I have a boomerang sprintjet with an older p70 on it. I am wondering how much flap to use for take off. I have heard everything from 5-45 degrees.

None. It does not need it and it does almost zero. For landing all you can get, you want it more as a airbrake than a flap.

It depends on the take off surface and wind conditions. If your runway is long and tarmac then you won't need any flap as the length of the takeoff run doesn't matter. If you fly off grass with a shorter runway then using flap will help. Also if there is no or little wind then flap will also help. I normally use around 30 degrees, I don't have a precise value as my flaps are on a slider not a switch. While you can take off without flaps and I often do if there is at least 5 mph winds using them does help on a rough grass surface.
For landing I have flaps set to give 90 degrees movement to give maximum airbrake effect. This does need quite a bit of down elevator mixed in to stop it ballooning but will slow it down well for landing. The flap has enough of a braking effect that I have to add throttle when it is deployed. The Boomerang is still stable and handles well at this slower speed so I normally put in full flap on the downwind leg to bring it down to landing speed keeping in some power until reaching the threshold..

Jim

I got my sprint early fall this year. I have about 10 flights on it total. I have my flaps set to 90 for landing. I also have a crow mix at full flaps of about 5 degrees up. Makes it slow down very nice. My take off performance is less then ideal. I have tried 0 flaps and I have tried about 30 degrees. Our field is grass a little rough and for most of the fall we have corn at both ends. Got a little close a couple of times on take off.

Have to agree with Scraper. The Sprint has so much lift on that wing that it doesn’t need it and I am at 20 lbs and 18 lbs of thrust with the Jets Munt VT80. If doing grass takeoffs you could go with a trailing edge drop of say 3/4 of an inch........as said they are more of a speed brake than a flap when dropped much past 60 degrees ie 90 degrees.

Airborn since your problem is takeoff and you seem to have a good setup for your landings with the crow (full flap. up reflex of the ailerons and down imput on the elevator) and if you are achieving this in "flight conditions" Then:

It would be relatively simple to set up flight conditions (assuming of course your radio has flight conditions) for take off of: around 20 degrees of flap which is approximately the point of max lift with the least trade off in drag.
And the application of a somewhat lessor degree of down aileron (flaperons).

This takeoff fight condition is likely to help with the shortest possible takeoff for your particular variables at your field. Two of which you did not mention which is of course length and typical density altitudes.


John

Originally Posted by JohnBuckner

Airborn since your problem is takeoff and you seem to have a good setup for your landings with the crow (full flap. up reflex of the ailerons and down imput on the elevator) and if you are achieving this in "flight conditions" Then:

It would be relatively simple to set up flight conditions (assuming of course your radio has flight conditions) for take off of: around 20 degrees of flap which is approximately the point of max lift with the least trade off in drag.
And the application of a somewhat lessor degree of down aileron (flaperons).

This takeoff fight condition is likely to help with the shortest possible takeoff for your particular variables at your field. Two of which you did not mention which is of course length and typical density altitude


John

I hadn’t considered using flaperons. I will play with that the next time I am out. I don’t know the exact measurement of our runway, probably 400ish ft. This past season they planted corn so we had 8 foot obstacles at both ends. Our field elevation is 300 feet and typical DA in the summer is around 2000.

I am also playing with the idea of a larger engine.

At 300 ft you will be getting max power and max lift. We operate at arround 2300 feet and don’t seem to have problems.

Good morning Airborn, After pondering a bit on the varibles you are dealing with I was intrigued most by the corn! Now I am certainly no expert on farming or corn but a bit of checking last night revealed that many varieties reach seven feet or more and feed corn can go to ten feet or more!

Holy cow and on both bitter ends? That will by any reasonable estimate reduce your four hundred foot runway to something around three hundred and change! Now if we throw in density altitude in the summertime that can easily add close to several thousand on top of your three hundred elevation, Well things can get marginal.

OK lets talk about your engine, Yes it is at the bottom of what is recommended, however it is an earlier generation and spool up times may not be what can be achieved with many of the newer turbines. When dealing with a rather short runway this spool up time can be critical. So using that engine: Yes I would do takeoff flight conditions I described in my previous post and I would use a helper to position the airplane in the takeoff position and have him hold the airplane to the side of either one of the booms while you ran up the engine to perhaps half power or more then release with a head nod from you.

Only just an opinion

John

Originally Posted by JohnBuckner

Good morning Airborn, After pondering a bit on the varibles you are dealing with I was intrigued most by the corn! Now I am certainly no expert on farming or corn but a bit of checking last night revealed that many varieties reach seven feet or more and feed corn can go to ten feet or more!

Holy cow and on both bitter ends? That will by any reasonable estimate reduce your four hundred foot runway to something around three hundred and change! Now if we throw in density altitude in the summertime that can easily add close to several thousand on top of your three hundred elevation, Well things can get marginal.

OK lets talk about your engine, Yes it is at the bottom of what is recommended, however it is an earlier generation and spool up times may not be what can be achieved with many of the newer turbines. When dealing with a rather short runway this spool up time can be critical. So using that engine: Yes I would do takeoff flight conditions I described in my previous post and I would use a helper to position the airplane in the takeoff position and have him hold the airplane to the side of either one of the booms while you ran up the engine to perhaps half power or more then release with a head nod from you.

Only just an opinion

John

The breaks on it will hold it till the engine is at power. So I do every take off that way.

I’m considering going big. I think I might change it out for a k120g2. That would probably take care of my problem in a hurry.

My hesitation is my 70 runs really well. Kind of a why mess with it if it works kinda thing.

We got snow today so I probably won’t get another chance to mess with it till spring, unless I got to an event someplace down south this winter.

Thank you for the help

Ryan

A 120 is too powerful. Had a P-140 in one of my sprints and the stab ripped off on a full up. Had a several hundred foot debris field to prove too much power is a problem. The plane lasted about 30 minutes total. Also, you will make the plane a lot heavier trying to balance it with a 120, adding to the problem of getting it to land on a short field. Have a P-100 in the current Sprint. If I do a carrier type takeoff, it lifts off in about 50' on asphalt w/o any take-off flaps. With about 60 degree flap in, it will land in ~100-130'. But you will be using the brakes. You don't need crow on a Sprint. But if you do add crow, be ready to add power on the approaches which kind of defeats the purpose of using crow to slow it down. Sprints don't tip stall. So you sure do not need crow for that.

I’m thinking I’m going to keep the 70 in her for now. As for weight. The k120 and k100 are in the same can and have the same weight. Would be the same balance either way. All of that being said putting a k85 in would take about a pound of weight out and add a little thrust.

I did just purchase a pilot viper and will be focusing on that for now. Hoping it will be a good second jet.

A viper ,.....and you are concerned with takeoff and landing with the Sprint......? Or are you at a different field location with much more runway for the Viper ? From what I have seen with those is they do need room . Pilot do make some nice aircraft though.

Longer ashphault runway for the viper. I won’t fly that at my home field. We have an airport about an hour from me that allows model jet flying. Home field is about 10min from my house. So I’ll fly sprint there. I did get 20 flights on it from there. Only got close to the corn a couple of times.

Originally Posted by Airborn900

We got snow today so I probably won’t get another chance to mess with it till spring, unless I got to an event someplace down south this winter.

Thank you for the help

Ryan

Jets work great off of snow. It is surprising just how fast they can accelerate and get airborne, and even more surprising on just how quick they slow down and stop after landing. Just do not try to retract the skies........