Maxy Posted October 29, 2012 Share Posted October 29, 2012 I have made one of those Blade making jigs, it is said that four blades can be made from a 1/4 sheet of balsa 48"x4". The problem I have found is that although 4 blades can be made with a good aerofoil profile, the trailing edges are very thin & there is not enough material to put on the chamfer, which is needed to catch the airflow to start the blades turning. If I slice off the thin edge sufficient material to make a effective chamfer, this will reduce the cord of the blade & also reduce the effective lift. I suppose I should have made the blades from 3" wide balsa to a clark section and then cut off the back inch then put on the chamfer as it says on the plans. yet I have seen many blades on Utube that do not appear to be chamfered on the T/E so I am a bit confused. Any advice or information on this matter would be appreciated. Regards Max Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted October 29, 2012 Share Posted October 29, 2012 Welcome to the forum Robert. Glad to hear you are having a go at an Autogyro.It would help if you could tell us which one it is. and what the length of each blade is. Pre rotation is not generally dependant on the blade t/e it's a matter of setting the blade at a slight negative angle to the air flow by adding wedges at the root . Getting the blades to run up easily can also be achieved without to much trouble by using a sharp l/e section with no under cut to the bottom eg more Aqulla than clarke Y . Tell us more as there are quite a few autogyro builders on this forum. Tom. Quote Link to comment Share on other sites More sharing options...
Maxy Posted October 29, 2012 Author Share Posted October 29, 2012 Hi Tom, Thank you for the reply. I have just finished building a Dag-R1 with a ST34H up front. I made a set of blades from the plan which are balanced & weigh 48 grms each & they have the chamfer, so they should be ok. They are 24"X2". I found too much movement in the tower 995 servo fitted for roll/ aileron control so I stopped there & ordered another servo a Tower 996 which will hopefully have less movement in the neutral position, ordered from HK will take a few weeks to come. So in the mean time I thought I would have a go making another set of blades just incase I have a mishap. Thats how I ended up making a jig & the resultant blade with no chamfer. I have been building & flying model aircraft for 36 years & I love it, but unfortunatley there are not many aeromodellers left in our club, it has been taken over by plastic electric planes & choppers if they break em they go and buy anew one. So the scratch built model aircraft are now very rare, so I thought I would branch out a bit and take on the challenge with Autogyros starting with the Dag-R1 which was a very nice build. I like what you said about a negative blade angle, but would that reduce the lift created by the blades camber? What I have decided to do now is to make new formers for my jig to produce a equal camber high in the middle round at the L/E & The T/E the same height & thickness then cut the camber in that. Also I may consider Negative blade angle as you have suggested. Its all new to me all my Dag is doing is looking pretty hanging from the ceiling waiting for a replacement servo, then I can move forwards & start with a few runs on our Common to get used to the steering & perhapps a few Hopps. Regards Max Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted October 30, 2012 Share Posted October 30, 2012 Hi Robert . Here is a video of my own trainer autogyro .This has a simple aquilla rotor section with a little twist steamed into the last 6in of the blade this makes run up very easy ,but is seen by some as a controversial way of doing things. Yes you are correct in saying that as the blade negative angle is increased the lift is reduced ,this is more noticeable as the rotor loading is increased eg a heavier model for a given disc area. The aqilla section,with a sharp l/e will spin up without twist or wedges but takes more airflow to achieve. I am not to familiar with the DAG but I know a man that is ,and will ask if can pass on some useful advice. My own experience suggests that learning the traits and flying characteristics should perhaps take priority over the finer points of blade design or other features that can enhance performance .Launching or rog with insufficient rotor speed are the cardinal sins closely followed by orientation perception when the model is to fast and gets some distance away . Some perseverance and repairs may be needed initially but the whole experience can be very invigorating.Do keep in touch and let us know how things go. Tom. Edited By Tom Wright 2 on 30/10/2012 01:12:29 Quote Link to comment Share on other sites More sharing options...
Maxy Posted October 30, 2012 Author Share Posted October 30, 2012 Hi Just come in from flying my touch & go fixed wing, nice to hear from you, love the video the music is well suited. The replacement servo for my Dag-R1 arrived this morning sooner than expected so I shall fit it & set up the head throws tonight & go for grass running trials next week if the weather is suitable. Thank you for your advice much appreciated . Regards Max Quote Link to comment Share on other sites More sharing options...
