Go Back  RCU Forums > RC Airplanes > Questions and Answers
Reload this Page >

Diving on downwind?

Notices
Questions and Answers If you have general RC questions or answers discuss it here.

Diving on downwind?

Old 06-13-2006, 08:24 PM
  #1  
wsmalley
Senior Member
Thread Starter
My Feedback: (6)
 
Join Date: Feb 2002
Location: Monterey, TN
Posts: 1,080
Likes: 0
Received 1 Like on 1 Post
Default Diving on downwind?

I have an Altech 'Tamecat', a trainer type F-14 ripoff. This was an ARF, and powered by an old Pico .46. It has been a pretty reliable flyer up until the last couple of flights. For no reason that I can determine, it started wanting to dive when flying downwind. Into the wind it behaves well and climbs out o.k. on t/o, but it has become a bear to keep in the air when going downwind. There are no apparent changes in incidence-wing or elevator- that I can see. I use a Futaba 8UAF radio. A real puzzler to me! Anyone got a clue what I might look for?
Old 06-13-2006, 10:19 PM
  #2  
Gollywock
Senior Member
 
Join Date: Sep 2002
Location: Santo, TX
Posts: 406
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

wsmalley- I'm not a know-it-all so please don't get me wrong. Your model doesn't know if it's flying with the wind or against it, or even cross wind. It's moving in a mass of air, so whatever direction the wind is coming from has no bearing on how it's going to fly. The only thing that can cause it to dive when flying upwind or downwind is going to be the elevator. Jim
Old 06-13-2006, 10:26 PM
  #3  
RCVFR
My Feedback: (7)
 
Join Date: Feb 2002
Location: Keller, TX
Posts: 2,051
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

I think his comment is that the plane is flying differently than it has in the past, and he is looking for some help as to what might be causing it to behave differently.
Old 06-13-2006, 10:43 PM
  #4  
Gollywock
Senior Member
 
Join Date: Sep 2002
Location: Santo, TX
Posts: 406
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Jim- There again, his airplane is moving in a mass of air. Whether the ground below it is moving faster or slower or even sideways has no effect on how it flies- Jim
Old 06-13-2006, 11:01 PM
  #5  
campbec
Senior Member
 
Join Date: Mar 2004
Location: South West Rocks N.S.W., AUSTRALIA
Posts: 495
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Hi,

Based on what the two Jims have said, (do two Jims make a James?). Do you change anything flying up wind or down wind?

All I can think of is you have something loose that changes if you vary the throttle or the battery has moved changing CoG. Jim/Gollowock is correct up wind or down wind the only thing that changes is ground speed unless you are flying close to a landform or structure that causes turbulence such as a hill top, building, stand of trees.

Sorry nothing more to suggest. You have me intrigued. Please post the problems cause when discovered.

Cheers,


Colin
Old 06-14-2006, 05:15 AM
  #6  
STLPilot
Senior Member
My Feedback: (21)
 
Join Date: Mar 2003
Location: Manhattan, NY
Posts: 9,227
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Well the obvious answer is that it has a high wing loading. The reason that it's diving is that it needs more air to stay aloft. If it's falling on downwind apply more power. If you can't get enough power then your engine is not powerful enough for the plane.

What is the wing area and weight? Actual weight, not what it says on the box. Also check the RPM of your prop. If it's just happening then maybe your engine is losing power, even if it sounds like it has power.
Old 06-14-2006, 06:39 AM
  #7  
CHassan
My Feedback: (13)
 
CHassan's Avatar
 
Join Date: Aug 2002
Location: MainevilleOH
Posts: 1,318
Likes: 0
Received 2 Likes on 1 Post
Default RE: Diving on downwind?

Once again as Gollywock said, it doesn't matter. If it will fly and climb upwind, it will fly and climb downwind.

Now is this wind 30mph? A quick turn from upwind, to downwind in high wind can cause a loss of airspeed, resulting in a loss of altitude, regardless of wingloading, or power.

