K.O.

My Feedback: (16)

John
What a breathtaking picture and the video was great. Thanks for sharing. I couldn't believe the bounce off the water and you it kept flying. Good job. I flew my Nothstar today and it was a text book flight untill I landed it the second time. There was a build up of alge along the edges of the pond so I had to plow through that. Not wanting to take a chance I brought the plane back to see if there was any weeds hanging on. That being OK I headed it into the wind, full power and full up elevator till it plained, backed off the back pressure and it took off straight and narrow. After airborn I throttled back to get use to it. I had a minor aileron trim and that was it. I was anxious to land so I made a good approach set it down like I knew what I was doing. The second landing I let it smack and put 2 holes in the bottom. Nothing that can't be fixed in a couple evenings. The bottom was covered with fiber glass and coverd with Solartex and never thought I break out the bottom. In reality no one thought it hit very hard to do that kind of damage. When I'm done it will have a plywood bottom and that should take care of it. My thoughts on the flying charastics are it is fast and very sensitive on the aileron axis. I didn't have chance to test it but I believe the roll rate will be fast. My Northstar weighs in @ 8 plus lbs. It amazes my how some build them at 6lbs or less???. Mine is powered with and OS 50. I installed a 12 OZ tank right on the CG and using an Iron Age pump. Seems to work ok. I'm looking forward to flying it again next week.
Keep the pics and videos coming/.
K.O.

Razguel

All I can say is WOW

That had plenty of power and quite the top speed. I fly with a ultra thrust muffler on a OS 46 and you would clean my clock[8D]

Looked like the elevator was a bit touchy on the first flight great save.

Great video keep em coming.

Strykaas

[sm=thumbup.gif]

John Hawkins

My Feedback: (2)

Thanks guys. As erazz pointed out finding the right CG is critical. That first flight with a tail heavy airplane made for some pretty hairy work on the elevator. Talk about touchy! If you tried to slow the airplane down as in the later flights it would fall out of the air. Pushing down elevator through approach and landing is unnatural but was the only way to get it back. The nose weight made a tremendous difference. Bob Hunt mentioned the severe porpoising he had. Moving the CG ahead should cure that Bob if my experience holds true.

Forgot to mention that the mousse can 'pipe' (MCP) brings out the power in the Magnum. In tests with various engines picking up a 1000 rpm is not unusual. The prop is a 10x6 and fuel 15%. With the same MCP the Webra 50 will turn a 10x7 at 15K. The 50 is in the Northstar. I think the Arrow is faster though because of its lighter weight and lower drag.

Strykaas

John,

Your engine really sings which tells a lot about your experience. I remember watching a video here of a pink Arrow (Laddie's ?), and the behaviour on the maiden was really similar to what you had to face, i.e. severe nose down pitch right after take off (most probably after elevator stick was put back to neutral). Too bad the plan hasn't been updated with this 'detail'...
Once you master the beast, could you please post a suitable CG range ? This is interesting because you've built it as per plan, so no additional downthrust, etc ...
Thanks for sharing this vid, it really dissipates serious questions about the design !
Cheers !

John Hawkins

My Feedback: (2)

Yes, I took that video while we flew from the same place last season when my friend lost his. He is flying in the last part of the video while I used the camera. I found by the most tricky part of flying the Arrow by far is the takeoff. The elevator control is quite different from the Northstar. It seems when airspeed is slow and thrust high it pitches down severely and that creates a big problem. It will accelerate out of a hover with no problem but then there is already a lot of up elevator being held in. Once its up to airspeed flying and reactions are normal

I'll be sure to post the new CG when I find out where it ends up. If building the plane again I would consider moving the servos one bay forward or at least providing a way to mount the battery up against F1. It would save a bit of weight but not a significant amount for the effort.

John Hawkins

My Feedback: (2)

Repairs are finished and the CG as the plane now balances is ½" behind the step. For ballast I rolled up some sheet lead into a cylinder that weighed three ounces and drilled a transverse hole in the nose block to accept it.

