Help Huge wing loading
 

Im building a v22 osprey that will have tilting rotors.The wing span is 65 inches chord 12 inches.Problem is transitioning from hover to forward flight with rotors at 60 degrees. The wing loading is 50 ounces per square foot. Further thought should be given to the fact that during low speed transition the rotors will impart significant down thrust. Was thinking of either a naca 23016 or a S8036. I need lots of lift and forgiving stall characteristics. Help!!!!

RE: Help Huge wing loading
 

I calculate that to come out to a 17 lb final weight on 780 sq inches of area. I hate to say it but frankly I think it's time for a redesign or some serious weight reduction mods. The S8036 is supposed to do well with heavier scale warbirds but in your case I think this is just way over the top.

RE: Help Huge wing loading
 

Ive already stretched the wing span and chord. I am building the fusealage out of carbon fibre.But there is just a lot of mechanics that are necessary. Remember that slow speed flite will be with rotors positioned like a heli so its just at transition and high speed forward flite that is at issue. I am ready to buil the mold now so a choice on wing is needed now. If you or anyone else has a better chioce please,lets hear your thoughts.

RE: Help Huge wing loading
 

I have to agree with B...

A 50 oz./sq. ft. wing loading is pretty stiff for an aircraft this size. I have no experience with Osprey-type aircraft, so can't speak to the takeoff/landing issues and how the rotors' thrust will help. But in normal flight. that's pretty hefty... in the turbine-powered jet category, and I think you're risking an expensive crash.

You can increase the lift coefficient by doing Osprey-ish things, like adding large slotted flaps, and that may be enough. (Huge camber change) Hard to be really specific without knowing the details of your design.

If you can tell us more, without giving up those things you may want to keep to yourself, it would help the analysis.

RE: Help Huge wing loading
 

It's not the slow speed flight I'm thinking off. Even the medium speed will be hairy I suspect.

There's always the Selig 1223 airfoil meant for the high lift SAE competition but I have no idea how it handles near the stall and how resistant it is to high G loads in steeper turns.

RE: Help Huge wing loading
 

Thanks for the reply. Basically it is a1/11 scale boeing vertol Osprey. Power is from a Wren 45 with 2nd stage turbine coupled to a Baileys gearbox. Turbine and support equiptment with gearbox weighs nearly 3.5 lbs. Add 32 ounces of kerosene 2 lbs it all adds up quick. I hope to keep the weight down as much as possible and dont know yet what the actual fuselage will weigh. The rotor systems weigh in at 3.5 lbs. Probably another 1 lb.for drive mechanics .The wing will have fowlerflaps but I have no clue as to what angle to use since there is a lot of prop blast that will be at a 60 degree angle from horizontal. Hopefully Ill be able to get the weight down to 14 lbs but I really dont know.Any questions Ill be happy to answer,no secrets here.

RE: Help Huge wing loading
 

Well it's certainly an ambitious project for sure. I can see how the weight is pretty much set even before you start.

A thought for you...... Since most of your weight is in the engine and drive train components it would seem to me that increasing the size of the shell a bit would not increase the weight by as much as it would up the wing area. Even a jump up to the high 70 inch to low 80 inch span would offer a big improvement in wing area if you stick with the fudged wing outline. Provided you think the power output will deal with perhaps a couple of extra pounds and with careful airframe work I would think it was possible.

Some possible avenues to lighten the weight but retain the strength. If the shells were made from light outer skins with a 1/4 inch foam core and an inner skin to simulate a honeycomb style laminate the skins could be made lighter for the same stiffness. I suspect that with care and if the foam inner cores could be heat formed before the layup then you could get away with about 1/2 to 2/3 the wieght of glass and resin that you'd need for a similarly stiff and strong shell. High stress areas could use wood or carbon fill to help spread the stresses out. Or even if you put the same weight of resin and cloth into the shells the double wall cored method would allow you to greatly reduce the inner structure neccessary to support the airframe. In effect all this would help you build in more air and less material for a lighter weight or an increase in size with minimal weight impact.

The Selig airfoil is basically already set up with "pre-deployed flaps" built in thanks to the high camber and severe trailing edge cusp. Adding flaps to that one would not really help with the lift but it would add a lot of drag. Probably not what you want. The 8036 would benifit from flaps. Fowler sounds good and at larger sizes I know it works better but at our model sizes it's hard to say what the airflow through that critical gap is really like. If the gap is "scale" it's likely it's too narrow to really blow the top of the flap. At that point you may as well just stick to simple flaps. Frankly I think you'd need a wind tunnel to design a proper fowler flap system for model sizes. Without such fine tuning I think it's doubtful that you'll get enough benifit to make up for the extra weight, not to mention complexity. If I had a choice I'd go for the reduction in weight and simplicity.

