SEN 1906

Table of Contents SEN 1906

  1. Robert Lesko Process
  2. Looking for F1C
  3. W&O Results




Robert Leško Raketa Nera building process
Everyone had admired both the looks and performance of Robert Lesko's "Raketa Nera" World and Euro Champs winning F1A.  Over recent months Robert has been generous in sharing information and drawings about his airplanes. He just wrote up his personal process of how be builds the aramid core, carbon covered wings.  This appeared on the F1A Flappers group on FaceBook.

In the words of Robert...
 Material used: Textreme IMS 76g/m2 (Torayca® M 30 SC 18k fiber) for wing skins. Aramid honecomb 29kg/m is used as sandwich material. Epoxy resin LF386 (pot time is long enough for using in this application). For spars Tenax UM46 carbon roving. For leading edge and wing joiner I used Tenax IMS65 carbon roving. Moulds-negatives, upper profile and bottom profile side. 

Carbon skins are made first (vacuum bag) use 40% resin compared to carbon weight (on 100g carbon 40g of epoxy). Do that carefully and make some pretest to get all carbon wet evenly not to exceed 40% resin. When carbon skins are cured take spar (carbon balsa carbon) and trailing edge (carbon cape strip 1.5 x 02 mm) and glued it on bottom carbon skins (still in mould) again with epoxy in vacuum bag. 

When this is done next I put few roving’s of carbon on front for leading edge, and glue 5mm balsa end ribs. Next in process is Aramid honeycomb gluing to bottom skins. Best way I have found to do that to get reasonable weight is little complicated but it works fine for me. First I cut honeycombs to fit in. Take bottom mold and carefully sand a carbon skin (just a bit to get better surface for gluing honeycomb). Take some flat table and cower it with large sheet of nylon. Take resin on piece of cloth and make thin film of epoxy evenly on nylon. Take Honeycomb and weight it. Put honeycomb sheet on nylon and make small circle moves while pressing it to soak resin from nylon. Weight honeycomb sheet to get info how much epoxy did soak in. Repeat the process until you get desired amount of epoxy on honeycombs. 

Maybe it would be the best to do some tests with honeycomb to get value of minimum resin needed to achieve adequate bond to carbon skins. When you get good sample just take amount of resin used and dive it with area to get formula for the wings. The amount of epoxy I used was 0.3g/dm2. When you get enough resin on honeycomb sheet press it to bottom mold on carbon skin, and put it in vacuum bag. When epoxy cures it is time to sand honeycombs top side to desired profile. Put profile templates on ends and sand it. Use large piece of wood board with sand paper grain 120 or similar. 

When you sanded to profile templates take fine sand paper grain 1500 on your fingers and sand honeycombs to get out all Aramid hairs from previous sanding process. Be gentil not to over sand, use forceps if needed to remove larger parts that bend in to honeycomb holes. After that next is boring process of drilling over 20000 holes (0.3 mm diameter) on aramid honeycomb walls to achieve open air flow all across thru aramid honeycomb. Every comb has to connected with hole to breathe freely, if not you will end with bubbles and caves on your wing after first sunny flights or heat treatment. Air has to circulate freely inside of wings. 

After drilling your wing is ready for closing process. Take out your wing from bottom mould and weigh it. Process is the same as it was for gluing honeycomb to bottom carbon sheet. Take some flat table and cower it with large sheet of nylon. Take resin on piece of cloth and make thin film of epoxy evenly on nylon. Put your wing top side (open honeycomb side) on nylon and make small circle moves while pressing it to soak resin from nylon. Weight honeycomb sheet to get info how much epoxy did soak in.

 Repeat the process until you get desired amount of epoxy on honeycombs, for safety reason I used 0.5g/dm2 that is more than on bottom side but I do not want to ruin all the work I done with possibly unboned area at the final step. If there are some dry area take resin on brush and gently wet honeycombs. When you are sure that every part is covered with epoxy press your wings on top carbon skin in top profile mould. Try to be precise in first attempt and not to move unnecessary so epoxy will stay on skin-honeycomb contact not to be smeared on area where it is not needed (inside honeycomb holes). Put some tape to secure wings from movement in mould, and put all in vacuum bag. Vacuum will press your wing to top profile mould and bonded it perfectly. Do not use too much pressure, I did it on -0.4 to -0.6 Bar. If there are some small imperfections in wings profile from sanding process it doesn’t matter and your wings will be bonded to top carbon skin perfectly. 