When I looked closer there was more damage to the forward hull bottom than I thought. Six inches forward from the step had to be replaced. I glassed the inside of the 1/8 balsa this time with light cloth and CA and added a keel of 1/8 x 1/2 hard balsa. This is quite strong and adds very minimal weight. The outside has supershrink coverite (the type made for painting) as a 'sort of' fiberglass approach and then Monokote over that. The Coverite is very tough and held the hull pieces together.

Two other spots on the bottom were damaged but not as badly. One in the servo bay was easily repaired; the other one is not so bad. I think it will be OK left as is. No doubt this damage was done on the hard smack into the water on the first takeoff. The hull isn't designed to take that. If I were to build another I would glass the inside of the hull bottom forward of the step with light cloth and probably do the same with the outside. This makes a strong light sandwich. Another poster suggested this as well. I have used this method in the past with great success. There us a commercial product like this that uses end grain balsa for the core. Possibly a keel could be used as well on the inside.

We are now ready to scramble for the next mission.

Bart[man]

K.O. I'm almost done with a Northstar build that is set up much like yours. I have a 10 oz tank located betwene f5 and f6 and a perry pump feeding an OS 46. I'm thinking that in the relocation of the fuel tank, there would be a change in the CG acording to the plans. I hung the aircraft from the ceiling with string doing a center of neutral test and the plum-bob location was 11 inches from the trailing edge of the wing which is 5 inches different from the CG on the plans. Any info would be greatly appreicated. Thanks Bart(man)

K.O.

My Feedback: (16)

Hi Bart(man)

I did more changes than was described my previous thread. I also raised the engine pylon 3/4 " so I could swing an 11" prop, moved the engine forward in an attempt to mimize the weight in the nose. My 4 servos and receiver are between F2 and F3. I have a 5 cell 1,200 MA battery between F1 and F2. I glued 20 oz of buck shot to the floor with epoxy between the balsa nose block and F2 to make it balance at the 16" mark from the trailing edge of the wing. Taking the advice from all I've read in the various threads the C/G is criticle so I added what balast necessary to make it balance at the recommended C/G. I have a micro throttle servo mounted behind the engine. After all that my plane still weighed 8 lbs. dry. Now I've added a plywood to the bottom of the fuselage (repairs) and that will probably add another 4 ozs or more.
I guess when its all said and done my plane flew great on the 1st flight at 8 lbs. I can't imagine 4 more oz will make a huge difference. It still baffels me how others can build theirs in the 6 - 7 lbs range. Go figure. I hope all this was of some help.
K.O.

P.S. Don't assume moving the fuel tank to the C/G will change anything. In my opinion with the tank on the C/G the flight characteristics will not change as fuel is burned off. I would still leave the C/G at 16"

John Hawkins

My Feedback: (2)

The Northstar can handle the weight so as long as it flies well why worry about what the scale says. The first one I built about ten years ago weighed 7 ¾ pounds and was typical of what they were coming in at around here. It needed 14 ounces in the nose up against F1. After dumb thumbing that one in I made another another with a few mods to try to get the weight down. The most significant ones were moving the engine ahead, lengthening the nose, lightening the pylon and nacelle structure and putting the servos and battery as for forward as I could get them. I played with materials some although that probably didn't make a lot of difference. Unfortunately I can't recall the finished weight but it now weighs 6 pounds 10½ ounces after repairs along the way including replacing the hull bottom with sturdier stuff. I called Laddie at the time to discuss the mods and he told me that he had experimentally lengthened the front by 12" which eliminated the nose ballast but introduced pitching problems. I think the amount I added was only two inches. With this and the engine placement change there was no difference in handling that I could detect.

A peculiar but useless experiment was the use of redwood in construction. I planed some down to 1/20" and used it for the hull.

