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RE: 50cc Su... - 4/28/2008 2:12:24 PM   
cmircman


 

Posts: 191
Joined: 8/17/2004
From: Rittman, OH, USA
Status: offline 		Roboto65 to me it soumds like you have to much up thrust. The trimming guide that fishdeth posted will help solve any questions you would have about getting your plane trimmed out properly.




Rich

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RE: 50cc Su... - 4/28/2008 2:15:00 PM   
roboto65



Posts: 173
Joined: 10/27/2004
From: Conroe, TX, USA
Status: online 		Yeah have to get the right tools but going to check it out for sure !!!!

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RE: 50cc Su... - 4/28/2008 3:26:51 PM   
SAL98



Posts: 569
Joined: 1/18/2002
From: Lindenhurst, NY, USA
Status: offline 		To me it sounds like your tailheavy with both of your simptoms happening at the same time. She will porpoise on you if she's tailheavy, but to check your up or down thrust you can just prop the tail up on the ground to were the plane sits level and then stand back and eyeball the prop to the cowl. With such large props its easy to see if the engine is pointing up or down. Look for it to be level and then you can check a few other things.

Start by flying straight and level and then pulling up to a 45 degree line, hold for a second and then roll inverted and let go of the sticks. If she holds the 45 then your on the borded line of tailheavy, if she climbs then your definitly over the line. I would suggest that you set up your cg as such that she falls slightly on that 45 degree line. This will make the sukhoi very user friendly while your getting use to her. It will come in for landings without the ballooning, and fly much more predictable in upright flight. Inverted will require a good bit of down to keep level but like i said for know just fly it that way and when your more relaxed and use to her you can slowly move the cg back for a more neutral feel on the sticks for precision flying.

Another test for cg would be to fly straight and level and then bank close to 90 degrees and use elevator alone (no rudder to hold the nose up) to carve a nice shallow turn. In precision flying with a slightly tailheavy setup you will notice that even at this step bank the nose dosent really drop and you can pull lightly on the elevator to carve the turn without losing altitude. Once again this is not what you want at first, but it is another way of checking if your cg is to far back for know.

If you do decide to use the trim charts thats out there just remember one thing, They are meant to be used in the order they were written in, If you decide to change something like the CG later on you will have to redo all of the settings that precided it. This will mean any programable mixes as well. Trimming for precision can be a long an tedious process but in the end I have found that it is truly worth all the effort. Well trimmed planes fly on rails and give you a feeling of being totally lock in and in control.

< Message edited by SAL98 -- 4/28/2008 3:34:44 PM >

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RE: 50cc S... - 4/28/2008 5:28:55 PM   
rctom



Posts: 5038
Joined: 5/8/2002
From: Flower Mound (near Dallas), TX, USA
Status: online 		To check up/down thrust angle follow this procedure. Do this a few mistakes high, not close to the ground.

Fly along in front of you at full throttle, with the plane trimmed for straight and level. Then carefully close the throttle quickly without touching any other control.

The plane should continue on in the same orientation for a while, eventually as speed bleeds off the nose will drop but initially there should be no change.

If the plane climbs when you close the throttle you need to add some up thrust, if it dives suddenly put a little down thrust in, then re-run the test.

If thrust angle is way out of whack for some reason it will make adjusting the CG more difficult, the two things interact so it's really important to have one correct before adjusting the other.

TF

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RE: 50cc S... - 4/28/2008 6:41:36 PM   
roboto65



Posts: 173
Joined: 10/27/2004
From: Conroe, TX, USA
Status: online 		Well for balance which I neglected to tell everyone sorry is right on the front edge of the wingtube. Thanks for all the replys I love this bird just want to make sure I have her correct and not lose her because of MY mistake and not making sure she is set up correctly and she flys true and it is my Dumb thumbs not setup which would also be my fault !!!

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RE: 50cc S... - 4/28/2008 9:48:55 PM   
chuck l


 

Posts: 868
Joined: 11/21/2002
From: Stacy, MN, USA
Status: online 		Prop question. I need to buy a new prop for my DL50 because of the bad landing I mentioned in an earlier post. BTW, thanks for the suggestions on the firewall. I've been running 22x8 props, but see people recommending 23x6 for 3D. What performance difference am I going to see with the bigger diameter prop?