Richard Harris Posted October 30, 2012 Share Posted October 30, 2012 Hi Robert, The idea of the chamfer on the lower TE is to help spin up, this type of blade works well on the DAG. The wire adds strength and moves the CG into the correct position. The chamfer moves the centre line of the blade into negative automatically. I believe the blade design was made by a chap called Steve Tilson who used to own a company dedicated to RC Gyro's making a few kits. Autogyro Comany of Arizona made some very nice but expensive kits, they used this type of blade on all there models including the Lazy Bee gyro. They were bought out a few years ago and the new owners never followed on with the kits. Fortunately I do have one of their 1935 Pitcairn PA-22 kits that I just haven't got around to starting yet. This morning a whipped out a blade blank from the box and can confirm that the thickness of the TE is about 5mm before the chamfer is sanded in. The blade is in fact lazer cut from some of the SIG profiled section which starts out at 3" in dia. Dave Surace the designer of the DAG (Dave's AutoGyro) used this blade type to good effect and it is recommended to stick to the plan section as it is forgiving. It is quite a few years ago but here is my DAG R1 flying, it was powered using a 32 SC 2 stroke and plenty of get up and go. Please excuse the music as I had to add it add it due to the camera automatic focus making a noise. Hope this helps? and a photo of the section of the SIG aerofoil with the blade lazer cut into it to give the thickness in the TE. Rich Edited By Richard Harris on 30/10/2012 15:48:01 Edited By Richard Harris on 30/10/2012 15:48:55 Quote Link to comment Share on other sites More sharing options...
Maxy Posted October 30, 2012 Author Share Posted October 30, 2012 Richard. Thank you for sending me the valued information on the Dag-1 blades. I have a feeling broken blades could be an issue when learning to fly a autogyro, so I am getting myself prepared to make a se tor two. I think the right way to go is as you have indicated to follow the plan & start off with 3"x1/4" this will ensure sufficient material on the T/E to form a chamfer, so I shall make a 3" profiled Jig former, then slice off the inch & form a decent chamfer. My first made set are balanced & weigh 48grms a piece but I am not over happy with the camber it looks a little flat at the top. Thank you for the Photos & Video of which I watch with envy as you make it look easy to fly the Dag. On my Dag I have now fitted a decent Tower 995 servo today for the roll control the previous new one had too much flop in it, all I have to do now is the final settings. So one day next week weather permitting I will off up the common for steering practise & if all is ok a hop or two. I put on a few snaps of my build. Best Regards Max Edited By Robert Maxwell Morris on 30/10/2012 22:17:33 Edited By Steve Hargreaves - Moderator on 31/10/2012 12:26:53 Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted October 31, 2012 Share Posted October 31, 2012 Hi Robert....I've just tidied up your post.....please can you remember to hit Carriage Return & "add a line" between each picture. If you don't the site puts the pictures in a continuous line & mucks up the page!!! Thanks... Quote Link to comment Share on other sites More sharing options...
Maxy Posted October 31, 2012 Author Share Posted October 31, 2012 Hi Steve, Thanks so much for tidying to mess I made of uploading my photos, i was a bit tired & gave up. I take your advise on board & hopefully next time they will be fine. Quote Link to comment Share on other sites More sharing options...
Steve Hargreaves - Moderator Posted October 31, 2012 Share Posted October 31, 2012 Quote Link to comment Share on other sites More sharing options...
Lazygit Posted October 31, 2012 Share Posted October 31, 2012 The rotor blades are probably the parts least likely to break. The most likely parts to break are those hit by the rotor blades. Quote Link to comment Share on other sites More sharing options...
Richard Harris Posted November 1, 2012 Share Posted November 1, 2012 LG, You haven't had a 'man' crash yet , when the blades are destroyed you know you have made a good job! Rich Quote Link to comment Share on other sites More sharing options...
