|Bob Parkinson Arrow||A New Ducted Fan Model|
|Arrow Airfoil Info||Arrow 2000 and CBC Movie Model|
I am an avid ducted fan flier. I have some information on Bob Parkinson. Yes, he has moved to the U.S. Here is the address... Bob Parkinson Flying Models 1140 Early Drive NW Palm Bay, Florida 32907 (407) 726-8401 He offers the ducted fan Aero for less than $200.00 U.S. Hope this helps you out.
OK, You asked so here it is.... You are right the Arrow did use a NACA 0004-6-3.7mod airfoil (according to Arrow, by the Arrowheads anyways). The ultimate reference on this stuff is Theory of Wing Sections, by Abbott and von Doenhoff. (its about $21 at your friendly neighbourhood bookstore). So, I looked it up, because I have always been interested. Here's the breakdown. The airfoil is a NACA 4 series (that means 4 digits in its designator). So, the airfoil starts life as a NACA 0004. The first two zeros means its symmetrical, the 04 indicates the section thickness as a perctentage of the chord. There is a formula in the book to generate the ordinates (and there are several on the 'net). Now comes the interesting part. As best as I can tell, the designator should be NACA 0004-63.7mod, without the extra dashes. The first digit after the dash indicates the leading edge radius. A six is the normal leading edge radius. For information, a sharp leading edge would be a 0, a fat an 8. The leading edge radius varies as the square of this number through this range. The second number (Theory of Wing Sections only recognizes it as an integer, but we can squint) indicates the position of the maximum thickness in tenths of the chord. So, in our case we have a NACA 0004 airfoil with normal leading edge radius and a maximum thickness at .37*chord length. Boy, that was fun, eh? Now. The mod indicates the drooped leading edge. This is not work documented in the book I have, and most likely indicates the Avro engineers took some liberties. The section shape is shown in the 3 views in Arrow by the Arrowheads. I have some further information from Design Progress, May 1959. The article indicates that the leading edge was drooped by 8 degrees inboard of the notch and by 4 degrees outboard of the notch. The notch is 'about a 5% notch at about midspan' and the outboard leading edge has ' a 10% increase' I presume they mean in chord. This chord increase is to cure pitch up. For information, the notch creates a vortex that limits spanwise flow. (Originally tried by English Electric, if I remember correctly). It was found that the depth of the notch was the most critical parameter.
We were at Quinte 1995 with our Avro Arrow CF-105, and you had expressed an interest in our jet at that time. We promised to keep in contact as thing progressed and until now, not much of news worthiness has occurred. It has taken all of the summer to bring what you saw at Belleville into flyable shape. This project has been bigger than anticipated.
Taxi trials occurred on Sunday afternoon August 27, 1995. Plenty of power and the fan picked up revs as the plane accelerated. Good ducting design I am told.
Monday September 4, 1995 was maiden flight day. Good static thrust lead me to believe that liftoff would easily occur. Was going to try a couple of taxis but when throttled up, the jet responded so well within the first 50 feet that I decided to go for broke. Held it on for a good 200 feet on paved runway then pulled back and crossed my toes. Observers said that it "Leapt" into the air. There was some left roll that needed trimming out and some tense moments to adjust to the extreme sensitivity on the ailerons but it flew and flew beautifully. Both high and low speed passes were very stable. The Arrow penetrates the wind very capably and will perform to the max. 6 minutes of flying and time to setup for a landing. Approached fairly high and what I thought was slow enough for a jet. Handling at medium-slow was very stable at about 30 % power, nose was not too high and had a good sink rate that could be easily controlled. On a go-around it came back up on the power very quickly. Reset for second approach and downwind was stable and level. Brought it in slower but not a high enough angle of attack as on flair it ballooned and stalled and pranged in from about 6 feet. The right main bogie arm bent and jammed the tires thus applying a full right wheel braking effect. This swerved the aircraft right and the 20 m.p.h. breeze got under the left wing and flipped the Arrow on its back. Some damage to the fin, right wing upper surface and the fuselage but all was repaired easily.
