wounded_bird

My Feedback: (1)

Flew my Midwest extra 300xs last Sunday.This is my first really aerobatic plane,been flying for about 3years . Took off smooth with engine (moki 2.10) running great! Made a few circles around the field to trim it up and was flying very stable and smooth. Had already run a couple of gallons of fuel on the test bench for break-in. I took it up to a safe altitute and did a couple of loops at about 1/2 throttle. On the forth loop I throttled up a to about 3/4 throttle and on the back side of loop I heard a awful fluttering sound. I immidiatly throttled back but it was too late the plane coming apart at the seams. I can only assume that my servos were not heavy enough. I was using s3010 on airlones and s9001 on elevators. Can anyone help me with an explanation? I put alot of time into trying to build this airplane strong. Sealed all the control surface seams. used the kits control arms.

Marcio Senger

how many flights you have done in this airplane?

Do you use to do a "walk around" to check all the traditional "checklist" before each flight?

Flying theese ladyes I discovered (well, it is pretty obvious) that after lots os flights the horns start to leave the balsa, well, my english doesn´t help now, but the point is that the wood seems to be stressed after flying a lot and the screws just fall off or something like that. It happens suddenly specialy if you screwed very tight (very firm) , this way, the horn will still aparently holding well on the wood, but it is ready to crash.

Well, this is valid only if you use horns

Sorry for the loss, i was a very beautifull plane!

Did you loose some receiver os engine part also, or the dammage was only at the plane?

Márcio

wahoo

My Feedback: (59)

Sorry for the loss, looked like a damn nice plane. I'm no expert but i would never dream of using anything other than metal geared servos on anything above a 1.20 size plane.

John

Chris Moon

My Feedback: (8)

Sorry for the loss. It looks like a beautiful plane. Let's look at what you had:

Futaba specs - 9001
Torque: 54 oz/in @ 4.8V

Futaba specs - 3010
Torque: 72 oz/in @ 4.8V

Midwest Extra Specs -
SPECS: Wingspan: 80"
Fuselage Length: 72.5"
Airfoil: Fully-Symmetrical, Low Wing
Wing Area: 1162 sq. in.
Weight: 14 - 17 lbs.

A 14-17lb plane does not have a chance with 54oz torque servos. Even the 3010's with 72 oz on ailerons is not enough. When you come around the back of a loop, and the G'S start to kick in and your 17lb plane @ 3 G's now weighs 51 lbs, the 54oz servos are toast trying to move and hold the flight surfaces.
I have a Great Planes Patty Wagstaff Extra with similar size and weight, and I remember the manual specifically stating that minimum 90oz servos are mandatory. I fly JR and have 8411's (155oz) on the flying surfaces.

I wish someone would have warned you before flying it that those servos were not enough. I'm surprised that Midwest did not have a warning in the manual.

davidmor

I am really sorry to hear about your misfortune. I really understand your pain as I lost my Midwest Extra on its 20th flight due to a dumb thumbs incident around 3 months ago. I have to agree with ual767 on this one. The servo's you installed were very undersized for the application. Even if you were running a 6V system, they were undersized. I used Hitec 5625 Digitals on the ailerons and elevator (131 oz/in at 6V) and 5645 on the rudder (168 oz/in at 6V). The instructions recommend S9202 on the Elev and Ailerons which are rated at 76 oz/in at 4.8V and 98 oz/in at 6V. These IMO are the minimum sized servos for this application. Also, if you had your linkages connected to the outer holes in the servo arms and close to the control surface to get big throws, the effective torque is less.

When I built mine, the thing I spent the most time researching before ordering was the servo's. As my budget was limited, I didn't want to break the bank on servos but I did want decent higher torque servos with good speed and metal gears. For what I was looking for, the 56xx series fit the bill. After destroying my Extra, I was able to take all of the servo's out, test them, and re-install them in my GP Patty Wagstaff. They work great, and the response and resolution is fantastic. Gotta love them metal gears too! If it makes you feel better, here is a picture of my plane after I strained it through a tree early this summer.