A variety of engines were used. The first one was a K&B Sportster 45 which was pretty lame. An OS 46FX was used next and worked well for about 80 flights until the liner peeled. Same thing with the second liner. Then I went with a Webra 50 which puts out more power and has a perfect liner eight years later. The Magnum 46 was in it for a period waiting for the OS to be repaired. While it seems hard to believe at that weight the Webra gives OOS vertical. A MCP is used with it. Head shims had to be used to keep from blowing plugs. The rpm on a WOT near vertical dive must get crazy. Occasionally the engine noise will change strangely and go quieter. I think there is a point where acceleration due to gravity exceeds prop speed and the air is actually pushing the prop ahead of engine speed. There is a short clip of the Northstar here:[link=http://rcalbum.machawk.net/video/northstar.wmv]Video[/link]

Strykaas

John,

Both birds have aileron hinges nearly completeley immersed. How did you perfectly seal all this region (wood/hinge/covering) ?
You also seem used to building mousse can mufflers. Any tip for building these ?

John Hawkins

My Feedback: (2)

On the Northstar I used Goldberg hinge points. These are something like the Robart ones but are all plastic so there is no hinge pin to rust. They fit in a drilled hole in hinge blocks. The hinge area is diamond shaped. The trailing edge and aileron were covered in the usual way; holes poked through at the hinge locations and the hinges installed with epoxy. There was a strip of covering over the joint but it came off after a few years and I never bothered replacing it. Its abscence makes no difference. The Goldberg hinges may not be available any more but polypropylene ones would do as well I think.

On the Arrow I used CA hinges and was aphrehensive that the CA wouldn't seal all of the slot. It is hard to say how this is working out at this point as water got in the wing when the covering got torn off the trailing edge. I think they will be ok. I covered the wing and ailerons separately and then slit the covering at the hinge locations.

There are brass pin hinges but they are quite large. I used them on the Emily except for the flaps which are Robart hinge points.

Today I was thinking that downthrust might help the nose dropping on the Arrow by pushing down behind the centre of lift. As it is now perhaps it is tending to rotate the tail forward before there is enough pressure under the plane to resist it. Perhaps by holding full up I am getting this resistance at low speed.

Bart[man]

K.O. Thanks for the input. I also did'nt mention that I am using a mini servo for the throttle directly behind the engine and a standard servo for the elevator is also in the nacelle. Along with the perry pump mounted on top of the nacelle I guess that would be the same as having a fuel tank plus some. I'm going to balance at 16 inches. Thanks Bart(man)

John Hawkins

My Feedback: (2)

Forgot about the mousse can mufflers. Here's a [link=http://webpages.charter.net/rcfu/ConstGuide/MCM.html]building guide[/link]

Strykaas

John,

Indeed using such hinges is IMHIO the way to go. Thanks for the building guide !

Flywellnz

I have been interested in the Arrow ever since the design was published in RCM (July 2004), now I am going to build it!
I found Mustang's post re the downthrust very interesting and it makes sense, however on looking at the reduced scale plan in the magazine, I cannot see the down thrust? Is there any on the full size plans, or should I go ahead and build it zero, zero.

Laddies Flying comments are also interesting: He says the model is easy to fly. Just point it into the wind and apply power. On your first flight, let the model pick up extra speed before rotating....
He also describes testing out the extreme slow speed characteristics of the model by reducing power and raising the nose with elevator as speed bleeds off. Then adding power back so the model travels forward at low speed with the nose high. He goes on to say that he enjoys using this flight mode on the landing approach. Maybe that is the best way to land it?

I like to fly fast or unusual models, and the Arrow looks like my style!

Any advice or personal experience on the downthrust issue or flying will be welcome!

Regards to all

Gordon

John Hawkins

My Feedback: (2)

The trust and wing chord are 0-0 in mine which is how it is drawn in the magazine plan. It flies well like that but there are pitch issues during TO. I have redrawn it with 3º of down thrust in hopes of addressing that and also lowered the pod so that the pitching arm is less. This required moving the engine ahead a little so the prop cleared the base of the fin. Apart from thrust the other changes I made are just tinkering and I suspect of little benefit.

Reading back in the thread I see that Laddie suggests up to 2º of down thrust although 3º is suggested by many.

