Dave357

I have a question about a sky raider low wing model. My nephew who is just starting
into rc aircraft bought a sky raider kit. I was checking the model out for him after he built it and I noticed he had installed the stab a little crooked. From the main wing at the back of the main wing tip to the front tip of the stab there is a 1/4 inch difference. However the tail is square. I dont know how he managed that because the the stab is screwed on and the screws go right up to the tail. Well you would think easy fix right, just loosen the screws and straighten it out. Problem is he epoxyed the stab in as well. He asked me if it would still fly and I realized I dont know. I have never had an airplane that far off. Hopeing someone can answer that question for me...Thanks

JohnBuckner

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I DAve and welcome to first time posting at RCU. I am guessing that the airplane you are talking about is the World Models Sky Raider Mach 11 ARF, if so the likely reason for the stab to wing mismatch is that your son probably skipped the step that should always be done first before ever attaching any of the tail feathers. That is the Process of 'marring the wing to the fuselage' On many ARF's of this type that just a matter of matching the wing tips with an even measurement from the aft tip of the fuselage. easiest done with a straight pin through the tall and some string.

if the stab looks straight on the fuse to you then the wing is probalbly not perpendicular with the fuse centerline. Marrying up the wing to the fuse often is very simple and involves opening up the trailing edge bolt holes laterally a bit to straighten the wing with the fuse.

Now the Skyraider is encellent flying airplane (but no trainer for initial training) so the little bit of out of square is not going to hurt a thing if it does not offend your eye to much. This is one of two airplanes approved for the popular Club Forty pylon racing around the country and I have assembled a number of them for the fellows and myself but agine I believe its a poor first trainer although an excellent pylon racer so for that reason a would not recommend it as his first airplane.

So what is the engine going to be??

John

52larry52

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Yea, it will fly. I usually try to get all the tail feathers squared up with the wing +/- 1/16". You have have that out of spec by 3/16". It's not ideal, but it will fly and trim out. "Measure 5 times and glue once". Try to get closer next time. I once made the mistake of using 5 min epoxy, instead of 30 min epoxy, to glue in the horz. stab. on a small balsa electric plane. Well the glue took a quick set before I had the stab in the correct spot and it was also out of alignment with the wing by at least 1/4', maybe more. It flew and so will yours. The longer set time of 30 min epoxy gives you enough time to measure and be sure of the alignment before it's too late. Live and learn and get better as you go along. FLY IT!

GREG DOE

Dave, I have 5 or 6 SR Mark II in my house right now, and I've built, or rebuilt another 6 or so. The stab comes with 2 brass bushings that the machine screws go through. The screws go into blind nuts in the rudder. This pretty much makes it impossible for the stab to be miss-aligned. Although anything is possible, and it could be that it is a defective stab, but I doubt it based on my experience with this airplane. Unless your nephew managed to punch the screws through the balsa stab, I'm inclined to agree with John B. that it's more likely that it's the wing which is out of "square".
Check what you can, and if it's the wing that is out, try to correct the issue. I also agree with Larry that it probably won't make a noticeable difference to most pilots. For example when you pull into a loop, the airplane will roll one way or the other. The same would be true for a "pylon" type turn, where, when turning one direction the airplane will roll up, the other direction the airplane would tuck, or roll down. By the way I glue my stabs, and then remove the screws. I've also salvaged several stabs from crashes, by using my heat gun to soften the epoxy. However this generally destroys the fuselage, which wasn't worth saving anyway! My SR MK II"s are for the Club 40 racing event, but they are also a great fun airplane. It may be a little advanced for your nephew. You'll have to make that decision. Good luck, and let us know how it works out. Greg

Dave357

Hello John, thankjs for your reply. Its my nephews plane. I agree that Sky Raiders are good flying planes and also a good buy. Yea he managed to somehow get the tail wing a little cocked when he built it 1/4". And he also epoxyed it as well as screw to the fuselage so there is no moving it now. You hit it on the nose when you mentioned offending my eye. I spotted it right off when I looked at it. Well he learned something about measuring before gluing this time. ( I thought I had already taught him that). He probably was in a hurry to get it built. Thanks for telling me that it will still fly. I thought it would but wasnt sure if being off that much would make it tip to one side when useing the elevator or not. As for the motor its an OS 46 AX. , great little motor and makes the Sky Raider go liike a rocket. I have already taught my nephew how to fly on a high wing Sly Raider and now we are ready for him to take on the low wing. I will stand with him in case he has any problems. He will be glad to hear he is clear for take off ! Thanks Dave

Dave357

Thanks for the reply.
As I said its my nephews plane. No seriously ,it really is. I have been flying RC for more than 20 years and never had to deal wit a stabilizer being off that much because I am very meticulous about getting things like that correct. Although having my measurements correct didnt matter much the time I took off with my correctly measured 1/4 scale Chimpmunk with my ailerons reversed, lol.
I have made my share of mistakes for sure but not this one. I know from now on my nephew will always check his measurements more than once before gluing. He catches on quick and is going to make one heck of an RC pilot. That 5 min epoxy problem you mentioned happened to me also one time. I was gluing the wings together on an ARF P-40 when my 5 minute epoxy trurned into 2-3/4 minute epoxy. On something like a wing its best to use 30 minute epoxy. And I will give my nephew the thumbs to fly the plane. Thanks Dave