I suspect you'll also be running into much of the same problems with the drivetrain that the original Boeing team did. Vibration from drive train harmonics and all that. Best of luck with the project

RE: Help Huge wing loading
 

BMathews has given you some excellent advice. I'll throw in my opinion for what it is worth. Your plane needs to go on a diet or get bigger. There's just no way around it.

You are proposing a very expensive power plant (x2). It would be a shame to destroy them on the first flight which will almost assuredly happen if you proceed. You need to decide if you are married to the size of the plane or the powerplant. If you want to keep your present power plant it needs to get bigger. If you want to keep the size then you should try to work out some sort of an option using a glow engine. I suspect it would be difficult to find a suitable gearbox to turn those big rotors, but you could probably get one made.

Good luck, this is a very ambitious prject. How do you intend to overcome the control issues during transition?

RE: Help Huge wing loading
 

This might help your heavy wing loading http://www.efluids.com/efluids/galle...wscientist.htm or you might be building a wonderful static display model equipped with a working turbine. Hope you understand the humor.

RE: Help Huge wing loading
 

Thanks for all the advice. I seems increasing wing area is a must. Scale means nothing if it doesnt fly. I am going to leave the chord the same and stretch the span. That way I wont have to rebuild the plug. Also I am going to make the flaps larger. By the way there is only one engine mounted low in the center of the fuselage. With 7 hp and 40 lbs of thrust from the rotor blades I dont need 2. Besides I still have to tie the two together to even thrust on both sides. I love the idea of using a foam core with inner and outer skins. There will be a box structure around the engine extending up to mount the spar drive tube structure. Im trying to make everything perform more than one task. that way it cuts down on weight. Up to 60 degree, thats the transition point on the real osprey, Heli controls at the swash plate will controll the model. When enough airspeed is gained normal aircraft flite controls take over, thats the harry point. a micro switch will lock the heli controlls out.By the way no way am I going to try to put this in the air without testing it first. Thought about a boom arm mounted on the back of my pickup with spring to zero weight of arm,simialar to those used on magnifying lites, them mounting plane with a ball soket at the bottom. That way I can test speed that controlls become usefull,speed needed for lift,stall speed etc. Since I live in so. california there are large drylake beds to test at.

RE: Help Huge wing loading
 

Hmmmm. If you're not using the wing for landing and takeoffs, the heavy wing loading wouldn't be a factor if you keep the speed up and don't try to do high-G maneuvers. Of course, the speed is the main problem. The model may need a high-enough speed to make the transition impractical.

One thing to remember is that most aircraft don't need a wing as large as they do in order to fly controllably. Witness the cruise missiles with their tiny wings. You need the large wing area in order to make takeoff, landing, and slow flight have reasonable airspeeds. If you can takeoff on the rotors and then have them rotate forward at a rate that allows the airspeed to build up well, you can likely live with the high wing loading. Just remember, though, that the high wing loading brings about a high stall speed, so you'll need to be rather careful in turns. Aerobatics would be out, of course.

As far as lengthening the span, do remember that you may need to change materials for the spar or go with a thicker section. The longer span will put increased bending loads in the inner portion, and you have to allow for that. Also remeber that the pods on the wingtips add bending loads once the weight is on the wheels. A hard touchdown will put downward 'G' loads on the wings that will be amazingly high...maybe even higher than in-flight positive 'G' loads in a turn or pullup.

Interesting project!

RE: Help Huge wing loading
 

I have to blame V22 chap for this project. He has been working on it since late 80`s. He actually built one that flies and has transitioned but transition is touchy. Mine is about 25% larger with much more power. His uses twin .46 2 stokes. Obviously a very ambitious project,but that is why I`m doing it.

RE: Help Huge wing loading
 

Do some research on the controls. I believe that there are some pitching issues as the craft transitions. It is much more complicated than it appears to be. What about building a small "foamy" type aircraft with electric propulsion to flight test? You could work out the controls and to some extent the loading.

RE: Help Huge wing loading
 

interesting,Just got E-Mail from V22 chap,seems his osprey weighed in at 20lbs with a wing area of 510 sq inches !!! WOW It did fly and transition but transition was touchy. Obviously theres more to the interaction between the wing and rotor blast at angle?

RE: Help Huge wing loading
 

There's no doubt the Osprey isn't exactly well endowed in the wing area department. Fudging in more area can only help. While you're at it though watch out for the tail area. Be sure you stay large there too. Although as I remember the sketches I've seen the Osprey has a large tail area for the wing. But I wonder if that's to ensure adequite control during the critical transitions where speed is low.... ????

