is because the fan has less work to do. I know this from IC Ducted fan days when I had on board tachos. Also ask Stumax if you don't believe me. It did suprise me because they do sound like they unload as they come towards you but it's the doppler effect. Think about a motorbike coming towards you and then going away. The sound changes but the speed of the bike doesn't Jim
Posted on: 10/8/2010 12:58 PM by Author "Foxman" in the forum "Electric RC Jets"
http://www.rcuniverse.com/forum/fb.asp?m=10055847

RE: Need Comp-Arf cosmetic repair technique help
Hi as Invertmast says it's a good idea to glass over the repair with lightweight glasscloth, or I think that's what he said. Many foams now seem to be cyno proof, I have a Chinese foamy thing that I thought was poystyrene but I can't sand it and it takes cyno and car body filler without any effect, probably EPP or some other foam. Comp ARF foam was always cyno proof. I worked there for a while so I have a little experience of the materials. They could have changed them of course since I was there. You can probably see the internal structure by looking down the root rib. Hope you get it fixed. Jim
Posted on: 10/8/2010 4:02 AM by Author "Foxman" in the forum "Composites Fabrication And Repair"
http://www.rcuniverse.com/forum/fb.asp?m=10055237

RE: TF Spitfire build
Ok thanks for that info on the Spitfire dihedral. I have been looking at many sources of info and couldn't get a definitive answer. I even looked at that You Tube video of the "Spitfire low pass" fantastic, as it shows a very head on shot. I understand fully that explanation of dihedral but I don't agree that it would be less maneuverable at 6 degrees. Fighters are designed to be as agile as possible with all controls as neutral as you can make them. You don't want the rudder rolling the aircraft. The same as you wouldn't want it pitching up with aileron. Dihedral controls the amount of roll the rudder induces. Too much dihedral and the aircraft rolls with the rudder, too little dihedral and the aircraft rolls against the rudder. Get it right and the aircraft yaws only with no induced roll. That is why you can roll a 3 channel rudder only model, the rudder effect reverses when it's inverted due to the "anhedral". This isn't a free flight model and a Spitfire does not need to level itself off after a gust of wind but having neutral controls makes flying any model so much better. You actually told that guy that by reducing the dihedral to 4 degrees from RJ Mitchells 6 degrees it would be more agile on the ailerons. Pity RJ didn't realise this in 1936 as he could have maybe improved it? What would happen is that it would probably roll right with left rudder and visa versa. I spent a lot of time with aerobatic models and getting the dihedral just right was part of the trimming process to get a very neutral flying model. I didn't know there were different ways to spell maneuverable, you can learn something every day. Jim
Posted on: 10/7/2010 10:10 PM by Author "Foxman" in the forum "RC Warbirds and Warplanes"
http://www.rcuniverse.com/forum/fb.asp?m=10054796

RE: Need Comp-Arf cosmetic repair technique help
Hi, you can dribble some thin cyno in the cracks and push them together. There shouldn't be an issue with the foam. It's cyno proof foam. Check though just in case. Then as you say you can mix some laminating resin and micro balloons into a fairly thick paste and push it into the damaged area. I would tape over the filler till it sets and then take off the tape and rub it down If you are going to paint it then the micro ballon mix is not good to paint onto so use a thin skim of car body filler. This is heavy but ok if you are only using a skim it gives you a good surface to rub down to. Then preferably give it a coat of primer filler 2 pack paint onto the filler, rub this down after a day or so and paint it. Try not to rub through the color that Comp ARF applied as it will become porous due to the paint being the gel coat. Obviously check the structure for any internal damage. If you have a hole then you can make a shape of plywood or balsa which is slightly larger than the hole. Place whatever shape you have made over the hole and cut around it with a scalpel. This gives a perfect fit and you can then glue this in place and fill and paint it. Hope you understand all that. Jim
Posted on: 10/7/2010 8:10 AM by Author "Foxman" in the forum "Composites Fabrication And Repair"
http://www.rcuniverse.com/forum/fb.asp?m=10053404

