Servos for a NES Kestral?

[Mike C]

I am building this plane, working on the fuse right now. This is my first sailplane and I was wondering if the HS-55 would be a good servo to use? I am going to install the spoiler option so I will need 3 of them and as always lightweight is king. If anyone has any other suggestions feel free to chime in.

[TThroop]

I think that the HS-55 is too small. It works fine in a HLG/DLG but a 2 meter is a little too big for my liking. I would use a HS-81 or HS-85 in the Hitec line or JR 341 or JR 331 or the Expert SL300. Expert is the economy line of servos from Horizon, who also make the JR line of servos.

Good luck,

Terry Throop :)

[Doc Data]

I used HS-81's in my 2M Kestrel.

Question... is this a recent purchase from NSP or did you get the kit second hand from someone? it makes a difference.

http://www.mustangone.com/MySailPlanes/Kestrel5.jpg

This was my first sailplane after being away for 23 years.

dd.

[Mike C]

The kit was given to me. The shipping label has a 1995 date on it. The instructions are pretty good but the pictures that go along with them are terrible. It looks like they are photocopies of photocopies! So far I have taken my time and have not had any problems that a little thought could not fix. What kind of changes have been made?

[Doc Data]

1995? Ok, I suspect you will find that you have a problem with the plans. I bought the kit new from NSP in 1999 and when I laid out the fuselage sides on the plan they did not line up. Checking ribs against the plan where the outline of the ribs run side to side, the ribs where longer then the matching drawing on the plan. However that same rib when place over the wing drawing where the ribs where oriented up and down, they fit!

I contacted Sal about this via email. He had me call and we talked more about it. He checked his stock of plans and there were all off! The master set was correct but all the copies he had made for the kits had been messed up by the company he had make them! He got them reprinted correctly and replaced mine. At that point, he told me he would replace anyone's plans that were from an old kit.

You might try to email him and reference this thread. I would hope he'll give you a replacement set of plans.

One thing to consider. If your plans are from 1995, they may be from an earlier batch and be correct. Do the tests I describe above (ribs and fuze sides). If they don't match up, get new plans.

I had heard a lot of complaints about how poorly everything fit on this kit. No one had ever told Sal the plans were off. People just grumbled and built it the best they could!

[Doc Data]

Next subject... It was recommended to me to reinforce the center area by and around the wing mounts. Seems they get a little loose after a few winch launches. 2 guys in the club had (still have, like me) this plane and they both had the same experiences.

Here are 2 images showing my fix (adapted from theirs)...
http://www.mustangone.com/images/KestralMount1.jpg
http://www.mustangone.com/images/KestralMount2.jpg
Yeah, they aint pretty but they are strong!

dd.

[rakm]

Doc:
Nice looking sailplane. I really like the color scheme, think I'll cover my GP Spirit I'm getting ready to start on the same. How's it show up in the air?

[fledge]

hey guys getting back to the servos,,,i would not use the hs 55 servos,,,they are to lite,i would use the hitec hs 81,,these are rated for up to 4 lbs and they are perfect for 2 m sailplanes,.


my experience with light servos is that ,they may not break inflight but they will strip the gears on landings if the rudder etc is nudged!!!OTOH hs 55 will do nice for the spoilers my 2 cents fledge

[Mike C]

I checkd the ribs against the plan and it looks like the actual ribs are about 1/16" shorter than the plan. They do sem to fit over the plan though. If it is only a hair shorter then it will all come out in theend won't it? If somone has a pic of the inside of the equipment bay I would like to see it. My pictures in the manual are very grainy.
As for servos, I wil get some HS-81s on the way.
Thanks again.

[Ollie]

There are better ways to save weight than to use micro servos. The place to start is in the tail. Every gram saved in the tail saves about 3 grams of lead in the nose. Here are some ideas:

1. Round the fuselage corners severely.
2. Use small plastic clevices instead of metal.
3. Sew the control horns to the elevator and rudder with thread and CA instead of metal screws and nylon nut plates.
4. Use Ultracoat lite to cover the tail.
5. Use contest balsa to build the tail.
6. Use contest balsa to sheet the back of the fuselage.
7. Sand long bevels into the trailing edges of the tail surfaces, starting at the hinge line and bring them to a maximum thickness of 1/32 inch at the trailing edge.
8. Replace the stock pushrods with 0.05 inch diameter carbon rods in teflon tube housings. See:
http://www.cstsales.com/carbon_push_rods.htm
CA the nylon clevices to the carbon rods at the tail end and put the adjustment at the servo end. Support the housing every 4 to 6 inches to prevent bowing under load.


By lightening the extremities less control deflection will be required to maneuver and drag will be reduced too. As the extremities are lightened, the plane will also signal lift more clearly. Apply items 4, 5 and 6 to the wing tip panels too.

Putting oval cut outs in the ends of ply polyhedral braces will not only save a little weight but will reduce the stress riser at the ends of the braces.

[Doc Data]

Originally posted by Mike C
I checkd the ribs against the plan and it looks like the actual ribs are about 1/16" shorter than the plan. They do sem to fit over the plan though. If it is only a hair shorter then it will all come out in theend won't it? If somone has a pic of the inside of the equipment bay I would like to see it. My pictures in the manual are very grainy.
.

