ameyam

Dont know whether this is the correct forum for this but anyway.

I am replacing the stock aluminium landing gear on a Phoenix Extra 60-90 with a CF landing gear from HobbyKing. I am doing this because the stock weighs 150 gms where as the replacement half of that and the model really needs to lose weight after I fitted it with a DLE20

Now, referring the pic, the CF gear is not as wide as the stock gear in terms of the width in the nose-to-tail direction.

1) On the fuse side, ther are three holes in the LG Block, two in line towards the nose and one in the middle towards the tail. I drilled so as to have more margin on the nose side as it will bear more load (the gear pulls back as the airplane moves forward causing the gear to rotate about its trailing edge and bringing the front two screws into tension. Therefore these need more bearing area). This means that the rear single screw has only 3-4mm from the edge but I am not as concerned because it is only for alignment. I fibreglassed this anyway

2) On the wheel side, the hole is in the middle. (This end will be subject to twisting and compressive shear as the airplane moves forward). After I drilled the gear for the wheel axle, I felt that the hole was a bit too close to the edge, even though it was in the middle as this end is really not wide enough.

At my mentor's advice I fibreglassed and then sanded down the same (hence the rough finish). But I still feel that this may not be strong enough. The gear is about 2mm thick and quite solid. Is it strong enough? If not, what should I do to strengthen it?

CGRetired

My Feedback: (1)

What is the weight savings? For that plane and engine, I can't imagine 2.5 ounces will make much difference.

CGr.

jetmech05

I just got rid of a carbon fiber gear on my Yak 54 and went to aluminum......I found the carbon fiber just wasn't durable......dead sticked just after takeoff...had maybe 10 ft of altitude...turned a little better than 90 deg when I knew I just wasn't going to make it back.....leveled the wings and touched down...I was near the end of the roll out when the gear found a hole....cracked that carbon fiber gear in a couple of places....
Since I needed weight up front I went with a TNT landing gear aluminum main gear......I'll think twice before I use carbon fiber again

MetallicaJunkie

do u have any spare cloth (fg or cf lyimg around?

ameyam

Actually, this airplane should be around 3.2-3.6Kg. When I last weighed it was 3.85kg with the DLE20, ignition, tank, batteries but not prop. Then I had just kept everything in to see the total weight. The plan was to lose 80g on the battery (by usnig LiFe instead of NiMH for ignition with regulator), 70g on the landing gear, 70g on the wheels. That would bring it closer to 3.6kg.

Well, yesterday night I burned the midnight oil setting up all the parts. I retained the stock aluminium gear because people told me it would be brittle. I did put 3.25" foam wheels. I put a 16x8 GRP MAS for the time being. Didnt dare put the cowl or spinner. Even without the battries its very nose heavy. The foam wheels just go flat where they contact the ground and the tail simply slides around when pushed as if on a cushion of air. If I lower the nose so that it touches the ground, it holds that position. I havent had the time to install the wings, weigh or do a CG yet but last time I found it required 35g in the tail (5 pieces of GP 7g segmented weights) to balance. I have already given up on the LiFe for ignition, will use 4.8v eneloop instead. So now you know what I mean when I say it needs to lose weight

I will post more details this evening when I sort out the CG and battery issues. May be I will then have the total unloaded weight as well. Remember I was to 3D with the dle which is looking increasingly difficult. Also, if this weight continues, I may need to go back to rubber wheels, which will be more weight again

Ameyam

jaka

Hi!
2mm thick carbon gear seem a bit too thin!
But why on earth have a heavy 20cc gas engine on a plane that small!?

On my 216cm span Yak-54 powereed by a MVVS 45cc gas engine I use a carbon gear bought from "Troy -Built-models" and it has hold up without problems for 3 years.

ameyam

Referring this model

http://www3.towerhobbies.com/cgi-bin...&I=LXBGZV&P=ML

Its 60-90 but most have flown it with a 120ax and it flies well. I started with aFS91SII and that required a lot of nose weight. When I weighed the whole lot with the 91 against the DLE20, the dle was lighter. However, the larger mount, further front engine location and additional ignition battery weight have made it heavier.

Anyway, I dropped thr CF gear for the time being. The airplane weighs 3.8kg (8.37lb) with everything except a aluminium spinner. Its more nose heavy than stock- the recommended CG is 120mm from leading edge and this is 110mm or so from LE. Not much, I know but its also heavy. The foam wheels just flatten at contact with the ground. The total weight is more my concern than the CG

Pics are on the way

Ameyam

ameyam

here are the pics. You can see the wheels flatten out clearly

Ameyam

ec121

My Feedback: (2)

When you are using the lightweight tires, the wheels will flatten like that with just about any weight in them . Better to calculate the wing loading. You could buy a battery eliminator and do away with the ignition battery. Also the flight battery could be moved. I have one 33% Cap232 that has had a hatch put in the belly, and the battery is about halfway to the tail from the trailing edge of the wing.