RE: TF Spitfire build
Why would it be less maneuverable if the dihedral is increased.? (is that how you spell maneuverable ?) Dihedral is used on most aircraft (not all) to control how much roll is induced when the rudder is used. Getting the dihedral right can eliminate that secondary roll effect. Pilots of fighters do not want the aircraft to roll when they use the rudder, it wouldn't help their aim. I would copy whatever RJ Mitchel put in there if possible. I have looked up Spitfire dihedral angles but I can't seem to get a definite answer. 4.8 degrees is quoted but that has to be on each wing to look right. 6 degrees is also mentioned. Does anyone know the exact angle that is on the leading edge of each wing. Needs to be on the centre line. Obviously the trailing edge has more because of the washout. [quote]ORIGINAL: ForcesR [quote]ORIGINAL: michel gravelle Hi Hey Roger ,................... why did you go to the 6 degree dihedral , from the 4 degree dihedral , thats in the kit . What would be the big difference in flight performance , not looks ? Michel [/quote] Good day Michel; the 6 degree dihedral will give the aircraft better lateral roll stability but there is a down side to the aircraft's manoeuverability. As the old saying goes, for everything that is gained through a change you will loose something in return. Since this is a sport flyer, I will not be doing any dog fighting anyway so the slight loss in manoeuverability is quite acceptable. As for your 530 retracts, maybe you know something I don't about the 530 series? From what I see you are in for quite a bit of modification work in the LG wing area to make them fit and work properly. The 530's are designed for conventional LG retraction, retracting the gear toward the fuselage, not outboard as is required on the Spitfire. The 605 retracts can be made to retract toward the outboard wing by switching the position of the air cylinder on the retract mechanism. From what I see the 530 retracts are not designed for the air cylinder to switch locations on the retract mechanism. Unless I am totally wrong about how the 530's retract? Roger [/quote]
Posted on: 10/6/2010 8:59 PM by Author "Foxman" in the forum "RC Warbirds and Warplanes"
http://www.rcuniverse.com/forum/fb.asp?m=10052684

RE: My plane experiences snaking
Hi Paul, I guess the other guys are favouring a gyro. I suppose for the cost and the weight it is a good idea but If it was mine I would like to find the cause anyway. Sloppy and flexible servo mount/linkages are the first thing to change. The more solid the better. How about 2 servos ? 1 either side? You could use small lightweight ones or is that too much hassle? Jim
Posted on: 8/13/2010 11:03 AM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9930728

RE: My plane experiences snaking
Hi Paul, yes I cured my problem by removing the aerodynamic tab and glueing it to the fin, but I have been wondering if I had mass balanced it with weight then I might have achieved the same result. It was just that you could tape some weight on and try it with out having to cut anything. I never tried it at the time so I don't know if that would have worked or not. I hope you cure it. Let me know if you do and how you did it. I wish I could remember the name of that model. Spinks Akromaster, maybe?? Not sure. Is that an aeroplane even, lol Jim
Posted on: 8/12/2010 9:45 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9929804

RE: My plane experiences snaking
Hi Paul, if there is a lot of slack then that could be it. I understand what you say about adding weight to a moving surface but if it is "mass balanced" it can only improve things. As an example if you lose a wing from a model then as the wing comes down it rotates. If some weight is added to the leading edge it doesn't. By adding weight to the leading edge of the rudder you are counteracting this tendency. As a test take the linkage off the rudder and quickly move the body from left to right. The weight of the rudder makes it carry on when you stop the movement but if it's "mass balanced" it doesn't want to carry on. If it is mass balanced to the point of being nose heavy then the leading edge of the rudder will want to carry on moving which has a damping effect instead of exagerating the problem. You could always just tape some weight on and try it, if it doesn't work you can take it off easily. Jim
Posted on: 8/11/2010 8:06 PM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9927271

RE: Finding CG
When you finally fly it, you can check to see if the calculations were correct by flying it inverted. If you have to push lots of forward stick then it's nose heavy. A little forward stick is a correct. If it doesn't climb or dive and still flies well then that's it's acceptable but marginal. If it climbs when inverted then it's tail heavy and will possibly have stability issues. The model will have less drag if the cg is correct and will generally fly faster as the elevator drag will be reduced. Not sure you would notice on a model but airliners can save substantial amounts of fuel by moving the cg back as far as they can. Jim
Posted on: 8/11/2010 10:59 AM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9926135

RE: My plane experiences snaking
Hi Paul, I just had a thought, is the rudder mass balanced? If it isn't then try getting enough weight into the leading edge of the tab till it is actually nose heavy. If you lay the fuselage on it's side the front of the rudder should be heavier and it will go down. This will naturally dampen out the the snaking, it may not cure it but it's an easy fix to try. If the rudder is tail heavy then as the body snakes to the left the weight of the rudder tries to carry on making the effect worse but if it is nose heavy it will do the opposite which could cancel out the snaking effect. Mail me if that isn't 100% clear, lol It's confusing to me and I wrote it, ha ha If you do add a lot of weight don't forget to check the cg of the entire model just in case you have moved it back. Not sure if the cg of the overall airframe would affect the snaking, the model should very slightly drop the nose when flown inverted but only a little bit. A customer of mine a long time ago had a large Mig 29, this had an elevator snaking effect. He found out it was because he had mounted the servos on the fibreglass body skin and they could flex. You could bend the skin by moving the stab. Some twin finned model jets like the F15 can have snaking and can benefit by putting the rudders outwards a little bit which gives them "toe in". I can't explain why this is but it seems to work. Some aircraft have a plate fixed on the rudder trailing edge. Someone mentioned this earlier in the thread but that is an easy experiment to try although I think it is to stop rudder flutter or rudder buzzing rather than snaking. Jim
Posted on: 8/11/2010 10:37 AM by Author "Foxman" in the forum "Aerodynamics"
http://www.rcuniverse.com/forum/fb.asp?m=9926084