Notices
Scratch Building, Aircraft Design, 3D/CAD If you are starting/building a project from scratch or want to discuss design, CAD or even share 3D design images this is the place. Q&A's.

Pumby Spanish plane.

Old 01-10-2020, 06:02 PM
  #1  
stearman70
Thread Starter
 
stearman70's Avatar
 
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
Posts: 48
Likes: 0
Received 0 Likes on 0 Posts
Default Pumby Spanish plane.

I built a high wing of Spanish plans called Pumby. 60" wingspan, balsa and ply. . The plane does not mark engine and the bench comes as for a .35 two strokes glow. I puted a .46 glow on it. His weight was 5 pounds.
The plane dials 4 degrees down trusth and 2 degrees right thrust and was what I encased the engine. I leveled according to the planes but with all the throttle, the plane taked off as if it were very heavy tail, when the throttle was lowered in half, the plane go down, as if it were somewhat heavy nose. Very very unstable, even with little elevator movement, he behaved very nervously. The only thing not attached to the planes, is that for lack of adequate wood at the time, I made the leading edge with wood a 16" thinner than the plane marked, so the edge was a little round and not as sharp as the plane marked , but I think this is not so influential as to have had such an unstable, erratic flight and almost on the verge of the accident. I will be grateful to help me define what may be the mistake I made in building it or what may be the solution to never risk it again with another bad flight. I include plan for consultation.
Thanks in advance for your help.
Attached Files
File Type: pdf
Pumby_Plan.pdf (442.5 KB, 24 views)
Old 01-11-2020, 02:14 AM
  #2  
rgburrill
 
rgburrill's Avatar
 
Join Date: Dec 2010
Location: Dallas, Tx CT
Posts: 2,326
Received 15 Likes on 14 Posts
Default

I had a plane that porpoised badly on first flight after a repair and the engine would rev up and slow down with each climb and dive. After getting it on the ground I found the engine mount had broken on one side which caused the engine to angle up a little on power up which caused the plane to climb and the throttle to reduce causing the airplane to dive and the throttle to increase which caused...you see where I'm going. I'm lucky I was able to get her back on the ground without damage.
Old 01-11-2020, 05:50 PM
  #3  
stearman70
Thread Starter
 
stearman70's Avatar
 
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
Posts: 48
Likes: 0
Received 0 Likes on 0 Posts
Default Pumby Spanish plane

The engine mount it is OK. I'll add weight to the nose and I'll change engine for smaller one, may be a .40. What do you think about this ?

Last edited by stearman70; 01-11-2020 at 05:56 PM. Reason: To modify the text
Old 01-12-2020, 06:10 AM
  #4  
alex5
 
Join Date: Jan 2006
Location: oakville, ON, CANADA
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default

The only thing I can see,is on the pdf,the wing appears to be set back a little much from the nose,and the cg as well.This ,on it's own, would make the plane highly reactive.To test this out,make two strips of foam that cap the leading edge and extend it by an inch and 1/2,or so.Really just extend the cord forward.
Old 01-12-2020, 06:17 AM
  #5  
alex5
 
Join Date: Jan 2006
Location: oakville, ON, CANADA
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default

you could add 2 degrees inclination up to the wing leading edge.This is basically a high wing trainer,with a sporty appearance...so find a Eagle 2 side view,scale it to suit your plane ,and set it up accordingly.
Old 01-12-2020, 06:35 AM
  #6  
alex5
 
Join Date: Jan 2006
Location: oakville, ON, CANADA
Posts: 340
Likes: 0
Received 0 Likes on 0 Posts
Default



Last edited by alex5; 01-12-2020 at 07:02 AM.
Old 01-12-2020, 07:49 AM
  #7  
speedracerntrixie
My Feedback: (29)
 
speedracerntrixie's Avatar
 
Join Date: Jun 2010
Location: Happy Valley, Oregon
Posts: 7,557
Received 35 Likes on 34 Posts
Default

I see nothing on the original plan that would alarm me. Keep the CG as per plan. I suspect that you simply have too much power. Modern .46 engines have very close power to what the .60 engines had back in the day. Depending on when that airplane was designed that .35 call out could be equivalent to a modern .25. What is the wingspan? A .46 size trainer with a flat bottom airfoil would be around 55"to 60".
Old 01-13-2020, 06:11 PM
  #8  
stearman70
Thread Starter
 
stearman70's Avatar
 
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
Posts: 48
Likes: 0
Received 0 Likes on 0 Posts
Default

Hello. Pumby has 60". I puted a .46 glow, two strokes and the plane take off simil to jet. IŽll change it for a old .40 and relevel CG.
Old 01-15-2020, 04:13 AM
  #9  
stearman70
Thread Starter
 
stearman70's Avatar
 
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
Posts: 48
Likes: 0
Received 0 Likes on 0 Posts
Default

Originally Posted by alex5 View Post
The only thing I can see,is on the pdf,the wing appears to be set back a little much from the nose,and the cg as well.This ,on it's own, would make the plane highly reactive.To test this out,make two strips of foam that cap the leading edge and extend it by an inch and 1/2,or so.Really just extend the cord forward.
Hello. I didn't quite understand how to put the foam on the leading edge. I'll appreciate it, you'll clarify a little more about what the mechanics are for doing it.
Thanks in advance
Old 02-07-2020, 04:48 AM
  #10  
stearman70
Thread Starter
 
stearman70's Avatar
 
Join Date: May 2012
Location: GuadalajaraJalisco, MEXICO
Posts: 48
Likes: 0
Received 0 Likes on 0 Posts
Default

Hello. You were right. The engine had too much power. I changed the .46 posse a .40 point and the problem was solved. Thank you and the other colleagues for their feedback.

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service - Do Not Sell My Personal Information

Copyright © 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.