A long time ago I started to silence the Carden, and today I managed to obtain some very good numbers. The weather was nice, the wind was calm, and I was off for the day. So, all ingredients were present to make it all happen. At the club we have built a heavy support on which to mount the plane to be tested. In the past I had tested this setup and had found that the power produced was enough to move and tip over this contraption. So, the largest part of the measurement session consisted of securing everything with spikes in the ground, etc. The plane itself is firmly strapped in place, I have an additional (temporary) anchoring point on the u/c, tied to the frame. I do not fancy the idea of something going flying at full power. Anyways, alle went well. At 25 meters/ 90 degrees downwind, according to the prescribed setup I measured 77dB, which is NotBad! The 45/135 degrees measuring stations also showed 77dB (tad less) and the one to the back of the plane only 56 dB. In all instances the exhausts are plainly visible to the dB meter. I had noticed in the past that the sound at the back and front of the plane is a lot less than you would expect. Which tells me I guess that most noise is produced by the prop-tips. The only thing I still need to worry about at some time is that in this test situation, the cylinder temps go a lot higher than when flying, even though nothing is blocked. Just goes to prove that just propeller wind is not the same as the airflow generated by flying. This is also the reason I had to wait for a cooler day, because initially I saw temps up to 180C! Now, with a modified hole at the botom of the cowl, it’s only 150C max. (In flight I see 130C max today. And yes, it is the left cylinder that is always warmer. Seams to be a feature of twins. Maybe one day I’ll try to add more ‘cool’ to that side. (or squeeze the other side, to get make it a bit higher.) As someone said: too much info, just fly!!
During our holidays in the home country I was entrusted with a handful of carbon, with the request to ‘just build it and enjoy’. Over the last few weeks that building process was finished. Even though the total amount of hours spend are not that many, it all adds up. Today I finally got a new receiver, so after the new batteries arrive, we should be all set to go. All up weight is 220 grams, which probably is a bit on the light side, if I compare it with the Tweagle. I ended up adding some extra weight to that one too. At 245 gram it has better penetration, and it fits my style better. For this one I decided to make the wing detachable with a home made connector. The pins originated from a scrap cable assembly. (Good thing about working with medical equipment is, that there’s lots of good stuff that we throw away.) Of course I have read stories about bad connections. This one will not have bad connections!
More after the first flights!
It has been some time, but today is as good a day as any other day for a wee update. A lot of time has gone into designing and building a retractable u/c. The final result is good, even though I say so myself. I still want to make a mudguard but that can wait.
Making the wheel doors work properly was alo a lot of work, where I had to made a negative from the fuse, and build the doors into that. (The old vacuum installation was a great help here! )
Mounted the elevator servo, I found a one in the box that will do nicely. I wanted to use a beefier link to the elevator, but there was not enough space. So a 2 mm version will have to do for now. Maybe change it for 3 mm if I work out how to do it.
I also cut slots into the rudder for hinges, but in hindsight I want to redo them in such a way that there is less visible ‘hinge’ on the outside. The whole rudder needs to be removable, there is a plastic rod for a 1.5mm steel wire built into the rudder, so this is easy.
Next task will be to think of a way to make a quick disconnect link to the elevator. I don’t want to use a standard quick-link, they do fail with repeated opening/closing. It has to be simpler, and less fiddly in daytoday use.
Let the mind think about it for a bit, it will find a good solution!
Flying this week is a bit of torture to be honest. 30 C plus and clear blue skies, with a slight haze is not the best weather, simply because it is very hard to see the plane beyond 200 meters altitude. No doubt I will regret saying this soon.
Part 1 is a bit back, describing how I did a quick and dirty cockpit frame. Today was the start of more serious stuff, like drilling the holes in the fuse for the all important bit in the middle! First I created a jig that holds and aligns the fuse, and made very, very sure that everything is perfectly level and square. Lasers and camera’s don’t seem to like each other, hence the lack of quality in the pic. I will probably be able to do another one, once the first expoy has hardened. To tricky to touch anything at the moment.