Old 06-14-2006, 07:21 AM
  #8  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Definitley an airspeed issue. That is all I can tell for sure.
When turning from upwind to downwind, there must be an increase in ground speed in order to maintain level flight.

Say that your plane is flying 60 MPH. The wind is 10 MPH. When flying up wind (level flight) your ground speed will be 50 MPH.
When Flying downwind, your ground speed must increase to 70 MPH to maintain level flight!

A 20 MPH (ground Speed) difference between flying upwind and downwind...... Well, theres your problem!

Doug
Old 06-14-2006, 08:27 AM
  #9  
wsmalley
Senior Member
Thread Starter
My Feedback: (6)
 
Join Date: Feb 2002
Location: Monterey, TN
Posts: 1,080
Likes: 0
Received 1 Like on 1 Post
Default RE: Diving on downwind?

Hhhmmmmmmmm! Well, lots of ideas to consider. First, the question centered about a plane that flew very consistently regardless of wind conditions, and didn't seem to need any major elevator changes upwind, or downwind. Then, fighting it to keep from going into a dive on the downwind side. I have to examine the power issue, possibly the engine is gradually losing power, though it would seem I'd notice that more on the t/o and climb-except it's a big wing with lots of lift. Another thought is what would happen if the thrust angle of the engine changed? Or, perhaps a loose elevator hinge. The wing is held on with rubber bands, maybe I've somehow changed the incidence without knowing. I have started to tear the plane down and see if I can figure it out. It's kind of like you get in your car one day and notice it just isn't running right, and the mechanic says there's nothing wrong with it.
Old 06-14-2006, 08:34 AM
  #10  
Crash90
Senior Member
My Feedback: (17)
 
Join Date: Oct 2002
Location: Cressona, PA
Posts: 2,320
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Have you changed props or added any weight recently? Shifted CG? Anything?
As STLPilot said. The only difference between flying up wind and down wind is airspeed. Generally you will need a bit more throttle when flying downwind.
Old 06-14-2006, 09:18 AM
  #11  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

STLPilot is on the right track. If your Tamecat was flying consistently, and is now lacking in performance,
the only area the problem can be is power. The engine may be running great on the ground, but not unloading in flight.

In level un-accelerated flight: Lift is equal to gravity and trust is equal to drag.
Therfore, the only thing that can cause your problem is a deficiancy in one of the above. You can eliminate gravity and lift.
That only leaves thrust and drag. You can eliminate airframe drag, as nothing has changed there. That only leaves thrust and propeller drag.

The first thing I would try is changing the glow plug and fly it again. (In my helis, when perfomance drops, It is almost always a plug that is worn out.)
The Pico is a pretty hot engine. So, that is the most likely possibility!

Before you go tearing into a perfectly good airframe, Change your glow plug.
If that doesn't do it, change the engine.

Doug
Old 06-14-2006, 09:22 AM
  #12  
Gollywock
Senior Member
 
Join Date: Sep 2002
Location: Santo, TX
Posts: 406
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Crash- The only difference between flying upwind or downwind is groundspeed, not airspeed. Jim
Old 06-14-2006, 11:15 AM
  #13  
Tall Paul
Senior Member
 
Join Date: Jun 2002
Location: Palmdale, CA
Posts: 5,211
Likes: 0
Received 1 Like on 1 Post
Default RE: Diving on downwind?

ORIGINAL: firstplaceaviator

Definitley an airspeed issue. That is all I can tell for sure.
When turning from upwind to downwind, there must be an increase in ground speed in order to maintain level flight.

Say that your plane is flying 60 MPH. The wind is 10 MPH. When flying up wind (level flight) your ground speed will be 50 MPH.
When Flying downwind, your ground speed must increase to 70 MPH to maintain level flight!

A 20 MPH (ground Speed) difference between flying upwind and downwind...... Well, theres your problem!