Dave357

Hello Greg and thanks for your reply.
I also have owned a few of the Sky Raiders myself. Still have 2 new kits to build. I understand about how the screws go through the stab into the rudder. As I said I dont know how he managed to get the tail wing off that much be he did. The main wing is perfect. The rudder is at a 45 degree with the stab , but the stab is cocked to one side 1/4 ". You can even see where the little notch for the tail wheel to go between the stab and elevator is lined up with the corner on the end of the fuselage instead of being in the center. There is a little play in that assembly before you tighten it all down . I guess there is enough play to get it crooked if you werent carefull. Although It seems like if you had it off that much it could cause a twist in the rudder. If he re kits the plane one day I will for sure do an autopsy to see what he did. I also was thinking that with the stab coocked like that it could make it roll to one side when useing the elevator. I was also wondering if it did roll badly if it could be corrected by trimming the balsa on the elevator at an angle to possibly compensate. Seems reasonable. What do you think?
Another vote to FLY IT! thanks

JohnBuckner

My Feedback: (1)

Good morning Dave and good on you for teaching your nephew. I actually have had a shot at the high wing Sky Raider and its a decent trainer. Was not sure what your involvement was with the first post but sounds like you are doing great. Often in these forums when a inappropriate airplane is to be used for a first trainer most here will point that out in the hopes of giving that individual the best shot possible as use of the wrong airplane is so often a sad mistake. Now in your case where you are closely mentoring your nephew things can be different with the use of a next step type of airplane can work. That is afer all what the low wing Mach 11 two is. its basically a next step type;

Now back to the wing back to the alignment problem, Yes my vote is to stay quite about it and even become more observant concerning that of other airplanes, I think you will be shocked at what you seen when you are looking for it It will fly just fine and he will never know it. Seeing that is however also offensive to my eye and you are correct about how a tilted stab will induce a turn in the direction of the tilt when there is no P factor or torque with the engine running. Its a very old free flighters trimming method during the period of each flight when the engine is off. Look at picture of many free flight airplanes and you often see tilted stabs done deliberately. Agine though its a very small and subtle effect only with the engines off. In your nephews case its 'no worries'.

I would like share one more technique that I have used on many airplanes over the years not only my own builds but of course many various arfs. I actually do not use the oft recommended method that I posted above or is virtually in every build manual but use something that actually works better for me and quicker, some would call it the 'bubble eye method'.

The idea is to not change the assembly order (this is important) Wing to Fuselage, Stab to Fuselage then Vertical Stab to Fuselage.

First the wing saddles are fitted and sanded so that the wing lays level in the fuselage with the fuselage blocked so it is level.

Next the wing is fitted so that is perpendicular with the fuselage and this is where the bubble eye is important. The fuselage and wing assembly is carefully stood on its nose up aginst a clear wall or garage door, The fuselage must be vertical to the eye and its important that you can get back around twelve or fifteen feet sititing directly in front. It will now be very easy to see if the wing is truly perpendicular or not and adjustment in the bolt holes are easy.

Moving on now to the Stab. Back to the work bench it will be easy to adjust the slots and see any tilting since we now have the wing as a level reference, before gluing agine we go back to the wall airplane standing on its nose with the fuselage standing vertical to your eye and you standing well back. its once agine very easy to see how to align the stab with the fuselage. Back to the table insert glue and the stab check and secure the stab if necessary on the table and level. next back to the wall in the vertical position and agine check the alignment and that its.

The last step after glue is cured of course is the vertical stab and this is done level on the table. alignment is checked standing directly from the rear and it easy to see now perhaps some tape to nudge the fin to one side or the other while glue cure and you now have a straight airplane and no measuring at all.

This method has worked very well for me over the years so just throwing it out there. What the current slang? just Sayin

John

Dave357

Good morning John and thanks for the reply,
Thanks for sharing the information. My nephew and I are planning to go tomorrow for the big flight. The weather here in Ca has been perfect for flying so hopefully tomorrow will be nice also, I will take it up the first flight and trim it out for him. It will be fun to watch him fly the Sky Raider low wing. He has done well with the high wing model. He can land it pretty well and seems pretty confident when he is flying. We didnt use the buddy cord his last 4 flights and there was no problem. Although I think I will use it on his new venture into low wings for a couple of flights. Until he figures out what I meant when I told him his low wing will not forgive mistakes like the high wing did. Im sure he will do fine. He really loves RC Planes. Good to know the hobby will carry on after we have made our last landings right? Thanks to all of you that replied to my post. I feel confident now that it will fly reasonably well. It still makes me chuckle when I think about him asking me if his low wing will fly with the stab like that and I didnt know. Poor kid , he thought uncle Dave knew everything. lol. And of coarse I will let you guys know how the big flight went.Thanks Dave

Dave357

Well the sky raider flew like a champ and the nephew did very well. Except when he tore the landing gear off on a rough landing. Its fixable. Thanks again you guys..Dave