Chuck

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RE: 50cc S... - 4/28/2008 10:03:07 PM   
rctom



Posts: 5038
Joined: 5/8/2002
From: Flower Mound (near Dallas), TX, USA
Status: online 		I've never seen a 23-6, but I would expect it to be very slow with lots of pull at low speeds. Without actual testing though that's just a guess.

TF

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RE: 50cc S... - 4/28/2008 10:33:11 PM   
chuck l


 

Posts: 868
Joined: 11/21/2002
From: Stacy, MN, USA
Status: online 		Should I have said 23x8? Sorry.

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RE: 50cc S... - 4/28/2008 10:34:33 PM   
Greg Cothern



Posts: 587
Joined: 1/7/2002
From: Seagoville, TX, USA
Status: offline 		Roboto its actually on the rear of the wing tube... It is a bit tail heavy, but still changes pitch slightly with throttle changes, so it needs another degree of down thrust as well as a bit more of right since we have some right rudder dialed in for trim.

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RE: 50cc S... - 4/28/2008 11:23:31 PM   
LeeHunt


 

Posts: 161
Joined: 2/2/2006
From: Katherine, AUSTRALIA
Status: offline 		Gee this is getting interesting, Ok my plane, in a vertical climb tracks very straight and just keeps going up and up and up ok good, looks great too!!
Now fly along full power and pull throttle back to idle, plane slows and starts to dive, increase throttle and plane continues on the the trck it had at idle, still good
so why from quater throttle, power up to full and the model starts to climb. At half power it still climbs but slowly. put in one click of down trim and the model decends not badly only enough to be annoying because I have to correct just a bit all the time. Would someone be so kind as to tell me why????? and or is it just that I need a small amount of down thrust put in. I must add that the landings of this plane are very elevator sensitive could this be the same problem. my CofG is right in the middle of the wing tube.
Regards
Lee

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RE: 50cc S... - 4/29/2008 12:02:49 AM   
Greg Cothern



Posts: 587
Joined: 1/7/2002
From: Seagoville, TX, USA
Status: offline 		As with Roboto's bird sounds like you need a bit of down thrust.
The weather conditions (winds) were a bit subpar for the initial 3 flights we put on Roboto's bird when I finished assembly to know what thrust angles were correct.

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RE: 50cc S... - 4/29/2008 2:49:57 AM   
LeeHunt


 

Posts: 161
Joined: 2/2/2006
From: Katherine, AUSTRALIA
Status: offline 		Greg, Thanks for the reply, could you tell me how much do you use, say one washer on the top two bolts???????? would this be ok
Regards
Lee

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RE: 50cc S... - 4/29/2008 8:47:28 AM   
pupmeister



Posts: 145
Joined: 1/20/2003
From: MaitlandNSW, AUSTRALIA
Status: offline
quote:

ORIGINAL: chuck l

Should I have said 23x8? Sorry.


I am running a 23x8 Mejzlik on mine at present but I do not think that it is the best 3D prop out due to it's slow spool up due to it's mass, however it is very good for IMAC. There is a lot more to a prop than just its diameter and pitch. A lighter prop such as the PT carbon fibre or the Vess props are often better for 3D since they have better spool up but are not necessary the best props for IMAC. I have a Vess 23A that I still want to try for playing around a bit.

Cheers
Pupmeister

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RE: 50cc S... - 4/29/2008 1:55:47 PM   
rctom



Posts: 5038
Joined: 5/8/2002
From: Flower Mound (near Dallas), TX, USA
Status: online
quote:



There is a lot more to a prop than just its diameter and pitch.



This is the understatement of the week! There is so much more to props than just the size.

Yesterday I did some testing of an engine on the bench, a TOC-53 with a canister on it. I was initially just testing the canister, but I figured what the heck, I'm here and have a bunch of different props, lets see how they each work.

I tried a Vess 22-a and a 22-B first, putting up impressive numbers of 7350 and 7150 respectively. I already knew these props were high revving, I flew my Extra this past weekend with the 22-B and found that it was just OK despiote the high RPM numbers.

Then I tried a few others. A TBM 22-8 put up 6750, while the Bunny 22-8 turned 7000 even. Finally I tried a 23-10 Mejzlik, which only allowed 6450 RPM.

I think that my preference would be a Bun