Doug
???
The wind "carries" the plane. The plane doesn't "know" this, it thinks 60 mph airspeed is what it flies at, regardless of the wind direction.
Adding the wind speed to the airspeed, upwind or downwind, changes the ground speed, but that is totally disconnected from the airplane.
Ground speed is what the pilot sees, but the plane doesn't.
A plane that's trimmed to fly level at 60 mph will fly level at 60 mph in any direction relative to the wind.
Similarly, wind speed doesn't affect the motor.
A motor doesn't know about upwind or downwind.
There's something aerodynamic going on.. the elevator returning to a different position after a commmand is a possible source.
Old 06-14-2006, 01:35 PM
  #14  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Tall Paul,
Better read that quote again!
You state EXACTLY the same thing in different words!

ORIGINAL: Tall Paul
???
Adding the wind speed to the airspeed, upwind or downwind, changes the ground speed, but that is totally disconnected from the airplane.
Ground speed is what the pilot sees, but the plane doesn't.
A plane that's trimmed to fly level at 60 mph will fly level at 60 mph in any direction relative to the wind. (unless it can't maintain 60 MPH - Doug)

There's something aerodynamic going on.. the elevator returning to a different position after a commmand is a possible source.
Here is what is happening with the Tamecat:

The engine is not producing as much power as it use to. When the plane is turning (accelerated flight), the engine is not producing enough power to maintain level flight. Therefore, the plane must dive to maintain airspeed. Or, Up elevator must be held in order to maintain altitude until the airspeed has returned to normal.

I will guarantee that if the plane is flown on a day with no wind, that the plane flys slower than it did before this problem came about!.

However, you are right. There is something aerodynamic going on.

The propeller is not producing as much lift/thrust/power as it use too!

By the way, airplanes don't know or think anything. They are not intelligent beings, just man made machines.

I have been flying R/C for 29 years.
Also, I am a full scale mechanic, inspector and pilot. I specialize in troublshooting and performance enhancements.
When a customer brings me an airplane that is not performing as it should, they pay me BIG BUCKS to fix it.
Sometimes, it takes some time to troublshoot. But, I have NEVER been wrong about the cause or the cure!

Would you care to explain how elevator trim could possibly change, only when flying downwind?

Doug
Old 06-14-2006, 04:26 PM
  #15  
JohnW
Senior Member
My Feedback: (6)
 
JohnW's Avatar
 
Join Date: Mar 2002
Location: Lincoln, NE
Posts: 1,815
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Yes, planes don't fly different in steady wind. The only time wind will affect handling is if the wind is changing velocity (either speed or direction.) Because of plane inertia, drag, etc., the plane will react to gusts. But a steady wind, no, the plane flies just like it does when it is dead calm. The only time steady wind becomes a factor is when the plane interfaces the ground, i.e. takeoff and landing, but even then the only diff is ground speed vs. airspeed... this is why planes takeoff/land into the wind, to gain the most benefit from the wind and to reduce ground speed required.

I'll throw out a bit different observation. It might be an illusion. From our reference as a RC pilot standing on the ground, downwind flight looks very fast. I often see many throttle back on downwind, or make an aggressive turn to downwind which kills airspeed, all due to the illusion that the plane is not performing as expected, so the pilot compensates. The illusion occurs because of our perspective of being firmly planted on the ground. Double whammy is the aggressive turn with throttle back. Pilot is "tricked" into thinking they have plenty of airspeed, or even excessive airspeed because downwind passes look fast. I'm not saying this is the issue, but I've seen it effect pilots before.
Old 06-14-2006, 04:52 PM
  #16  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

JohnW,
You are Sooo right!
Even I have fallen victim to the "illusion"
I got too slow on downwind. As I started my 180 degree turn to final, the plane stalled and spun in!
That resulted in total destruction of my Lanier Laser 200....
Doug
Old 06-14-2006, 04:58 PM
  #17  
Tall Paul
Senior Member
 
Join Date: Jun 2002
Location: Palmdale, CA
Posts: 5,211
Likes: 0
Received 1 Like on 1 Post
Default RE: Diving on downwind?