RE: Help Huge wing loading
 

Yes know about that. Gyroscopic pressesion off big blades. Will have gyros in pitch and roll helps a lot per V22 chap. Still you will need enough airspeed to make the tail effective to contrll pitch. The V22 uses an inverted flat bottom air foil for Horizontal Stabilizer .Thanks for the thought its a big issue you normally wouldnt consider.

RE: Help Huge wing loading
 

You might also think about coordinating flap deflection with nacelle position. I seem to remember the videos of the V-22 showing full flaps for takeoffs and landings - I'm assuming to minimize the surface area blanking issue with the nacelles in the vertical position. The Harrier also takes off with full flaps, probably to ease the transition as well.

RE: Help Huge wing loading
 

Oh, that's right. The wings stay level and only the pods rotate. Yeah, in that case a major sized flap and drooping ailerons would be a big help. But remember that the ailerons should come up to level again quicker than the flaps to avoid adverse yaw during the transition.

20 lbs and only 510 sq inches? I'll bet it was touchy. And I can only wonder at what it would be like in even high speed flight. Of course the big fans pushing air over the top of the wings would help I suppose. Sort of like a flat version of that tunnel prop plane.

RE: Help Huge wing loading
 

Right! The plan is flaperons going full width. When flaps are down roll controll comes from differential pitch on rotors. When rotors rotate past 60 degrees flaps will move from 85 degrees to about 45 degrees. At this point aileron controll should take over.Then as speed builds the rotor pods will move to full horizontal and flaps will retract fully. I think I need a computer on board to read airspeed and not allow pod rotation untill a certain airspeed the like the real one!! Wishfull thinking. I was however thinking of wiring in a reed microswitch with a a air flap at the end ,Low airspeed switch normally off. Higher airspeed switch will open and allow pod rotation. Just fearfull that complexity will reach the point that failure is emminante.

RE: Help Huge wing loading
 

To 8178 yes I did enjoy your post, I see the parrellel trying to make it fly when all good sense says it cant. It may not!!!

RE: Help Huge wing loading
 

If you can make it a soft mix changeover between rotor differential and aileron action from about 70 degrees through to about 30 degrees deployed. In playing with flaperons on a sailplane I found that 30 degrees of flap was the absolute most you could use before the ailerons started producing so much adverse yaw that they became totally ineffective. But in your case the flaps are being "blown" by the rotors so this may not apply to at least the outer wings. Either way the changeover should be a smooth transition over quite a range to smoothen the transition as airspeed comes up and the normal surfaces can take over. My angles may need some fine tuning as the closer to level the pods get the more yaw you'll have as well. In any event I suspect avoiding a sudden switch over would be a good thing.

RE: Help Huge wing loading
 

First I would like to thank all that offered advice to my inquiries. Thank You. Second there is a video on http://www.geocities.com/v22chap/vtol that shows his model in flight. Yes there are huge questions about control because at one point it is neither a plane or a heli. The only answer I see is to be sure it is flying fast enough to be a plane before quiting to be a heli. Also note that the prop/rotor blade does cover all but 1 inch off the wing(inboard) I think this is possible,not easy or assured but worth trying.
I assume the flaps will need to be flat verses a slight downward curve since they are also ailerons?

RE: Help Huge wing loading
 

Just thinking. Since I beed to get air for the turbine anyway. Getting it from the top would help with F.O.D. What would be the effect of a slot at the top of the wing to draw air thru? I would think it would create one heck of a low pressure area. Question is would it mess up the air going over the top of the wing so much that it would make the wing unpredictable(large pitch changes) I know Im reaching here but I need lift.

RE: Help Huge wing loading
 

As I understand about feeding air to turbines it's the cleanliness of the duct work as well as the cross section that leads into the mouth. It's not enough to just have a big void with an indirect opening unless that opening is cavernous. But check with the Jet boys over in their forum for comfirmation or alternatives. In the end you may need to provide a very non scale opening to properly feed your turbine.

RE: Help Huge wing loading
 

I pretty sure its not. The compressor on the turbine is a centrifugal actually from a turbocharger. While it is true that you dont want any
restrictions or pressure drops at the inlet ,size and location are not important as long as they are large enough to not restrict. I have done extensive work with turbochargers (drag racing) and we have packaged the air inlet many ways,doesnt seem to affect performance.
Of course its a major concern on supersonic aircraft since the inlet has to slow the air to subsonic speeds before the compressor section. If I am wrong on this please let me know I am always open to opinions. But will pulling air at the top off the wing create lift? Some govt plane or nasa must have tried this. Since I dont see any it is probably a no go.