Sounds like the plans are OK. The real test is the fuze sides. Lay the fuze side pieces on the plans. If they are bad, you fuze will be significantly longer than the plan area. It seems the repro company shrunk the length wise but not height wise.

Photos on the way.

dd.

[Doc Data]

More images....
http://www.mustangone.com/images/KestrelDetail1.jpg
http://www.mustangone.com/images/KestrelDetail2.jpg
http://www.mustangone.com/images/KestrelDetail3.jpg

One thing you can't see... the wing mount cross pieces where doubled in thickness.

dd.

[Mike C]

Originally posted by Ollie

Putting oval cut outs in the ends of ply polyhedral braces will not only save a little weight but will reduce the stress riser at the ends of the braces.

That went way over my head! What is a stress riser?
I didn't know that they were "that" weight sensitive, I haven't given any thought to balancing it out at the end. If this plane was built around regular servos then by using HS-81's I will be making it even more tail heavy!

DD: My fuse sides seemed to be very close to the plan specs. I guess the copies made around that time were OK.

Let the fuse sheeting begin!

[Ollie]

Mike,

A fishing pole is a good example of a structure that bends smoothly with out breaking because it has little or no stress risers. A notched stick is a good example of a structure with a stress riser. When the notched stick is bent enough, it breaks at the notch. A structure like a wing spar with a feature that causes the stiffness to change abruptly also has a stress riser. The wing spar with a dihedral brace that ends abruptly will break at the spot where the ply brace ends if put under enough load. The recommended cut outs in the ends of the ply braces cause the stiffness of the spar to change more gradually along the spar's length. The result is that the spar becomes more resilient and survives better.

Another example of a stress riser is a glue joint. Most of the glues used in model building are stronger than balsa wood. One of the differences in glues is their stiffness. CA, for example, is very stiff (brittle). Yellow carpenters glue is not as stiff. Both are stronger than the wood. The yellow carpenters glue results in structures that are more resilient and, thus more survivable.

Crinkle, crinkle little spar,
Stressed beyond the yield point far.
Up above the world so high,
Bits and pieces in the sky.

(The yield point is the place in the stress-strain characteristic of ductle materials where the material takes a permanent deformation and in brittle materials where they break without warning.)

[Kestrel]

I had a lot of trouble with HS-81's. Yes, Hitec was very good about replacing or repairing them. But, a servo failure at 1000' isn't good! Most of the trouble was with plastic gears. If you so use the 81's I would suggest metal gears. Many have told me that the 85's are a lot better servo. Again most seem to like the metal gears better. I have a set of Dymond 200 on the rudder and elev. of my Kestrel. They have been working very well and I think they center better than the 81 Hitecs did.

[Mike C]

Just when I thought that this was going to be an easy build I ran into someting that I can't figure out last night. I have the fuse built and the bottom sheeting on and the top rear sheeting on. I can't figure the canopy out. I have two questions.
1) how does this canopy attach at the rear next to the LE?
2) In step #23 of the fuse it says "Tape the two 1/8" blasa canopy sides iin place with masking tape." Where do the pieces go? In the cross secction AA I see the triangle stock on the canopy but don't see the pieces mentioned above.
Sorry to ask questions that probably have a very simple straight in front of my eyes answer.

[Kestrel]

I will try to attach a sketch. It has been awhile since I built my Kestrel. The canopy is not attached to the LE. The canopy is trimmed to fit over the wing. In the sketch, the red outline is the canopy side. the black strip is a long thin strip that is glued to the inside of the fuse. Part of it is above the side and part of it is below. (where it is glued) It forms a lip or shelf for the canpoy side to rest on. The side is put into position and then taped to hold it in place while building the canopy. Hope this helps. Duey

[Kestrel]

Don't know why the attachment didn't go

[Mike C]

Kestrel, I could not get the attachment to open. I can usually figure things out pretty easily if I think about them, but this canopy has had me puzzled all day :o Is it just held in my friction from the triangle 1/4" and the 1/8" square balsa?

[Kestrel]

Don't know why it wouldn't open. It is a bmp. Paint should do it. Anyway, there is a short wire rod that is installed into the forward part of the canopy and into a hole that is drilled down into the nose block. Is this what you are missing? I chose not to use the wire and made a hook in the fuse and on the inside of the canopy to hook a small rubber band to. Works good. Duey

[Mike C]

Well after a lot of pondering over Kestrel's last post in bed last night while waiting for my eyelids to get heavy I solved my canopy problem! Went downstairs and double checked and all I can say is "DUH"!!!!!!! When building my fuse sides I had attached the canopy sides to the fuse sides with CA! On the side view it appeared to me that this was part of the fuse and in a later step I installed the 1/16" spruce as a doubler over the joint the same way as I did the fuse joint where the front and rear meet. If a picture of the finished canopy by itself would have been included in the instruction sheet or on the plans it would have not been a problem. Of course if I would learn to READ that might help as well! The sketch of the part was clearly marked "Canopy side"
Thanks again for the help.

[Kestrel]

OH,OH, sounds like razor saw time!