Saturday, September 23, 1995 second flight day. Mechanically reduced the aileron throw to 12 degrees and put in a low rate on the radio of 8 degrees with lots of exponential ( -38 and -44 on my Futaba Super 7). Reduced the elevator to 15 degrees high and 10 degrees low with moderate exponential. Stupidly I didn't mechanically reduce the rudder throw but left it at 20 and 15 degrees. A heavy duty five cell battery was installed which moved the C. of G. about 3/8" forward. Take off was smooth as I pulled back on the stick sooner and it flew into the air. Climb was very good and all the erratic behaviour of over sensitive aileron was gone. However, because I left the rudder with too much throw, it not only yaws the plane to great authority, it also severly rolls the plane. This could have added to my problems on first flight as I am used to flying with rudder and instinctively correct with both sticks. Rudder is now mechanically fixed at 12 degrees high rate and I am sure this will be enough. Forcing myself to fly only aileron/elevator the jet is very smooth, goes where you point it and does what you tell it to do.
Both high and low speed passes were rock stable in the 15-20 m.p.h. breeze. The plane wants to fly. 40-50% power and pull up slightly to slow the plane down and all it does is climb.
After rereading all the Jet International articles on landing deltas I thought I knew what to do on landing but not so. First attempt was far too hot with too much power left on, about 30% after turn to final at 100 feet up. The Arrow didn't want to sink. Chopped to idle too late to really slow down enough. Flair was nose very high ( about 20 degrees up) and I applied power from idle. The Arrow climbed into the air with no hesitation ready for another attempt. However, I wasn't ready, and I repeated the approach the same way just a little lower. Still too hot and too much power left on for too long. I did get it down ... hard, but not too badly hurt. We did have it on video tape though, and watching the film after, the landing procedure is obvious. On the down wind, trim for level at 50 % power. The power is needed to get you through the turns as sink is pretty quick if there is not enough. (Power, not necessarily speed.) Stay high and after the turn to final, immediately chop to idle. Pull the nose high to slow way down and then adjust the glide with power. The video shows that once I got to idle, I could pull the nose up without the chance of ballooning, and still maintain control. Touchdown will be nose high ( 20 degrees ?? ) and surprisingly slow once the proper technique is accomplished.
Ramtech Fan, O.S. 91 DFVR and J.H.H. twin tuned pipe. Fixed wire undercarriage, fuselage unpainted weight 13 lbs. Estimated high pass speed 90- 100 m.p.h. This is with big open wheel wells in wing and undercarriage down. With retracts, doors and all cleaned up should hit 150 m.p.h.??? I'd like to paint it before next test flights as visibility in epoxy beige is pretty low but I also want to get in as much flying this year as possible so that I can really know what to adjust for next year and for the kit. (2nd flight had a dayglow red vertical fin and it helped alot.)
Over the winter the retractable undercarriage will be finished and some changes need to be made to some moulds. While the ducting seems to perform well, it is a bit of a bear to assemble so work on a splitable mould is needed. I am also seriously considering moulding the wings rather than sheeted foam. The profile is very difficult to cut and assembly of the wing is complicated. Moulded wings could be honey-combed, allowing for an undercarriage support spar, and a great deal more strength.
This has been a richly rewarding experience for both Michael and myself. We thank you for expressing an interest in our project. You will probably get one more letter in the spring to let you know how the winter fine tuning has gone then we hope to meet you again at Quinte 1996. Until then, have a constructive winter.
Just to let you know that Doug Hyslip of R/C Hangar in Calgary has been flying his 1/8 scale model for a few months now in preparation of the CBC filming. It uses 2 K&B 100 ducted fans for power and weighs approx 40 lbs. Its quite a sight and I am going to be trying to put some video clips on for down loading The model flies well and at a deceptive speed due to its size. It is built from fiberglass molds and foam wings, any one interested should contact Doug at R/C Hangar.