That is all, your work with moulds is done. When you completely finish your wings last thing is to do heat treatment according to epoxy resin technical datasheet. In my case for LF386 it was 80 degrees Celsius for 15 hours. Since we did all that drilling on honeycomb walls there will be free air flow inside the wings there will be no bubbles or caves on wing surface that will reduce flight performance.

I believe this is in short words all that you need to take care when building your wings using Aramid honeycombs. Or let’s say after many planning, samples testing and problem solving this was the way I get the best overall results at the end. Finished wings weight was 220 g. Time I spent to build last wings was over 400 working hours, for first one it was more than double time, but at the end you have stiff and long lasting beautiful wings.

Robert Lesko

Looking for F1C Model
Hello free flight community,
I am making a transition from F1P to F1C and would like to know if anyone has F1C models that they are willing to sell to me. It can also be damaged just as long as it can be repairable. You can contact me through my email at This email address is being protected from spambots. You need JavaScript enabled to view it.
-          Junior Team Member Taron Malkhasyan

Wilbur & Orville Sep 6-7, Wawaywanda NY

It was expected to rain on Saturday. The day started off being windy, then it 
calmed down and later it begun to rain. Maxes for F1Q were set at 2 minutes 
and the motor runs were reduced to 2/3rd. Dave Lacey CDed the Saturday 

It continued raining overnight but was over by dawn. On Sunday the drift was 
expected from the north.  This time of year he field has very high corn and beans 
on its south western side and we were also constrained by segments with fresh 
sod planting.  So in the third round when the drift started coming from the north 
west, across the narrowest portion of the field, the maxes were cut to 2-minutes. 
Next round the drift shifted and came from the north allowing flying 2:30 minute 
maxes. John Clapp’s F1B model landed on a tree along the eastern part of the field,
required the services of a tree climber. The tree climber came with his two young 
kids and his daughter enjoyed flying a small Cat glider. 

In E36 we experimented with 10 second motor runs in the first three rounds. This 
was sufficient to determine the winner. The contest was attended by 15 adults and 
two juniors - Joel Yuri  and Rebbecca Avla. 


 Saturday Sep 6          
 F1Q            120 120 120 120 120 600  Dick Ivers    120 120 87 120 120 567  Joel Yuri J    101 91 120 79 110 501  David Lacey    120     120  Yuda Avla    
 F1H             65 92 117 120 120 514  Bob Sifleet     120 59 59 63 86 387  Andrew Barron  
 F1G    120 83 95 120 120 538  Carrol Allen     66 120 120 84  390  John Clapp     96 80 120 60  356  Don Rousseau   120 67    187  Bill Buss    120    120  Larry Pelatowski  
 HLG (both days)    129       Larry Pelatowski   116       Bob Morris                
 Sunday Sep 7  
 Dawn Unlimited           120       Rich Wagener  
 160 180 120 150 150 150 150 150 1210  Bob Sifleet  210 180 66 150 150 150 150 150 1206  Andrew Barron  146 71        217  Tzvetan Tzvetkov 
 F1B    240 150 120 150 150 150 150 150 1260  Tom Vaccaro   240 124 120 150 150 150 150 150 1234  Carrol Allen   240 98 59 55 150 150 150 150 1052  Aram Schlosberg   177 150       327  John Clapp  
 E36      120 120 120  360  Dick Ivers      120 120 98  338  Drake Hook       87 120 120  327  Rebbecca Avla J     92    92  Dave Lacey       
 Electric B      120 120 120  360  Rich Wagener     120 119 120  359  Drake Hooke     109 120 120  349  Dick Ivers      120 76    196  Yuda Avla     
 Open Rubber          120 120 64  304  Rich Wegener      1/2 Classic 120 93 67  280  Ronald Monkres
 ........ Roger Morrell