Once the sleeve is in position, I can cut off the outer parts, which will go into the wings. The manufacturer states in the manual they kept the hole in the wing slightly oversized to allow for wiggle room. What slightly worries me, is there anything other than the sleeve in the wing holding things up? Do I need to add something? Glass the wingroot maybe? Time for more research!
I discovered a fun website the other day, where you can ‘virtually’ compare your achievements with other pilots. Of course I am no match for 6 meter ships, but it is fun. Soaringleague.net is the place to visit. It is a pretty new site, I guess it’s real goal is to log GPS flights, but it works fine for me too!
Tagging the flights is a bit of an adventure yet, but I am sure things will improve over time, since the admin, Pascal is working really hard on it!
My best flight sofar was a mindbogling, neck hurting flight of altogether 33 minutes. I defenitely need to invest in an easy chair to sit through long flights, standing and looking at the sky does not work!
Up to this point in life I had been concentrating on 10 min fligths, which are not to hard, but stretching things beyond 10 min is hard work when you start from 200 meter or less. (my trusted lady always tell me when I cross 150 meter, so usually I switch off at that altitude and a bit. )
One minute you contemplate building yourself a nice big glider, next time you wake up you have a shed with a few big fish! So far it’s only a 5 meter ASK21 en a 4 meter DG800. Both in need of minor assembly. Since the DG800 is the smaller (and cheaper) one, I am going to try to get that one started first. The DG800 is a Rödel Modell kit, probably something that was made 10-15 years ago. (Haven’t been able to get details yet) However, the ”kit” is in pristine condition. The only giveaway of its age is the papertape holding various bits together.
- Spannweite: 4150 mm (mit Winglets 4400 mm)
- Länge: 1790 mm
- Gewicht: ca. 5700 g
- Profil: E 207
- Steuerung: Quer, Seite, Höhe, Störklappen, Einziehfahrwerk, Schleppkupplung erstanden.
Leider habe ich sie bei diesem Erstflug fast verschrottet.
Das Problem ist, dass die DG, wenn du schon sehr langsam bist (z.B. Landeanflug) und dann die Störklappen voll ausfährst, schlagartig abreißt. Ich habe meinen Absturz zufällig auf Video aufgezeichnet und ihn x-mal angesehen. Kollegen von mir haben alle bestätigt, dass die Maschine nicht zu langsam war. Da scheint es wirklich ein kleines Problem zu geben, da der Abriss exakt mit dem Ausfahren der Klappen kommt.
Sobald die Klappen drin sind besteht keinerlei Gefahr und man kann die DG herrlich langsam fliegen.
Auch wenn sie es nicht zugeben, ich glaube das Problem ist bei Rödel bekannt, da ich nach dem Absturz von Rödel folgenden Rat bekam:
“Die Klappen nur halb ausfahren und gut Tiefenruder beimischen”
Die Serie E-205/207/209 hat bei den typischen Modellflug-Re-Zahlen starke laminare Ablöseblasen bei mittleren Geschwindigkeiten, d.h. deutlichen Zusatzwiderstand beim beschleunigten Gleiten.
Die Ablöseblase kann man sichtbar machen, wenn man an einem ruhigen kühlen Abend, bei dem Tau entsteht, einen Flug mit gleichmäßiger Geschwindigkeit macht; man sieht dann nach der Landung einen “Tau-Streifen” auf dem ansosnten trockenen Flügel. Das ist das sog. “Totwasser-Gebiet” der Ablöseblase, in dem sich der Tau am Flügel absetzen kann, obwohl der Flügel eigentlich umströmt ist.
Warum erzähle ich das? Weil es sich gerade beim E-205/207 lohnen wird zu versuchen, die Ablöseblase mit einem Turbulator zu zerstören. Es genügt ein gerader Tape-Streifen (Zierstreifen aus dem Autozubehör), 2 mm breit, 2-3 Lagen übereinander, bei ca. 25 – 30 % der Profiltiefe (kurz vor dem “höchsten Punkt” der Profiloberseite). Der Leistungsgewinn kann spürbar sein, erst recht die (gerade bei Vorbildgetreuen zu beobachtende) Verbesserung des Überziehverhaltens.