Ron Stahl

My Feedback: (12)

The weight of the plane has nothing to do with what size servo torque you need to safely fly it. What does have a direct requirement is the size of the surfaces/ defection angle/and the airspeed at with that will occur. I will try and post the link I have at work for figuring out what you would need for that size plane. I just ran a test for a friend of mine and we found out that he had 25% of what he really needed on rudder but 200% of what he needed on ailerons and just a little over1 00% on elevator for servos using the same size everywhere on his plane. Many people think that weight of the plane matters but it is the area of the surface that dominates the loading as well as what king of linkage your setup has.

scoli121

My Feedback: (20)

What size were your pushrods? You know, I have a U-Can-Do that came with 256 pushrods... They bend SO EASILY. I'm getting ready to change them out to 440's. Is it possible that you could have had a similar problem?

JoeAirPort

My Feedback: (41)

The servos were way undersized. I would have used something well into the 100's of ounce-inch torque. The Hitech 5645's are are 168 ounce-inch at 6 volts. That would have been a good servos all around. Also I'd like to see pic's of the control linkages. That has a big effect on the servos failing. I had this same thing happen to me using 635's and setting the throws for 3D. Big mistake. Luckily I only damaged the wing and the fuse was fine. I now use the 5645's, my linkages are set up 1:1 and I have about 30 flights with no problems at all. Also that Moki is a VERY powerful engine and needs to be respected. I have a 1.80 Moki and find myself constantly having to throttling back and bleed off speed.

Joe

davidmor

I can't speak for zajax918 but the kit comes with 4-40 rods and pull/pull for the rudder. The linkages are short and on mine there was no flex at all in the system. If he did it per plans, the included pushrods and clevesis are adequate.

RC_Pilot2k

My Feedback: (26)

Hehe...I had flutter with my Midwest Extra 300 a few years ago...here's the carnage...and the rebuilt afterwards...

JaredM25

My Feedback: (26)

Not only weight, but surface size too, 54 oz has no chance on a big elevator of an extra....sorry for your loss, but trying to cheap out on servos doesn't work on bigger planes.

GPitts

My Feedback: (6)

Just untill now I've never really realized what flutter is and how much important an adequate powered servo is. Really learned alot from this thread....I guess your loss is my gain...

real nice airplane btw...

highflyermark

My Feedback: (-1)

Spend the $115 on the futaba s9402!!!!! You can never have too fast or too strong of a servo. Some would say it is overkill, but it isn't. This servo will kick your ass!!!!

wahoo

My Feedback: (59)

I think the weight of the plane has everything to do with how much torque a servo needs. Post that link and enlighten us please.

bentgear

wahoo,

Try telling that to some of the 3D fliers using massive control surfaces and throw rates.

I think its a combination of both. Even on heavier planes that have small control surfaces and reduced throw it does not take as much servo torque because you can use the mechanical advantage in the linkage to your advantage.

Ed M.

hopkimf

My Feedback: (56)

For once I would like to see a semi-analytical approach to servo selection. We all know the control system forces are what the servos feel. We also know that control surface area and aircraft velocity determine the magnitude of these forces. We also know that the lever arm lengths on the servo and control surface has a direct effect on the servo torque. I can easily calculate the surface areas on my control surfaces. I can measure the control horn and servo arm lever. But what I can not easily calculate is the force on the deflected control surface. To do so I would need the angle of deflection and aircraft velocity. I don't have either for actual conditions. I would like to se something in print providing "typical" values for these items for each class of aircraft. Armed with that information, people could make intelligent decisions on servo size. An earlier post suggested model weight. I can't buy that. I would really appreciate well informed, knowledgeable information, not BS. Comments?

bentgear

hopkimf, there is a great little excell file that already does this. Can't remember the author or company name but its cheap and gives you backa lot more information than you need to make an informed choice. It's on my office computer and I will post the link to it tomorrow.

Ed M.

bentgear

This is the site I mentioned above. Takes a lot of the guesswork out.

[link]http://members.cox.net/evdesign/pages/linkage_design.html[/link]

Ed M.

KFalcon

My Feedback: (18)

Flutter, a model planes worst enemy. Sorry for your loss.

frank99

My Feedback: (29)

767 in the manual midwest SAID to use 54oz servos on the airlerons i know lost one too [:@]call midwest and and the have the worst support in the hobby[:@]. was new and did not know THAT the size servo was for a .40 trainer boy oh boy i have it in print if any one wants to see the manual we need more folks like hanger9, great planes, sig, and others THAT stand behind there products and if they make a mistake they will make it right.