Last year I posted a video of my friend's maiden flight and crash. The video has been moved to [link=http://rcalbum.machawk.net/video/arrow.wmv]here[/link].

The title was confusing. I called it 'Laddie's version' of the Arrow to distinguish if from the AVROW Arrow but it was not Laddie's plane or flight.

Flywellnz

Thanks John - That gives me the confidence to go ahead and build in 2 or 3 degrees of downthrust. It was probably your video that was worring me about this design!

I will look for Laddie's other posts later. I have experienced the same problem with another flying boat, except it was trimmed to fly level with power on, but pitched up as you throttled back on the landing approach! [] I was going to try mixing a little down elevator with the throttle and trimming it to glide with power off. (maybe I still will try that)

Kind Regards
Gordon

John Hawkins

My Feedback: (2)

Well yesterday didn't go all that well. Near vertical dive at WOT; just about to pull out; big time flutter; no control; kapow! The clevis came off on one elevon and the hinge pulled out of the other. I suspect the engine was turning 16K or more. I'll make another one and pay attention to controlling flutter - or lay off the vertical dives at full power, which is asking for it.

K.O.

My Feedback: (16)

John

I had a mishap yesterday with my Northstar although not as bad as your. The engine came off the pod in flight. It held on by the fuel lines and I managed to make a good water landing close to shore. Plane and engine recovered. Only damage was the prop chewed up the top of the fuselage. After looking at the whole scenario I didn't do a very good job securing the engine firewall to the pod. ie trying to conserve on weight. Ounce wise and lb. foolish or something like that. I was lucky the damage was minimal and will be ready to fly after a couple nights work. This tail heavy thing made me paranoid and didn't want to use more nose weight than necessary.

Last week it was 2 holes in the bottom of the fuselage after a hard water landing. I didn't use plywood on the bottom again trying to save weight.

I hope this is the end of it.


K.O.

John Hawkins

My Feedback: (2)

Good recovery on your part K.O. The stock balsa bottoms on the Northstar and Arrow won't take those bangs on the water will they? After the demolishing the Arrow I went and got the Northstar (Just a short boat ride across the lake to home.) It was interesting to fly the two back to back. I would compare the the NS to the Arrow as a exceptional road car to a hot sports car. I like the NS and have had many years of enjoyment from it but I would rather have another Arrow than to settle for it.

In the early flights of the NS I got flutter on the elevator. This was overcome with stiffer linkage and a counterbalance. Now you can rip it down in as steep a dive as you dare with the engine wide open without any flutter at all. With the Arrow I think I will shorten the elevons and add a fixed piece out at the tip; use a heavier horn and metal clevis with thin ply in the mounting area; extra hinging; sealed gaps and counterbalances. The servos and pushrods seem adequate to me. There are no stripped gears, Things let go at the other end. The balance was a guesstimate on the NS. The elevons on the Arrow are 30 grams and say the average chord is 2.5cm. I figure then that the counterbalance should be the same weight and distance in front of the hinge line. It adds a bit of weight but if it means the survival of the plane the price is fair.

For the most part none of those measures would be needed except for extreme situations like long, steep full power dives. Normally a person wouldn't do that but sometimes, as in the fable of the scorpion and the frog, a person just can't help themselves.

Strykaas

John,

I'm glad you have so much time to build a sequel to this Arrow story. This one will probably be a benchmark for all what has been said about how to improve the "per plan" design (downthrust, etc...). Don't hesitate to start a new thread, as this new one may become a reference for new builders to come !

John Hawkins

My Feedback: (2)

I had been enjoying some time away from work but now there are several projects coming all at once that I will soon have to start. Later today though I will print the plans and perhaps cut a few pieces out. When things get underway I'll take your suggestion Strykaas and start a new thread. My friend who crashed the pink one in the video says he is ready to build again after seeing this latest one fly.

Mustang Fever

My Feedback: (2)

Good luck to all of you.

I would really like to see a summary of all the changes you end up making.

Please post a note on this thread when you start the new one.

Strykaas

Bob, I think you might end up building a new one too Good point, never give up [sm=thumbup.gif]