ORIGINAL: firstplaceaviator

...

Would you care to explain how elevator trim could possibly change, only when flying downwind?

Doug
.
As I mention, if the elevator doesn't come back to the -same- neutral after a command, the trim will change.
Old 06-14-2006, 05:06 PM
  #18  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

But why only when the airplane is flying downwind?
Doug
Old 06-14-2006, 05:30 PM
  #19  
aerowoof
 
Join Date: Jun 2006
Location: pembroke, NH
Posts: 2,985
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Diving on downwind?

could even be a stripped gear in elevater servo.i would hold the elevater and move the stick up and down and see if any hinges wiggle or a clicking sound is heard from the servo.
Old 06-14-2006, 05:37 PM
  #20  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

If it were a bad servo, stripped gears or a loose hinge, than it would be flying eratically all the time.

Anyway, I'm done arguing.
Mike, change your glowplug!
I'm out!
Doug
Old 06-14-2006, 07:14 PM
  #21  
aerowoof
 
Join Date: Jun 2006
Location: pembroke, NH
Posts: 2,985
Likes: 0
Received 2 Likes on 2 Posts
Default RE: Diving on downwind?

throttle controls altitude
elevator controls pitch.
statement made says diving not loss of altitiude.diving to me means a sudden change in pitch not a gradual loss of altitude,therefore this being an older plane that something has changed to create this problem.if changing the glow plug does not work one must look else where,the next place to look is in the elevater control from servo to elevater to see if all is operating properly,could also be rubber bands on the wing breaking causing a problem or not enough.or the wrong size.should be #64 and at least 10 per side.should be changed each flying seasion.break a prop recently?did you replace it with the same pitch prop?usually a worn engine will idle poorly and the top end will be down and this will show up on take off and climb out.
Old 06-14-2006, 08:20 PM
  #22  
Crash90
Senior Member
My Feedback: (17)
 
Join Date: Oct 2002
Location: Cressona, PA
Posts: 2,320
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Gollywock. Check your statement. I think you are reversed. If you are moving along at 50mph and all of a sudden a 50mph tailwind hits, your plane is still moving 50mph ground speed but there is no air flowing over the wings and you will fall from the sky because you have lost all "airspeed".


Anybody else want to chime in?
Old 06-14-2006, 08:48 PM
  #23  
Tall Paul
Senior Member
 
Join Date: Jun 2002
Location: Palmdale, CA
Posts: 5,211
Likes: 0
Received 1 Like on 1 Post
Default RE: Diving on downwind?

ORIGINAL: firstplaceaviator

But why only when the airplane is flying downwind?
Doug
.
Do you comprehend the airplane can't "know" upwind from downwind?
Old 06-14-2006, 09:28 PM
  #24  
firstplaceaviator
My Feedback: (27)
 
firstplaceaviator's Avatar
 
Join Date: Feb 2004
Location: Norton, OH
Posts: 737
Likes: 0
Received 0 Likes on 0 Posts
Default RE: Diving on downwind?

Yes, I comprehend. Please go back and carefully read wsmalleys original post.

According to RCU policies, I should not degrade, insult or embarass anyone.
According to RCU policies, I should not degrade, insult or embarass anyone.
According to RCU policies, I should not degrade, insult or embarass anyone.

Doug

I'm OUT and I really really mean it this time![sm=lol.gif]
Old 06-15-2006, 10:09 AM
  #25  
wsmalley
Senior Member
Thread Starter
My Feedback: (6)
 
Join Date: Feb 2002
Location: Monterey, TN
Posts: 1,080
Likes: 0
Received 1 Like on 1 Post
Default RE: Diving on downwind?

I found the firewall is able to flex when I grab the engine and move it. Haven't pulled the cowl off yet to determine the exact cause. Partly, the design has, I think, a weak link in that the firewall is open on the top with a long ABS cockpit sitting on top. Would changing the downthrust/sidethrust cause this problem, if the prop is 'loading' and unloading?

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service -

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.