Maxy Posted November 6, 2012 Author Share Posted November 6, 2012 I took my Dag-R1 with ST34H for its first outing this morning, forecast was for 8 mph wind but on arrival at our common it was more like 12 to 15. I had a positive feeling that the Dag does not like wind, once the blades were free they revved up very quickly & it fell over hitting my flight box. So I then proceeded with caution to try taxing into wind & a hop or two I managed a few straight runs but it was difficult on our lumpy common run way, ground steering with the 1" dia tailwheel is not very good & the rudder does very little at low speed the wind was the commanding feature which pushes the Dag about a bit, once out of head into wind it just gets blown over, the blades dig into the ground but with no damage. My blades are balanced & weight difference is within 1grm but there does appear to be vibration through the model & it flexes the U/C but this may be normal. It certainly feels that it wants to fly, I shall try again on a calm day. I am happy it came home in one piece. Max Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted November 6, 2012 Share Posted November 6, 2012 Maxy Accessing the trim by holding the model into wind and above your head ,then trimming as required can be a useful tactic.Then when happy with trim and rotor speed a hand launch can be preferable to attempted rog. During taxi trials in windy conditions the rotor should be held forward on the stick .Vibration is often encountered but is regarded as undesirable . Are the rotors able to find a natural position ,eg pivot at the root fixing ? If not vibration can occur if tracking / lag angles are not correct. Glad you got it back un damaged . Tom. Quote Link to comment Share on other sites More sharing options...
Maxy Posted November 6, 2012 Author Share Posted November 6, 2012 Tom. Thank you so much for the advise, do you mean that in conditions when the wind speed is up a bit & sufficient to produce good rotor speed you trim the Dag into neutral attitude balancing it & then just let go when lift is felt? with no running involved. This would avoid a lot of ground problems but sounds a bit hairy. The forward stick idea sounds good to maintain a bit of stability while taxiing. I think the rotors are ok they should be free to pivot on the bolt & not tight . Max Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted November 6, 2012 Share Posted November 6, 2012 Max. Your interpretation of my suggestions do seem to be about right .The exact techniques do depend on factors particular to the model in question. So assuming the trim is is not to far out then it's a matter of identifying when the rotors are up to speed .This is normally determined by a change in the sound and a positive pull that equals the weight of the model. A brisk walk forward often helps to achieve this ,but so much does depend on the willingness of the rotors to reach operational speed for a given wind speed . As an example I recently flew one of my Autogyros on a day when the wind was very light perhaps 2-4 mph and yet walking forward holding the model with the rotor at 45 degrees produced sufficient rotor rpm to enable a safe launch, but other machines would get no where near sufficient speed due to differences in blade design. In crude terms easy spin up designs often have less lifting ability, so some lift can be sacrificed if, the model is on the light side for a given rotor blade area. As for the hand launch being a hairy process I personally find it very reliable ,but if the model is way out of trim or the pilot is slow to react quickly then the chances of a heavy crash are higher.Having said that I have seen many autogyros badly damaged during a failed rog attempt ,so that subject is up for debate. Don't know if any of that is any help as I can only relate my personal experiences. Tom. Quote Link to comment Share on other sites More sharing options...
crispin church Posted February 28, 2013 Share Posted February 28, 2013 is there a program for working out what size blades for a autogyro ie if i make my own but there are smaller in width but longer ? Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted February 28, 2013 Share Posted February 28, 2013 Crispin. The method most used relates the rotor disc area to the AUW , to achieve a loading of between 2.5 and 4 oz per sq ft . Although this method is widely used it does not take into account blade chord ,or overall efficiency . Tom. Edited By Tom Wright 2 on 28/02/2013 17:25:33 Quote Link to comment Share on other sites More sharing options...
crispin church Posted February 28, 2013 Share Posted February 28, 2013 so if my blades 400mm by 55mm and 460x 45mm the width dont come into it just the lenght to the area covered or are we on 400x55 x3 for 3blade as in just the area the blades Quote Link to comment Share on other sites More sharing options...
Tom Wright 2 Posted February 28, 2013 Share Posted February 28, 2013 Crispin. I think the formula makes assumptions based on average blade aspect ratio and section.But it is still a good guide to predict lift performance for a given AUW . An example for 18" blades and AUW of 24 oz. 18" = rotor radius so 18 x 18 x 3.14 = 1017.36 now divide by 144 to convert to sq ft = 7.06 sq ft . Divide the weight in ozs into the area in sq ft =3.4 oz per sq ft . Tom. Quote Link to comment Share on other sites More sharing options...
crispin church Posted February 28, 2013 Share Posted February 28, 2013 got it many thanks once again tom Quote Link to comment Share on other sites More sharing options...
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