Das Profil ist für den gleichen Einsatzzweck gedacht wie das E 205, jedoch sollte wegen seiner größeren Dicke die Re-Zahl sicher über 100000 liegen. Das bedeutet Flügeltiefen möglichst über 240 mm. Das E 205 wurde für RC-Segelflugmodelle berechnet, die sowohl langsam in der Thermik kreisen sollen als auch schnell fliegen müssen, ohne daß die Sinkgeschwindigkeit zu groß wird. Es war daher bei seinem Erscheinen ausgezeichnet für die Klasse F3B geeignet. Inzwischen gibt es leistungsfähigere Profile. Auch für den Hangflug ist das Profil gut geeignet, da es bis hinunter zu ca = 0,1 recht niedrigen Widerstand aufweist. Die Polaren wurden im Stuttgarter Windkanal gemessen. Zum Vergleich wurden die theoretischen Polaren mittels des Eppler-Programms errechnet. Weiterhin sind die Ergebnisse der Messungen im Delfter Windkanal und die der Messungen in Princeton von zwei von verschiedenen Erbauern hergestellten Meßmodellen aufgeführt. Die theoretischen Polaren für den Einsatzbereich von HLG im Re-Zahlbereich von 50000 bis 300000 wurden mittels des Winprof-Programms errechnet.
Entwurf: Prof. Eppler
Quelle: MTB 1 und MTB 1/2; Model Builder 5/1982; Soartech Nr. 8 “Airfoils at Low Speeds”; H. Eder “Mehr Leistung mit dem Hand-Launch-Glider”, Verlag für Technik und Handwerk GmbH, Baden-Baden 1996, S. 106.
Anyway, since a challenge is only a challenge if you create on, I decided to try and make a 2016 scale canopy. The original blow-molded plastic afair will be kept for nostalgic reasons). First I wanted to see if my idea sort of works. (My idea: likely something I read somewhere on ye interweb. )
I want to create a well fitting carbon frame. Easiest way to make it well fitting, is to build it on the existing fuse. I stuffed some foam in the inside, and some foam on the outside to create a channel in which to stuff the carbon/epoxy/microballoons. Since it is a trial, it does not yet have to be perfect.
First impressions are: This works! Now I need to order some fresh epoxy, and do it for real. This time I will try to make the frame an even thickness, and offset it a bit to the inside, leaving enough space for the hood.
It’s been a while, I must admit. We have the odd bit of summer, interspersed with bouts of autumn and spring and winter. That’s summer for you! Given the general uncertainty of the results of the plans of our minister Dobrin (He who wants to put a ceiling on all model-aircraft activities of 100 meters, so that amazon can deliver their stuff) I have decided for the moment to go gliding. That way I will most certainly be above 100 meters! Once you set the mind to gliding, big ones, all of a sudden the universe throws a lot of them at you. Looking to acquire an 5 meter ship, and possibly 2 pieces 4 meter something. All of them in ‘GFK fuse, and the rest is up to you!’ format. I love it.
So, plans for large biplanes are shelved for now, plans for more F3A-X/Imac planes are shelved. We goes gliding!
I have motorized the PURES a while back, and I must admit that e-PURES makes life easier on the bones. And I get to go up real quick, because I did not have a suitable size motor in the box, I took something that looked about right. On a small 1000 mAh battery it goes up like a homesick angel. Almost as fast as the Orion. And I can repeat that a dozen or so times on one charge. What more do you want?
Speaking of Orion, it’s getting there too, being tuned in that is. We had a few quiet evenings, which allowed me to tweak CofG without too many disturbances. I am getting to the stage where hands-off circling is happening. Move the battery just a tad more to the front, and we are there. (at least in quiet conditions) This flight was on a Sunday, around 4 in the afternoon. Not bad for one of the first outings!